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In the early 1990s Agriculture Canada's Permanent Cover Program (PCP) converted over 445,000 ha of cropland to perennial vegetative cover. The wildlife benefits of the PCP have not been the subject of previous research. We conducted grassland bird surveys on 629 PCP sites and 564 cropland sites across Alberta, Saskatchewan, and Manitoba between 25 May and 3 July 1998. PCP sites showed higher avian species richness than cropland, and nine of 10 commonly detected grassland bird species occurred at higher frequencies in PCP than cropland. PCP sites were characterized by taller, denser vegetation and less bare ground than cropland sites. Hayed and grazed PCP sites differed significantly in their vegetative structure and avian community composition, but did not differ in species richness or evenness. Mean bird species richness at both cropland and PCP sites was significantly lower in the aspen parkland ecoregion than in the mixed and moist-mixed grassland ecoregions. Logistic regression identified 18 geographic and vegetative variables that significantly influenced the occurrence of individual species, but models for only two species predicted both presence and absence with greater than 50% accuracy. Avian productivity on PCP lands must be determined to appraise definitively the quality of this habitat for grassland birds.
Studies on small wintering birds often monitor body mass variation over days or seasons. Typically, birds are weighed manually or data are obtained using an electronic balance which displays the bird's mass during visits to a feeder. The problem with these techniques is that they require the manipulation of the animals and/or are labor intensive. We built an automated system which combines a transponder-based radio identification device (RID) and an electronic balance fitted with a weighing perch. This setup permits daily mass variation in birds to be monitored automatically without human presence. The system provides reliable estimates of inert masses (r2 = 1). We also used it to monitor bird masses in an aviary. For five days birds were caught periodically and weighed manually to measure their “real” masses for comparison with the system's estimates. Again a strong relationship was found between calculated and real masses (r2 = 0.92 and r2 = 0.89 using two different balances). This system offers great promise and could be adapted to many forms of field work.
The foraging behavior and resource use of four syntopic species of antwrens (Drymophila) was studied at Intervales State Park (24°17′S, 48°25′W) in the southeastern Brazilian Atlantic forest. Ochre-rumped Antbirds (D. ochropyga) foraged mainly by probing for arthropods in dead leaves. The Ferrugineous Antbird (D. ferruginea) and Bertoni's Antbird (D. rubricollis) gleaned or sallied for insects mainly on live foliage in bamboo tickets. Dusky-tailed Antbirds (D. malura) used many kinds of substrate such as live leaves, dead leaves or twigs, and tended to hang while gleaning insects from herbaceous vegetation. Foraging speed during prey search was significantly slower for D. ochropyga, whereas differences in attack rate among other species were not significant. Niche overlap was measured for 11 substrate-maneuver combinations; D. ferruginea and D. rubricollis had large overlap (82%). Sympatric and syntopic coexistence of these four antwrens may be maintained by habitat and substrate specialization through exploitation of dead leaves and bamboo thickets.
We conducted point counts three times during the 1994 breeding season at 48 stations across the northwestern United States, and used cumulative totals from the three visits to rank the sites by two potential indices of conservation value: species richness and overall abundance of birds. We then recalculated each of the indices (1) using data from only a single visit to each site and (2) using data from only two visits. Rankings based on only one or two visits revealed that eliminating one, and even two of the visits had relatively minor effects on species richness rankings but affected rankings based on overall abundance more substantially. We also evaluated how effectively one or two visits to each site detected particular species of management concern. We conclude that when resources are limited, species richness based on point counts conducted during just one or two visits to potential conservation sites may provide a reliable index for prioritizing conservation efforts. When the primary objective is to determine the presence or absence of a particular species, however, at least two visits may be warranted. Finally, we conclude that, in general, researchers must be careful when using overall abundance as an index for establishing conservation priorities, as values may fluctuate substantially throughout the season.
Analysis of a banded population of American Goldfinches (Carduelis tristis) showed that frequencies of recaptured birds wearing at least one of nine different colored leg bands did not differ from expected frequencies over a 6-yr period. In a similar analysis, the likelihood of a bird becoming part of a local breeding population over a 4-yr period was independent of the color of its bands. For nine colors (yellow, orange, red, green, light blue, dark blue, black, pink, and white) analyzed separately, returning or breeding birds did not carry a particular color more often than expected. The use of colored leg bands in this breeding population did not appear to affect return or breeding frequencies of birds wearing at least one of a particular colored leg band. A trend towards returning and breeding males being less likely to carry a yellow band bears further study since yellow is the color of plumage characteristics associated with dominance during the nonbreeding season and mate choice in this species.
Backpack radio-tags can be used to monitor survival of raptors for several years after fledging, but may reduce survival if a poor fit results from subjective judgments. We present an attachment method that can use bird measurements to predict harness sizes. Relationships between body mass of Saker Falcons and harness size predicted the size for smaller falcon species. Harnesses were fitted when birds had reached full size in the nest, which required age estimation at a previous visit to predict a fledging date. Equations based on wing length provided objective aging of nestlings. A pump-pressured water gun aided capture of young falcons and toggle-loops restrained the feet during marking. Saker Falcons with radio-tags and others marked only with leg bands and implanted transponders had the same recapture rate (7%) in autumn, indicating similar survival. This retrap rate should be adequate to estimate harvest rates and population sizes for Saker Falcons.
The little-known Pale-mandibled Araçari is endemic to wet forests of western Ecuador. I quantified population density, feeding ecology, reproductive biology, and vocalizations. Population density in the study area was one group (nine individuals) per 333 ha. They were observed to consume fruits of 34 species of plants, of which Lauraceae and Palmae were the most important. Pale-mandibled Araçaris fed their young fruits from at least eight species of plants, insects from five orders, adult and nestling birds, and bird eggs. Nests were made in cavities within live trees, typically Carapa guianensis, and clutches consisted of at least two eggs. At one nest, incubation lasted approximately 17 d. Nestling care in one nest lasted at least 44 d, and was shared by the female, the male and at least one helper. Pale-mandibled Aracaris roosted in groups of up to seven individuals. Ninety-five percent of primary forest in the range of this species had been cut by 1988, and less than 1% of its original habitat lies within protected areas.
We gathered data on the habitat and general characteristics of 24 nest mounds (14 active, 10 inactive) of Micronesian Megapodes (Megapodius laperouse senex) in the Palau Islands of western Micronesia. Most (92%) mounds were found in strand forests near beaches. Active mounds in this habitat were composed mostly of sand and averaged (± SD) 108.8 ± 20.6 cm in height, 6.2 ± 0.7 m in width, and 7.3 ± 1.2 m in length (n = 10). In contrast, mounds in uplands were made of organic matter and were smaller in size (82.0 ± 17.0 cm in height, 3.6 ± 0.4 m in width, and 3.7 ± 0.6 m in length; n = 2). Mounds were usually located at the bases of one to three large live trees. Historic and current patterns of megapode distribution and abundance in Palau correspond well with the distribution of strand forests in the archipelago, suggesting that the species' occurrence is linked with this habitat.
Gadwalls (Anas strepera) hatched at Mono Lake, California, exhibit two types of severe foot damage, one manifested by the formation of hard white nodules on the plantar surface, the other by necrosis, which results in deformed and eroded webs and, in extreme cases, loss of podotheca and toes. Unknown in Gadwalls elsewhere or in other waterbirds at Mono Lake, these conditions may be evident in ducklings only three weeks old. They presumably stem from infections incurred after ducklings abrade their feet on the harsh lake substrate. The causative agent(s) is unknown.
We studied survival immediately after banding of Greater Snow Geese (Chen caerulescens atlantica) captured in mass banding drives on Bylot Island (Nunavut, Canada) during the late brood-rearing period. Shortly after release, the banding sites and the surrounding areas were checked for dead banded birds. Logistic regression was used to model post-banding survival in relation to mass and age at banding, size of catch, banding year, and their interactions. Between 1993 and 1996, 6577 adults and 6736 juveniles were banded, of which 6 adults and 192 juveniles (goslings) were found dead. Apparent survival immediately after banding was high for juveniles (0.971 ± 0.002) and close to 1.00 for adults. The post-banding survival of juveniles decreased with catch size and increased with mass at banding, although the magnitude of the latter effect varied among years. Age at banding also affected survival in interaction with banding year and catch size. Post-banding survival was lowest for the youngest goslings captured in the largest catches in some years. Our analysis suggests that banding has a negligible effect on post-banding survival of juvenile snow geese when catch size does not exceed 600 individuals and goslings are heavier than 1400 g or older than 34 d, and has virtually no effect on adults.
Although the gypsy moth (Lymantria dispar) is a significant insect pest of eastern deciduous forests in the United States, relatively little is known about its effects on forest bird communities. We used six Breeding Bird Census sites from Connecticut, Pennsylvania, and Virginia to assess changes in bird species richness and individual species density in the years surrounding a gypsy moth outbreak. Individual species' responses were variable among states, and only a few species showed consistent responses to outbreaks across sites. Yellow-billed Cuckoos (Coccyzus americanus) and Black-billed Cuckoos (C. erythropthalmus) appeared two years prior to an outbreak and then disappeared immediately after an outbreak on four of the sites and increased in numbers on another site. Indigo Buntings (Passerina cyanea), which are usually associated with open habitat, increased temporarily after outbreaks and then returned to pre-outbreak densities within 5 yrs after the outbreak. At the community or guild level, there was a significant reduction in species associated with closed-canopy forests during the outbreak year(s) compared with the average of all other years (before and after the outbreak). There were no other general responses by the avian communities to the outbreaks, including associations with habitat preference, foraging guild, or nesting substrate. This study suggests that the effects of gypsy moth defoliation on the avian community are likely to be short-term (assuming that tree mortality is not severe) and spatially variable. The minimal nature of these effects also suggests that compared with pesticide options for gypsy moth control, allowing the gypsy moth to defoliate, when feasible, is preferable when managing for forest birds.
Although significant numbers of the federally endangered Red-cockaded Woodpecker (Picoides borealis) occur at military installations, little research has been initiated to determine what effects military activities have on the birds. From 1994–1996 we collected data at Ft. Benning Military Installation, Georgia, to assess the effects of selected military activities on reproductive success of the birds. Noise and vibration levels were recorded at or directly adjacent to active woodpecker clusters that received significant use by the military on a regular basis (i.e., firing of small arms and artillery). Identical data were collected at active clusters that were not normally used by military personnel and that we perceived to be relatively free of such disturbances. Surprisingly, we found no significant differences in noise or vibration levels between treatments and controls. There also were no significant differences between treatment and control sites with regard to the numbers of eggs, nestlings, adults, return rates of adults feeding young, or masses of nestlings and adults. Habitat assessments revealed no differences in basal area or midstory density; however, understory was significantly more pronounced at treatment sites.