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Current estimates of annual survival, an important process affecting population dynamics, are lacking for breeding-waterfowl populations in Washington. I used hunting-season recoveries in conjunction with band-recovery models (program MARK) to estimate survival and recovery probabilities of Mallards (Anas platyrhynchos) and Gadwalls (A. strepera) banded in eastern Washington during 1981–1998. I also evaluated hypotheses about sources of variation in these rates and described the geographical and temporal distribution of band recoveries. Mallard survival and recovery probabilities were sex and age-specific, and recovery rates were year-specific but not strongly correlated with harvest regulations. Survival probability of Mallards was 0.661 for adult males, 0.660 for immature females, 0.606 for adult females, and 0.560 for immature males. Average recovery rates were generally highest for immature males (0.083) followed by adult males (0.050), immature females (0.050), and adult females (0.029). Survival and recovery rates of Gadwalls were 0.576 and 0.054, respectively, but sample size was small (52 recoveries from 436 banded birds) and sex-age classes were pooled prior to analysis. Seventy-two percent of Mallards banded in eastern Washington were recovered in the Columbia Basin of central Washington. The proportion of adult-male recoveries decreased in the Columbia Basin (from 75% in 1981–84 to 54% in 1995–98) and increased in California (from 4% to 22%). The distribution of direct recoveries of Gadwalls was similar to Mallards. My data suggest that annual survival of Mallards and Gadwalls banded in eastern Washington was similar to or slightly higher than survival probabilities in other North America populations.
Female Swamp Sparrows (Melospiza georgiana) give a loud series of chips as they leave their nest during incubation and brooding. I tested the efficacy of basing breeding population surveys on the nest departure call (NDC). For a subset of point-count surveys designed to estimate the abundance and distribution of Swamp Sparrows in the coastal mid-Atlantic States, I surveyed singing males and (in a longer survey) the number of different females uttering NDCs. A set of 31 points was surveyed in early June and a subset of 21 in early July. The number of NDCs was well correlated with the number of singing males detected in the early season. The number of females giving NDCs was consistently smaller than the number of singing males. In part, this is because the detection distance for NDC is significantly shorter than for male song. However, even within a small fixed circular plot, more males were detected. Singing-male surveys provide more data over a shorter period of time and are appropriate for large-scale surveys. However, female NDCs provide an index of actual reproductive activity with no unmated birds included. Although a longer survey period is required, the surveys can be conducted throughout the day. It is suggested that female vocalizations related to nesting activity are more widespread than is generally appreciated and, when possible, should be used at least as complementary data to singing-male surveys.
From 1980 to 2000, we mist-netted 2412 Allen's Hummingbirds (Selasphorus sasin) and 203 Rufous Hummingbirds (S. rufus) at a site in central coastal California. Adult Allen's occurred from late January to early August and juveniles from early April to early September. Overall ratios of female to male Allen's were 2.5:1 for adults, 1:1.1 for juveniles. The breeding season female-to-male ratio for adult Allen's of 6.2:1 probably reflected net placement at riparian edges between nests and feeding areas for females. Adult Rufous occurred as transients from mid-February to early May and late June to mid-August and juveniles from mid June to late September. Overall ratios of female to male Rufous were 2.3:1 for adults in spring, 1:1.1 for juveniles. For adults, there was little evidence for a spring migration peak in Allen's, but a fall migration peak was marked. In contrast, adult Rufous showed a spring migration peak but were rare in fall. The two species' main southbound routes in California (coastal for Allen's, interior for Rufous) may, in combination with temporal separation, help partition nectar resources. Capture rates for both age groups of Allen's Hummingbirds indicated a stable population. Juvenile Rufous showed a significant decline in capture rates, reasons for which are unknown.
We documented Bachman's Sparrows (Aimophila aestivalis) entering natural burrows on six different occasions on a dry prairie in central Florida. Use of burrows was apparently an attempt to escape potential predators. Although Bachman's Sparrows were usually flushed from grass-dominated microsites, they preferred to fly to palmetto clumps (Serenoa repens) that had burrows rather than palmetto clumps lacking burrows. This behavior has inherent risks because these burrows are often used by a variety of animals, including predators of small passerines.
Using direct observations of Buff-breasted Wrens (Thryothorus leucotis), I examined timing and duration of egg laying, the behavior of females and males around the time of laying, and duetting and solo singing on laying and non-laying mornings. When laying, females roosted either alone in breeding nests or with their mates in dormitory nests, and left them on average 3.5 min before sunrise. Females returned to their nests at 18.6 min after sunrise and took 21.1 min to lay their eggs. Almost all females were accompanied by their mates to the nest before laying, most males foraged near the nest during laying, and nearly all pairs re-united shortly after laying. Pairs sang significantly fewer duets and females gave significantly fewer solo songs on laying versus non-laying mornings, while males did not change their solo singing behavior. Singing was not restricted to times when females were off their nests, as some pairs duetted and some males gave solo songs while females were laying. These results suggest that females lay their eggs at a time of day which is unfavorable in terms of duetting, and, in turn, for defence of mates and territories.
We compared the nesting success of the Meadow Bunting (Embriza cioides) along different kinds of habitat edges at three sites (166 total nests) in northeast China from 1998 to 2000. Nest loss rates along abrupt edges were more than twice as high as rates on gradual edges where plant succession was allowed to occur. Meadow Bunting nests failed mostly because of nest predation and nest occupation. Nest predation varied significantly among different kinds of habitat edges, with predation rates significantly higher on abrupt edges than on gradual edges. Levels of nest occupation by Brown Shrikes varied significantly among edge types but did not vary among sites and among years. Brood parasitism by cuckoos did not differ among edge types and years. Clutch sizes, however, were significantly smaller along agricultural edges, suggesting either decreased food availability or a population dominated by younger or lower quality birds.
Philopatry and habitat selection were examined for migratory populations of the two sympatric shrike species, the Bull-headed (Lanius bucephalus) and Brown (L. cristatus) shrikes in northern Japan between 1992 and 1997. Although 18% of banded Bull-headed Shrike males returned to the previous breeding area, no female did. In Brown Shrikes, 43% and 13% of banded males and females, respectively, returned to the area. Brown Shrikes are significantly more philopatric than Bull-headed Shrikes. Even successful breeders in Bull-headed Shrikes did not always return to the area near their nesting site of the previous year. Successful breeders in Brown Shrikes were faithful to their past breeding site. Brown Shrikes decreased by 67% due to habitat loss over four years, while the population of Bull-headed Shrikes was stable. The degree of philopatry was inconsistent with the population trends of the two shrikes. While Bull-headed Shrikes did not have habitat preferences in the study area, Brown Shrikes bred mainly in natural grasslands with shrubs. Since available habitat for Brown Shrikes has decreased rapidly in and near the study area, the philopatry of Brown Shrikes may result from a scarcity of habitat that inhibits dispersal. Bull-headed Shrikes may have a higher tendency to disperse because they are habitat generalists. With its more narrow requirements, the Brown Shrike appears to have suffered significantly from habitat loss, while the Bull-headed Shrike has not been adversely affected.
The ability to attract wading birds to a specific location is an important tool for wading bird research. We examined the effectiveness of three commercially available decoy types in attracting free-ranging wading birds to a precise location. There was a statistically significant effect of decoy type on the abundance of wading birds. Wading birds were more attracted to sites with plastic flamingo and Tyvek® bag decoys than with Texas rag decoys or no decoys (control sites). The flamingo and Tyvek® bag decoys have a rigid three-dimensional shape, which may be a more important characteristic than the detailed features of a decoy in attracting wading birds. White wading birds showed a significant effect of decoy type on abundance, whereas birds with dark plumage did not.
We studied the species composition and seasonality of the bird community in the semi-arid west pampa grasslands of Argentina. The study was carried out in natural grasslands with and without a history of cattle grazing (“mixed grassland” and “sorgastral,” respectively). We counted birds using the strip-transect method. We recorded a total of 22 bird species including only 12 grassland-dependent species. The more representative species of these grasslands were Chaco Pipit (Anthus chacoensis), Long-tailed Meadowlark (Sturnella loyca), and Grassland Sparrow (Ammodramus humeralis). Richness and abundance of birds were higher in mixed grasslands than in sorgastral in spring and summer, but not in winter. Inside habitats, richness and abundance were higher in spring and summer than in winter. We observed a seasonal change in guild dominance, with granivores dominant in winter, although bird density decreased during winter for all guilds. Despite the low richness recorded, the presence of certain rare species, such as the Chaco Pipit and the near threatened Greater Rhea (Rhea americana), add conservation value to west pampa grasslands.
We studied seven mixed-species colonies of terns and skimmers on the Virginia barrier islands in 1990 and 1991 to determine the effect of gull predation on nesting success. We compared intensity of gull predation and other agents of egg or chick mortality between tern and skimmer colonies on islands that also contained nesting gulls and colonies on islands that lacked nesting gulls. Terns and skimmers fledged about 3% of all eggs produced, with confirmed gull predation (27%) and tidal flooding (21%) accounting for the majority of nest failures. Gull-present colonies experienced significantly greater rates of disturbance from Herring and Great Black-backed gulls than did gull-absent colonies. Overall levels of gull predation were similar between gull-present and gull-absent colonies, likely due to the added impact of aerially foraging Laughing Gulls. Anecdotal evidence suggests that nest site competition with Herring and Great Black-backed gulls may have led to many terns and skimmers nesting in areas that were prone to frequent tidal flooding. In addition, floods may have indirectly prevented terns and skimmers from adequately protecting their surviving eggs and young, thus rendering flooded colonies more susceptible to gull predation.
We surveyed Mountain Plovers (Charadrius montanus) wintering in the Imperial Valley of California in January 2001, and also recorded the types of crop fields used by plovers in this agricultural landscape. We tallied 4037 plovers in 36 flocks ranging in size from 4 to 596 birds. Plovers were more common on alfalfa and Bermudagrass fields than other field types. Further, most birds were on alfalfa fields that were currently being (or had recently been) grazed, primarily by domestic sheep. Plovers used Bermudagrass fields only after harvest and subsequent burning. Examination of Christmas Bird Count data from 1950–2000 indicated that the Mountain Plover has abandoned its historical wintering areas on the coastal plains of California. Numbers in the Central Valley seem to have undergone recent declines also. We believe that the cultivated landscape of the Imperial Valley provides wintering habitats for about half of the global population of Mountain Plovers. We attribute the current importance of the Imperial Valley for Mountain Plovers to loss of native coastal and Central Valley habitats rather than to a behavioral switching of wintering areas through time. Future changes in specific cropping or management practices in the Imperial Valley will have a major impact on the conservation status of this species.
Body mass and fat reserves of Sedge Warblers (Acrocephalus schoenobaenus) on nocturnal departure and arrival were studied by two methods (capture in high nets and playback of songs) on the Courish Spit (Eastern Baltic, Russia) in spring 1998–2000. The average body mass of departing Sedge Warblers was 13.7 g, and the average body mass of arriving birds was 13.1 g. The difference between arrival and departure masses was not significant. The calculated flight range of departing Sedge Warblers in still air varied from 19 to 665 km, with a mean of 295 km. The high fuel loads of Sedge Warblers on departure and on arrival may be explained by the necessity for Scandinavian populations to cross the Baltic; the risk of drifting out to sea for birds migrating over land; or the general vernal migratory strategy of Sedge Warblers, involving a series of short (4.5–6.2 h) flights on several consecutive nights.
We studied molt and size variation in Whiskered Auklets collected at sea in August from the Aleutian Islands in 1992 and 1993. We evaluated size differences from external and skeletal measurements. Adults were molting extensively in August, indicating that molt began in July. Primaries 1–5 had been completely replaced, while primaries 6–8 were in various stages of replacement, and primaries 9 and 10 were old in most birds. We also found that juveniles were not molting. This pattern is similar to other species of small auklets where breeding and molt in adults overlap, but juveniles do not molt until the following summer. This suggests that Whiskered Auklets are subjected to similar ecological constraints as other auklets. We provide the first skeletal measurements of Whiskered Auklets and some new external measurements. Results of statistical analyses indicate that there is no sexual dimorphism in adults. A small sample of juveniles suggests that they are similar in size to adults.