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Over a span of 50 years, native Californian Donald Lee Johnson made a number of memorable contributions to our understanding of the California Channel Islands. Among these are (1) recognizing that carbonate dunes, often cemented into eolianite and derived from offshore shelf sediments during lowered sea level, are markers of glacial periods on the Channel Islands; (2) identifying beach rock on the Channel Islands as the northernmost occurrence of this feature on the Pacific Coast of North America; (3) recognizing of the role of human activities in historic landscape modification; (4) identifying both the biogenic and pedogenic origins of caliche “ghost forests” and laminar calcrete forms on the Channel Islands; (5) providing the first soil maps of several of the islands, showing diverse pathways of pedogenesis; (6) pointing out the importance of fire in Quaternary landscape history on the Channel Islands, based on detailed stratigraphic studies; and (7), perhaps his greatest contribution, clarifying the origin of Pleistocene pygmy mammoths on the Channel Islands, due not to imagined ancient land bridges, but rather the superb swimming abilities of proboscideans combined with lowered sea level, favorable paleowinds, and an attractive paleovegetation on the Channel Islands. Don was a classic natural historian in the great tradition of Charles Darwin and George Gaylord Simpson, his role models. Don's work will remain important and useful for many years and is an inspiration to those researching the California Channel Islands today.
Internal waves at both diurnal and semidiurnal frequencies are common on island slopes in the Southern California Bight (SCB). Amplitudes in both regimes are similar, although the phenomenology at the 2 frequencies is expected to be different since the bight is north of the critical latitude (30°), making diurnal modulations evanescent though semidiurnal waves can propagate. Understanding the driving forces for the internal waves may provide insight into vertical mixing in the bight. We used long-duration time series of ocean temperatures measured near the Wrigley Institute for Environmental Studies (WIES), Santa Catalina Island, to study highly resolved spectra and seasonal characteristics of internal waves. These characteristics were analyzed using available, sometimes nonconcurrent, ancillary data sets that include local tide and wind measurements. We conclude that the semidiurnal waves are driven by tides, whereas the diurnal waves are due to meteorological forcing.
Understanding how early humans on the California Channel Islands might have changed local fire regimes requires a baseline knowledge of the frequency of natural wildfires on the islands prior to human occupation. A sedimentary sequence that was recently discovered in a small canyon on San Nicolas Island contains evidence of at least 24 burn events that date to between ∼37 and 25 ka (thousands of calibrated 14C years before present), well before humans entered North America. The evidence includes abundant macroscopic charcoal, blackened sediments, and discrete packages of oxidized, reddish-brown sediments that are similar in appearance to sedimentary features called “fire areas” on Santa Rosa Island and elsewhere. Massive fine-grained sediments that contain the burn evidence are interpreted as sheetwash deposits and are interbedded with coarse-grained, clast-supported alluvial sediments and matrix-supported sands, pebbles, and cobbles that represent localized debris flows. These sedimentary sequences suggest that the catchment area above our study site underwent multiple cycles of relative quiescence that were interrupted by fire and followed by slope instability and mass wasting events. Our 14C-based chronology dates these cycles to well before the arrival of humans on the Channel Islands and shows that natural wildfires occurred here, at a minimum, every 300–500 years prior to human occupation.
Santa Rosa Island (SRI) is the second-largest of the California Channel Islands. It is one of 4 east—west aligned islands forming the northern Channel Islands chain, and one of the 5 islands in Channel Islands National Park. The landforms, and collections of landforms called landscapes, of Santa Rosa Island have been created by tectonic uplift and faulting, rising and falling sea level, landslides, erosion and deposition, floods, and droughts. Landscape features, and areas delineating groups of related features on Santa Rosa Island, are mapped, classified, and described in this paper. Notable landscapes on the island include beaches, coastal plains formed on marine terraces, sand dunes, and sand sheets. In this study, the inland physiography has been classified into 4 areas based on relief and degree of fluvial dissection. Most of the larger streams on the island occupy broad valleys that have been filled with alluvium and later incised to form steep- to vertical-walled arroyos, or barrancas, leaving a relict floodplain above the present channel. A better understanding of the processes and mechanisms that created these landscapes enhances visitors' enjoyment of their surroundings and contributes to improving land and resource management strategies in order to optimize and balance the multiple goals of conservation, preservation, restoration, and visitor experience.
Paleontological resource inventories for the parks of the National Park Service's Mediterranean Coast Inventory and Monitoring Network (MEDN) indicate a significant Late Cretaceous and Cenozoic fossil record for the southern California coast and islands. These inventories document over 100 million years of biologic and geologic changes along the Pacific coast of southern California. During 2012, comprehensive paleontological resource data were compiled for Cabrillo National Monument (CABR), Channel Islands National Park (CHIS), and Santa Monica Mountains National Recreation Area (SAMO). This recent work expands the paleontological resource data previously compiled for each of the parks in 2003 and during the SAMO paleontological survey of 2004. Fossil plants, invertebrates, and vertebrates and trace fossils represent both marine and terrestrial life along the ancestral coast of southern California. Within the boundaries of SOMA, 38 fossil taxa have been described from specimens discovered there, and 19 more have been described from CHIS. Among the significant fossils found within the MEDN are the pygmy mammoths of CHIS, which continue to be a subject of scientific research. Recent work at SAMO has helped refine the stratigraphic interpretation of the park's geology; helped provide additional documentation of the Miocene flora and fauna; and led to the description of new taxa, including the Upper Cretaceous gastropod Pyropsis aldersoni (Squires 2011) and the Paleocene crab Costacopluma squiresi (Nyborg et al. 2009). The recent MEDN paleontological resource inventory will help stimulate future research, education, interpretation, and proper management of these important paleontological resources.
Marine invertebrate faunas with mixtures of extralimital southern and extralimital northern faunal elements, called thermally anomalous faunas, have been recognized for more than a century in the Quaternary marine terrace record of the Pacific Coast of North America. Although many mechanisms have been proposed to explain this phenomenon, no single explanation seems to be applicable to all localities where thermally anomalous faunas have been observed. Here, we describe one such thermally anomalous fossil fauna that was studied on the second emergent marine terrace at Eel Point on San Clemente Island. The Eel Point terrace complex is a composite feature, consisting of a narrow upper bench (terrace 2a) and a broader lower bench (terrace 2b). Terrace 2b, previously dated from ∼128 ka to ∼114 ka, was thought to date solely to marine isotope stage (MIS) 5.5, representing the peak of the last interglacial period. Nevertheless, the fauna contains an extralimital northern species and several northward-ranging species, as well as an extralimital southern species and several southward-ranging species. Similar faunas with thermally anomalous elements have also been reported from San Nicolas Island, Point Loma (San Diego County), and Cayucos (San Luis Obispo County), California. U-series dating of corals at those localities shows that the thermally anomalous faunas may be the result of mixing of fossils from both the ∼100-ka (cool-water) and the ∼120-ka (warm-water) sea level high stands. Submergence, erosion, and fossil mixing of the ∼120-ka terraces by the ∼100-ka high-sea stand may have been possible due to glacial isostatic adjustment (GIA) effects on North America, which could have resulted in a higher-than-present local sea level stand at ∼100 ka. The terrace elevation spacing on San Clemente Island is very similar to that on San Nicolas Island, and we hypothesize that a similar mixing took place on San Clemente Island. Existing fossil records from older terraces elsewhere in California also show thermally anomalous elements, indicating that the scenario presented here for the last interglacial complex may have applicability to much of the marine Quaternary record for the Pacific Coast.
On the northern Channel Islands, the occupation of interior sites during the Middle Holocene (6650–3350 cal BP) has been attributed, in part, to terrestrial resource exploitation. The presence of groundstone artifacts, particularly mortars and pestles, in Middle Holocene sites and burials supports the idea that plants were important during this time period. The current study presents macrobotanical data from 4 Middle Holocene sites on Santa Cruz Island. Of the 4 sites, 3 are located within the Central Valley, the island's most productive watershed; whereas the fourth site is located on a coastal bluff on the eastern end of the island. This arrangement allows for a comparison of contemporary coastal and interior sites. Although very few seeds were recovered from these samples, the results provide clues to seasonality of occupation and exploited habitats. The presence of seeds from medicinal plants at all 3 interior sites and the absence of seeds at the coastal site suggests that access to these resources played a role in settlement decisions. Though all of the plants recovered have medical uses in the ethnographic record, very few have any recorded use as food. This study contextualizes the macrobotanical results by addressing issues of preservation and recovery and by identifying areas for future research.
Although the majority of prehistoric habitation sites on Santa Cruz Island are located within interior areas more than 0.5 km from the coast, little is known about these sites and how their occupation articulated with coastal settlement. To address this lack of knowledge, small-scale excavation was undertaken at 2 interior habitation sites (CA-SCRI-555 and CA-SCRI-574) in the western sector of the island. Habitation deposits at both sites are <60 cm deep. Radiocarbon dating reveals that CA-SCRI-555 experienced occupation during 3 time intervals: 1800–1400 cal BC, ~2400 cal BC, and ~4400 cal BC. In contrast, dates for CA-SCRI-574 indicate only one time interval: 2800–1900 cal BC. Remains of marine shellfish and vertebrates in the deposits indicate transport of marine foods to both sites. The repertoire of shellfish remains implies that site inhabitants obtained marine foods from coastal areas closest to each site. These interior sites may have been occupied for one or more reasons: (1) as habitation sites occupied occasionally for the purpose of acquiring and perhaps consuming plant food or other interior resources; (2) as easily defended locations given their placement on ridgetops; (3) as way stations during travel to distant parts of the island; and (4) as locations where freshwater is available during dry seasons or years when water is scare at nearby coastal locations. The data resulting from small-scale testing makes evaluating these alternatives difficult, but the variety of food remains, the various types of stone tools, and the wood charcoal from hearth fires all indicate that at least some intervals of occupation were for periods that exceeded a few days. The results highlight the need for data from a large number of interior sites to understand island settlement patterns and ecological adaptation of the island's prehistoric inhabitants.
Discovery and analysis of 43 pearl oyster (Pinctada mazatlanica) artifacts and associated shell-processing tools from middle and basal levels of Covacha Babisuri, a rock shelter on Espíritu Santo Island, Baja California Sur, provide evidence of Early and Middle Holocene fishhook production along the southern Gulf of California coast. AMS 14C analysis of a fishhook preform recovered from the lowest stratum of the rock shelter returned a date of 8380 ± 50 RCYBP (Beta-236254), or 8750–8500 cal BP, with a reservoir effect of 250 ± 20 years, making this artifact one of the earliest known examples of a shell fishhook in the world. An additional pearl oyster artifact was found in a deeper level dating closer to 10,000 RCYBP, suggesting that this type of fishhook may date to this earlier period.
The Chumash village of Qshiwqshiw, located on eastern Santa Rosa Island, is described in ethnographic sources as one of the largest Chumash villages on the northern Channel Islands, with 4 chiefs and 119 baptisms according to mission records. The village is thought to correlate with 2 archaeological sites (CA-SRI-85 and CA-SRI-87) that contain large and dense shell-midden deposits. Despite the importance of these sites for helping understand Late (650–168 cal BP) and Historic (AD 1769–1830) Period Chumash lifeways, only limited surface collections, one small column sample, and 4 radiocarbon dates were previously available, leaving unanswered important questions about the chronology and structure of these sites. To help fill these gaps, we recently excavated, mapped, and obtained several new radiocarbon dates for CA-SRI-85 and CA-SRI-87. Radiocarbon dating and artifact analyses demonstrate that CASRI- 85 served as an important Late Period village that had continued occupation into the Historic Period. Additional radiocarbon dates and glass beads confirm that CA-SRI-87 was likely the epicenter of Historic Period occupation, but testing also revealed that the site was occupied about 3000 years ago. The data paint a complex occupational history for both sites and provide the chronological and spatial context for future investigations into the historical ecology and cultural landscape of eastern Santa Rosa Island.
From 1801 to late 1803, captains and co-owners of the Lelia Byrd, William Shaler of Boston and Richard J. Cleveland of Salem, Massachusetts, voyaged to the west coast of North America where they traded for sea otter fur that they then sold in Canton, China. They traveled to the Hawaiian Islands and made a gift of horses, the first in Hawaii, to King Kamehameha I, “the Great.” During 1804–1805, Shaler sailed back to the California coast to continue trading while Cleveland sailed to Boston. Shaler's narrative of the 1804–1805 voyage is the earliest, most extensive account of California written firsthand by an American observer. On 1 May 1805, Shaler was the first American to name a California locale: a “small but very fine port” on Santa Catalina Island, which he named after his friend M. De Rouissillon. At Port Roussillon, Shaler and his crew careened the Lelia Byrd between 1 May and 12 June 1805 and stayed with their “Indian friends.” This harbor is identified as Avalon Bay in California Place Names (Gudde 1949), but further investigation indicates Port Roussillon is actually Isthmus Cove at Two Harbors.
The floristic connection between the mediterranean region of Baja California and the Pacific islands of Alta and Baja California provides insight into the history and origin of the California Floristic Province. We present updated species lists for all California Floristic Province islands and demonstrate the disjunct distributions of 26 taxa between the Baja California and the California Channel Islands. These 26 plant taxa are found among the 16 Pacific islands without occurring on the intervening mainland of Alta California. Separate species lists for each island group (8 California Channel Islands and 8 Baja California Islands) were compiled. These lists were compared to the mainland California flora to identify species that occur on the California Islands and either the Baja California Pacific Islands or the mediterranean region of the Baja California Peninsula, but not the mainland of Alta California. This first compilation of the flora of the Baja California Islands and nomenclatural updates for the Channel Islands provide a platform for future research and conservation planning.
Lecanora annularis, n. sp., is described from collections from Santa Cruz Island and Santa Barbara Island in Channel Islands National Park and from San Simeon and Point Lobos on the central California coast. The crystalinspersed parathecium, egranulose epihymenium, and maritime habit distinguish L. annularis from all other members of the L. dispersa group. It occurs on sandstone and decaying basalt.
San Miguel Island is the westernmost of the California Channel Islands and one of the windiest areas on the west coast of North America. The majority of the island is covered by coastal sand dunes, which were stripped of vegetation and subsequently mobilized due to droughts and sheep ranching during the late 19th century and early 20th century. Since the removal of grazing animals, vegetation and biological soil crusts have once again stabilized many of the island's dunes. In this study, historical aerial photographs and field surveys were used to develop a chronosequence of the pattern of change in vegetation communities and biological soil crust levels of development (LOD) along a gradient of dune stabilization. Historical aerial photographs from 1929, 1954, 1977, and 2009 were georeferenced and used to delineate changes in vegetation canopy cover and active (unvegetated) dune extent among 5 historical periods (pre-1929, 1929–1954, 1954–1977, 1977–2009, and 2009–2011). During fieldwork, vegetation and biological soil crust communities were mapped along transects distributed throughout San Miguel Island's central dune field on land forms that had stabilized during the 5 time periods of interest. Analyses in a geographic information system (GIS) quantified the pattern of changes that vegetation and biological soil crust communities have exhibited on the San Miguel Island dunes over the past 80 years. Results revealed that a continuing increase in total vegetation cover and a complex pattern of change in vegetation communities have taken place on the San Miguel Island dunes since the removal of grazing animals. The highly specialized native vascular vegetation (sea rocket, dunedelion, beach-bur, and locoweed) are the pioneer stabilizers of the dunes. This pioneer community is replaced in later stages by communities that are dominated by native shrubs (coastal goldenbush, silver lupine, coyote-brush, and giant coreopsis), with apparently overlapping or cyclical succession pathways. Many of the dunes that have been stabilized the longest (since before 1929) are dominated by exotic grasses. Stands of biological soil crusts (cyanobacteria) are found only on dunes where vascular vegetation is already present. Biological soil crusts are not found on dunes exhibiting a closed vascular plant canopy, which may indicate that the role of soil crusts in dune stabilization on the island is transitory. Particle-size analyses of soil samples from the study area reveal that higher biological soil crust LOD is positively correlated with increasing fine grain content. The findings indicate that changes in vegetation communities may be the most rapid at earlier and later stages of dune stabilization and that regular monitoring of dunes may help to identify the interactions between vegetation and soil crusts, as well as the potential transitions between native and exotic plant communities.
Island scrub oak (Quercus pacifica), a keystone chaparral species on Santa Rosa, Santa Cruz, and Santa Catalina islands, provides habitat for a diverse assemblage of plant and animal species. The restoration of oak habitat is a management priority, but little is known about Q. pacifica stand structure and acorn production, 2 parameters that are important in the species' recovery. To investigate whether species interactions and abiotic conditions have an effect on stand structure and acorn production, we sampled within-stand densities, tree sizes, and acorns in the 3 island populations that have been exposed to different herbivores, seed predators, and climate conditions. Stand densities varied more within than between islands; but Santa Rosa, the coldest of the 3 islands, had smaller trees with smaller acorns than the other 2 islands. To quantify the temporal and spatial variation in acorn production on Santa Cruz Island, we conducted acorn counts at 2 spatial scales: (1) an island-wide survey of 200 trees along the east—west axis of the island (2008–2012) and (2) small-scale surveys within three 100-ha study plots (150 trees; 2009–2012). Acorn production varied strongly, both temporally and spatially, with little temporal synchrony and spatial autocorrelation. Trees at higher elevations produced more acorns, but the roles of temperature and precipitation were unclear in this relatively short study. To increase our understanding of the drivers of Q. pacifica acorn production, we propose that annual oak surveys be incorporated into a long-term monitoring program across the California Channel Islands.
The Farallon Islands in the Gulf of the Farallones National Marine Sanctuary (GFNMS) is a 7-island chain located 48 km west of San Francisco, California. Since 1993, GFNMS biologists and associates have monitored algal and invertebrate species abundances on the intertidal shores of the 2 South Farallon Islands. The monitoring occurred 1–3 times yearly in 6 study areas. In each study area, 3–4 permanent, 0.15-m2 quadrats located between the upper and midintertidal zones were sampled for algal and sessile invertebrate cover and invertebrate counts. Taxonomic surveys were also completed to document other species in the vicinity of the sampling quadrats and to further characterize the sampling areas. Here we report monitoring results for the period 1993 to 2011. While species richness has remained relatively stable and high compared to the nearest mainland sites (Sonoma County through San Mateo County), there has been a slow, long-term net decline in the abundance of algal species and mussels at various sites on the islands. Causes for the declines remain unknown, but increased trampling from rising numbers of pinnipeds and increased waste from pinnipeds and seabirds are among the influences suspected to be important.
California's 8 Channel Islands host a large diversity of insects, the vast majority of which are shared with mainland southern California. The existence of a small number of recognized endemic species, however, suggest that, for some lineages, the islands are isolated enough to have permitted significant differentiation. Here we investigate the phylogeographic relationships of 4 beetle species (Thinopinus pictus, Hadrotes crassus, Hypocaccus lucidulus, and Nyctoporis carinata): all occurring on the mainland and on multiple (up to 6) Channel Islands. Sequences of the cytochrome oxidase I mitochondrial gene (and, for one species, an intron in the nuclear guftagu gene) are analyzed by Bayesian, haplotype network, and population genetic methods to examine relationships and gene flow among island and mainland populations. In no instances were all island populations resolved to be monophyletic, and northern (Santa Cruz, Santa Rosa, San Miguel) and southern (San Nicolas, San Clemente, Santa Catalina) island groups generally showed separate relationships to the mainland. Northern island populations of Hy. lucidulus were also found to be closely related to those on the southern island of San Nicolas. Populations on San Clemente and Santa Catalina islands did not show close relationships to each other or to San Nicolas Island populations in any species. San Clemente and especially San Nicolas islands hosted disproportionately high levels of diversity in all species examined. This study suggests that the Channel Islands do not function as a biogeographical unit and that several of the islands exhibit levels of diversity comparable to, or even exceeding, similarly sampled populations on the mainland. Thus, as an insular refuge from southern Californian development, the Channel Islands constitute a center of high conservation importance.
Arthropods have been understudied on Santa Cruz Island, resulting in an incomplete understanding of these diverse and ecologically important members of island ecosystems. To enhance the current understanding of Santa Cruz Island biodiversity, we sampled arthropods in 2 native plant habitats: island scrub oak (Quercus pacifica) woodland and patches of island morning glory (Calystegia macrostegia ssp. macrostegia). We used 4 standardized sampling techniques to sample arthropods in 16 Q. pacifica woodland plots. We sampled arthropods associated with C. macrostegia by pan trapping within 1 m of blooming morning glory individuals. In total, we sampled over 18,000 arthropod specimens, sorted the specimens to morphotypes by order, and had taxonomic specialists identify 10 orders to the narrowest possible identification (n = 458 total species or morphotypes). The taxonomic distribution of our identified specimens is as follows: 1 species of Scorpiones, 5 morphospecies of Pseudoscorpiones, 74 species of Araneae, 4 species of Orthoptera, 10 species of Psocodea, 10 species of Hemiptera, 1 species of Neuroptera, 60 species of Coleoptera, 8 species of Lepidoptera, and 42 species of Hymenoptera (Formicidae and Apoidea). Of these, 62 species represent newly recorded arthropod species on Santa Cruz Island. The diversity of our collections within the Quercus pacifica and Calystegia macrostegia habitats, the deficiency of current knowledge of Channel Island arthropods, and the fundamental role of arthropods in island ecosystems emphasize the need for a more comprehensive arthropod inventory across the California Channel Islands.
Concealed nest sites, mostly inaccessible breeding habitats, and nocturnal colony visitation have long hindered studies of Scripps's Murrelets (Synthliboramphus scrippsi); but conspicuous and seasonally predictable at-sea congregations adjacent to nesting areas provide a valuable index for assessing murrelet colony size and population trends at all 12 breeding islands. We developed a boat-based nocturnal spotlight survey for counting murrelets in at-sea congregations at Anacapa Island, California. A high-intensity spotlight was used to count murrelets during standard surveys conducted on 2 parallel transects (1.9 km each) located 200 m (“inshore”) and 500 m (“offshore”) from shore. We conducted 130 standard surveys over 58 nights in 2001–2006. Difficulties estimating densities with strip transects and distance sampling led to use of raw counts as the best index for assessing population trends. Standard counts averaged 136 (SD 94) murrelets per survey (range 0–470). Strong correlations were noted among counts within nights, but consistent trends were not evident. We also noted a strong correlation between maximum counts on consecutive survey nights but much more variation in counts over the breeding season (annual CV range 27%–92%). Annual maximum counts occurred from 42 days before to 32 days after mean egg-laying dates. Round-island counts ranged from 29 to 564 murrelets during 12 surveys conducted along a 19.2-km transect circumnavigating Anacapa Island. Strong correlations between inshore and offshore standard counts and between standard and round-island counts indicated that major local shifts in distribution did not occur; instead, varying proportions of the murrelet population returned to the Anacapa Island congregation each night. Increases in standard counts from 2001 to 2006 and a positive correlation between standard counts and the annual number of clutches in monitored plots suggested an increase in the murrelet population after eradication of black rats (Rattus rattus) in 2002, but limited posteradication survey data were not sufficient to detect significant popu lation trends. Intensive surveys (minimum of 10 nights each year) over at least 3 consecutive years per decade are recommended to track the progress of the Scripps's Murrelet population and to validate rates of population growth observed in small nest plots on Anacapa Island.
The small population of Scripps's Murrelets (Synthliboramphus scrippsi) at Santa Catalina Island, California, has been restricted for at least several millennia to isolated pairs nesting in cliff and shoreline habitats that are mostly inaccessible to island fox (Urocyon littoralis catalinae). Prior to 1994, the only evidence of murrelets breeding at Catalina was a single nest reportedly found on Bird Rock in 1967. In 1994–1995, a larger and more widespread population estimated at 25–75 pairs was indicated through vocal detection surveys of murrelets attending nocturnal at-sea congregations in nearshore waters near breeding areas. Murrelets were heard at 11 of 25 survey stations, with highest vocal activity between Land's End and Ribbon Rock (6–62 detections per survey). In 2004 and 2012, round-island spotlight surveys better assessed the distribution and abundance of murrelets in congregations, with 101 and 291 individuals, respectively, observed along the 82-km transect. Highest numbers in 2012 suggest a current breeding population of roughly 100–200 pairs at Catalina, the fourth largest colony in southern California. Congregations were strongly associated with coastal cliffs between (1) Isthmus Cove and Twin Rocks and (2) Iron Bound Bay and Catalina Harbor. In 2000–2013, night-lighting captures of 79 birds in congregations recorded 10 (13%) murrelets with brood patches, usually indicative of egg-laying. During captures in 2008 and spotlight surveys in 2012, three family groups (adults with small downy chicks) departing island nests were observed in nearshore waters. No nests were found during searches on offshore rocks (including Bird Rock) in 1991–1996, but 7 nests were discovered in 2012–2013 during searches of boataccessible shoreline cliffs between Isthmus Cove and Twin Rocks. Overall, 6 of 8 clutches (75%) with known fates were successful, but evidence of mammalian predators preying on murrelet eggs was also present. A long-term monitoring, research, and restoration program is needed at Catalina. Initial restoration efforts should focus on reducing predation by introduced mammals and reducing impacts from oil pollution and bright lights.
Spatial overlap between predators and prey is often a key component of predator-prey interactions. Barn Owls (Tyto alba) are important predators of some species of conservation concern on the Channel Islands in southern California; therefore, understanding patterns of owl space use on these islands could provide insights on variations in predation risk that may be useful for conservation efforts of Barn Owl prey. In this study, our objectives were to investigate home-range size and space use by individual owls on Santa Barbara Island, which at 2.6 km2 is the smallest island within the Channel Islands National Park. Specifically, we were interested in owl space use in relation to the spatial distribution of owl prey, in particular the state-listed Threatened Scripps's Murrelet (Synthliboramphus scrippsi)—a small nocturnal seabird whose largest breeding colony in California is on this island and whose nesting habitat is strictly along the island's perimeter. In contrast, the distribution of the Barn Owl's primary prey, deer mice, includes both murrelet habitat and the island interior. We therefore conducted a radiotelemetry study of Barn Owls in combination with a novel technique of applying colored reflective tape to colored plastic leg bands to aid in the identification of individual owls at night. Home-range size estimates for 3 owls were 0.02–0.53 km2 using the 100% minimum convex polygon method and were 0.06–1.12 km2 using a fixed-kernel method. Owl resight locations for 8 marked individuals were no farther than 1.24 km apart, which suggests that owl home ranges do not generally encompass the entire island. Nocturnal observations of owls also tended to be not far from their diurnal roost sites, which were located close to the edges of the island and near murrelet nesting habitat. This spatial overlap suggests there may be patchiness in predation risk for the owls' seabird and rodent prey in relation to proximity to owl roosts.
We investigated morphological divergence between mainland and California Island populations of the Song Sparrow (Melospiza melodia). Body size in small terrestrial vertebrates has been hypothesized to be larger in island forms than in their mainland relatives. Previously, we established that although bill size in island populations was similar to that in mainland populations with similar climate, bill-size dimorphism averaged much greater on the islands. In this paper, we compare various measures of structural body size and body mass between the California Islands and the mainland. We found that average body mass is over 10% higher in island Song Sparrows than in comparable mainland populations. However, a lack of commensurate structural body size suggests that body condition might be better in island Song Sparrows. This higher size-corrected mass may be explained by the dominance hypothesis, greater food availability and/or reduced competition, or adaptive mass regulation in the face of reduced predation pressure on adults. Both greater sexual bill dimorphism and greater body mass suggest reduced competition for food for the island Song Sparrow: a possibility that invites further investigation.
New telemetry technologies have recently become available for research on island foxes (Urocyon littoralis). These include GPS units, which collect location data, and proximity logger units, which record contacts between individuals. We evaluated these technologies on island foxes through 4 field studies. GPS collars were deployed on foxes on Santa Catalina during 2007–2008 (n = 20) and 2010–2011 (n = 5) and on Santa Rosa during 2009–2010 (n = 14). The GPS units had multiple issues including malfunctioning drop-off mechanisms, failure of some units to yield data, low location acquisition rates, improper factory programming, high rates of premature failure of VHF transmitters and GPS units, poor VHF signal strength, faulty mortality sensors, and breakage of the unit housing or antenna. Proximity loggers were deployed on foxes on San Miguel during 2009–2010 (n = 17). Performance was satisfactory and consistent with expectations. Both the GPS and proximity logger units yielded high-quality data when the units worked correctly. Some minor collar-related injuries were noted on 4 foxes with GPS units. We conclude that both technologies can potentially collect valuable data that would be more difficult and expensive to collect using conventional VHF methods and therefore could benefit island fox conservation. We recommend (1) using GPS units with a remote download function; (2) downloading data from both types of units as frequently as is practicable; (3) attempting GPS-unit data downloads from the air; (4) frequently monitoring foxes using the VHF transmitters to determine areas of use; and (5) rigorously pretesting all functions on both types of units prior to deployment on foxes.
The island fox (Urocyon littoralis) represents an unusual case of a species that achieved virtual recovery a mere 15 years after population declines were first discovered. Island fox subspecies on San Miguel, Santa Rosa, and Santa Cruz islands declined precipitously in the mid-1990s due to predation by Golden Eagles (Aquila chrysaetos), which had not historically bred on the islands. In 2008, a 10-year period of recovery action implementation ended. The recovery program had included captive breeding and reintroduction of island foxes and capture and relocation of Golden Eagles. Free-ranging fox populations have been monitored to assess recovery of each subspecies and to detect potential threats of disease and predation. Monitoring included (1) annual grid trapping to allow estimation of annual population size via capture-mark-recapture methods and (2) systematic surveillance of radio-collared foxes to allow estimation of mortality rates and causes. A comprehensive demographic modeling effort produced a population recovery tool that uses adult mortality and population size estimates from the monitoring programs to estimate extinction risks for each fox population. The tool allows managers to assess when threats are sufficiently mitigated to consider populations acceptably safe from extinction. Population monitoring indicates that island foxes on the northern Channel Islands have increased up to 30-fold from population lows and that annual survival has been 90% or better in most years. The San Miguel and Santa Cruz subspecies have approached or reached predecline population levels, and application of the recovery tool indicates they will be biologically recovered by 2013. Biological recovery of the Santa Rosa subspecies, hindered by predation which caused lower survival in 2010, will occur by 2017.
Santa Catalina Island was home to an estimated 1342 adult island foxes (Urocyon littoralis catalinae) in 1990. Nine years later, fox sightings declined and reports of dead or dying foxes increased. An island-wide trapping effort was initiated after a fox carcass tested positive for Canine distemper virus (CDV). In 1999, only 10 foxes were captured east of the Two Harbors isthmus during 1046 trap-nights. A multifaceted conservation plan was implemented in 2000 to conserve the Santa Catalina population of island fox. Initial recovery actions took place from 2000 to 2005 and resulted in the translocation of 22 juvenile foxes from the unaffected West End of the island to the depopulated eastern portion, the production and release of 37 pups from the captive breeding facility, and the vaccination of >80% of the wild fox population against CDV. Since 2006, fox recovery activities have included an annual island-wide population survey, vaccination of 300 foxes per year, weekly mortality monitoring of 50 radio-collared individuals, blood sampling to monitor the prevalence of CDV, veterinary treatment of injured foxes, and public outreach. Low mortality rates, successful breeding in the wild, and mitigation of the original cause of decline allowed for Catalina's fox population to grow to an estimated 1115 adults by 2012 and to be considered biologically recovered. The outbreak of another virulent canine disease on Santa Catalina Island, such as CDV or rabies, continues to be the greatest threat to the long-term survival of U. l. catalinae due to the species' restricted distribution and small population size, as well as the continued presence of domestic dogs on the island.
Islands host exceptionally high levels of endemism compared to mainland regions and are subject to disproportionately high rates of extinction and imperilment. Therefore, the protection and preservation of taxonomic units that are endemic to islands is a key component in mitigating the loss of global biodiversity. However, determining what is “endemic” on islands can be challenging. Conservation units are commonly delineated based on genetic divergence at neutral loci (e.g., genetic differentiation at microsatellite loci or reciprocal monophyly based on mitochondrial genes). Island populations of nonvolant species are expected to meet this criterion, regardless of adaptive differences, due to geographic isolation, founder effects, and small effective population sizes. We therefore argue that the delineation and management of island endemic populations should not be based on neutral genetic divergence and reciprocal monophyly alone. Instead, we recommend identifying island populations that have genetically based adaptations to their unique environments. A comprehensive framework specifically designed to delineate evolutionarily significant units (ESUs) on islands should be based on metrics of both neutral and adaptive genetic divergence. The California Channel Islands host several taxa considered to be endemic, and we highlight 2 case studies to illustrate how this framework can be applied. This approach can be applied broadly to continental islands and island archipelagos, enabling conservation practitioners to use an objective framework to prioritize units of biological diversity for management.
Islands provide refuge for many rare and endemic species but are especially vulnerable to invasion by nonnative species. Invasive alien species are a major factor in the imperilment and extinction of island biota. Biosecurity protocols are designed to prevent or quickly detect the transport of harmful nonnative species, with the goal of eliminating the high economic cost of invasive species removal and the biological cost of damage caused by nonnative organisms. Effective biosecurity protocols require a balanced approach to on-island monitoring, off-island surveillance and prevention practices, rapid response, and educational outreach. Here we use the biosecurity program on Santa Cruz Island, California, to illustrate how risk evaluation, program priorities, and funding constraints intersect to define programmatic scope. Santa Cruz Island land managers have chosen to invest in early detection programs such as remote camera trapping, off-island prevention and education, and rapid-response planning for rats and in on-island biosecurity to prevent the spread of the most harmful plant species. We suggest that biosecurity efforts will be more effective—as well as cost effective—as an archipelago-wide initiative than as a single-island program. A newly formed collaboration with managers of other California Islands is designed to enhance visibility of the biosecurity initiative and attract new funding sources. With the economy afforded by collaboration, we will expand our program and prioritize annual audits, augment educational programs, measure project success, and increase compliance with and effectiveness of biosecurity protocols.
Restoring large, complex landscapes can be challenging, especially given that some threats to native diversity and ecological function cannot be wholly eliminated. Santa Catalina Island, California, provides a valuable case study because its challenges include a variety of ecosystem threats, legal restrictions, and cultural attachments, as well as a vocal resident human population that often does not agree with conservation actions. Catalina Island has been highly modified by numerous invasive species, fragmentation and erosion from roads, altered hydrology from dams, and increased fire frequency. In this paper, I build on a previously published review of resources and threats and discuss potential management actions for those threats. Although the island's large size, rugged topography, and pervasive human influence limit management options, several feasible actions could have an important restorative effect. In particular, “bottom-up” invader management may be a relatively noncontroversial way to produce multiple positive outcomes. Reducing fragmentation, restoring natural hydrologic regimes, and augmenting native plant cover could disadvantage invasive plant and animal species while promoting the native flora and fauna.
Science-based planning and prioritization can help achieve greater return on investment of limited conservation funds. We conducted a GIS-based multicriteria decision analysis to prioritize efforts to eradicate populations of invasive alien species that threaten native biota on the islands of Mexico. We evaluated 29 Mexican islands with documented presence of invasive mammals and characterized the following attributes of each island: presence of endemic taxa, presence of threatened species, presence of important seabird nesting areas, species richness, likelihood of reinvasion, eradication feasibility, and economic cost. We categorized the islands into 4 priority categories for eradication action. The highest priority islands where eradication efforts are feasible are Socorro, Espíritu Santo, María Cleofas, and María Magdalena islands, where eradication of 11 invasive mammal populations could advance the restoration of an additional 35,813 ha, thereby reducing the extinction risk of approximately 80 endemic taxa.
Prisoners Harbor of Santa Cruz Island, California, was historically the site of a 4.86-ha coastal wetland and riparian system—the largest on the California Channel Islands. The site was occupied by native people for 3000 years until the 1830s. During the late 1800s, ranchers filled about half of the wetland area to build livestock corrals and other facilities. They also rerouted the main stream channel, Cañada del Puerto, and built a stone wall and earthen berm along its west bank. This disconnected the stream from its floodplain and inadvertently caused erosion of a Native American archeological site. The National Park Service developed a wetland and riparian restoration design for Prisoners Harbor based on topographic and hydrologic analyses and on relationships between vegetation community and depth to water table estimated from neighboring reference wetlands. In 2011, Channel Islands National Park and The Nature Conservancy restored 1.25 ha of coastal wetland and reconnected the stream to its floodplain by removing the earthen berm. This restoration was accomplished by excavating 7645 m3 of fill material and planting the site with over 15,000 native wetland and riparian plants. Postproject vegetation monitoring showed that only one of the 8 planted wetland species had a significant increase in abundance between 2012 and 2013, likely due to severe drought conditions that began soon after project implementation. However, hydrologic monitoring in the first year after restoration showed that the restored marshes met federal criteria for wetland hydrology just before the drought began. These data provide early but promising evidence that our approach to restoration will convert the filled corral area at Prisoners Harbor to functional coastal wetland habitat as more-typical (wetter) precipitation levels return. The restoration also helped to protect the archeological site and is expected to provide an enjoyable and educational destination for visitors.
Santa Cruz Island, California, has been free of nonnative vertebrates since 2007, but nonnative invasive plants remain one of the most significant threats to the recovery of the island's native ecosystems. Just over one-fourth of the island's flora is comprised of nonnative, naturalized plant species. In 2007, an island-wide invasive plant survey indicated that several species were candidates for eradication based on factors such as their distribution, abundance, invasiveness, and known or projected harmful impacts on the native biota. In 2008, The Nature Conservancy (TNC) and Native Range, Inc., initiated a program to eliminate 15 invasive plant species from TNC's portion (76%) of the 246-km2 island. An additional 9 species were targeted in subsequent years. As of 2012, a total of 882 populations of 24 weed species have been mapped and treated, and 73% of these populations are considered inactive (dead), with no aboveground living biomass. The majority of the remaining active infestations are due to resurgence from the soil seed bank. Continued monitoring and annual follow-up treatments of invasive plants will be required. Utilization of a small helicopter provides surveyors and herbicide applicators with efficient access to remote infestations and a platform from which to treat populations and detect individual plants. Most important in achieving project success is consistent treatment from year to year, which prevents reproduction and recovery of infestations. Long-lived soil seed banks for some species will be a management issue for years to come. Continued commitment to eradicating these weeds and the ability to detect incipient infestations and respond rapidly to eliminate them will be key determinants of success of this program.
Santa Cruz Island is the largest of the California Channel Islands and supports a diverse and unique flora which includes 9 federally listed species. Sheep, cattle, and pigs, introduced to the island in the mid-1800s, disturbed the soil, browsed native vegetation, and facilitated the spread of exotic invasive plants. Recent removal of introduced herbivores on the island led to the release of invasive fennel (Foeniculum vulgare), which expanded to become the dominant vegetation in some areas and has impeded the recovery of some native plant communities. In 2007, Channel Islands National Park initiated a program to control fennel using triclopyr on the eastern 10% of the island. We established replicate paired plots (seeded and nonseeded) at Scorpion Anchorage and Smugglers Cove, where notably dense fennel infestations (>10% cover) occurred, to evaluate the effectiveness of native seed augmentation following fennel removal. Five years after fennel removal, vegetative cover increased as litter and bare ground cover decreased significantly (P < 0.0001) on both plot types. Vegetation cover of both native and other (nonfennel) exotic species increased at Scorpion Anchorage in both seeded and nonseeded plots. At Smugglers Cove, exotic cover decreased significantly (P = 0.0001) as native cover comprised of Eriogonum arborescens and Leptosyne gigantea increased significantly (P < 0.0001) in seeded plots only. Nonseeded plots at Smugglers Cove were dominated by exotic annual grasses, primarily Avena barbata. The data indicate that seeding with appropriate native seed is a critical step in restoration following fennel control in areas where the native seed bank is depauperate.
The natural vegetation of Santa Cruz Island was severely disturbed by nonnative herbivores for well over a century. As the livestock and feral ungulates (primarily sheep, cattle, and pigs) were removed from the island over the last 30 years, many of the native plant communities began to recover naturally. Recovery has been extremely slow in other areas, especially where nonnative annual grasses and fennel (Foeniculum vulgare) dominate several hundred hectares that were under intense agricultural use (pastures and farmed lands). We experimentally tested the feasibility of speeding up the recovery process in a postagricultural area of the island's Central Valley using active restoration techniques. We assessed how weed control via herbicide application and planting of small nursery stock without irrigation might contribute to restoring natural plant assemblages in 3 different areas of the Central Valley (valley bottom, upper south-facing slope, and midsouth-facing slope). In February 2009, we planted the same 21 species of native plants in experimental plots with and without weed control at each location. In December 2009, we planted 28 species in adjacent plots after 2 seasons of weed control. We assessed natural recruitment in weeded and unweeded plots that were not planted. At all 3 locations, a single early season herbicide treatment prior to planting had strong positive effects on the survival, cover, and reproduction of planted natives compared to no herbicide treatment; the effects persisted and grew stronger in the second and third years. Repeated herbicide treatments over 2 years before planting did not result in any additional significant positive effects on native survival or growth compared to only one herbicide treatment. We saw virtually no natural recruitment of native shrubs in unplanted plots. We found that typical coastal sage scrub species performed best at the upper slope site and poorly at the valley bottom site. Grasses and shrubs tolerant of poorly drained soil did better in the valley bottom. We found that planting native species from small nursery stock without irrigation is effective for a wide range of grassland and coastal sage scrub species. All of the restoration techniques we used are cost effective and can be scaled-up to restore large areas of postagricultural lands.
Plant communities dominated by Leptosyne gigantea (tickseed, formerly giant coreopsis) are distributed widely across the California Islands and provide critical habitat for understory plants and vertebrates, especially in landscapes where trees are absent. Leptosyne gigantea populations were severely impacted by nonnative herbivores and by grazing and ranching practices during the last century. Although these impacts have been absent from most of the islands for over 2 decades, extensive spatial heterogeneity exists both within and across the islands in relation to population growth. Many sites support very dense stands of L. gigantea that established postgrazing; whereas others, particularly on Santa Barbara Island, have experienced relatively minimal increases in L. gigantea abundance and are still dominated by alien annual grasses. To determine the factors that most affect L. gigantea establishment and survival, I conducted seed amendment experiments across populations of variable density and age structure on San Miguel Island. These experiments tested the relative effects of seed predation, seed density, microhabitat conditions, stand density, and competition on germination and seedling survival. Postdispersal seed predation by deer mice reduced germination rates only in the highest density stands. Reduced soil moisture and interspecific competition with alien annual grasses had the strongest negative effects on both germination and seedling survival. The results suggest extreme spatial variability in regulating factors for L. gigantea that include rainfall, the abundance of annual grasses, consumer abundance, and intraspecific density dependence. The presence or absence of these influences on existing site conditions will determine succession following loss of the oldest-aged stands, which will likely occur soon.
A large eelgrass (Zostera pacifica) meadow was present at Frenchy's Cove, Anacapa Island, prior to the late 1980s. Extensive grazing by white sea urchins (Lytechinus anamesus) in the late 1980s eliminated the meadow by 1991, when a 60-m transect (10-m depth) was established; no natural recovery was observed from 1991 to 2002. In 2002, approximately 450 eelgrass shoots were transplanted to Frenchy's Cove from 2 large meadows at Santa Cruz Island (Smugglers Cove, Prisoners Harbor), and a second transect (7-m depth) was established in 2004. Shoot planting densities ranged from 0.11 m-2 to 11 m-2. Meadow dimensions, shoot density and reproductive status, along with density and species abundance of associated benthic invertebrates and fishes were surveyed annually along each transect from 2003 to 2012. Densities of white urchins remained low, thereby facilitating expansion of the meadow via vegetative growth and seedling recruitment. Individual patches eventually coalesced into an overall meadow at Frenchy's Cove of 0.87 ha in 2009, retracting slightly to 0.62 ha in 2012. Shoot density reached a mean of 108 m-2 in 2009 and ranged from 23 m-2 to 90 m-2 in 2012, comparable to natural meadows at nearby Santa Cruz Island. Increased diversity and abundance of invertebrates and fishes were evident, with an average of 5 (2001), 9 (2005), and 14 (2011) fish species recorded during 30-minute surveys and a dramatic shift in fish guilds, with black perch, pile perch, and halfmoon only associated with the new meadow. As a result of the initial 2002 eelgrass transplantation, eelgrass meadows returned to northern Anacapa Island; and by 2012, they expanded along nearly 3 km of nearshore sandy habitat. A diverse biotic assemblage is becoming reestablished at Frenchy's Cove and adjacent shallow sandy substrates along the north side of Middle Anacapa Island.
Argentine ants (Linepithema humile) have invaded many areas of conservation concern, including half of the California Channel Islands. On Santa Cruz Island, the species has invaded approximately 2% of the island, and the infestations are expanding. Argentine ants displace many other invertebrates, and their expansion throughout the island could lead to the extirpation of native invertebrate species and the disruption of key ecological processes (e.g., plant-pollinator interactions and seed dispersal). We describe a treatment protocol to manage or eliminate Argentine ants on Santa Cruz Island developed by The Nature Conservancy and the National Park Service, in collaboration with academic and pest control specialists. We combined low-concentration toxicant baits with efficient dispersal methods to treat landscape-scale Argentine ant infestations in rugged terrain and dense vegetation with minimal impact to nontarget species. From May to October 2012, we applied our baiting protocol within 2 study sites, totaling 7.8 ha on Santa Cruz Island. In May 2013, one year post treatment, we observed >99% reduction in Argentine ant activity in treatment plots compared to untreated plots, using 2 different monitoring techniques. While further testing and monitoring is needed, these results suggest this protocol may be an effective tool to eliminate Argentine ant infestations from this type of habitat and terrain.
Most invasive alien vertebrate populations on the Channel Islands of California have been eradicated over the past 30 years. Unfortunately, removal of these introduced herbivores or predators came too late for some native flora and fauna, and numerous populations are now extinct. Here, we describe a systematic approach to reintroducing extirpated native taxa as a means for rebuilding natural communities and enhancing the resiliency of island ecosystems. Reintroduction efforts typically focus on a single species or site. In contrast, we propose that if reintroduction is a shared conservation goal of managers across the islands, the associated planning, implementation, and monitoring should be conducted as a cross-island initiative for the archipelago. A coordinated effort based on best practices in reintroduction biology could accrue programmatic efficiencies and economies of scale, more quickly advance ecosystem and species conservation goals, and create unique opportunities to test hypotheses in basic and applied ecology and evolution. The philosophical and technical approaches developed through this program may apply to other island and mainland systems and could be adapted to develop conservation strategies for species that may be candidates for assisted colonization in the face of climate change.
Guadalupe Island, off the Baja California peninsula, México, hosts the most important growing Laysan Albatross (Phoebastria immutabilis) breeding colony in the eastern Pacific. Since this seabird's first arrival in 1983, it has been affected by predation from feral cats (Felis catus), present on Guadalupe since the late 19th century. Heavy predation events have been recorded on the island, so we initiated a feral cat control campaign in 2003 and began collecting baseline information for developing an eradication plan. At the same time, we conducted seasonal monitoring of Laysan Albatross reproductive success in order to assess the benefits from control activities. Cat relative abundance on Guadalupe was estimated through spotlight surveys, and control was done at the southernmost end of the island around the 2 locations where Laysan Albatross nest: Colinas Negras and Punta Sur. Laysan Albatross population growth rate was calculated based on the number of reproductive individuals, while breeding success was estimated as the proportion of laid eggs that resulted in fledged chicks. A total of 203 cats were removed from the south end of Guadalupe between 2003 and 2013. During this same period, high reproductive success (0.8) was recorded for Laysan Albatross, suggesting a positive effect of cat control activities. We found significant differences in reproductive success between years with predation and no predation by feral cats. The Laysan Albatross colony on Guadalupe has grown steadily during the past 30 years, increasing from 4 to 143 breeding pairs between 1984 and 2013, respectively, and with a population growth rate of 1.10 between 2004 and 2013.