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Birds with both eastern and western distributions occur in the Black Hills of western South Dakota. This forest is mostly ponderosa pine (Pinus ponderosa) and is managed for timber. Logging alters forest characteristics and the bird community. We studied habitat relations of breeding songbirds at the stand- and site-level scales in ponderosa pine and quaking aspen (Populus tremuloides)/paper birch (Betula papyrifera) forest. Sixty bird species were observed ≤50 m from count points. Species richness was greater in aspen/birch than in ponderosa pine. Species richness was generally lower in ponderosa pine with >40% overstory canopy cover (OCC) than in ponderosa pine with ≤40% OCC and than aspen/birch of any structural stage. Seven bird species were associated with the ponderosa pine, while four species were associated with aspen/birch. Bird associations at the stand-level were further refined by OCC and diameter-at-breast-height (DBH) structural stage of each forest type. Habitats for most birds in the Black Hills can be managed using current forest inventory descriptions that include OCC and DBH. However, Red-naped Sapsuckers (Sphyrapicus nuchalis), Red-breasted Nuthatches (Sitta canadensis), White-breasted Nuthatches (S. carolinensis), Ovenbirds (Seiurus aurocapillus), and Western Tanagers (Piranga ludoviciana) were strongly associated with site-level vegetation characteristics. Snag density, snag condition, and deciduous trees beneath the ponderosa pine canopy should be included in forest inventories to better quantify habitats for these birds.
Using cameras at artificial ground nests we found no major quantitative differences in species richness or the relative abundance of nest predators photographed in farm/forest edge and forest-interior sites at five locations in eastern Pennsylvania. Raccoons (Procyon lotor) were the most commonly photographed visitors to nests at both farm/forest edge and forest interior sites, followed by female Baltimore Orioles (Icterus galbula), southern flying squirrels (Glaucomys volans), gray squirrels (Sciurus carolinensis), eastern chipmunks (Tamias striatus), and Gray Catbirds (Dumetella carolinensis). Rate of egg loss was higher at the edges than in the forest interior. Although the total number of photographs of predators averaged 11 among the five edge sites and 7.4 among interior sites, this was not significantly different.
The timing, pattern, and extent of the first prebasic wing molt of White-winged Crossbills (Loxia leucoptera) were determined during a 6-yr banding study in interior Alaska. Hatching-year birds were not caught in substantial numbers until May, and all crossbills molted from juvenal to first basic plumage between September and December. A subsample consisting of 65 males and 55 females in first basic plumage was used to determine the pattern and extent of wing covert molt. On average, birds molted three greater coverts (GC) and retained two juvenal medial coverts (MC) per wing. The number of molted GCs was negatively correlated with that of juvenal MCs. Twenty-three percent of the individuals molted no GC, and no crossbill replaced all these feathers. The pattern and extent of covert molt was similar in males and females and was symmetrical in 69% of the individuals, but differed by one or two feathers in the remaining birds. Males in first basic plumage and with partially red or pink contour feathers molted more GCs and retained fewer MCs than males without contour feathers of these colors, although both groups apparently were of the same age. Remex molt was found in only one bird, which also showed partial proximal secondaries (=tertial) replacement.
We examined whether regular researcher visits affected egg hatchability or nest predation for three ground-nesting bird species that incur high levels of nest predation, primarily by small mammals. Frequently visited finch-lark (Eremopterix verticalis and E. australis) nests suffered similar predation to nests visited infrequently, suggesting that regular visits had no additive effects on nest survival. A comparison of finch-lark nests visited for the second time either one or two days after the first visit found that predation during the first 24 h (7.4%) was lower than predation during the second 24-h period (9.9%), suggesting that the act of visiting a nest did not increase the risk of predation. Daily predation rates on Namaqua Sandgrouse (Pterocles namaqua) and finch-lark nests showed no observable trend with an increasing number of visits over time, indicating that frequent visits had no cumulative effect on predation probabilities. Nests of both Grey-backed Finch-lark (E. verticalis) and Black-eared Finch-lark (E. australis) discovered at the egg stage did not fledge significantly fewer young than nests discovered at the nestling stage, suggesting that investigator disturbance had no effect on egg hatchability. These results from the southern hemisphere subtropics support the findings of limited north-temperate studies that largely mammalian nest predation does not increase after researcher disturbance.
We investigated nest-site selection of sympatrically breeding skuas (Catharacta spp.) and Kelp Gulls (Larus dominicanus) in the Antarctic Peninsula. We evaluated habitat preferences of nesting skuas and gulls in a patchy landscape by counting the numbers of nests in each of ten habitat types. Additionally, we evaluated the importance of 11 habitat variables (known to be influential to the reproductive success of marine birds) on nest-site selection by skuas and gulls. Both skuas and Kelp Gulls did not used habitat types in proportion to their availability. Skuas tended to nest in highlands with a north-northwest aspect, and in depressed areas with stable substrata. Kelp Gulls nested exclusively on coastal cliffs and pebble beaches, with no difference in tendency to use either habitat. Skua and gull nest sites were differentiated by elevation, percent of vegetation cover, slope, and microtopography. Grasses (for Kelp Gull), mosses (for skuas), and rockiness were the main variables predicting differential use of the available environment. Factors such as type of nest materials, proximity to foraging areas, social interactions, and presence of other species, among others, probably also affect nest-site selection for both skuas and gulls at Cierva Point, Antarctic Peninsula.
The scientific value of avian research specimens is immense, but the accumulation rate of this resource is too low to meet either present or future needs. This may be due, in part, to the fact that few students are currently being taught to prepare specimens. Modern specimen preparation is a routine but detailed and meticulous process in which comparatively few are expert. I summarize methods for obtaining bird specimens and preserving them both for the short term and for the long term as high quality scientific research specimens. The preparation method outlined preserves skin, partial skeleton, stomach contents and two duplicate tissue samples for every specimen, maximizing the scientific usefulness of each bird. The resulting skins and skeletons augment current samples, simultaneously increasing the sample sizes available for studies involving either type of specimen. These methods allow a diverse array of data to be taken from every individual, and are thus suitable for general preparation or focused, single-species research projects. These archival quality methods assure that, if prepared as outlined, the skin and skeleton specimens possess a useful life of half a millennium or more. I suggest that this is an unparalleled opportunity to make a personal, signed, long-term contribution to science with relatively little time investment.
From 1992 to 1997, I monitored population size and productivity of Ospreys (Pandion haliaetus) nesting along 80 km of coast on the eastern side of the Gulf of California, Mexico. During the study period, the number of nesting pairs increased by an estimated 5–14%. The percentage of successful pairs varied significantly among years, ranging from 5–50%. In three of the six years, the productivity of breeding pairs exceeded the estimated level necessary to maintain Osprey population size in at least parts of the species' range. However, three of the last four years were characterized by low reproductive success and by a higher proportion of late clutches. In 1997, the most unproductive of the six years, 38 of 40 (95%) nesting pairs failed to produce any fledgling. That same year, however, the observed productivity of 10 pairs on two nearby islands was 15 times higher than on the mainland. In 1994, 1995, and 1996, successful pairs were significantly clumped, indicating that in the study area, nesting success was strongly influenced by local factors. The results of this study warrant further research to identify the source(s) of annual and spatial differences in nesting success.
Lake Ontario is the only Great Lake where a significant number of Red-throated Loons are seen during fall migration. Observations from Hamlin Beach State Park, New York during fall months, 1993–1997, were used to analyze their movements. Annually, an average of 7750 Red-throated Loons were counted moving mostly west on the south shore of Lake Ontario. Their median date of occurrence was 22 November with the peak period of migration from 17 November to 1 December. The earliest migrants appeared in mid-October and became extremely rare after December. The seasonal timing on Lake Ontario corresponds to that observed on the Atlantic Ocean at Avalon, New Jersey. Their occurrence on Lake Ontario was analyzed with respect to local and mid-arctic weather conditions. The variable which best correlates with their appearance is mid-arctic temperature. On average, large flights (>200 loons per day) began on Lake Ontario 3 d after the invasion of a cold air mass is centered approximately 1100 km to the north. After this event, the period of sustained flight was maintained for 7–16 d when 80% of migration takes place. The fall arrival pattern of Red-throated Loons on Lake Ontario implies that migration takes place under any type of weather conditions, but local temperature, wind direction, and the movement of cold fronts are all weakly correlated to their migration. Inland fall sight records of Red-throated Loons from American Birds suggest that the main inland migration route is through western Pennsylvania. This is consistent with observations of Red-throated Loons leaving the western end of Lake Ontario. A smaller part of the inland migration is east of Lake Ontario based on these records.
Surveying birds during the non-breeding season in prairie environments can be difficult because birds are less visible and vocal during this period than they are during the breeding season. We compared the effectiveness of using fixed-radius point counts and rope-dragging transects for surveying non-breeding birds and determining their relative abundances in the Florida Everglades, from November 1997 through January 1998. Effort (person work hours) was compared using species-effort and abundance-effort curves. Relative abundances of total birds, American Bittern (Botaurus lentiginosus), Sedge Wren (Cistothorus platensis), Common Yellowthroat (Geothlypis trichas), and Seaside Sparrow (Ammodramus maritimus mirabilis) were greater using transects. Abundances of other common species were similar using both techniques. More species were detected on transects than on point counts. When considering effort involved, transects detected more total species, but point counts detected a greater total number of birds. Overall, transects took more effort to cover similar amounts of habitat. Differences in detection using these two techniques may be attributed to species-specific behaviors. Research focused on non-breeding season bird communities should consider using rope-dragging transects in appropriate habitat because point counts may underestimate abundances of some species.
Accurate population models for the endangered Interior Least Tern (Sterna antillarum) cannot be generated without age-specific survival estimates. Our purpose was to estimate chick survival from hatching to fledging, for Least Terns nesting at two sites on the Lower Mississippi River in Missouri, using mark-recapture methodology. We banded 110 Least Tern chicks during 1995 on sand island nesting colonies situated at river kilometers (Rkm) 1431 and 1481 on the Lower Mississippi River. We used Program JOLLY to compute survival point estimates, their associated variances, and goodness-of-fit tests for Jolly-Seber open population models (Pollock et al. 1990). The mean daily survival rate for Least Tern chicks at Rkm 1431 was 0.951 (SE = 0.03) with 95% confidence intervals of 0.899–1.003. Mean daily survival rate for Least Tern chicks at Rkm 1481 was 0.972 (SE = 0.03) with 95% confidence intervals of 0.911–1.034. Estimated survival of Least Tern chicks throughout the entire 17-d fledging interval was 0.43 at Rkm 1431 and 0.62 at Rkm 1481. Based on survival rate estimates and number of known pairs producing chicks we estimated 0.72 and 1.0 fledglings/pair were produced at Rkm 1431 and Rkm 1481, respectively.
At Flathead Lake Biological Station in western Montana, Violet-green Swallows (Tachycineta thalassina) sunbathed during a restricted period and under specific meteorological conditions in an apparent attempt to rid themselves of ectoparasites. Sunbathing was done only in direct sunlight, at mean ambient temperatures ≥23.4 C and wind velocities of 14 km/h or less. The number of birds sunbathing at any given time was a function of both ambient temperature and wind velocity. Swallows basked at lower temperatures when wind velocities were low. Duration of basking likewise was a function of both ambient temperature and wind velocity. Length of basking bouts decreased as numbers of birds increased. Relative humidity did not significantly affect number of birds sunbathing or duration of bouts. Although numerous sites were available, swallows sunbathed only at one specific site, a reflective silver roof, and then only over a period of a few weeks from late June through July.
We compared the efficacy of 400-m line transects and sets of three point counts at detecting avian richness and abundance in bottomland hardwood forests and intensively managed cottonwood (Populus deltoides) plantations within the Mississippi Alluvial Valley. We detected more species and more individuals on line transects than on three point counts during 218 paired surveys conducted between 24 March and 3 June, 1996 and 1997. Line transects also yielded more birds per unit of time, even though point counts yielded higher estimates of relative bird density. In structurally more-complex bottomland hardwood forests, we detected more species and individuals on line transects, but in more-open cottonwood plantations, transects surpassed point counts only at detecting species within 50 m of the observer. Species richness and total abundance of Nearctic-Neotropical migrants and temperate migrants were greater on line transects within bottomland hardwood forests. Within cottonwood plantations, however, only species richness of Nearctic-Neotropical migrants and total abundance of temperate migrants were greater on line transects. Because we compared survey techniques using the same observer, within the same forest stand on a given day, we assumed that the technique yielding greater estimates of avian species richness and total abundance per unit of effort is superior. Thus, for monitoring migration within hardwood forests of the Mississippi Alluvial Valley, we recommend using line transects instead of point counts.
Nearly all previous studies of saltmarsh-nesting Common Terns on the east coast of the United States have concluded that tidal saltmarshes were suboptimal or marginal breeding habitats. Questioning that conclusion, we analyzed patterns of both saltmarsh and nonmarsh colony use (stability, movement, establishment, abandonment, and size) obtained during 5 yr of annual helicopter censuses of all Common and Roseate terns breeding on Long Island, New York. We found 1900–3600 pairs at 10–33 saltmarsh and 22–30 nonmarsh sites; there were few biologically important differences between Common Terns nesting at marsh and at nonmarsh sites. We did find that (1) marsh sites and colony sizes increased through the study period; (2) both marsh and nonmarsh colonies grew with duration of occupancy; (3) smaller marsh and nonmarsh colonies (<50 pairs) usually lasted only 1–2 yr, while larger colonies were equally likely to persist for 1, 2, 3, 4, or 5 yr; (4) numbers of marsh and nonmarsh sites used each year were generally unrelated to population sizes; (5) 5-yr sites composed only 10.6% of total marsh and 17.6% of total nonmarsh sites; (6) the mean sizes of both newly established and about-to-be-abandoned colonies were smaller than the mean sizes of all others when averaged between but not within years; (7) most previously occupied sites, once abandoned, remained so for only 1 yr, and most new sites were occupied for only a single year; (8) annual turnover rates were 32%–49% for both marsh and nonmarsh sites; (9) marsh and nonmarsh breeding populations were correlated each year, allowing estimation of the total Long Island population to within ±4% by censusing only the 20–25% in saltmarshes. Roseate Tern data were few, especially in marshes, obviating marsh-nonmarsh comparisons, except that Roseates failed to persist in saltmarshes, and their overall mean colony sizes across the same numbers of years' occupancy were usually smaller than Commons', although their turnover rates were roughly the same. We conclude that saltmarsh-nesting Common Terns are well adapted to marsh nesting and that they have probably been doing so for perhaps hundreds of generations. We hypothesize that it may have been a relict population of saltmarsh-nesters that saved the species from extirpation in the late 1800s. In contrast, Roseate Tern's failure to exploit extensive saltmarsh habitat seems yet another factor abetting its precarious status in northeastern North America.