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Using standardized mist-net captures collected over a 32-year period (1970–2001), we examined changes in the capture rates of passerines recorded in coastal Massachusetts during fall (78 species) and spring (72 species) migration. Capture rates of 45 species of fall migrants (58%) declined significantly between early (1970–1985) and late (1986–2001) years of the study; 36 species of spring migrants (50%) showed significant declines. Only Carolina Wren (Thryothorus ludovicianus), Tufted Titmouse (Baeolophus bicolor), Northern Cardinal (Cardinalis cardinalis), and Orchard Oriole (Icterus spurius) showed significant increases during spring migration; fall sampling indicated that Carolina Wren, Tufted Titmouse, Black-throated Blue Warbler (Dendroica caerulescens), and Northern Cardinal had significantly higher capture rates. Of 37 species included in the migration monitoring data but not reliably represented by Breeding Bird Survey (BBS) data in any of the northeastern physiographic strata, 23 (62%) showed significant declines at Manomet during at least one of the two migration periods. There were significant correlations in percent changes in migrant capture rates between fall and spring. BBS trends reported from the southern New England and northern New England physiographic strata were correlated with changes in migrant capture rates. However, there were also inconsistencies between results obtained by the two monitoring approaches, suggesting that factors in addition to actual changes in breeding populations may be reflected in the migration capture data.
We video-recorded three, natural, brood-parasitism events by Brown-headed Cowbirds (Molothrus ater) at nests of Least Bell's Vireos (Vireo bellii pusillus). All instances occurred near dawn, during both egg-laying and incubation stages of the nesting cycle. In each case, an adult vireo was on the nest when the female cowbird arrived. Both members of each parasitized pair vigorously attacked the intruding cowbird, but in no encounter did a pair of vireos successfully defend its nest from parasitism. Thus, Least Bell's Vireos in our study were unable to prevent a female cowbird from parasitizing their nests once the cowbird had reached the nest.
We examined effects of incubation mate feeding on female incubation behavior and correlates of fitness by providing female Bewick's Wrens (Thryomanes bewickii) and House Wrens (Troglodytes aedon) with food supplements. Males of these species vary in their rates of feeding; Bewick's Wrens feed their incubating mates frequently, whereas House Wrens seldom engage in this behavior. Average length of incubation bout and nest attentiveness (proportion of time spent on the nest) were higher for supplemented female Bewick's Wrens and House Wrens compared to controls. Furthermore, mates of supplemented Bewick's Wrens provisioned females at lower rates than controls, and their rate of feeding was inversely correlated with ambient temperature. Incubation length and hatching success were not significantly different between treatments for either species. These results suggest that incubation mate feeding can increase female nest attentiveness and perhaps enhance fitness of both males and females. In House Wrens, potential tradeoffs between the benefits of parental care and opportunities to obtain additional mates may explain why males rarely feed incubating females.
We obtained nestling provisioning and reproductive data from 24 Red-cockaded Woodpecker (Picoides borealis) groups occupying two different pine habitats—longleaf pine (Pinus palustris) and a mixture of loblolly (P. taeda) and shortleaf pine (P. echinata)—in eastern Texas during 1990 and 1991. Habitat data were collected within 800 m of each group's cavity-tree cluster. Feeding trips per nest and prey biomass per feeding trip were significantly greater in loblolly-shortleaf pine habitat. There were few significant correlations between reproductive/provisioning and habitat variables in either pine habitat. Pines dying from infestation by southern pine beetles (Dendroctonus frontalis) were more common in loblolly-shortleaf than in longleaf pine habitat. In addition, adult male Red-cockaded Woodpeckers weighed more in loblolly-shortleaf pine habitat. Indices of southern pine beetle abundance in loblolly-shortleaf pine habitat were negatively correlated with number of feeding trips per nestling, but positively correlated with prey biomass delivered to nestlings. We hypothesize that the greater abundance of southern pine beetles and associated arthropods in loblolly-shortleaf pine habitat, and the resulting higher frequency of dying pines containing an abundant food source, were associated with an elevated prey biomass available to both nestling and adult Red-cockaded Woodpeckers.
We studied the consequences of nest predation and brood parasitism on a population of Wilson's Warblers (Wilsonia pusilla) breeding in coastal riparian woodlands in northern California. We monitored 90 warbler nests from 1997 to 2000; only 16 of these produced Wilson's Warbler young. Of 74 failed nests, 73% (54/74) failed due to nest predation. Overall, 33% (30/90) of the nests were parasitized by Brown-headed Cowbirds (Molothrus ater). Nest success, as calculated by the Mayfield method, was 0.085 and notably lower than values reported for other warbler species. We used a simple demographic population model—under scenarios of high, average, and low productivity and survival—to evaluate the viability of this population and found it to be at risk of local extirpation without immigration. This was due to the combined effects of high levels of nest predation and the impacts of brood parasitism.
Lowland coniferous forests adjacent to northern Lake Huron provide important stopover habitat for landbirds during spring migration. Large numbers of aquatic insects emerging from nearshore waters of northern Lake Huron appear to be an important food source. In this study we compared the foraging behavior of a long-distance landbird migrant, the American Redstart (Setophaga ruticilla), in areas with high densities of emergent aquatic insects to areas with few or no emergent aquatic insects to assess the significance of these arthropods as an early spring food source. Redstarts foraged differently in shoreline habitats relative to inland habitats of similar vegetation composition. Both males and females gleaned significantly more in shoreline habitats as compared to inland areas of similar vegetation composition, and inland birds performed more sally strikes than birds at the shoreline. Both sexes also varied the use of tree species in which they foraged. Redstarts used northern white cedar (Thuja occidentalis) more at shoreline than inland, while inland redstarts foraged in deciduous trees more than at the shoreline. We suggest that differences in foraging between shoreline and inland locations were responses to differences in prey types and abundance, most notably the presence of emergent aquatic insects (Diptera: Chironomidae) in shoreline habitat. Our results complement those of previous work, suggesting that midges provide a critical early season resource for landbirds migrating through Michigan's eastern Upper Peninsula during spring.
Many species of Neotropical migrant songbirds have declined in recent decades, due in part to loss and fragmentation of stopover habitat. To properly manage forested landscapes for migrating songbirds, information is needed on how size and habitat structure of forest patches influence their use by migrants during stopover. We conducted surveys of Neotropical migrant birds in eight oak hammocks of varying size (0.32–3.08 ha) at the Savannah National Wildlife Refuge, Jasper County, South Carolina during spring migration 1999 and 2000 and fall migration 1999. Hammock size was the most important factor related to number of total species, species per day, individuals per day, and density of migrants. Differences in vegetation structure and patchiness among hammocks did not explain differences in migrant abundance. Density of migrants tended to be higher in smaller hammocks, particularly during spring. Hammock use was generally similar between seasons and years. Two forest-interior breeding species occurred more often in the largest hammocks, suggesting that interior species are susceptible to forest fragmentation while en route. We suggest that protection of larger (versus smaller) tracts of forest is more beneficial to migrating songbirds, especially declining forest interior species.
We radio-tracked Summer Tanagers (Piranga rubra) at a Gulf coast stopover site to study en route activity budgets. Tanagers were inactive a majority of the time, with scanning, foraging, and preening being the next most commonly observed activities. When foraging, tanagers primarily used sallying to capture a variety of insect prey. Possible explanations for inactivity during stopover include the need for rest following prolonged flight, muscle repair, reduced digestive capacity, and the short distance remaining to the breeding grounds.
Extensive observations and experiments suggest that collisions with plate glass result in more avian mortalities than any other human-associated factor. We tested the effects of window angling and the distance of bird feeders from windows on bird-glass collisions. Strike frequency differed among windows oriented vertically (control) and those angled 20 and 40 degrees from vertical; as the angle of orientation increased, strikes and fatalities decreased. Strike frequency and fatalities at windows also increased as the distance between bird feeders and the glass surface increased. No fatalities were recorded when feeders were located within 1 m of a window, but a marked increase in mortality occurred when feeders were placed 5 and 10 m from the glass. Most glass-collision victims may go unnoticed, hidden by vegetation where they remain out of view or are removed by scavengers. We found that scavengers frequently removed baits from beneath windows at six buildings, but no baits were taken from a site without windows that served as a control. The importance of window strikes as an avian mortality factor, and the likelihood that it will increase over time, compel us to recommend a reevaluation of the Migratory Bird Treaty Act (MBTA). Angling panes in new and remodeled buildings and placing bird feeders closer to windows can potentially reduce avian mortality.
Two new locations, vocalizations, and the nest of the little known Selva Cacique (Cacicus koepckeae, Icteridae) are described from southeastern Peru. Similarities between the vocalizations of Selva and Ecuadorian caciques (C. sclateri) indicate that the two species may be closely related. The Selva Cacique may be ecologically restricted to narrow rivers and headwater regions, where found in river margin habitats and nearby transitional forest. Its occurrence from an elevation of 300 m at the type locality to ≤575 m at the headwaters of the Río Manu Chico, 240 km from the type locality, indicates that it may occur in small numbers over a much larger area than was previously known.
The Neotropic Cormorant (Phalacrocorax brasilianus) is a widespread and abundant species distributed throughout the Neotropics. We report on diving behavior and foraging areas of Neotropic Cormorants in inshore marine waters of Patagonia, Argentina. Mean dive duration was 18.9 ± 5.3 sec and differed significantly among birds. Maximum dive duration was 43 sec. Birds spent 58–79% of their time at sea underwater. Mean recovery time at the surface between successive dives was 6.7 ± 1.5 sec, and was also significantly different among individuals. Mean diving efficiency (mean dive duration time/mean recovery time) was 2.6 ± 0.5 (range: 0.5–4.6). We were able to locate birds while feeding on 112 of 215 occasions. Almost 90% of mapped locations (68 feeding trips) were within 2.5 km of the colony. However, we did not receive a signal on 103 occasions, suggesting that foraging may also occur in waters outside the inlet where the colony was located. High variability in dive duration and recovery time is congruent with flexible foraging techniques and diet, as Neotropic Cormorants feed on both bottom and pelagic schooling fish.
From March 1999 to August 2000, we conducted monthly mist netting in the Chamela-Cuixmala Biosphere Reserve, Jalisco, Mexico to document the phenology and habitat use of the Red-breasted Chat (Granatellus venustus). We collected information on its nesting biology during the breeding season of 2001. Chats (n = 116) were caught throughout the 18 months of the study; however, far fewer captures occurred during the dry season than during the wet season. Our capture data revealed that chats made greater use of deciduous (n = 88) than semi-deciduous forest (n = 28); there were no interactions among forest type, season, and gender. Birds in breeding condition were captured June–September and molting birds were captured August– October. We found 10 cup-shaped nests in June and July. Nests were 48–103 cm above ground in saplings ≤2 m high. Clutch size was 3–4 and only the female incubated. The incubation period was 14 days, and we estimated the nestling period to be approximately 8–10 days. Of eight nests found with eggs or young, three were depredated during the egg stage, three during the nestling stage, and two were successful.
Although intraspecific brood parasitism is common in many bird species, including several secondary cavity-nesting birds, it does not appear to have been reported in woodpeckers. We report a case of intraspecific brood parasitism in the Northern Flicker (Colaptes auratus) in which six to eight eggs were dumped into the host nest box during a 2- to 3-week period. We estimate that the host female laid a clutch of 8 to 10 eggs, and at the end of the nestling period we confirmed that 16 flicker eggs had been laid in the nest box. This instance of egg-dumping by a floater female or another resident female in the same territory or on an adjacent territory, could have been facilitated by a lack of suitable nest sites in the area coupled with intense nest-site competition from European Starlings (Sturnus vulgaris).
Common Loons (Gavia immer) normally lay a single clutch of two eggs each breeding season. They occasionally lay one- or three-egg clutches, and rarely, four-egg clutches. Participants of the Canadian Lakes Loon Survey provided seven independent observations of loon pairs rearing four-chick broods. Photographic evidence confirmed two separate instances of adult loon pairs at Anglin Lake, Saskatchewan, and Kasshabog Lake, Ontario, exhibiting parental behavior toward a four-chick brood. Occurrence of four-chick broods may be the result of supernumerary clutches, nest parasitism, post-hatch brood amalgamation, or a combination of these factors.
Some species of birds commonly forage by following other animals and capturing prey flushed by the movements of the latter. Here we describe a possible foraging association between White Hawks (Leucopternis albicollis) and white-nosed coatis (Nasua narica) in Tikal National Park, Guatemala. The frequency of association varied seasonally, perhaps due to differences in availability of reptiles, the hawks' main prey.
Wilson's Plover (Charadrius wilsonia) occurs year-round along the Caribbean and Pacific coasts of Colombia. The species frequents a variety of coastal habitats including sandy beaches, tidal flats, and small swamps and wetlands. Its breeding range extends from Virginia south through the West Indies to Surinam, and from Baja California to Peru. Here, we report the first nesting record on the Pacific coast of Colombia.
We provide the first description of the nest, eggs, young, and breeding behavior of the Great Antpitta (Grallaria excelsa) in Yacambu National Park, Venezuela. The nests (n = 3) were large, bulky, open-cup structures composed of a dense assortment of live and dead mosses, rootlets, wet leaves, small stems, detritus, and live and dead fern fronds, and were lined with a thick mesh of black rootlets and rhizomorphs. Nests were built >3.8 m above the ground in live trees where dense clusters of aroid plants, epiphytes, and lianas secured them to either a vertical fork or against the trunk itself. Both adults participated in nest building; incubating two unmarked, turquoise eggs; and feeding nestlings. Mean nest attentiveness (time spent on the nest/total video time when corrected for human disturbance) was 98.8 ± 1.8% SD, and nestling feeding rates were low (one visit by each adult/5 hr total video time).
We report the first record of a Blue-crowned Motmot (Momotus momota) feeding on a long-tongued bat (Glossophaginae) in a secondary forest in southwestern Costa Rica. The motmot incapacitated the bat, then swallowed it alive, head first. Motmots and bats are found in close proximity along river banks where the former nests and the latter roosts