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Rising sea levels in the mid-Atlantic region pose a long-term threat to marshes and their avian inhabitants. The Gull-billed Tern (Sterna nilotica), Common Tern (S. hirundo), Black Skimmer (Rynchops niger), and American Oystercatcher (Haematopus palliatus), species of concern in Virginia, nest on low shelly perimeters of salt marsh islands on the Eastern Shore of Virginia. Marsh shellpiles are free of mammalian predators, but subject to frequent floods that reduce reproductive success. In an attempt to examine nest-site selection, enhance habitat, and improve hatching success, small (2 × 2 m) plots on five island shellpiles were experimentally elevated, and nest-site selection and hatching success were monitored from 1 May to 1 August, 2002. In addition, location, elevation, and nesting performance of all other nests in the colonies were also monitored. No species selected the elevated experimental plots preferentially over adjacent control plots at any of the sites. When all nests were considered, Common Tern nests were located significantly lower than were random point elevations at two sites, as they tended to concentrate on low-lying wrack. At two other sites, however, Common Tern nests were significantly higher than were random points. Gull-billed Terns and American Oystercatchers showed a weak preference for higher elevations on bare shell at most sites. Hatching success was not improved on elevated plots, despite the protection they provided from flooding. Because of a 7 June flood, when 47% of all nests flooded, hatching success for all species was low. Nest elevation had the strongest impact on a nest's probability of hatching, followed by nest-initiation date. Predation rates were high at small colonies, and Ruddy Turnstones (Arenaria interpres) depredated 90% of early Gull-billed Tern nests at one shellpile. The importance of nest elevation and flooding on hatching success demonstrates the potential for management of certain waterbird nesting sites. Facing threats from predators on barrier islands and rising sea levels especially in the mid-Atlantic region, several species of nesting waterbirds may benefit dramatically with modest manipulation of even small habitat patches on isolated marsh islands.
A captive study was conducted to determine the most appropriate method for attaching radio transmitters to a medium-sized (20–100 g) passerine, the European Starling (Sturnus vulgaris). Using mock transmitters, three methods of attachment were tried: a body harness, a glued backpack, and a tail-mount. The harness was the most reliable in terms of duration of attachment, with six of eight attachments (75%) retained by the birds at the completion of the 24-d trial. In contrast, just two of eight (25%) glued backpack attachments remained in place at the conclusion of the study. Tail-mounts performed only slightly better than glued backpacks, with only three of eight tail-mounts remaining in place at the conclusion of the study. Flight, feeding, and perching activities were not affected by the attachments; however, some birds showed initial annoyance toward the mock radio transmitters, inferred by pecking directed at the attachment site. Each attachment method was found to slightly alter the activity (pecking) of the starlings compared to the control group, but this persisted only for the first day following attachment. On the basis of the pecking response, tail-mount attachments were the least aggravating to the birds followed by the harness method. Once adjusted to the attachment, we observed no difference in starling activity, and the body condition of control and treated birds remained similar for the duration of the trials. We recommend the use of the harness for attaching radio transmitters to European Starlings and other similar sized passerines, particularly if birds are expected to molt during the experimental period.
We monitored 67 Golden-cheeked Warbler (Dendroica chrysoparia) nests with infrared video cameras and time-lapse recorders to identify predators. Rat snakes (Elaphe spp.) were the most frequent predators, depredating 12 nests and capturing three adult females. A variety of avian predators depredated seven nests, including three American Crows (Corvus brachyrynchos), two Brown-headed Cowbirds (Molothrus ater), one Western Scrub-Jay (Aphelocoma californica), and one Cooper's Hawk (Accipiter cooperii). Fox squirrels (Sciurus niger) depredated four nests and were the only mammalian predators recorded. Post-outcome recordings (i.e., after young fledged or nests failed) revealed western coachwhips (Masticophis flagellum testaceus), mice (Peromyscus sp.), and Greater Roadrunners (Geococcyx californianus) as potential predators, though they were not recorded at active nests. Video proved to be an effective method of monitoring Golden-cheeked Warbler nests, because all but one predator was identified and only two nests (3%) were abandoned.
The Long-tailed Wood-Partridge (Dendrortyx macroura) is a species endemic to Mexico, inhabiting dense coniferous forests of the Trans-Mexican Volcanic Belt and the Sierra Madre del Sur, of which little is known about its ecology and conservation status. The abundance and density of the Long-tailed Wood-Partridge was estimated by point counts with playback distance sampling from March–October of 1998–2000 in a temperate coniferous forest managed for timber production by a Mexican indigenous community. The average detection rate was 0.31 individuals per point, resulting in a mean estimate for population density of 20.9 birds/km2 and a mean population estimate of 2679 individuals, estimated using the half-normal key function with cosine adjustments. Density estimates of the Long-tailed Wood-Partridge were 8 individuals/km2 in dry, open, scrubby habitats with deep ash and sand volcanic deposits subject to intense human use and in closed canopy, humid forests with moderate human disturbance. Density estimates were 14.6 and 21.5 individuals/km2 in humid, closed canopy, multi-stratified forests. The latter areas are recommended as the core area for protection of the Long-tailed Wood-Partridge.
We provide data on three instances where Tree Swallows (Tachycineta bicolor) that fledged from the same nest (broodmates) eventually bred together in subsequent years. Two instances were detected in Ontario and a third was detected in Nova Scotia. Based on demographics at the times of each event, we estimated probabilities of these broodmate pairings as approximately 1 in 16,000, 1 in 5600, and 1 in 29,000, respectively, whereas the number of identified pairs in the populations was less than 65 in each case. Thus, inbreeding occurred at a higher frequency than expected by chance. We cannot distinguish whether these identical natal dispersal responses arose from similarity in genes or in rearing environments.
We used a recorded song of the Bachman's Sparrow (Aimophila aestivalis) to determine whether recorded vocalizations improved detection of this secretive species in winter. Surveys were conducted in the Red Hills region of northern Florida and southwestern Georgia under a range of climatic conditions. Bachman's Sparrows responded readily to taped vocalizations and were detected only on surveys where recorded vocalizations were used. A total of 251 individuals (mean = 1.01 per stop) was observed, or approximately 10–15 observations/h. Detections decreased at lower ambient temperatures and also varied among sites, but adequate numbers were observed even when maximum daytime temperatures remained < 3° C. We believe variation in the number of sparrows observed among sites may relate to variation in ground cover. Bachman's Sparrows were most common in areas with extensive native ground cover, but further studies are needed. We recommend use of recorded vocalizations in winter surveys of Bachman's Sparrows and suggest recorded vocalizations may help in winter surveys of other secretive sparrows.
We examined nest predation rates at artificial nests in two contrasting habitats (open woodland and shrubland) inside the Reserve of Ñacuñán, west-central Argentina and in open woodlands within the reserve and a nearby grazed area, to assess whether between-habitat differences in vegetative structure were associated with changes in nest predation levels. We also quantified diurnal and nocturnal predation rates to further characterize the predator assemblage of the reserve. Nest predation rates and the estimated daily mortality rates were quite high in both open woodland and shrubland and did not differ significantly between them. Nest predation rate and daily mortality rate of nests in open woodlands of the reserve were high but similar to the rates for nests in adjacent grazed open woodlands. Nearly all predation events occurred during daylight hours. This result was not an artifact of the use of quail eggs because the proportion of depredated nests during the night was similar when we used smaller eggs of captive passerines. Our results support previous findings on the prevalence of birds as nest predators in this area. Avian predators seemed to be efficient at locating our artificial nests in all habitats, leading to the lack of differences between treatments. Conversely, our results suggest that extensive cattle grazing does not greatly modify nest predation risk for above-ground nests, although this conclusion is provisional given the conditions under which our experiments were carried out.
Identifying the arthropods present in the digestive tracts of human-imprinted gamebird chicks after foraging may provide a more biologically relevant assessment of arthropod availability in brood-rearing habitats. It may also provide information on food selection by chicks. An assumption of this methodology is that diagnostic fragments of arthropods (i.e., those body fragments used to identify taxa) are not passed out of the gizzard before chicks are euthanized. We investigated the passage of diagnostic fragments of six arthropod species within the digestive tract of 10 d-old Northern Bobwhite (Colinus virginianus) chicks. Although fragments of arthropods were found in the intestines of a few chicks, arthropod-diagnostic fragments were only found in the crop and gizzard. The results of this study suggest that diagnostic fragments of arthropods ingested by human-imprinted chicks are not excreted within a 40-min foraging period.
American Avocets (Recurvirostra americana) and Black-necked Stilts (Himantopus mexicanus) are large ground-nesting shorebirds whose eggs and flightless chicks are exposed to a variety of predators during a period of approximately two months. Parents respond to potential predators by ignoring them, by performing a variety of diversionary displays, or by aggressive mobbing. I observed the responses of avocets and stilts to natural predators and to predator models placed near their nests. Responses to mammals were relatively weak, involving mostly aerial circling and terrestrial distraction displays, and mammals rarely were mobbed. Responses to birds were more aerial, with ground displays rarely used, and birds often were mobbed. The response to humans was intermediate between the responses to other mammalian predators and to avian predators, and involved both distraction displays and mobbing. The number of avocets and stilts participating in mobbing eight different avian predators correlated with a subjective ranking of the danger the predators posed to mobbing adults. Mobbing of gulls, raptors, and herons was consistent with the hypothesis that avocet and stilt mobbing behavior is influenced by the relative threat of particular predators to eggs versus chicks. Overall, the observations reported here provide evidence that parent avocets and stilts discriminate among predators on the basis of both the risk to the adults of mobbing the predator and the risk to the eggs or chicks of not doing so.
We measured wing chord, tail length and mass and estimated levels of subcutaneous fat deposits of Sharp-shinned Hawks (Accipiter striatus) trapped at Cedar Grove, Wisconsin. Wing chord, tail length, and mass all showed a sudden increase beginning about 10 October in adults and juveniles and in males and females despite the fact that adults migrate about 20 d later than juveniles and males migrate later than females. Migrants captured at Cedar Grove late in the season did not differ significantly in wing chord or tail length from migrants captured at the Goshutes in eastern Nevada. We suggest that an increasing proportion of the birds captured at Cedar Grove after 10 October are of western origin because winds are more westerly in October than in September. The greater mass of Cedar Grove birds may be because of greater availability of prey than in the Goshutes or because the lower mass of birds in the Goshutes is a facultative adaptation for easier passage through the arid west.
Male Tree Swallows (Tachycineta bicolor) face intense sperm competition because mated pairs copulate frequently, extra-pair copulations are common, and females store sperm. We examined the effects of repeated sampling on the characteristics of Tree Swallow semen by manually expressing semen from 15 males immediately after capture (T0) and then hourly for 4 h (T1–T4). The semen characteristics of individual males varied in response to repeated sampling. The total number of sperm cells we obtained from each male over the 4-h sampling period varied from 104–107. Semen samples lacking sperm increased from 6.7% of T0 samples to 26.7– 33.3% of subsequent samples. Forty percent of males provided at least one semen sample that lacked sperm. There were no significant differences among hourly samples in semen volume, sperm concentration, or in the total number of sperm cells obtained from each male. However, there were significant differences among males in each of these variables. Semen volumes represented small proportions of cloacal protuberance volumes. We did not detect significant correlations between total semen volumes or total number of sperm cells obtained from males from T0–T4 and cloacal protuberance volumes. Total semen volume and number of sperm cells obtained from T0–T4 significantly increased with date. However, sperm concentration was not significantly correlated with date. We did not detect significant correlations between semen characteristics and male morphology. Individual variation in responses to repeated sampling has implications for the copulatory strategies of male and female Tree Swallows.
I examined vigilance behavior of Mallards (Anas platyrhynchos) feeding in flocks with Greylag Geese (Anser anser) on stubble-fields in northern Germany. I measured scans/min and total scan duration, and I calculated mean scan duration. There was an inverse correlation between group size and scanning for Mallards, but not when geese and Mallards were considered as a combined flock. Mallards did not benefit from the presence of geese in terms of reduced vigilance, and they seemed to adjust their vigilance according only to Mallard flock sizes. Vigilance was higher in the presence of geese and may have been directed towards geese as potential competitors. No differences in vigilance between male and female Mallards were found. In August, when males were in eclipse plumage, they showed reduced vigilance.