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Effective monitoring programs are designed to track changes in the distribution, occurrence, and abundance of species. We developed an extension of Royle and Kéry's (2007) single species model to estimate simultaneously temporal changes in probabilities of detection, occupancy, colonization, extinction, and species turnover using data on calling anuran amphibians, collected from 2002 to 2006 in the Lower Mississippi Alluvial Valley of Louisiana, USA. During our 5-year study, estimates of occurrence probabilities declined for all 12 species detected. These declines occurred primarily in conjunction with variation in estimates of local extinction probabilities (cajun chorus frog [Pseudacris fouquettei], spring peeper [P. crucifer], northern cricket frog [Acris crepitans], Cope's gray treefrog [Hyla chrysoscelis], green treefrog [H. cinerea], squirrel treefrog [H. squirella], southern leopard frog [Lithobates sphenocephalus], bronze frog [L. clamitans], American bullfrog [L. catesbeianus], and Fowler's toad [Anaxyrus fowleri]). For 2 species (eastern narrow-mouthed toad [Gastrophryne carolinensis] and Gulf Coast toad [Incilius nebulifer]), declines in occupancy appeared to be a consequence of both increased local extinction and decreased colonization events. The eastern narrow-mouthed toad experienced a 2.5-fold increase in estimates of occupancy in 2004, possibly because of the high amount of rainfall received during that year, along with a decrease in extinction and increase in colonization of new sites between 2003 and 2004. Our model can be incorporated into monitoring programs to estimate simultaneously the occupancy dynamics for multiple species that show similar responses to ecological conditions. It will likely be an important asset for those monitoring programs that employ the same methods to sample assemblages of ecologically similar species, including those that are rare. By combining information from multiple species to decrease the variance on estimates of individual species, our results are advantageous compared to single-species models. This feature enables managers and researchers to use an entire community, rather than just one species, as an ecological indicator in monitoring programs.
Human activities, including the harvesting of natural resources and land development, place substantial pressure on wildlife. The diamondback terrapin (Malaclemys terrapin) is a small, estuarine species of emydid turtle in decline and at risk due to a suite of human activities. Vehicle-induced mortality from increasing coastal traffic and bycatch mortality in crab pots have been recognized as 2 of the primary conservation concerns for terrapins. We used mark-recapture estimates of terrapin density and sex ratio from repeated seining samples of 29 randomly stratified selected tidal creeks to evaluate the current relationships between road and crabbing pressures and the abundance, sex ratio, and size distribution of terrapin populations along the Georgia coast. We obtained 2005 captures of 1,547 individual terrapins among 29 tidal creeks sampled. Population density estimates ranged from 0 to 1,040 terrapins/km among tidal creeks with a median density of 65 terrapins/km. Among all sites, terrapin density declined with increasing crabbing activity within the creek, but was not related to proximity to roads. Sex ratios did not vary significantly with crabbing activity or proximity to roads; however, we found a significantly larger proportion of smaller-sized terrapins in creeks with no crabbing activity. Although roads may have significant localized effects on terrapin populations, we found no measurable association between proximity to roads and current variation in terrapin density along the Georgia coast. However, we did find that terrapin density and the proportion of smaller sized individuals within the population were negatively associated with crabbing activities. Bycatch from commercial and recreational activities threaten many species. We add to a growing body of research showing crabbing activities are affecting diamondback terrapin populations across much of the species' range. States committed to the conservation of terrapins and coastal species should focus on reducing bycatch risk; for example by regulating soak times and locations, requiring the use of bycatch reduction devices, and removing abandoned or lost crab pots from coastal habitats.
Lesser prairie-chickens (Tympanuchus pallidicinctus) are traditionally monitored by spring roadbased lek surveys and counts of males attending leks. Several weaknesses exist with ground-based monitoring methods such as the bias of restricting surveys to roads, unknown probability of lek detection, and man-hours required to survey large tracts of habitat. We evaluated aerial surveys to locate lesser prairie-chicken leks in Texas and New Mexico using a Cessna 172 airplane (C172), R-22 Beta II helicopter (R-22), and R-44 Raven II helicopter (R-44) during spring 2007–2008. We determined lek activity during surveys with remote cameras placed on leks and cross-referenced time on the photo frame to time on our Global Positioning System flight log. From remote cameras we found that 305 leks were available for detection during survey flights. We determined lek detectability was 32.7% (95% CI = 20.3–47.1%) in the C172, 72.3% (64.50– 79.14%) in the R-22, and 89.8% (82.0–95.0%) in the R-44. We created 16 a priori logistic regression models incorporating aircraft platform, distance to lek, survey date, lek size, and lek type to explain lek detection from aerial surveys. Our top ranked model included platform, distance, and lek type (model weight; w1 = 0.288). We had four competitive models and model averaged to draw inferences. Model averaging showed that detectability was generally greatest with the R-44, followed by the R-22, and lowest with the C172, with a slight deviation from this ranking at increased distances. Within our transect width, model averaging also suggested that detectability decreased as distance from the transect to the lek increased during helicopter surveys, and detectability increased as distance from the transect to the lek increased during C172 surveys. Furthermore, man-made leks were more likely to be detected than natural leks and large leks were more likely to be detected than medium or small leks. Aerial surveys effectively locate new leks and monitor lek density, and alleviate weaknesses associated with ground-based monitoring. We recommend using the R-44 to conduct lek surveys while flying at an altitude of 15 m at a speed of 60 km/hr on sunny mornings.
Previous field studies of hunter-harvested mourning doves (Zenaida macroura) have reported the percentage of birds with ingested lead shot as 0.2–6.5%. To reduce the uncertainty concerning the number of doves that ingest shot, we conducted an experiment to test the proportion of mourning doves that ingested lead shot on the bare soil of a disked field (typical of a managed dove field) to simulate more natural feeding conditions. In each of 3 treatment groups of 80 birds, we exposed 35 birds to low-density lead shot (1.5 million shot/ha), and35 birds to high-density lead shot (29.5 million shot/ha), and 10 birds served as controls (no shot). We dosed 5 positive control birds with 2 lead shot each in trials 2 and 3. We scattered lead shot and mixed seed on the loosely packed soil of treatment cages and after 4 days of exposure, 2.9% of doves voluntarily ingested ≥1 lead shot. The proportion of birds that ingested shot when exposed to the high-density shot treatment (4.9%) was not different (P = 0.098) from that of the low-density shot treatment (1.0%). Lead concentrations in liver, kidneys, and blood reached maxima of 94.402 ppm, 346.033 ppm, and 13.883 ppm wet mass, respectively. Differences in delta-aminolevulinic acid dehydratase (ALAD) activity, packed cell volume, and heterophil:lymphocyte ratio (H:L) were greater posttreatment in doves that had ingested shot than in those that did not. The risk posed to mourning doves from lead shot ingestion can be reduced by banning lead shot on management areas or dove fields or disking fields after hunting season to reduce shot availability.
Conservation of rare populations requires managing habitat throughout the year, especially during winter when northern populations may be limited by food and predation. Consequently, we examined distribution of nonbreeding western snowy plovers (Charadrius alexandrinus), including individually marked birds that were year-round residents and others that were migrants, in coastal northern California. Over 2 years, banded plovers exhibited high site faithfulness, occupying small linear stretches of beach (752 ± 626 m). Sites occupied by plovers had more brown algae (e.g., Macrocystis, Nereocystis, Postelsia, and Fucus) and associated invertebrates (e.g., amphipods, and flies), were wider, and had less vegetation than unoccupied sites. Our findings suggest that wintering plovers select habitats with more food and where they could more easily detect predators. Maintaining habitat with attributes that support abundant food (i.e., brown algae) and reduce predation risk (i.e., wide beaches, limited obstructive cover) may be important to individual survival and maintaining the Pacific Coast population of snowy plovers. Protecting occupied sites from human disturbance, which adversely alters nonbreeding habitat (i.e., beach grooming) and directly causes mortality, may be essential for conserving the Pacific coast population of the snowy plover, and it may benefit other shorebirds.
Salvage logging practices in recently burned forests often have direct effects on species associated with dead trees, particularly cavity-nesting birds. As such, evaluation of postfire management practices on nest survival rates of cavity nesters is necessary for determining conservation strategies. We monitored 1,797 nests of 6 cavity-nesting bird species: Lewis's woodpecker (Melanerpes lewis), hairy woodpecker (Picoides villosus), black-backed woodpecker (P. arcticus), northern flicker (Colaptes auratus), western bluebird (Sialia mexicana), and mountain bluebird (S. currucoides) from 1994 to 2004 in ponderosa pine (Pinus ponderosa), mixed-severity burned forests (partially logged and unlogged) of Idaho, USA. Based on a priori hypotheses, we modeled daily survival rate (DSR) of nests as a function of abiotic (temperature, precipitation), temporal (time since fire, calendar year) and biotic factors (distance to unburned forest, nest height, and tree harvest [partial-salvage logging vs. unlogged]). Multiple abiotic and biotic factors, other than direct effects of salvage logging, affected daily survival rates of breeding cavity-nesting birds. Hairy woodpecker was the only species in which partial-salvage logging had a measurable, negative impact on DSR. Managers implementing carefully planned salvage logging prescriptions that include both unlogged reserves and partially logged areas can expect to maintain habitat for successfully breeding cavity-nesting birds of the interior northwestern United States. Our results also suggest that nest survival for some species of cavitynesting birds could be improved if unlogged reserves are located centrally in postfire forests, distant from unburned habitats that potentially serve as sources of nest predators.
With the popularity of wind energy increasing globally, concerns surfaced in the 1980s as to the potential adverse effects of wind turbines on migrating birds. Understanding how weather conditions influence passage rates can help determine the potential for increased avian-turbine collisions. Using vertical and horizontal mounted marine radars, raptor stand watch observations, and portable handheld weather stations, we studied how temperature, cloud cover, barometric pressure, wind direction, and wind speed affected avian passage rates and height of migrants over 3 ridges (Wartenbe, North Dokie, and South Dokie) being developed for wind energy in northern British Columbia. Using an Akaike's Information Criterion (AIC), we determined that a reduced model combining wind speed, barometric pressure, and cloud cover was best at explaining and predicting higher passage rates (expressed as no. birds/hr) in the fall migration for both diurnal and nocturnal migrants. Wind speed proved the most important predictor of passage rates for spring nocturnal migrants and a combination of cloud cover, temperature, and wind direction for diurnal spring migrants. Wind speed also predicted decreases in flight altitude among nocturnal migrants but increased altitude in diurnal migrants. This information coupled with migration timing and topographical areas of higher migrant activity can be useful to wind energy proponents who wish to mitigate collision risk with migrating birds.
Oil and natural gas development in the Intermountain West region of North America has expanded over the last 2 decades, primarily within sagebrush dominated landscapes. Although the effects of energy development on high-profile game species such as the greater sage-grouse (Centrocercus urophasianus) have been documented, studies examining responses of non-game birds are lacking. Simultaneously, many songbirds that breed within sagebrush steppe habitats have shown range-wide population declines that are likely due to widespread habitat loss and alteration. We evaluated songbird abundance and species richness across gradients of oil and natural gas development intensity, as indexed by well density, at 3 energy fields (2 natural gas and 1 oil) in the Upper Green River Basin, Wyoming, USA during 2008–2009. While simultaneously accounting for important habitat attributes, increased well density was associated with significant decreases in Brewer's sparrow (Spizella breweri) and sage sparrow (Amphispiza belli) abundance, particularly in the Jonah natural gas field. Vesper sparrows (Pooecetes gramineus) were also negatively influenced by increased well density. Horned larks (Eremophila alpestris) increased with well density in the Pinedale Anticline natural gas field, and sage thrashers (Oreoscoptes montanus) showed no response to energy development. Species richness was not significantly affected by well density. Results suggest that regional declines of some songbird species, especially sagebrush-obligates, may be exacerbated by increased energy development. Understanding the specific mechanisms underlying responses to energy development is an important next step and will aid land managers in the development of effective mitigation and management strategies for the maintenance of stable bird communities in sagebrush habitat.
The effects of habitat edges on nest survival of shrubland birds, many of which have experienced significant declines in the eastern United States, have not been thoroughly studied. In 2007 and 2008, we collected data on nests of 5 shrubland passerine species in 12 early successional forest patches in North Carolina, USA. We used model selection methods to assess the effect of distance to cropland and mature forest edge on nest predation rates and additionally accounted for temporal trends, nest stage, vegetation structure, and landscape context. For nests of all species combined, nest predation decreased with increasing distance to cropland edge, by nearly 50% at 250 m from the cropland edge. Nest predation of all species combined also was higher in patches with taller saplings and less understory vegetation, especially in the second year of our study when trees were 4–6 m tall. Predation of field sparrow (Spizella pusilla) nests was lower in landscapes with higher agricultural landcover. Nest predation risk for shrubland birds appears to be greater near agricultural edges than mature forest edges, and natural forest succession may drive patterns of local extirpation of shrubland birds in early successional forest patches. Thus, we suggest that habitat patches managed for shrubland bird populations should be considerably large or wide (>250 m) when adjacent to crop fields and maintained in structurally diverse early seral stages.
Assessing wildlife management action requires monitoring populations, and abundance often is the parameter monitored. Recent methodological advances have enabled estimation of mean abundance within a habitat using presence—absence or count data obtained via repeated visits to a sample of sites. These methods assume populations are closed and intuitively assume habitats within sites change little during a field season. However, many habitats are highly variable over short periods. We developed a variation of existing occupancy and abundance models that allows for extreme spatio-temporal differences in habitat, and resulting changes in wildlife abundance, among sites and among visits to a site within a field season. We conducted our study in sugarcane habitat within the Everglades Agricultural Area southeast of Lake Okeechobee in south Florida. We counted wintering birds, primarily passerines, within 245 sites usually 5 times at each site during December 2006—March 2007. We estimated occupancy and mean abundance of birds in 6 vegetation states during the sugarcane harvest and allowed these parameters to vary temporally or spatially within a vegetation state. Occupancy and mean abundance of the common yellowthroat (Geothlypis trichas) was affected by structure of sugarcane and uncultivated edge vegetation (occupancy = 1.00 [95% C = 0.96–1.00] and mean abundance = 7.9 [95% C = 3.2–19.5] in tall sugarcane with tall edge vegetation versus 0.20 [95% C = 0.04–0.71] and 0.22 [95% C = 0.04–1.2], respectively, in short sugarcane with short edge vegetation in one half of the study area). Occupancy and mean abundance of palm warblers (Dendroica palmarum) were constant (occupancy = 1.00, 95% CI = 0.69–1.00; mean abundance = 18, 95% C = 1–270). Our model may enable wildlife managers to assess rigorously effects of future edge habitat management on avian distribution and abundance within agricultural landscapes during winter or the breeding season. The model may also help wildlife managers make similar management decisions involving other dynamic habitats such as wetlands, prairies, and even forested areas if forest management or fires occur during the field season.
Every year an estimated 4–5 million migratory birds collide with communication towers in the United States. We examined the relative risks that tower support systems and tower height pose to migrating and other birds. We collected data comparing tower support systems (guyed vs. unguyed) and tower height categories in Michigan during 20 days of the peak of songbird migration at 6 towers in September–October 2003, 23 towers in May 2004, 24 towers in September 2004, and 6 towers in both May and September 2005. We systematically and simultaneously searched for bird carcasses under each tower and measured carcass removal and observer detection rates each season. Of those towers, 21 were between 116 and 146 m above ground level (AGL, medium) and 3 were >305 m AGL (tall). During the five 20-day sample periods we found a mean of 8.2 bird carcasses per guyed medium tower and a mean of 0.5 bird carcasses under unguyed medium towers. During four 20-day sample periods we detected a mean of 34.7 birds per guyed tall tower. Using both parametric and nonparametric tests (Mann—Whitney U—test, Kruskal—Wallis test, and Tukey's Honestly Significant Difference multiple comparison procedure) we determined that unguyed medium towers were involved in significantly fewer fatalities than guyed medium towers. We detected 54–86% fewer fatalities at guyed medium towers than at guyed tall towers. We found 16 times more fatalities at guyed medium towers than at unguyed medium towers. Tall, guyed towers were responsible for 70 times as many bird fatalities as the unguyed medium towers and nearly five times as many as guyed medium towers. These findings will provide managers and regulators, such as the US Fish and Wildlife Service, with quantitative data; thereby, allowing them to effectively work with the Federal Communications Commission in siting and authorizing tower placement.
Survival is a key life-history trait in animals. However, most methods of survival estimation require substantial human and economic investment in the long term, particularly in species occurring in low densities, the case of most endangered species. An alternative to traditional recapture (CR) methods is estimation of adult survival based indirectly on either age ratios (AGR) or turnover rates (TOR) in territorial species. These 2 methods are applicable to bird species in which recruited individuals enter into the breeding population whilst still exhibiting the external traits that distinguish those animals from experienced adults. The main advantages of these methods are that survival can be easily estimated for all monitored individuals after just 1 or 2 breeding seasons and that disturbance to the species is minimized. The main constraints of indirect methods are that the assumptions are more restrictive than in CR methods, and survival estimates, although comparable between sites and years, may be biased. We used data from a long-term monitoring survey of 2 populations of the endangered Bonelli's eagle (Aquila fasciata), one in Catalonia (NE Spain) and the other in Provence and Languedoc-Roussillon (SE France). We evaluated survival estimates using the AGR and TOR methods and compared them with CR methods and provide suitable corrections for refining survival estimates based on indirect methods. In Catalonia (2002–2008), survival was estimated at 0.84 by CR methods (SE = 0.047; n = 25 radio tagged eagles), at 0.86 by the corrected AGR method (SE = 0.011; n = 558 bird * year), and at 0.86 by the corrected TOR method (SE = 0.022; n = 547 bird * year). In France (1999–2008), survival was estimated at 0.88 by CR methods (SE = 0.040; n = 45 darvic banded eagles), at 0.87 by the corrected AGR method (SE = 0.015; n = 443 bird * year), and at 0.87 by the corrected TOR method (SE = 0.015; n = 438 bird * year). All analyses suggest that females survive better than males and that individuals from the French population survive better than individuals from the Catalan population. We conclude that indirect methods, which should not be regarded as a substitute of CR methods, will allow wildlife managers and researchers to estimate accurately adult survival in a territorial species over a short period of time and to monitor survival across populations over large geographic ranges and over time.
Although bears may expand their home ranges in times of low food availability, it is unclear what mechanisms directly affect home range extension in times of low mast production in Japanese forests. To clarify the relationship between home range utilization by Japanese black bears (Ursus thibetanus) and abundance and distribution of mast production, we collected data on habitat use from 13 bears (6 M and 7 F) fitted with Global Positioning System (GPS) collars equipped with activity sensors in the Ashio-Nikko Mountains on the eastern part of Honshu Island, Japan, during 2006–2008. We also collected data on mast production by 5 Fagaceae species. We categorized each fall as either poor (2006) or relatively-good (2007 and 2008) based on mast production. Bears used small patches in their large home ranges and the distances between core areas increased in the fall of 2006, when the mast of Japanese oak (Quercus crispula) were poorly distributed. Our findings suggest that localized patches of Japanese oak are the staple food for bears in our study area, even in poor mast years. However, in the fall of 2006, we also found that bears moved to lower elevations, relative to 2007 and 2008, in search of alternative foods (e.g., Konara oak [Q. serrata] and Japanese chestnut [Castanea crenata]), which were mostly at lower elevations and produced mast consistently over the study period. Our results suggest that dispersion and elevational distribution of mast-producing trees affect bear habitat use in fall, as well as amount of mast.
We tested the hypothesis that predation by coyotes (Canis latrans) impacts pronghorn (Antilocapra americana) and mule deer (Odocoileus hemionus) populations. We did so by examining the effects of coyote removal on pronghorn and mule deer populations within 12 large areas (>10,500 km2) located in Wyoming and Utah during 2007 and 2008. Pronghorn productivity (fawn to adult female ratio) and abundance were positively correlated with the number of coyotes removed and removal effort (hours spent hunting coyotes from aircraft) although the correlation between pronghorn productivity and removal effort was not statistically significant (P = 0.08). Mule deer productivity and abundance were not correlated with either the number of coyotes removed or removal effort. Coyote removal conducted during the winter and spring provided greater benefit than removals conducted during the prior fall or summer. Our results suggest that coyote removal conducted over large areas increases fawn survival and abundance of pronghorn but not mule deer.
The Bathurst herd of barren-ground caribou (Rangifer tarandus groenlandicus) in the Canadian central arctic declined from an estimated 203,800 to 16,400 breeding females from 1986 to 2009, with the most rapid decline from 2006 to 2009. A key research and management question was whether the decline was mainly due to decreases in productivity alone or also due to reduced adult female survival. Investigating causes of the decline was hampered by a lack of direct estimates of caribou demographic parameters. We developed a demographic model that could be objectively fitted to field data to explore the mechanisms for the Bathurst decline, with a focus on the recent accelerated decline from 2006 to 2009. Our modeling indicated that the decline was driven by increasing negative trends in adult female and calf survival rates and possibly reduced fecundity The effect of a constant hunter harvest on the declining herd was one potential cause for the recent accelerated decline in adult survival. The demographic model detected negative trends in adult female survival that were not detected using standalone analyses of collar-based survival data. The model allowed rigorous interpretation of trends in productivity by controlling for the simultaneous influence of trends in adult, calf, and yearling survival and adult fecundity on field-based calf—cow ratios. Stochastic simulations suggested that large increases in adult survival and productivity would be needed for the herd to recover. Our methods enable objective modeling of caribou demography that can assist in caribou management based upon all sources of available data.
We studied survival of elk (Cervus elaphus) ≥ 1 yr old and quantified mortality sources in the Blue Mountains of Washington, 2003–2006, following a period of extensive poaching. The population was managed under a spike-only general hunting season, with limited permits for larger males and for females. We radiomarked 190 elk (82 males and 39 females >1 yr old and 65 males 11 months old), most with rumen transmitters and neck radiocollars; 60 elk only received rumen transmitters. We estimated annual survival using known fate models and explored survival differences among sex and age classes and in 2 potentially different vulnerability zones for males. We found little support for differences in survival between younger (2–3-yr old) and older (≥4-yr old) branch-antlered males or zone differences for yearling males. A model with zone differences for branch-antlered males was the second ranked model and accounted for 14% of the available model weight. From the best-supported models, we estimated annual survival for yearling males at 0.41 (95% CI: 0.29–0.53). We estimated pooled adult female survival at 0.80 (95% CI: 0.64–0.93); when an age-class effect was included, point estimates were higher for prime-aged females (2–11 yr: S = 0.81 [0.70–0.88]) than for older females (≥12 yr: S = 0.72 [0.56–0.83]), but confidence intervals broadly overlapped. Only 1 of 7 models with a female age effect on survival was among the competitive models. For branch-antlered males, survival ranged 0.80–0.85, depending on whether zone variation was modeled. We recorded 78 deaths of radiomarked elk. Human-caused deaths (n = 55) predominated among causes and most were of yearling males killed during state-sanctioned hunts (n = 28). Most subadult male deaths were from tribal hunting (n = 5), and most mature males died from natural causes (n = 6) and tribal hunting (n = 5). We detected few illegal kills (n = 4). Our results suggest that increased enforcement effectively reduced poaching, that unreported tribal harvest was not a trivial source of mortality, and that spike-only general seasons were effective in recruiting branch-antlered males.
Coyotes (Canis latrans) may affect adult and neonate white-tailed deer (Odocoileus virginianus) survival and have been implicated as a contributor to the decline of deer populations. Additionally, coyote diet composition is influenced by prey availability, season, and region. Because coyote movement and diet vary by region, local data are important to understand coyote population dynamics and their impact on prey species. In southeast Minnesota, we investigated the effect of coyotes on white-tailed deer populations by documenting movement rates, distances moved, and habitats searched by coyotes during fawning and nonfawning periods. Additionally, we determined survival, cause-specific mortality, and seasonal diet composition of coyotes. From 2001 to 2003, we captured and radiocollared 30 coyotes. Per-hour rate of movement averaged 0.87 km and was greater (P = 0.046) during the fawning (1.07 km) than the nonfawning period (0.80 km); areas searched were similar (P = 0.175) between seasons. Coyote habitat use differed during both seasons; habitats were not used in proportion to their availability (P < 0.001). Croplands were used more (P < 0.001) than their proportional availability during both seasons. Use of grasslands was greater during the fawning period (P = 0.030), whereas use of cropland was greater in the nonfawning period (P < 0.001). We collected 66 fecal samples during the nonfawning period; coyote diets were primarily composed of Microtus spp. (65.2%), and consumption of deer was 9.1%. During the study, 19 coyotes died; annual survival rate range was 0.33–0.41, which was low compared with other studies. Consumption of deer was low and coyotes searched open areas (i.e., cropland) more than fawning areas with dense cover. These factors in addition to high coyote mortality suggested that coyote predation was not likely limiting white-tailed deer populations in southeast Minnesota.
Controlled feeding experiments can provide valuable insights into food selection of herbivores. We conducted cafeteria trials on captive yearling white-tailed deer (Odocoileus virginianus) during 2 years to determine feeding preferences in relation to plant chemical constituents, i.e., nitrogen and fibers. We simultaneously offered 8 species of cultivated and wild plants in monthly foraging trials conducted from June to October. We predicted that species preferences would be positively related to protein content from June to August and to digestible energy in September and October. As predicted, crude protein (CP) was positively related to feeding preferences, particularly as summer progressed. Feeding preferences were also negatively related to fiber content, especially in early summer. Our results indicate high protein needs over the complete growing season for yearling deer but a decrease in overall plant selectivity as summer progresses. Our results also suggest that deer browsing on cultivated plants might be due to higher CP content of cultivated plants than wild plants. To prevent deer impact on crops, managers should favor regeneration of plants rich in CP content in forests.
In many mule deer (Odocoileus hemionus) populations, recruitment of fawns drives population dynamics. The quality of food available to females and their fawns in summer and autumn may play an important role in fawn recruitment. We examined direct links between digestible energy (DE) content of food and the DE intake of females on the nutrient concentration of milk and between the nursing behavior, DE intake, growth, and survival in captive mule deer fawns. We offered females and their fawns diets that simulated the natural decline in DE content of forage from mid-summer to late autumn in many western landscapes. Fawns fed a higher DE diet weighed 14% more at the onset of winter, had fewer unsuccessful nursing attempts, consumed milk with more protein and energy, and had higher survival than fawns fed a low DE diet. Differences between fawn performances among treatments were greatest when diet quality began decreasing earlier in the summer. Because our results indicate that summer and autumn nutrition is likely to influence fawn recruitment, wildlife biologists should include metrics for summer precipitation and late autumn fawn mass in population models, and land managers should focus on methods for improving the nutritional carrying capacity of summer and early autumn habitats.
The pygmy rabbit (Brachylagus idahoensis) is a cryptic, burrowing lagomorph of conservation concern for which an efficient method to monitor populations is needed for conservation planning. We developed an index of abundance based on density of active burrow systems at 7 sites (57.2–118.5 ha) in east central Idaho. We conducted censuses of burrow systems and used mark-resight surveys of 80 radio-collared individuals to estimate density of rabbits. At 5 sites, we also used a second method to estimate rabbit numbers based on presence of tracks in snow around burrow systems. We evaluated patterns of burrow use by individuals and examined the relationship between vegetation structure and density of rabbits. Density of active burrow systems varied from 0.19 to 3.46 per ha, and density of rabbits ranged from 0.02 to 0.46 per ha. Number of burrow systems used by individuals increased with density of available burrows, which supported a nonlinear relationship between abundance of burrows and rabbits. Population density increased curvilinearly with density of active burrows accounting for >75% of the variation (r2 = 0.79) in population estimates across sites. We documented a positive relationship between visual obstruction of vegetation and density of rabbits across 6 of the study sites. Our results suggest that density of burrows can serve as an index for monitoring changes in abundance of pygmy rabbits in east central Idaho and that this index also might be useful for monitoring changes in relative abundance over time at other locations. To assess abundance at larger spatial scales or across different regions, the index should be calibrated under regional conditions and site-level covariates should be evaluated.
Control of mid-sized mammalian predators (hereafter, mesopredators) is sometimes advocated in an attempt to reduce their impact on wildlife populations, particularly economically important (i.e., game) or endangered species. However, mesopredators may play a role in regulating small mammal populations; thus, lethal control of mesopredators may have unintended consequences. The hispid cotton rat (Sigmodon hispidus; hereafter, cotton rat) is one of the most common small mammals in the southeastern United States and is an important prey species for several of the region's predators. Within fire-maintained communities, such as the longleaf pine (Pinus palustris) forests of the Coastal Plain, cotton rat populations dramatically, yet temporarily, decline following prescribed fire. To evaluate the effects of mesopredator removal on cotton rat survival and cause-specific mortality, we conducted a large-scale mesopredator exclusion experiment that incorporated a prescribed fire during the winter of study. Between 18 May 2006 and 20 June 2007, we used radio-telemetry to monitor 252 cotton rats (131 in exclosures and 121 in controls) and documented 184 mortalities. During the 37-week period of monitoring prior to the prescribed fire event, weekly survival of cotton rats was greater in mesopredator exclusion plots. During the 19 weeks following the prescribed fire, there were no differences in weekly survival relative to mesopredator treatment, but fire caused a short-term reduction in weekly survival within both exclosures and controls. Of 36 cotton rats monitored on the date of prescribed fire, 18 were depredated within 1 month, 4 emigrated, and 5 were killed by the fire event. Overall, raptors preyed on cotton rats more in exclosures than in controls, but evidence for compensatory predation (raptor-caused morality greater in exclosures than in controls although survival rates were similar between treatments) only occurred following the prescribed fire event. Our results suggest that managing mesopredators may result in a temporary increase in cotton rat survival, but dormant season prescribed fire removes this effect until well into the following growing season.
Regulations and directives associated with enabling legislation for management of national forests in the United States require maintenance of viable populations of native and desired non-native wildlife species. Broad-scale assessments that address ecosystem diversity cover assessment of viability for most species. We developed an 8-step process to address those species for which management for ecosystem diversity may be inadequate for providing ecological conditions capable of sustaining viable populations. The process includes identification of species of conservation concern, description of source habitats, and other important ecological factors, grouping species, selection of focal species, development of focal species assessment models, development of conservation strategies, and designing monitoring, and adaptive management plans. Following application of our screening criteria, we identified 209 of 700 species as species of conservation concern on National Forest System lands east of the crest of the Cascade Mountains in Oregon and Washington State, USA. We aggregated the 209 species of conservation concern into 10 families and 28 groups based primarily on habitat associations (these are not phylogenetic families). We selected 36 primary focal species (78% birds, 17% mammals, 5% amphibians) for application in northeast Washington State, USA based on risk factors and ecological characteristics. Our assessment documented reductions in habitat capability across northeast Washington State compared to historical conditions. To address such changes, for each focal species we developed conservation strategies that included habitat protection and restoration and amelioration of threats. We combined conservation strategies for individual species with other focal species and with management proposals for other resources (e.g., recreation, fire, and fuels management) to develop a multi-species, multi-resource management strategy. The information generated from our approach can be directly translated into land management planning through development of desired conditions, objectives, and standards and guidelines to improve the probability that desired population outcomes will be achieved. However, it should be noted by practitioners that a practical conservation planning process, such as ours, cannot remove all uncertainty and risk to species viability.
Scientists estimate seed abundances to calculate seasonal carrying capacities and assess wetland management actions for waterfowl and other wildlife using soil core samples. We evaluated recovery of known quantities of moist-soil seeds from whole and subsampled experimental core samples containing 12 seed taxa representing small, medium, and large size classes. We recovered 86.3% (SE = 1.8) of all seeds added to experimental cores; 8.3% (SE = 1.2) of seeds were destroyed during the sieving process and 5.4% (SE = 1.2) were not recovered by observers. Recovery rates varied by seed size, but not seed quantity or disproportionate ratios of seed-size classes. Overall seed recovery rates were similar between subsampled ( = 81.2%, SE = 3.6) and whole—processed core samples ( = 86.3%, SE = 1.8). We used recovery rates to generate size-specific, taxon-specific, and constant correction factors and applied each to actual core sample data. Size-specific correction factors increased seed mass estimates in the Mississippi Alluvial Valley ( = 10.1%, SE = 0.32), upper Midwest ( = 21.2%, SE = 0.61), and both regions combined ( = 15.7%, SE = 0.51) differently, as seed composition in core samples varied regionally. We suggest scientists consider using size-specific correction factors to account for seed recovery bias in core samples because these factors may be applied to a variety of taxa and produced similar mass estimates as taxon-specific correction factors. However, if data from core samples are unavailable at the resolution of seed size classes, we suggest increasing seed mass estimates by 16% to account for seed recovery bias.
We assessed the effects of prescribed burning and cutting on mouflon (Ovis gmelini musimon × Ovis sp.) spring habitat using an experimental design (17.28 ha) of 2 burned, 2 cut, and 2 untreated plots within a homogeneous stand dominated by heather (Erica cinerea and Calluna vulgaris). Overall, we found a shift in treated plots from ligneous species to herbaceous species with high digestive and energetic values for mouflon. We also found a consistently higher number of mouflon feeding on these treated habitats compared to untreated plots. Such effects were still apparent 4 years after habitat modifications. Our approaches could be used by managers to improve and maintain the range of mouflon populations experiencing habitat loss (e.g., woody plant encroachment) and for which the condition of an animal has often a high economical value through trophy hunting.
We present a novel method to improve individual identification of animals based on cameratrapping data. The method combines computer tools and human visual recognition to help multiple users to reach identification agreement. Application of this method to a bobcat (Lynx rufus) picture database from the Jasper Ridge Biological Preserve resulted in a progressive increase in identification agreement between 2 users, as measured by the adjusted Rand index (ARI). An initial ARI value of 0.28 increased to a final value of 0.84 (1 = maximum agreement). In contrast, comparisons involving random picture groupings consistently rendered low ARI values (≤0.05). The numbers of individuals named by the 2 users decreased from initial values of 46 and 43 to final values of 25 and 29, respectively. The tool presented here will help researchers and wildlife managers to identify individual mammals and monitor populations.