Most recent references describe the winter range of the Veery (Catharus fuscescens) as including an extensive area from northern Colombia, Venezuela, and Guyana south to south-central Brazil. Analysis of seasonal distribution of specimen records in South America, however, shows that 91 of 105 specimens were taken during spring and fall, not winter; the remaining 14, taken from 2 December to 20 February, are all from three small areas at the periphery or south of the Amazon basin. Thus, the true winter range is almost completely south and east of the area generally described. The seasonal distribution of specimen records is consistent with observational data from South America and banding data from the Neotropics. Although those data must be treated cautiously, it appears that the true winter range of the Veery is in south-central and southeastern Brazil, an area where habitat destruction threatens many natural habitats, rather than in the relatively undisturbed areas of western Amazonia. Widespread erroneous portrayal of the winter range of the Veery seems to have been caused largely by the assumption that the species winters in South America wherever it has been recorded and by overlooking a previously published analysis of its winter distribution.

We studied relationships of five extant members of the endemic Malagasy family Brachypteraciidae, the ground rollers, using several mitochondrial genes (cytochrome-b, NADH dehydrogenase 2, 12S ribosomal RNA, and cytochrome oxidase I). As outgroups, we used other coraciiforms including the Cuckoo Roller (Family Leptosomatidae, Leptosomus discolor), several true rollers (Corcaciidae) and a tody (Todidae). Partial sequences of the Long-tailed Ground Roller (Uratelornis chimaera) were obtained from toe pad samples taken off museum specimens. For a combined data set of all genes, Kimura two-parameter distances between sequences of the five ground roller species were high, averaging 11% divergence. For several species, samples were available from widely separated geographic regions and intraspecific sequence divergence was low (≤0.8%). Unweighted and weighted parsimony and maximum-likelihood analyses consistently recovered monophyly of the family, a sister relationship between Brachypteraciidae and Coraciidae, and monophyly of one of three currently recognized ground roller genera (Atelornis). At the base of the Brachypteraciidae clade, we could not fully resolve relationships between Uratelornis and two species currently placed in Brachypteracias. Because of the uncertainty of basal nodes in our phylogenetic reconstructions, we recommend returning B. squamigera to the monotypic genus Geobiastes. High levels of divergence among ground rollers are similar to levels found in other avian groups endemic to Madagascar. However, we suggest that molecular divergences appear far too low to be consistent with mid-Eocene fossils attributed to the family.

Potential source populations of forest-breeding Neotropical migrant birds may be threatened by anthropogenic changes that increase brood parasitism by Brown-headed Cowbirds (Molothrus ater) and nest predation in heavily forested breeding areas. In south-central Indiana, corridors of agriculture and rural development, ranging from <50 m to several thousand meters in width, penetrate interior portions of the heavily forested landscape. These corridors provide habitat for cowbirds and nest predators. We monitored breeding success of six species of Neotropical migrants and one resident species near an agricultural corridor and in interior forest. We found that nest survival was lower near the agricultural corridor for most of the species in the nestling stage, but no consistent difference in nest survival was detected during the egg stage. Levels of cowbird parasitism were generally elevated near the agricultural corridor. Estimates of the number of fledglings per nesting attempt indicated that seasonal productivity was lower near the agricultural corridor for six of the seven species. Status of populations of birds in south-central Indiana as sources in the Midwest may be compromised by extensive intrusion of agricultural corridors within the contiguous, heavily forested landscape.

Evolutionary history of the dove genus Streptopelia has not been examined with rigorous phylogenetic methods. We present a study of phylogenetic relationships of Streptopelia based on over 3,600 base pairs of nuclear and mitochondrial gene sequences. To test for monophyly of Streptopelia, we used several other columbiform taxa, including Columba (Old and New World), Macropygia, Reinwardtoena, and the enigmatic Pink Pigeon (Nesoenas mayeri). On the basis of our analyses, Streptopelia (as currently defined) is not monophyletic; Nesoenas mayeri is the sister species to S. picturata, resulting in paraphyly of Streptopelia. Three main clades of Streptopelia are identified: (1) S. chinensis plus S. senegalensis, (2) S. picturata plus Nesoenas mayeri, and (3) all other species of Streptopelia. It is unclear whether those clades form a monophyletic group to the exclusion of Old World Columba, but several analyses produce that result. Species of Old World Columba are closely related to Streptopelia, with species of New World Columba clustering outside that group. Taxonomic changes suggested by our results include merging Nesoenas with Streptopelia and changing the generic name for New World Columba species to Patagioenas. Vocal similarities between S. picturata and N. mayeri are striking, given the general diversity of vocalizations in other species.

We investigated site fidelity and apparent survival in a promiscuous population of Saltmarsh Sharp-tailed Sparrows (Ammodramus caudacutus) in southern Rhode Island. Based on capture–recapture histories of 446 color-banded sparrows studied from 1993 to 1998 at our primary study site, Galilee, we observed significant variation in apparent survival rates among years, but not between sexes. Return rates of adult males (37.6%) and females (35.6%) were not significantly different during any year. Juveniles exhibited high return rates, ranging from 0 to 44%, with males (61% of returns) more likely to return than females (35%). In addition, we monitored movements of 404 color-banded sparrows at nine satellite marshes in 1997 and 1998, which supported our findings at Galilee and documented intermarsh movements by 10% of all banded birds. Lack of gender-bias in adult dispersal and strong natal philopatry of sparrows in Rhode Island occurs regularly among passerines possessing a variety of mating systems. Despite emancipation from parental and resource defense duties, adult male Saltmarsh Sharp-tailed Sparrows exhibited apparent survival rates similar to adult females. Availability of high-quality breeding habitat, which is patchy and saturated, may be the most important factor limiting dispersal for Saltmarsh Sharp-tailed Sparrows in Rhode Island.

Like males of many bird species, male House Finches (Carpodacus mexicanus) have patches of feathers with ornamental coloration that are due to carotenoid pigments. Within populations, male House Finches vary in expression of ornamental coloration from pale yellow to bright red, which previous research suggested was the result of variation in types and amounts of carotenoid pigments deposited in feathers. Here we used improved analytical techniques to describe types and amounts of carotenoid pigments present in that plumage. We then used those data to make comparisons of carotenoid composition of feathers of male House Finches at three levels: among individual males with different plumage hue and saturation, between age groups of males from the same population, and between males from two subspecies that differ in extent of ventral carotenoid pigmentation (patch size): large-patched C. m. frontalis from coastal California and small-patched C. m. griscomi from Guerrero, Mexico. In all age groups and populations, the ornamental plumage coloration of male House Finches resulted from the same 13 carotenoid pigments, with 3-hydroxy echinenone and lutein being the most abundant carotenoid pigments. The composition of carotenoids in feathers suggested that House Finches are capable of metabolic transformation of dietary forms of carotenoids. The hue of male plumage depended on component carotenoids, their relative concentrations, and total concentration of all carotenoids. Most 4-keto (red) carotenoids were positively correlated with plumage redness, and most yellow carotenoid pigments were negatively associated with plumage redness, although the strength of the relationship for specific carotenoid pigments varied among age groups and subspecies. Using age and subspecies as factors and concentration of each component carotenoid as dependent variables in a MANOVA, we found a distinctive pigment profile for each age group within each subspecies. Among frontalis males, hatch-year birds did not differ from adults in mean plumage hue, but they had a significantly lower proportion of red pigments in their plumage, and significantly lower levels of the red piments adonirubin and astaxanthin, but significantly higher levels of the yellow pigment zeaxanthin, than adult males. Among griscomi males, hatch-year birds differed from adults in plumage hue but not significantly in pigment composition, though in general their feathers had lower concentrations of red pigments and higher concentrations of yellow pigments than adult males. Both adult and hatch-year frontalis males differed from griscomi males in having significantly higher levels of most yellow carotenoid pigments and significantly lower levels of most red carotenoid pigments. Variation in pigment profiles of subspecies and age classes may reflect differences among the groups in carotenoid metabolism, in dietary access to carotenoids, or in exposure to environmental factors, such as parasites, that may affect pigmentation.

Rate of oxygen consumption was measured in eight species of toucans, one barbet, and one hornbill to examine factors that influence their energy expenditures. Basal rate of metabolism in those species, supplemented with measurements from three woodpeckers and three mousebirds, is correlated with body mass and either food habits or climate: temperate acorn- and insect-eating species have basal rates that are ∼70% greater than tropical fruit-eating species. The temperate, insect- or acorn-eating species are woodpeckers, so level of basal rate is also correlated with familial affiliation. The toucans, barbet, and hornbill have basal rates similar to those of frugivorous pigeons and bats, which collectively are low by avian standards. The effects of climate, food habits, and family affiliation on basal rates in endotherms are difficult to separate, given the restricted data set available. Earlier conclusions that the basal rates of birds greatly exceed those of mammals are confounded by character interactions that influence dependence of basal rate on body mass. The largest toucan showed a remarkable ability to reduce energy expenditure at low ambient temperatures without reducing core body temperature, possibly as a result of peripheral vasoconstriction.

Interspecific kleptoparasitism (food stealing) occurs in many seabird species and can sometimes significantly affect host individuals and populations. We investigated effects of kleptoparasitism by Glaucous-winged Gulls (Larus glaucescens) on a population of Tufted Puffins (Fratercula cirrhata) in which almost all chicks die before fledging in some years. Rates of kleptoparasitism were estimated during two seasons and compared with several spatial and temporal factors that have been predicted to influence kleptoparasitism rates both within and among seasons. Kleptoparasitism rates increased from 2% in the first year to 19% in the second, whereas puffin fledging success declined precipitously from 81% in the first year to 11% in the second. Within years, kleptoparasitism rates increased with number of puffins returning with fish, decreased during fair weather, and were unaffected by tidal height. Spatially, those rates increased with puffin burrow density and declined with angle of the nesting slope. Gull kleptoparasitism success increased during foul weather and at higher puffin nesting elevations. Despite those associations, survival of puffin chicks was not influenced by kleptoparasitism activity near their nests although it increased with a combination of low elevation and high slope at the nesting burrow. Neither kleptoparasitism nor predation by gulls were exceptional relative to other seabird colonies and they were unlikely to cause reproductive failures that characterize puffins at that site. Other factors, particularly food shortages at sea, merit further attention in explaining those failures.

Understanding ecological consequences of avian developmental modes requires knowledge of energy requirements of chicks of different positions in the precocial–altricial spectrum, but those have rarely been measured in birds with self-feeding precocial young. We studied prefledging energy budgets in chicks of Black-tailed Godwit (Limosa limosa) and Northern Lapwing (Vanellus vanellus) in the field and in the laboratory. Lapwings show slower growth than godwits, reaching a 29% lower fledging mass (142 vs. 201 g) in a 32% longer period (33 vs. 25 days). Daily energy expenditure (DEE), measured by the doubly labelled water (DLW) technique, and daily metabolized energy (DEE plus energy deposited into tissue) increased proportionally to body mass at similar levels in both species. Total metabolized energy (TME) over the fledging period was 8,331 kJ in godwits and 6,982 kJ in lapwings, 39 and 29% higher than an allometric prediction (Weathers 1992). That suggests that self-feeding precocial chicks have high energy requirements compared with parent-fed species, due to costs of activity and thermoregulation associated with foraging. Those components made up 50–53% of TME in the shorebirds, more than twice as much as in seven parent-fed species for which DLW-based energy budgets are available. In captive lapwings and godwits growing up under favorable thermal conditions with food readily accessible, thermoregulation and activity costs were 53–58% lower and TME was 26–31% lower than in free-living chicks. The proportion of TME allocated to tissue formation (13–15% deposited as tissue plus 10–12% synthesis costs) was low in the shorebirds, and reductions in food intake may therefore sooner lead to stagnation of growth than in parent-fed chicks. Furthermore, the need to forage limits potential for saving energy by reducing activity in periods of food scarcity, because that will further decrease food intake. Self-feeding precocial chicks thus seem to operate within fairly narrow energetic margins. At the same time, self-feeding may allow birds to use food types that could not be profitably harvested if they had to be transported to the young.

We examined patterns of geographic variation in contact calls of Orange-fronted Parakeets (Aratinga canicularis) during the nonbreeding season. Calls were recorded throughout the range of that species in Costa Rica. Recordings of wild-caught birds held for one to two weeks indicated that each individual favors one dominant call type and different birds use different favored calls. We used that fact to cull replicate calls from the same individual in field recordings of flocks observed at various locations throughout the sample area. Remaining recordings from a given year were submitted to spectrographic cross-correlation and principal coordinates analysis as described by Cortopassi and Bradbury (2000). Principal coordinates were then correlated with site location using MANOVA. Call durations were also examined for geographical patterns. Like sympatric Yellow-naped Parrots (Amazona auropalliata) studied over the same region by Wright (1996), Orange-fronted Parakeets exhibited significant geographic variation but, unlike the larger species, showed no discrete dialect patterns. Call duration varied clinally but with different patterns for the Nicoya Peninsula and the Guanacaste mainland. Two principal coordinates also showed clinal variation even after removing any correlated duration effects. Scale over which local calls were statistically homogeneous was 7–10 km. We compared that figure to home ranges of 18 birds radio-tracked concurrently with call sampling. Both range areas and range lengths were asymptotic after a week of tracking. Asymptotic range lengths were 2–9 km. Scale of movements of birds, at least during that period, was thus similar to distance within which calls tended to be statistically homogeneous. This study and that by Wright show that several well-known patterns of geographical variation seen with passerine song are replicated quite closely in contact calls of parrots, despite the fact that the functions of vocal signals are quite different in the two taxa.

We developed deterministic models on the basis of nest survival rates and renesting behavior capable of predicting annual fecundity in birds. The models calculate probabilities of fledging from one to four nests within a discrete breeding season. We used those models to address theoretical issues related to clutch size. In general, birds require at least one day to lay an egg, and many species delay incubation until their entire clutch is laid. Because it takes longer to complete a larger clutch, and fewer such clutches can fit into a limited breeding season, there exists a clutch size for which annual fecundity is maximized. We asked, for a given amount of reproductive effort (i.e. a set number of eggs), does the age-old maxim “don't put all your eggs in one basket” apply? If so, in how many “baskets” should a nesting bird place its eggs? The answer depends on both likelihood of nest predation and length of the breeding season. Those results are consistent with the observed increase in clutch size with latitude (shorter breeding season length) and larger clutch sizes characteristic of cavity-nesting species (with higher nest survival rates). The models also predict that the size of replacement clutches should decrease as the breeding season progresses, and that intraseasonal decline in clutch size should be more pronounced when the breeding season is short.

European Shag (Phalacrocorax aristotelis) nestlings were studied on a small island off the coast of central Norway. Increase in body mass (BM) with age (t, days) was described by the logistic equation: BM = 1,622 g/[1 e^{−0.172(t−19.9)}]. All growth parameters measured (body mass, and length of tarsus, wing and head) showed highest relative growth rate when the nestlings were 5–10 days old, that is, before the nestlings had achieved homeothermy. An incipient endothermic response was noted when nestlings were 9 days old, and they became homeothermic at ages of 15–18 days. Respective mass-specific resting metabolic rates for nestlings 0, 15, and 45 days old were 47, 261, and 147% of the predicted value for adult nonpasserine birds of similar body masses. Mass-specific minimal thermal conductance decreased from 366% of predicted adult value at hatching, to 220% of that predicted when nestlings were 21 days old. For nestlings 15 days old, the factorial metabolic scope (resting metabolic rate/peak metabolic rate) was only 1.5, but that increased rapidly thereafter. Rapid increase in the mass-specific RMR and decrease in minimal thermal conductance is suggested to contribute importantly to improve homeothermic ability during the first two weeks of the developmental period. At hatching, leg and pectoral muscles constituted 5.3 and 2.2%, respectively, of total wet body mass. Relative leg-muscle mass increased rapidly and had almost reached adult proportions when the nestlings were 25–30 days old. In contrast, pectoral-muscle mass increased in an almost direct proportion to the body mass during the first 30 days of the growth period, and increased rapidly thereafter. At hatching, the water fraction (water content/lipid-free wet mass) was significantly lower in the leg than in the pectoral muscles (0.920 vs. 0.931). The water fraction of leg muscles also remained lower during the entire growth period. Judging from the proportionately greater mass and higher degree of maturity of the leg compared to pectoral muscles, the former would seem to be the main site of cold-induced heat production during early development of homeothermy in European Shag nestlings.

Age of first breeding (AFB) and natal dispersal distance (NDD) were investigated relative to proximate and ultimate factors in 276 known-age Cassin's Auklets (Ptychoramphus aleuticus) breeding during 1981–1999 on Southeast Farallon Island, California. Breeding density in 446 study boxes declined significantly during the period 1987–1999, confirming other information indicating a long-term decline (since at least the 1970s) in the population. Mean AFB was 3.34 years when sexes were combined, ranging from 2–10 (mean 3.36) years in females and 2–9 (mean 3.36) years in males. AFB showed a significant linear increase with decreasing colony density, suggesting that increased stress on the entire population, such as that caused by decreasing food availability, may have prevented younger birds from attaining breeding condition at an early age. Median NDD was 8.84 m, ranging from 0–448.7 m; two individuals of each sex recruited into their natal boxes. NDD showed a significant linear increase with decreasing breeding density but no significant linear or curvilinear correlations with mate fidelity, annual reproductive success, or lifetime reproductive output. A significant proportion (66.9%) of movements after recruitment (breeding dispersal) resulted in closer proximity to the natal site. Thus, although natal philopatry was strongly developed in the Cassin's Auklet, it did not seem to be adaptive. Those paradoxical results suggest that selective equilibrium may be acting on natal philopatry in response to the population decline: a low-philopatry, low-cost (later breeding and increased survival) strategy has become increasingly adaptive in Cassin's Auklets, explaining increases in AFB and NDD with the declining breeding densities. The lack of sex-specific effects on AFB and NDD suggests that an even sex-ratio and roughly equal roles in reproduction among Cassin's Auklets exists on Southeast Farallon Island, and that inbreeding avoidance may be counter-balanced by relatively low mate fidelity in this species.

A major decline in submerged aquatic vegetation (SAV) in Chesapeake Bay has altered the diet of wintering Canvasbacks (Aythya valisineria) from historically plant to a combination of benthic animal foods, especially the ubiquitous Baltic clam (Macoma balthica), supplemented with anthropogenic corn (Zea mays). Because the isotopic signature of corn is readily discriminated from bay benthos, but not SAV, we used stable-isotope methodology to investigate the corn–SAV component of the winter diet of Canvasbacks. Feeding trials with penned Canvasbacks were conducted to establish turnover rates and fractionation end-point loci of δ¹³C and δ¹⁵N signatures of whole blood for individual ducks fed ad libitum diets of (1) Baltic clams, (2) Baltic clams and corn, and (3) tubers of wild celery (Vallisneria americana). Turnover time constants averaged 4.5 weeks, indicating that signatures of wild ducks would be representative of bay diets by late February. Isotopic signatures of wild Canvasbacks sampled in February fell on a continuum between end-point loci for the Baltic clam and the combination Baltic clam and corn diet. Although that finding verifies a clear dependence on corn–SAV for wintering Canvasbacks, it also reveals that not enough corn–SAV is available to establish ad libitum consumption for the 15,000 Canvasbacks wintering in the upper bay. On the basis of mean δ¹³C signature of bay Canvasbacks (n = 59) and ingestion rates from feeding trials, we estimated that 258 kg corn per day would account for the observed δ¹³C enrichment and supply 18% of daily energetic needs for 15,000 Canvasbacks. That level of corn availability is so realistic that we conclude that SAV is likely of little dietary importance to Canvasbacks in that portion of the bay.

Although area and isolation effects on avian communities in highly fragmented landscapes are well known, importance of landscape composition in more forested landscapes remains poorly understood. We determined if the type (agriculture and silviculture) and extent (percentage within 1 km radius) of disturbance within forested landscapes influenced avian nesting success, and then examined if differences in stand-level habitat structure, nest-patch microhabitat, distance of nests to habitat edges, brood parasitism rates, and nest-predator abundance were potential underlying mechanisms of observed associations between landscape composition and nesting success. We monitored active songbird nests (n = 341), surveyed Brown-headed Cowbirds (Molothrus ater) and nest predators, and measured stand-level and nest-patch microhabitat from May–July 1998 and 1999. Each of 10 study sites was located within contiguous mature forest in central Pennsylvania and contained either agricultural or silvicultural disturbances (n = 5 each). Sites of the two landscape types had similar ranges of disturbance within 1 km (21–55% for agriculture, 18–51% for silviculture). Daily nest survival for all species combined (94.0 ± 0.55 in agriculture and 96.9 ± 0.87 in silviculture) and midstory-canopy nesters (93.8 ± 0.97 in agriculture and 97.4 ± 0.75 in silviculture) were greater within forested landscapes disturbed by silviculture than by agriculture, but rates did not significantly differ between landscapes for ground nesters (92.2 ± 1.32 in agriculture and 94.6 ± 1.63 in silviculture) or understory nesters (95.4 ± 1.60 in agriculture and 95.0 ± 1.47 in silviculture). Nest survival was not significantly associated with disturbance extent. Rates of brood parasitism were low, with only 11% of nests containing cowbird eggs or young. Neither nest fate nor differences in daily nest survival between the two landscape types were explained by variation in brood parasitism rates, stand-level or nest-patch habitat characteristics, or distance of nests to edges. Instead, the lower nest success within forested landscapes disturbed by agriculture was best explained by greater abundances of some avian and small mammalian predators (American Crow [Corvus brachyrhynchos] and squirrels) in those landscapes in one or both years. Results suggest that landscape composition within forested landscapes significantly influences avian nesting success by altering interactions between nest predators and nesting birds.

Radio transmitters were deployed on Marbled Murrelets (Brachyramphus marmoratus) at Desolation Sound, British Columbia, Canada, during the 1998 breeding season to assess individual variation in distance birds nested from foraging areas, and potential energetic and ecological consequences of commuting those distances. Radio-tracking from a helicopter was used to locate nests, and tracking from the air and boats was used to locate murrelets on the water. Twenty-three nests were found, with active incubation at 16, and active chick-rearing at 12. A minimum of 3 nests fledged chicks, 9 were failures, and 11 were unknown. Nests were at an elevation of 806 ± 377 m and a distance of 39.2 ± 23.2 km (range 12–102 km) from locations on the water. Birds spent an estimated 1.2 ± 0.7 h per day commuting to and from nests (range 0.3–3.5 h per day). It was estimated that birds expended 3,883 ± 2,296 kJ (range 1,200–10,144 kJ) over the breeding season when commuting to those nests, which was 5–41% of their estimated field metabolic-rate during the breeding season. There was no relationship between distance to nests and breeding success. Either Marbled Murrelets can accommodate that additional energy expenditure, or reduce commuting costs by modifying their foraging behavior. They may forage closer to nest sites when provisioning chicks, thereby reducing commuting costs with a payload, or alter nest visitation rates in relation to distance they nest from foraging areas. Nests further inland may also confer advantages that compensate for the added commuting, or birds might replenish body reserves at the end of the breeding season.

Intensity of nest defense against a human intruder was recorded for 42 male and 43 female Northern Hobbies (Falco subbuteo) from 1992 to 1994. Defense did not vary between repeatedly and rarely visited nests. Except during incubation, intensity of nest defense by females was higher than that by males. For both sexes, defense intensity increased from incubation to fledging, within the nestling stage, and from fledging to the first 10 days of the postfledging period. Intensity of nest defense was positively correlated with brood size in females, but not in males. Experiments with dummy nests showed that defense was effective in deterring nest predation, and that its effect was positively related to its intensity. Hobby nest defense was an individually varying “plastic” trait, probably tuned to the reproductive value of the offspring. Parents apparently trade off the costs and risks of the behavior against the increasing likelihood of offspring survival.

Proper management of endangered species requires an understanding of habitat use at a variety of spatial scales, and information on nesting habitat is especially important in that regard. We examined vegetation features associated with nest patches of the Golden-cheeked Warbler (Dendroica chrysoparia), a federally endangered migrant songbird that breeds only in central Texas. We used a spatially paired design to measure 13 vegetation variables at 43 nests and at an equal number of randomly chosen nonuse patches, one located near each nest. Canopy closure was greater at nest patches than at nonuse patches. However, none of the other vegetation variables differed between a nest patch and its paired non-use patch on the same territory, despite high power to detect such differences. In contrast, 8 of the 13 variables exhibited significant variation among territories. For all 13 variables, effect size was substantially greater for variation between territories than for variation between nest patches and their paired nonuse patches. Lack of within-territory variation may reflect the scale at which vegetation varies in that habitat. Such a result suggests that territory selection may be more important than nest-patch selection in this species.

Birds are unique among vertebrates in that they protect their eggs with rigid, calcium-rich shells. Thus, for a short period of time during the annual reproductive cycle, birds experience extraordinarily high demands for calcium. Two strategies appear to exist for meeting those temporally high demands. Some birds apparently seek out calcium-rich foods immediately prior to and during egg laying whereas others may store calcium in their skeletons over a much longer period of time, mobilizing those reserves only when they are needed for production of eggshells. In this study, we used dual energy, X-ray absorptiometry and inductively coupled plasma mass spectroscopy to monitor annual shifts in bone mineral content in the legs of White-tailed Ptarmigans (Lagopus leucurus). The study organisms were known to live on calcium-poor soils. Despite an apparent shortage of calcium in their diets, the test subjects stored substantial amounts of calcium in their leg bones in months prior to reproduction. Those stores were subsequently depleted during the egg-laying period. We suggest ability to store calcium in the skeleton may afford this species more flexibility in selecting suitable breeding habitats than would be possible otherwise.

Seabird mortality from large oil spills and chronic oil pollution is often significant. Total mortality estimates are derived from counts of dead birds that wash ashore and are corrected for numbers lost at sea. Past attempts to estimate proportion of birds that die at sea and wash ashore have included several experiments using carcasses and different types of wooden drift blocks. Results varied greatly depending on environmental conditions and distance from shore where blocks or carcasses were released. Wind seemed to be the predominant factor determining movement over large distances, whereas tidal currents influenced deposition on specific beaches. Determining timing and location of arrival of dead birds on beaches are crucial for accurate mortality estimates. Drift experiments using beached birds that have already drifted at sea for an undetermined length of time are inaccurate due to natural buoyancy loss and decomposition. To determine accuracy of drift block designs used in the past, we compared drift characteristics and patterns between four drift block designs and fresh murre (Uria spp.) carcasses. Our experiments showed that drift blocks used in the past have none of the drift characteristics of dead seabirds, because they have much larger areas exposed to wind and hence drift much faster and farther than murre carcasses. Past mortality estimates using those blocks are therefore doubtful. The drift block design that most accurately mimicked murre carcass drift during our experiments was a 9 × 9 × 14.5 cm wooden block with a 450 gram steel weight that adjusts buoyancy and area exposed to the wind. We propose that in areas where murres are predominant victims of oil spills, that block design be used for all future estimates of oiled seabird mortality.

Visits to nest holes by birds other than their owners is a familiar phenomenon for students of breeding biology. In this study, we evaluate that behavior using a transponder reading system. Eighty-five males and females were fitted with transponders at the end of the incubation period or just after hatching. Nest boxes were fitted with transponder readers from just after hatching until all nestlings fledged. That system revealed 123 visits by birds to nest boxes other than their own, a visit being defined as at least one visit to a separate nest box on a separate day. Males were more often detected at other nests than females (53% of males vs. 29% of females visited) and males on average made more visits than females did (4.8 vs. 2.5 visits). However, both males and females devoted time to visiting other nests while still feeding nestlings. That behavior is more common than previously suspected and is consistent with birds prospecting for future nest sites or investigating patch reproductive success.

I recorded details of 231 copulations of American Avocets (Recurvirostra americana) and 39 copulations of Black-necked Stilts (Himantopus mexicanus) in northern Utah. Those data are presented as quantitative descriptions of the copulatory behavior of each species, complementing and clarifying qualitative descriptions in the literature. I observed no qualitative differences between copulatory behavior of avocets and stilts. Small quantitative differences may be related to differences in morphology and habitat preference. Across the family Recurvirostridae, the distinctive copulatory displays of avocets (Recurvirostra spp.) and stilts (Himantopus spp.) seem relatively uniform, but the behavior of the monotypic Banded Stilt (Cladorhynchus leucocephalus) of Australia appears to differ somewhat from typical recurvirostrid copulatory behavior. Attempted copulation with inanimate objects has been reported for at least 6 of the 10 recurvirostrid species.

Seasonal declines in rates of renesting following clutch loss are common features of avian breeding, and are generally thought to reflect underlying seasonal declines in food availability that lower survival prospects for late-season offspring. However, in Thick-billed Murres (Uria lomvia), long-lived Arctic seabirds that lays a single-egg clutch, previous research has shown that early laying females will continue to relay until late in the laying period. Moreover, hatching success is similar between first and replacement attempts, as are nestling growth and survival, when parental quality is controlled. I compared survival between departure from the breeding site and recruitment age (4–5 years) for Thick-billed Murres that hatched from first and replacement eggs, but that were raised by parents that laid their first eggs early in the season. Replacement-egg offspring hatched and departed the colony about three weeks later than did first-egg offspring, but despite that, they were no less likely to survive to recruitment age. That result indicates that the potential fitness payoff from a replacement egg is similar to that from a first egg for the more capable members of the population. I suggest that an adequate and predictable late-season food supply ultimately underlies the considerable relaying capacity exhibited by Thick-billed Murres.

For those few bird species that are exclusively frugivorous, the low protein content of fruits is likely a major nutritional constraint. Physiological mechanisms that allow strict frugivory remain enigmatic, but reduced protein requirements may suffice. We investigated protein requirements of Pesquet's Parrot (Psittrichas fulgidus), a highly specialized, obligate frugivore. Three isocaloric, fruit-based diets of varying protein content (6.1, 3.3, and 2.6% dry mass crude protein) were used in feeding trials lasting three to five days per diet. A minimum dietary protein requirement of 3.2% dry mass was estimated from balance trials. Endogenous nitrogen losses were 0.05 gN kg^−0.75 day⁻¹ and nitrogen equilibrium occurred at 0.32 gN kg^−0.75 day⁻¹. Those values are extremely low compared to those of granivorous and omnivorous bird species, but higher than those of nectarivorous species. In terms of nitrogen losses and requirements, Pesquet's Parrot most closely parallels the highly frugivorous Cedar Waxwing (Bombycilla cedrorum). Thus, reduced protein requirements appear to play an important physiological role in ability of highly frugivorous birds to subsist on fruit diets.

We examined variation in growth of Black Brant (Branta bernicla nigricans) goslings among two colonies on the Yukon-Kuskokwim Delta in southwestern Alaska and the Colville River Delta on Alaska's Arctic coast. We simultaneously measured abundance and quality of a key food plant, Carex subspathacea, and grazing pressure on that plant at the three colonies. Our goal was to measure variation in gosling growth in relation to variation in grazing pressure and food abundance because growth of goslings is directly linked to first-year survival, and consequently is the principal mechanism for density-dependent population regulation. Goslings grew substantially faster on the arctic coast and were nearly 30% larger than those on the Yukon-Kuskokwim Delta at four to five weeks old. Faster growth on the arctic coast was associated with 2× greater standing crop of C. subspathacea during brood rearing than on the Yukon-Kuskokwim Delta. Dispersal rates are high enough (Lindberg et al. 1998) to rule out local adaptation and genetic variation as explanations for observed variation in growth. Our results are consistent with lower survival of goslings from the Yukon-Kuskokwim Delta during their first fall migration and stronger density-dependent regulation on the Yukon-Kuskokwim Delta than on the Arctic coast.

Both sexes of adult Western Screech-Owls (Otus kennicottii) sing in response to playback of conspecific song within their territories. Two primary songs are the bounce and double trill. Using sonographic analysis of tape-recorded vocalizations, our study quantified characteristics of bounce and double trill songs uttered by individuals within a population of Western Screech-Owls inhabiting riparian woodlands in southwestern Idaho. We asked if songs of males and females differed and, if so, how accurately could songs be classified by sex. On average, male bounce songs were ∼30% lower in frequency than bounce songs of females, but song duration, note duration, number of notes per bout, and internote duration did not differ. Similarly, double trill songs of males were significantly lower in frequency than those of females, and double trill songs uttered by females had significantly greater internote distances in the leading portion. A discriminant model based on frequency at maximum amplitude of bounce songs correctly classified all males and females in our sample. Presence of sex-specific patterns of vocalizations in that species would allow owls to assess the sex of potential intruders and respond appropriately. Moreover, sonographic analysis of Western Screech-Owl songs provides a means for noninvasive classification of sex.

Many birds exhibit seasonal switches in diet and thus alter nutrients predominating their food intake. We tested for dietary modulation of pancreatic enzymes in Yellow-rumped Warblers (Dendroica coronata), a species for which such dietary changes are documented. Birds were fed three diets formulated from either fruit, insect, or seed. We predicted that pancreatic carbohydrase amylase, and the proteases trypsin and chymotrypsin, would be modulated in direct correlation with relative levels of dietary carbohydrate and protein, respectively. In contrast to the prediction, there was no significant dietary effect on activities of amylase and chymotrypsin, and a significant change in trypsin activity (highest on seed diet) occurred in the wrong direction with regard to the prediction. Considering the statistical power of our tests, we conclude that Yellow-rumped Warblers represent a case of only modest ability, at best, to modulate pancreatic enzymes. For some diets, especially high-starch diets that they digest relatively poorly and on which they tend to lose body mass, they may lack sufficient enzyme and hence are constrained in their dietary niche.