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Piracy (kleptoparasitism) accounted for 14% of observed foraging attempts on vertebrates (n = 125) by Aplomado Falcons (Falco femoralis) in southern Texas and northern Mexico, and was over twice as successful as hunting (82% versus 37%). Aplomado Falcons pirated prey cooperatively as well as individually. Eight bird species were targeted for piracy, six of which were as large or larger than the falcons. The majority of prey items stolen were mammals.
The Pale-headed Brush-Finch (Atlapetes pallidiceps) is a critically endangered endemic bird species that is restricted to a single valley in southern Ecuador. We present the first description of the nest, eggs, breeding behavior, and juvenal plumage of this species. Seventy-two percent of nests (n = 18) were placed on thin overhanging branches 1–3 m above the ground, directly beneath the top layer of foliage in dense thickets. Nesting material consisted of various proportions of grass, twigs, and bamboo stalks and leaves. Clutch sizes ranged from 1–3 eggs (n = 22), and ≥55% of nests (n = 18) were parasitized by Shiny Cowbirds (Molothrus bonariensis). The background color of eggs was buffish white to bluish, and they were spotted and blotched with diffuse brown markings. Mean egg size was 24 × 17.8 mm. Fledgling plumage differed from adult plumage and had some characteristics similar to the adult White-winged Brush-Finch (Atlapetes leucopterus). Females alone incubated the eggs, and both parents fed the offspring. Incubation and nestling times were 12–14 days each. Fledglings of the Pale-headed Brush-Finch were led for several weeks after fledging. No pair initiated a second clutch after a successful first one (n = 16), but we observed second and third clutches after nest failure had occurred. Prolonged postfledging care is assumed to prevent multiple broods of the Pale-headed Brush- Finch during one season.
We discovered and monitored a nest of the Rusty-winged Barbtail (Premnornis guttuligera) on the eastern slope of the Andes in Napo Province, Ecuador. The nest, in a hollow Cyathea tree-fern snag, was a deep cup composed entirely of Cyathea tree-fern petiole scales (ramenta). A single nestling fledged successfully on 13 March 2002. During the latter half of the nestling period, adults visited the nest with food a mean of 4.7 ± 1.9 (SD) times/h and removed fecal sacs 2.2 ± 1.1 times/h. Nest visitation rates generally decreased throughout the day. Adult Rusty-winged Barbtails foraged by gleaning from or probing into suspended dead leaves or moss, often while hanging onto the substrate, and did not hitch up trunks or creep along branches. Nest structure, composition, and location, and foraging behavior all raise doubts about the taxonomic placement of Premnornis in the Margarornis treerunner-barbtail assemblage.
Marbled Murrelets (Brachyramphus marmoratus) observed at sea usually are in pairs throughout the year. Although it has been assumed that these pairs are mates, this assumption has not been formally examined. Using data from three study sites during the breeding seasons of 1997–2001, we found that 92% of the birds that were paired at capture were of male-female pairs, and that paired females were more likely (73%) to be producing eggs than were single females (8%). Fourteen of fifteen pairs were tracked to a single nest location per pair. No pair members caught at sea were found breeding at separate nest sites. One pair was caught in two successive seasons, suggesting that at least some pairs are long lasting. Notably, pair members breeding together and radio tracked throughout the summer were detected without their breeding partners for 77% of the time. Thus, while pairs of Marbled Murrelets observed at sea most likely are members of a breeding pair, single murrelets observed at sea should not be assumed to be unpaired or nonbreeders.
We examined habitat use of sympatric Fish Crows (Corvus ossifragus) and American Crows (C. brachyrhynchos) nesting in the vicinity of waterbird breeding locations at the Rockaway Peninsula, New York City. Fish Crows nested significantly more often at natural habitats, including coastal dunes and salt marsh islands; American Crows nested significantly more often at residential and recreational areas. In regard to potential foraging areas, Fish Crows nested closer to waterbird colonies and to the water's edge while American Crows nested closer to a garbage source and to lawns. Fish Crows nested significantly more often in deciduous trees that were native, while American Crows nested significantly more often in evergreen trees that more frequently were exotic, especially Japanese black pine (Pinus thunbergii). Finally, we consider the potential predatory impact of sympatric crow species on waterbirds in light of their habitat use.
We explored nest site habitat selection patterns for six grassland passerine species in northcentral Montana: Sprague's Pipit (Anthus spragueii), Savannah Sparrow (Passerculus sandwichensis), Grasshopper Sparrow (Ammodramus savannarum), Baird's Sparrow (A. bairdii), Chestnut-collared Longspur (Calcarius ornatus), and Western Meadowlark (Sturnella neglecta). We quantified habitat characteristics at sites chosen for nesting and compared them to randomly selected sites, both spatially and temporally. Using discriminant analysis, two species groups were discernable based on a combination of habitat characteristics, which were distinct from random sites. Nest sites had greater foliage height and density than random sites. This pattern generally was shown most strongly by Western Meadowlarks, Baird's, and Savannah sparrows. Three bird species selected nest patches (5-m radius plots centered on nests) having little or no clubmoss (Selaginella densa) cover, which was one of the most powerful discriminating variables in this analysis. The conservation implications of increasing clubmoss cover in relationship to nest site selection in northern Great Plains grasslands are discussed.
We examined resin chemistry of loblolly (Pinus taeda) and shortleaf (P. echinata) pines selected as cavity trees by Red-cockaded Woodpeckers (Picoides borealis) in eastern Texas. We sampled resin from (1) pines selected by Red-cockaded Woodpeckers that contained naturally excavated active cavities, (2) pines selected by forest biologists that contained artificially installed cavity inserts and were actively being used by Red-cockaded Woodpeckers, and (3) control pines of similar age and appearance to the active cavity trees. We hypothesized that if woodpeckers are inducing a change in resin chemistry by excavating resin wells, this change should appear in active cavity trees selected by woodpeckers and trees selected by biologists, but not in control pines. If woodpeckers are selecting pines that have specific resin chemistry, concentrations of some resin components in active cavity trees selected by the woodpeckers for natural cavity excavation should be different from both control pines and pines selected by biologists. A large diterpene acid peak containing an isopimaric- levopimaric-palustric methyl-ester mix in active natural cavity trees was approximately 20% greater than controls and 22% greater than trees with artificial cavities. None of the other eight resin chemicals differed among treatments. The activity of Red-cockaded Woodpeckers at resin wells did not appear to affect the composition of cavity tree resin. Woodpeckers, however, may select pines with specific resin chemistries for cavity trees.
I conducted a vegetation removal experiment using American Goldfinch (Carduelis tristis) nests to test the hypothesis that predation rates vary with concealment in old field habitats in eastcentral Illinois. Daily predation rates were 0.05 for manipulated nests and 0.04 for control nests. Although manipulated nests were much less concealed than control nests, the probability of predation did not differ significantly between treatments or years. Logistic regression models indicated that nests initiated earlier in the breeding season had a greater probability of predation than nests initiated later in the breeding season. These results indicate that time of breeding season may be more important than concealment in explaining probability of predation of American Goldfinch nests in this old field system.
We report on the relationship between Mallard (Anas platyrhynchos) clutch size and cropland area in the landscape in western Minnesota during 1997–1999. We measured clutch size in two types of nest structures and fit a mixed-effects model to the data to examine the relationship. Our model also included covariates to control for the effects of year, nest initiation date, estimated pair numbers, and nest structure type. Unique landscapes associated with each nest (n = 134) ranged from 46.4–84.8% cropland. Clutch size was unrelated to cropland area, nest structure type, and estimated number of pairs with access to structures. Mean clutch size declined with nest initiation date early in the nesting season, but increased somewhat for nests initiated after 30 May. Clutch size also differed among years. Mean clutch size, adjusted for nest initiation date, was 11.0 ± 0.19 SE for 1997, 10.5 ± 0.19 SE for 1998, and 11.0 ± 0.19 SE for 1999. Conclusions regarding the significance of the year effect and the degree of nonlinearity due to nest initiation date were sensitive to potential clutch size outliers, but cropland area had no effect on clutch size regardless of the way we constrained clutch size. Nest parasitism by philopatric females laying in certain structures might explain the observed increase in clutch size in late nest initiations.
We examined variation in meal size, feeding frequency and daily food delivery in relation to age, nest, day, year, and weather by White-tailed Tropicbirds (Phaethon lepturus) using repeated weighing of chicks. We focused particularly on the differences between chicks which survived and those which died. Unsuccessful chicks became significantly lighter than successful chicks at the age of 30 days; however, some were fed until they were 60 days old. Feeding frequency and meal size differed significantly between both age classes and between surviving and nonsurviving chicks. In surviving chicks, feeding frequency remained relatively constant until chicks reached 60 days and dropped progressively thereafter. In this group, meal size was significantly lower in chicks up to 20 days old and over 70 days old than those aged 21–70 days. We found significant relationships between chick food provisioning and day, nest, and year. Feeding frequency was more important than meal size in explaining the difference in food delivery between surviving and nonsurviving chicks. This was due to much greater significant differences for feeding frequency than for meal size between surviving and nonsurviving chicks, including annual differences in feeding frequency (but not in meal size) for surviving chicks. Our study suggests that parents of unsuccessful chicks had difficulty in obtaining sufficient food for their chicks from very early on, but responded to this problem first by decreasing the feeding frequency and, later, decreasing both feeding frequency and meal size. Our study shows that parents vary in their abilities to provide optimal provisioning to their chicks. Environmental conditions determine further energetic constraints in food delivery to chicks.
Age specific survival and movement are important components of demography and population structure, and quantification of these rates is useful for management and conservation. However, information on the postfledging ecology of waterfowl species frequently is unavailable to managers. I studied postfledging survival and movements of juvenile Harlequin Ducks (Histrionicus histrionicus) in the Strait of Georgia, British Columbia, using radio marking and capture-mark-recapture analysis of banded birds captured at coastal wintering areas. Survival of juvenile females was high, providing evidence that female winter survival may be similar among age groups. Radio-marked juvenile males were more likely to die than juvenile females, and juvenile males had lowest local survival rates of all sex-age classes. Proportions of banded juveniles found at their capture location during their second winter did not differ significantly between males and females, suggesting equal dispersal rates, and at least 25% (n = 9) of radio-marked females moved >30 km from their capture location. These results were unexpected, based on previous evidence for female philopatry and theories of male- biased dispersal in waterfowl, and suggest that males and females both likely contribute to gene flow and demographic connection among populations.
We report on the exponential growth of the Eastern Brown Pelican (Pelecanus occidentalis carolinensis) in Louisiana, following its extirpation in 1963, and its subsequent reintroduction (1968–1980). This population growth pattern is remarkable since the Brown Pelican exhibits low fecundity, a long life span, and is considered largely nonmigratory in the Gulf of Mexico. To understand the regional changes in breeding numbers of Brown Pelicans in the northern Gulf of Mexico, we investigated the long term trends of the other subpopulations in Florida and Texas. The Florida subpopulation of Brown Pelicans has exhibited a stable-limit cycle, but within the last decade the number of nesting birds has declined while the number of nesting colonies has steadily increased. The number of Brown Pelicans in Texas now exceeds estimates prior to the time pesticides caused reproductive failure of the subpopulation. The Louisiana subpopulation now equals or exceeds its historical (pre-pesticide) numbers. Although local recruitment can account for the exponential growth of Brown Pelicans in Louisiana, we believe that dispersal from colonies outside of Louisiana may have augmented the growth of its nesting population.
We analyzed seasonal variation in avian species richness and relative abundance at the community and guild level during a 13-month period in central Bolivia in an 11-ha patch of Polylepis (Rosaceae) forest, a high-Andean ecosystem that has suffered from extreme anthropogenic fragmentation. Birds were surveyed audio-visually (supplemented with mist net data) and assigned to five relative abundance categories for 2-month survey periods. We recorded 35 core species, including 16 insectivores (46%), 11 frugi-granivores (31%), seven nectarivores (20%), and one carnivore (3%). Core species richness varied from 25 (June–July) to 33 (October–November). Insectivores had a significantly higher proportion of year-round residents (81%) than frugi-granivores (45%) or nectarivores (14%); the same trend was evident with respect to seasonal variation in species richness of each guild. Although most species varied considerably in their relative abundance, no guild showed significant variation in relative abundance scores among survey periods. However, frugi-granivores and nectarivores combined, both of which depend upon plants as food resources, reached a significant minimum in mid-winter (June–July), and the same result was found at the community level. The insectivore guild thus was the most temporally stable both in terms of species richness and abundance. Qualitative observations indicated that the fluctuations in frugi-granivores and nectarivores were related to the availability of food resources.
The biology of the endangered Tuamotu Sandpiper (Prosobonia cancellata) is essentially unknown. We analyzed vocalizations from presumed adult individuals and pairs, and family groups, recorded in French Polynesia during March 1990 and 2003. We recognized three types of vocalizations. Presumed adults uttered types I and II. These were brief (about 30–40 and 20–120 ms, respectively) and simple in structure (increasing then decreasing in frequency) but harmonically rich, with most energy in the second or third harmonics (peak fundamental frequency was about 775–1,380 Hz), as in some other Scolopacidae. Higher harmonics reached unusually high frequencies for a scolopacid (approaching 14 kHz). Call types I and II were uttered singly or as couplets, triplets, or longer sequences. Type III calls were longer (about 115–470 ms), of narrower bandwidth, and with modulations of a carrier frequency that decreased from about 1,925 to 1,305 Hz; they were given by a presumed family group and may represent calls of dependent young birds. Harmonic richness and variation in frequency and temporal variables within call types are consistent with a short range communication system.
Females of many species of birds possess either a reduced version of male ornaments or conspicuous but hidden ornaments. No female specific ornament display has been described previously in a species with reduced or hidden female ornaments. We describe such a display in Northern Cardinals (Cardinalis cardinalis). The display consists of a perched female rotating her wings open to expose the red, carotenoid-pigmented underwing coverts, which are indicative of individual quality in this species.
In this paper we report the copulation behavior of the Greater Rhea (Rhea americana), a species in which males defend a harem of females. We describe the females' behavior during 14 copulation events observed from 1995–1997 at Buenos Aires province, Argentina. During copulations, females performed a more active role than previously suggested. Moreover, on three occasions we observed that harem females performed a complex copulation solicitation display, forming a closed circle to attract the male. We hypothesize that this display could be a reliable signal to the male of the tendency of females to be inseminated and lay eggs communally.
Most female birds have only a left ovary and associated oviduct. The entry to the oviduct is on the left side of the urodeum of the cloaca. This arrangement may favor males that mount females from the left during copulation if it results in sperm being placed closer to the opening of the oviduct. Therefore, we predicted a left-sided directional bias of cloacal contacts during House Sparrow (Passer domesticus) copulations. Cloacal contacts from the left outnumbered those from the right 74 to 25 (3:1) during 25 bouts of copulation at 11 House Sparrow nests. While this pattern suggests that a left-sided bias in mounting by males during copulation may be related to the asymmetry of the female reproductive tract, it also might be related to brain lateralization.
We describe for the first time the characteristics of the nest sites, nests, eggs, and nestling behavior of the endemic Snowy-cheeked Laughingthrush (Garrulax sukatschewi). During May and June 2002, at the Lianhuashan Natural Reserve in central China, we found five nests in coniferous forest at an elevation of 2,850 m. All nests, built by both members of a pair, were cup shaped and built 1.2–2.8 m above the ground in the branches of spruce (Picea spp.) trees or willow (Salix spp.) shrubs. The eggs were unspotted and greenish blue. We observed one brood of three nestlings. The parents fed the nestlings at a frequency of about 7.9 times/h ± 2.8 SD, with the female performing 51.6% of the feedings. Both male and female adults removed the feces from the nest at a mean rate of 6.9 times/h.
We analyzed the body condition of nestling Burrowing Owls (Athene cunicularia) at Buffalo Gap National Grassland during the summers of 1999 and 2000. In 1999, which had a wet spring, body condition was negatively related to brood size and distance from nest to colony edge. There was no relationship between body condition and brood size during 2000, which had normal precipitation. In 2000, nestlings of early arriving pairs were in better body condition than those that arrived later. The variance in body condition within a brood was not related to brood size.
We report an apparent nonlethal predation attempt on and subsequent adoption of a Glaucous-winged Gull (Larus glaucescens) chick by a pair of Bald Eagles (Haliaeetus leucocephalus) in the Aleutian Archipelago, Alaska. To the best of our knowledge, this is the first report of a live Glaucous-winged Gull chick in a Bald Eagle nest. We describe our observations of this occurrence and offer explanations on how it may have occurred.
Northern Goshawks (Accipiter gentilis) typically hunt in forested habitats and feed upon birds and mammals there. Relatively little is known of goshawk food habits in coastal landscapes, and few seabirds have been documented in their diets. Although guillemots (Cepphus spp.) are potentially available to Northern Goshawks in most coastal landscapes within its range, they have not been documented previously in this raptor's diet. I observed the delivery of a Pigeon Guillemot (C. columba) to a goshawk nest on a coastal island in Southeast Alaska. Guillemots forage in shallow, inshore waters, making them a potentially difficult prey item for goshawks to capture. In addition, Bald Eagles (Haliaeetus leucocephalus) occur in large numbers in Southeast Alaska and probably harass goshawks when they are foraging in open habitat near the beach edge. Therefore, even in areas where guillemots occur, it is likely that they are only rarely hunted by goshawks.
Diets of puffbirds and mortality sources of adult hummingbirds are poorly known. I observed a White-necked Puffbird (Malacoptila macrorhynchus) attack and capture a Rufous-tailed Hummingbird (Amazilia tzacatl) in the Republic of Panama. This is the first report of birds as prey of puffbirds and identifies another source of natural mortality for hummingbirds.
The Village Weaver (Ploceus cucullatus) usually is found in moist areas, breeding near water during the rainy season. On Hispaniola I observed the Village Weaver breeding in the desert, despite a lack of rain, and consuming the fruits of a columnar cactus (Stenocereus hystrix). I propose that the carbohydrate and, especially, water content of these fruits is a substitute for rainfall, facilitating Village Weaver breeding in an arid environment. Weavers also may disperse the cactus seeds.
In July 2001, during seabird surveys in dense montane rainforest at the summit of Ta'u, we documented the occurrence of the Spotless Crake (Porzana tabuensis) in American Samoa for the first time in 17 years. The last sightings were made during 1985–1986 in lowland agricultural areas, semiwetland, and secondary forests. Norway rats (Rattus norvegicus) also were discovered in the montane forests and pose a threat to the continued survival of the crake at its only colony in the Samoan archipelago.