Parental care is regarded as one of the most influential forces acting on the evolution of mating systems. Polynesian Megapodes (Megapodius pritchardii) are burrow nesters and rely on geothermal heat for incubation. Because they provide no parental care, either before or after hatching, they can provide insights into selective forces that have shaped mating systems in the absence of parental care. Our study of their mating system—the first such study of any burrow-nesting megapode—suggests social monogamy. The partners of 10 marked pairs stayed together in the same territory for ≤12 months and were seen with their partner significantly more often than on their own. In 64% of all observations, pair partners foraged <5 m apart, and females fed on food items uncovered by the male. Duets also indicated long-lasting pair bonds. We propose that monogamy in this species is related to the fact that females lay only one large egg at a time (which weighs, on average, 24% of her body weight), in intervals of several days or weeks. Producing eggs year-round, females require a high intake of protein-rich food. They seem to benefit, within the pair bond, from the male-defended feeding territory and from the invertebrates the male uncovers while feeding close by. While being guarded by the male, females can spend more time searching for food and are protected from forced copulations by other males. The monogamous pair bond seems to benefit the male by enhancing his chances of fertilizing his partner's eggs; with an unpredictable laying interval and year-round egg production, males cannot predict when their partner will be fertile and thus benefit from staying with her year-round.

We present a phylogenetic analysis of relationships among members of the Amazona ochrocephala species complex of parrots, a broadly distributed group in Middle and South America that has been a “taxonomic headache.” Mitochondrial DNA sequence data are used to infer phylogenetic relationships among most of the named subspecies in the complex. Sequence-based phylogenies show that Middle American subspecies included in the analysis are reciprocally monophyletic, but subspecies described for South America do not reflect patterns of genetic variation. Samples from the lower Amazon cluster with samples collected in western Amazonia—not with samples from Colombia and Venezuela, as was predicted by subspecies classification. All subspecies of the complex are more closely related to one another than to other Amazona species, and division of the complex into three species (A. ochrocephala, A. auropalliata, and A. oratrix) is not supported by our data. Divergence-date estimates suggest that these parrots arrived in Middle America after the Panama land-bridge formed, and then expanded and diversified rapidly. As in Middle America, diversification of the group in South America occurred during the Pleistocene, possibly driven by changes in distribution of forest habitat.

Stable-isotope analyses of egg components can illuminate the contributions of endogenous and exogenous nutrients to egg formation in cases where birds move from one isotopic biome to another just before egg-laying, as in Red Knots (Calidris canutus islandica) and Ruddy Turnstones (Arenaria interpres interpres) nesting in the northeastern Canadian High Arctic. Those populations use inshore marine habitats during the winter and northward migration periods, but switch to feeding and breeding in terrestrial C-3 habitats in the Arctic. Upon the birds' arrival at Alert, Nunavut, Canada, stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values for their red blood cells were consistent with those expected from an inshore marine diet. After the birds switched to a terrestrial diet, those values decayed in a negative exponential fashion until they reached asymptotic values consistent with a local terrestrial C-3 diet. Components of eggs laid later in the season, including lipid-free yolk, albumen, yolk lipid, and albumen lipid, generally showed isotope values consistent with routing from exogenous (i.e. local) nutrient sources, which supports the notion that High Arctic shorebirds are primarily income and not capital breeders. However, eggs in earliest clutches were enriched in ¹³C and ¹⁵N, which suggests that some residual marine nutrients were available for reproduction. The extent to which endogenous stores are transferred to eggs in High Arctic shorebirds may depend on year and climatic conditions.

In many avian species, including Tree Swallows (Tachycineta bicolor), females that lay eggs earlier in the season have higher fitness. It has been hypothesized that nonheritable variation in individual quality could explain how variation in laying date persists in the face of this apparently directional selection. Previous experimental work on Tree Swallows has suggested that natural variation in flight ability enables early-laying females to attain feeding rates high enough to support egg production on earlier, sparser food than later-laying females. We tested that hypothesis with standardized flights through a 9.75-m flight-performance test tunnel. One group of female swallows was tested at the height of the breeding season on 28 May regardless of their nesting phenology; another group was tested on the 11th day of incubation. Average acceleration in the tunnel was negatively correlated with clutch initiation date for the females tested on 28 May. Daily variation in ambient environmental conditions had strong effects on swallow flight performance in the tunnel, and no relationship was observed in the day-11 birds. Because natural variation in foraging performance is correlated with variation in female Tree Swallows' clutch initiation dates, flight ability appears to be a key element of individual quality in this species.

Theoretical questions and conservation concerns have prompted numerous, intensive studies of songbird nesting ecology. Such studies use several techniques (flushing, capture, and blood sampling) that have the potential to negatively affect reproduction, survival, and site fidelity. Although studies have examined the effects of those techniques on avian reproduction and survival, the effect on the return rate of breeding songbirds has not been researched. We used data from a 28-year demographic study to investigate the possible effect of those three common research practices on the return rate of female Wood Thrushes (Hylocichla mustelina). We also tested reproductive success and age as predictors of return because they have been shown to influence site fidelity. Number of successful nests in a breeding season was the variable that best predicted return the following year. None of the research practices negatively affected return rate. That pattern held even among yearlings with zero production, a group that should be the most easily disturbed. We also show that using all years of return for site-faithful birds as observations (i.e. repeated sampling) inflates the estimated return rate.

Although the effects of habitat edges on avian nesting success are well documented for forest ecosystems and for forest-interior species, there is almost no evidence for nonforest, agriculturally dominated landscapes, namely for the matrix of shrubby wetlands and agricultural land. In 1995–1998 I searched for and monitored nests of the Scarlet Rosefinch (Carpodacus erythrinus) in pristine patches of shrubby wet meadow to evaluate the generality of the “edge effect on nest predation” hypothesis. Predation was the major cause of nest failure, accounting for 92.3% of total nest losses. Microhabitat features of the nest sites were not related to proximity to agricultural edges. The model best describing variation in daily nest-survival rates (DSRs) included nest concealment and distance to agricultural edge. Nest survivorship for the entire nesting period was estimated at 41% (1,143 exposure days, n = 79 nests) for edge nests (<100 m from an edge) and 83% (1,831 exposure days, n = 96) for interior nests, respectively. The DSRs were also consistently higher in large than in small wetland patches. Using habitat-specific demographic parameters, I found that per-capita annual productivity was 66.3% higher in core areas than in edge areas (4.14 and 2.49 fledglings, respectively). Three key components of annual reproductive success—brood size, nest success, and renesting rate—contributed unevenly to variation in site-specific annual per-capita productivity, only the latter two being important predictors. The results indicate that edge habitats may not be perceived as suboptimal by breeding individuals, despite high rates of brood loss there.

In European Starlings (Sturnus vulgaris), mass of new primary feathers increases linearly with time for most of the duration of molt (Dawson 2003). Here, we had two aims: (1) to confirm that mass of new primary feathers increases linearly in other species, and (2) to use that linear increase as the basis of a system to score the progress of molt. Increase in length of primary feathers during molt was recorded for captive Eurasian Magpies (Pica pica), Carrion Crows (Corvus corone), European Greenfinches (Carduelis chloris), and Eurasian Bullfinches (Pyrrhula pyrrhula). Wing shape differs among those species. Feather lengths during molt were converted into mass by using information on final feather length and mass and the distribution of mass from tip to base of feather. Rate of increase in total mass of new primary feathers was largely linear in all four species. A molt scoring method is described in which individual feather scores are weighted to account for the contribution of each particular primary feather's mass toward total primary-feather mass. When the method was tested on eight captive starlings, the increase in mass-corrected molt score was almost linear, unlike the increase shown by the standard scoring system, which exaggerated molt rate during the early part of molt and underestimated it later. In the four species studied here, mass-corrected molt score likewise closely tracked the actual increase in mass, unlike the standard molt score. Because it is based on feather mass, the method presented here is of greater physiological and energetic relevance than the standard method. Because the mass-corrected score increases more linearly with time, it has the additional advantage of enabling less complicated, and potentially more accurate, estimations of molt start dates and molt durations.

Seabirds move throughout the day in changing, patchy environments as they engage in various behaviors. We studied the diurnal abundance dynamics of Glaucous-winged Gulls (Larus glaucescens) in a habitat patch dedicated to loafing in the Strait of Juan de Fuca, Washington. We constructed three differential equation models as alternative hypotheses and then used model selection techniques to choose the one that most accurately described the system. We validated the model on an independent data set, made a priori model predictions, and conducted a field test of the predictions. Clear dynamic patterns emerged in the abundance of loafing gulls, even though individuals moved in and out of the loafing area more or less continuously throughout the day. Temporal patterns in aggregate loafing behavior are predicted by three environmental factors: day of the year, height of the tide, and solar elevation. This result is important for several reasons: (1) it reduces the aggregate behavior of complicated vertebrates to a simple mathematical equation, (2) it gives an example of a field system in which animal abundances are determined largely by low dimensional exogenous forces, and (3) it provides an example of accurate quantitative prediction of animal numbers in the field. From the point of view of conservation biology and resource management, the result is important because of the pervasive need to explain and predict numbers of organisms in time and space.

We studied sexual size dimorphism, intrasexual competition, and sexual selection in an individually marked population of Wattled Jacanas (Jacana jacana) in the Republic of Panama. Males are the sole incubators of eggs (28-day incubation) and primary providers of chick care (50–60 days). Females were 48% heavier than, and behaviorally dominant over, males. Females also showed greater development of secondary sexual characters (fleshy facial ornamentation and wing spurs) than males. Both sexes defended territories throughout the year against same-sex conspecifics. Competition for territorial space was intense, and many individuals of both sexes did not become breeders. Resident females further competed with one another to accumulate multiple mates, resulting in a mating system of simultaneous polyandry. Female and male residents (territory holders) were larger, heavier, and more ornamented than adult floaters of the same sex. Larger and heavier females also had more mates than smaller females. Body size was thus a critical predictor of success in intrasexual competition for territories (both sexes) and for mates (females). Three measures of sexual selection—(1) sex difference in the opportunity for sexual selection, (2) female-to-male ratio of potential reproductive rates, and (3) operational sex ratio—each indicated that sexual selection is currently operating more strongly on females than on males (female-to-male ratios ranged from 1.43:1 to 2.22:1). Values of 1.61:1 and 1.43:1 represent the first published quantitative estimates of the opportunity for sexual selection for any sex-role-reversed bird. Our study supports the theory that when increased parental care entails reduced opportunities for future reproduction, asymmetries in parental care behaviors of the sexes can influence the intensity of competition for mates and the direction and strength of sexual selection.

We used radiotelemetry to study behavior of White-throated Robins (Turdus assimilis) during the postfledging dependent period. The study was conducted in a mixed agricultural and forested landscape in southern Costa Rica from March through August of 2001 and 2002. A transmitter was attached to one fledgling per brood (n = 53). Each bird was located daily prior to dispersal. We compared survivorship, habitat use, and movements of fledglings from (1) nests in coffee plantations and (2) nests in cattle pastures. The probability of surviving the first three weeks out of the nest was 0.67 ± 0.07 (SE) for fledglings from nests in all habitats, 0.58 ± 0.10 for fledglings from nests in coffee, and 0.74 ± 0.26 for fledglings from nests in pasture. Fledglings from nests in pasture left their nesting habitat at younger ages than did those from nests in coffee, and most birds from both habitats moved into forest when they left their nesting habitat. Pasture was rarely used during the postfledging period, whereas coffee plantations were used extensively. Fledglings that remained in agricultural habitats (coffee or pasture) were less likely to survive until dispersal than were those that moved into forested areas. Average daily distances from the nest gradually increased until fledglings dispersed away from the natal area, always into forest, and were not different for birds from pasture or coffee. White-throated Robins can nest successfully in agricultural habitats, but use of forest positively influenced survivorship of young during the postfledging dependent period.

Berlioz (1959) described Serpophaga griseiceps on the basis of four specimens from Cochabamba, Bolivia, housed at the Museum National d'Histoire Naturelle (Paris, France). Traylor (1979) subsumed the taxon, without justification, in S. munda after examining other specimens from Cochabamba at the Field Museum of Natural History (FMNH; Chicago, Illinois). Remsen and Traylor (1989) added that S. griseiceps represents the juvenal plumage of S. munda. Straneck (1993) presented new data from central Argentina to revalidate S. griseiceps, and although that account has methodological problems, numerous authors have endorsed its taxonomic conclusions. We re-evaluated the validity of S. griseiceps by examining the type series and specimens deposited at the Museo Argentino de Ciencias Naturales (Buenos Aires, Argentina) and our own field data from Cochabamba, and by critiquing Straneck's taxonomic conclusions. The type specimens of S. griseiceps clearly resemble juvenile S. munda. Photographs of those specimens were compared by T. S. Schulenberg with the FMNH specimens examined by Traylor, confirming that the former are referable to S. munda. Both “forms” differ consistently in plumage coloration from Argentine specimens considered by Straneck to be referable to S. griseiceps. The type series of S. griseiceps coincides with S. munda in wing chord, tail, and tarsus length, and both “forms” have significantly longer wings and tails than Straneck's birds from Argentina. Intensive field surveys in the Cochabamba basin documented the occurrence of only one species of Serpophaga tyrannulet, S. munda. Serpophaga griseiceps should therefore be considered a junior synonym of S. munda, whereas Straneck's S. griseiceps is apparently referable to an undescribed cryptic species of Serpophaga tyrannulet.

A phylogeny of extant penguins (18 forms) was estimated on the basis of 70 integumentary and breeding characters. Integumentary characters included structure and color of bill and legs, and plumage of adult, immature, and downy chick. Breeding characters included eggs, nesting, and sociability of immatures. Gavia was placed at the root, and 11 species of representative procellariiform groups completed the outgroup. A heuristic parsimony analysis under implied character weights was performed. Ingroup resolution was complete. The analysis recovered monophyly of Sphenisciformes and all the traditional genera. The ingroup topology was ((Eudyptula Spheniscus) (Aptenodytes (Pygoscelis (Megadyptes Eudyptes)))). Two suprageneric groups, (Eudyptula Spheniscus) and (Megadyptes Eudyptes), were well supported. Additional analyses under equal weights resulted in a consensus topology that differed only in the internal resolution of Spheniscus. Integumentary and breeding characters performed optimally at the ordinal and generic levels, and also provided resolution and varying degrees of support at the supra- and intrageneric levels.

Feather waxes are ubiquitous in passerine birds, but their composition, phylogenetic distribution, and function are poorly characterized. We used gas chromatography–mass spectrometry to survey the diversity of saturated fatty acids in feather waxes of 91 taxa representing most major passerine groups, and used an independent phylogenetic hypothesis to explore evolutionary variation in the expression of those compounds. Saturated fatty acids are highly stable, and we obtained congruent results in comparisons of extracts from fresh material and from museum skins as much as a century old. All taxa expressed unbranched fatty acids, but in a broad range of proportions relative to their total saturated fatty-acid profile. The expression of three other classes of fatty acids was more variable, although each showed a high degree of conservation at the phylogenetic level corresponding approximately to avian families. The 2-methyl fatty acids were expressed in a number of families, often in high proportions, but were absent or low in all fringillid taxa surveyed except the Dickcissel (Spiza americana). The 3-methyl fatty acids were common only in fringillids and allies and in one genus of turdids (Zoothera). The 4-methyl compounds were comparatively rare and were abundant only in the Paridae, Polioptilinae, and Troglodytidae. Feather-wax composition is unlikely to be highly informative for reconstructing phylogenetic relationships, but study of secretion diversity in a comparative phylogenetic context holds promise for characterizing the functions of those compounds.

Resource availability and distribution are hypothesized to be the primary ecological mechanisms driving variation in avian mating systems. Although food supplementation experiments have been used to examine plasticity in mating strategies, variation in avian mating strategies across naturally occurring gradients of prey availability has rarely been examined. Here, we test the hypothesis that the polygynandrous mating system of Bicknell's Thrush (Catharus bicknelli) results from food limitation on female home ranges in the species' harsh montane breeding environment. In 2000, number of chicks fledged per nest was significantly positively correlated with prey biomass on a female's home range, and number of male feeders at a nest was significantly negatively correlated with prey biomass. Neither relationship was significant in 2001, a year with high nest-predation rates, which suggests that nest predation may ultimately limit the species' productivity. These results are consistent with the hypothesis that (1) female productivity is limited by prey biomass, and (2) female mating decisions may be influenced by their assessment of home-range food abundance prior to egg laying.

In alcids, growth rate and hatching date of chicks appear to affect fledging age and mass. Underlying mechanisms are hypothesized to be (1) critical wing length at fledging for postfledging survival, (2) synchronization of fledging to dilute predation risk, and (3) variable parental provisioning according to timing of breeding. To elucidate the effects of growth rate and hatching date on fledging age and mass, and to test those mechanistic hypotheses, we measured chick growth and fledging periods in Rhinoceros Auklets (Cerorhinca monocerata) at Teuri Island from 1995 to 2000. The multiple-linear regression analysis showed that intrayear variations of fledging age and mass were explained by growth rate or hatching date in five out of six years. Faster-growing chicks fledged younger and heavier, and earlier-hatched chicks fledged older and heavier. Consequently, no apparent correlation between fledging age and mass was observed in five out of six years. Analysis of interyear variation showed a negative correlation between fledging age and mass, which indicates that growth rates rather than hatching dates had a major effect. Wing length at fledging was independent of growth in mass. More than 80% of chicks fledged when they attained a narrow range of wing length (130–150 mm), presumably because they remained in their nests until they attained the critical wing length. In five out of six years, the chicks did not synchronize timing of fledging relative to timing of hatching. Later-hatched chicks attained lighter peak masses and at younger ages, which may indicate that their parents decreased provisioning rates when the chicks were still young. We suggest that (1) critical wing length at fledging and (2) variable parental provisioning according to timing of breeding could be underlying mechanisms determining these relationships between fledging age and mass.

I used a supplemental feeding experiment to determine whether adult Tufted Puffins (Fratercula cirrhata) would decrease provisioning effort in response to a reduction in nestling nutritional requirements, and to investigate the relationship between parental provisioning effort and timing of fledging. As predicted, parents of the supplemented nestlings decreased the number of provisioning trips but did not alter bill-load size or prey composition. Supplemental feeding significantly increased the growth of the culmen and tarsus but had no detectable effect on wing growth or body mass of chicks. Supplemented nestlings fledged significantly older than control nestlings. The maximum mass attained by the nestling and the age at which mass peaked also influenced timing of fledging. These results demonstrate that fledging age is influenced by both the energy provided by the parents and the nestling's developmental state and are consistent with the hypothesis that nestlings time their departure from the nest based on the costs and benefits of remaining.

Passerine birds are favored models for studies of sperm competition and extrapair paternity, yet the intraspecific chronology of testicular maturation and its empirical and theoretical consequences in avian mating systems have been largely ignored. I analyzed age-dependent variation in testicular morphology in 25 breeding populations of the Black-throated Blue Warbler (Dendroica caerulescens) distributed throughout its geographic range in eastern North America. Yearlings (first breeding season) had significantly smaller testes than older males (≥2 years). Latitude, altitude, and Julian date had negligible effects on testicular morphology when effects of core body size were controlled. Preparator effects had significant influence on the estimation of testicular volume and asymmetry. Contrary to Moller's hypothesis that the smaller testis compensates for deficiencies in the larger, the volumes of the left and right testes were positively correlated in both yearlings and older males. Older males exhibited a higher degree of directional asymmetry because of the disproportionate enlargement of the left testis. These data suggest that testicular morphology and reproductive capacities of yearling passerines may not be equivalent to those of older males. In a broader context, these findings demonstrate that age class should be factored into quantitative models of sperm competition in birds.

We investigated the yearlong territorial behavior of White-bellied Antbirds (Myrmeciza longipes) in Panama by conducting 17 experimental removals during the nonbreeding season on both sexes. We also monitored the territorial behavior and occupancy of 48 males and 34 females throughout the nonbreeding and breeding seasons. We tested the importance of territory switching, mate advertisement, foray behavior, and role of floaters. In seven of the removal experiments, both members of a pair were radiotagged and tracked throughout the duration of the experiments. It was predicted that widowed birds would attempt to attract a new mate through increased song rate or unique vocalizations; however, that behavior was not observed in White-bellied Antbirds. We documented a weak response in floaters to territorial vacancies and found that territory switching occurs regularly in response to experimental removals and naturally within populations. We found density of birds in an area influences the probability of replacement and is likely a reflection of territory quality given that birds in high-density areas were in better physical condition, spent less time off-territory, and competed more for those territories. Telemetry revealed that individuals made silent extraterritorial forays during the nonbreeding season. Birds could use those forays to assess the quality and status of neighboring territories and to find food during this period when food abundance is low. Several birds were observed to temporarily abandon territorial behavior for periods from 2 to 13 months, a previously undocumented behavior in this type of territorial system.

Covariation among factors that may affect nest success of dabbling ducks in the Prairie Pothole Region of North America (e.g. productivity of upland and wetland habitat related to climate variation, and duck and predator densities) often confounds efforts to interpret the effect of any individual factor. A comparison of nest success of dabbling ducks at sites with and without predator management provided an opportunity to separate the effect of predation pressure from other factors because predator management has occurred over a range of climatic conditions. We updated an existing study on temporal trends of nest success for prairie ducks in the Prairie Pothole Region of North America by compiling recent estimates of nest success for five species of dabbling ducks (Mallard [Anas platyhrynchos], Northern Pintail [A. acuta], Northern Shoveler [A. clypeata], Blue-winged Teal [A. discors], and Gadwall [A. strepera]). In addition, we compared trends of nest success at unmanaged sites and sites where nest predators were excluded or removed. We used pond density calculated from annual surveys for breeding waterfowl as an index of upland and wetland productivity and a correlate of predator and duck density. At unmanaged sites, the best approximating local regression model suggested that, rather than having undergone a monotonic decline, average nest success has fluctuated through time, although those changes do not appear to be associated with changes in pond density. At sites where predators were excluded, nest success did not vary with time but varied positively with pond density in the previous year, although that effect was tempered by high pond density in the year of observation. At sites where predators were removed but could emigrate back into study plots, nest success varied widely over time and we found no evidence of an effect of pond density. We show that nest success of dabbling ducks is higher under predator management than at sites without predator management, and that this relationship varies with climatic conditions, possibly related to complex interactions within and among duck species, their predators, and their prey.

We held an adult Guadeloupe Woodpecker (Melanerpes herminieri) in captivity for two weeks and documented its tongue movements as it caught grubs placed into holes that had been excavated out of a log. We provide evidence that the Guadeloupe Woodpecker does not spear grubs with its tongue but instead grabs them with the tongue's horny tip, which is barbed and coated with saliva, and pulls them out of the holes.

In South American temperate rainforests, five endemic understory birds (four Rhinocryptidae and one Furnariidae) are often associated with the main understory plant, the native bamboo Chusquea valdiviensis (Poaceae: Bambusoideae). We studied the effects of bamboo cover on species abundance and richness of those understory birds and explored the functions of bamboo as food resource and escape cover. In Chiloé Island (42°S), southern Chile, we selected four old-growth forest patches >100 ha and in each patch conducted bird surveys in six plots with >70% understory cover. Three plots were dominated by native bamboo and three plots had a sparse bamboo cover. Bird abundance (point counts) was significantly correlated with both total understory cover and percentage of bamboo cover but was not correlated with other kinds of understory plant cover. Bird species richness was positively correlated with bamboo cover and negatively correlated with other kinds of understory cover but unrelated to total understory cover. Leaf-gleaners Magellanic Tapaculos (Scytalopus magellanicus), Ochre-flanked Tapaculos (Eugralla paradoxa), and Des Murs's Wiretails (Sylviorthorhynchus desmursii), and the ground-gleaner Chucao Tapaculos (Scelorchilus rubecula) were more abundant in high-bamboo plots; but the ground-gleaner Black-throated Huet-huet (Pteroptochos tarnii) was recorded more times in plots with low-bamboo cover.

Availability of invertebrates per unit of understory dry mass did not differ between high- and low-bamboo plots; but plant biomass was greater in high-bamboo plots, so total invertebrate abundance per plot was higher there. Ground-litter invertebrate abundance was similar in all plots. To examine escape-cover preferences, nine captured Chucao Tapaculos were released in front of two different understory scenarios (high-bamboo cover or bamboo-free understory); 88% of released birds moved into bamboo cover. We suggest that the structure of native bamboo understory is critical for the maintenance of four of those species, and retaining bamboo cover in managed stands may help minimize the effect of logging on understory birds.

Logistic regression has become increasingly popular for modeling nest success in terms of nest-specific explanatory variables. However, logistic regression models for nest fate are inappropriate when applied to data from nests found at various ages, for the same reason that the apparent estimator of nest success is biased (i.e. older clutches are more likely to be successful than younger clutches). A generalized linear model is presented and illustrated that gives ornithologists access to a flexible, suitable alternative to logistic regression that is appropriate when exposure periods vary, as they usually do. Unlike the Mayfield method (1961, 1975) and the logistic regression method of Aebischer (1999), the logistic-exposure model requires no assumptions about when nest losses occur. Nest survival models involving continuous and categorical explanatory variables, multiway classifications, and time-specific (e.g. nest age) and random effects are easily implemented with the logistic-exposure model. Application of the model to a sample of Yellow-breasted Chat (Icteria virens) nests shows that logistic-exposure estimates for individual levels of categorical explanatory variables agree closely with estimates obtained with Johnson (1979) constant-survival estimator. Use of the logistic-exposure method to model time-specific effects of nest age and date on survival of Blue-winged Teal (Anas discors) and Mallard (A. platyrhynchos) nests gives results comparable to those reported by Klett and Johnson (1982). However, the logistic-exposure approach is less subjective and much easier to implement than Klett and Johnson's method. In addition, logistic-exposure survival rate estimates are constrained to the (0,1) interval, whereas Klett and Johnson estimates are not. When applied to a sample of Mountain Plover (Charadrius montanus) nests, the logistic-exposure method gives results either identical to, or similar to, those obtained with the nest survival model in program MARK (White and Burnham 1999). I illustrate how the combination of generalized linear models and information-theoretic techniques for model selection, along with commonly available statistical software, provides ornithologists with a powerful, easily used approach to analyzing nest success.

Recorded vocalizations from 18 known Great Bitterns (Botaurus stellaris) were analyzed, both quantitatively and qualitatively, to determine the amount of intra- and inter-individual variation. All parameters examined showed significant variation among males, and vocalizations of the same male were not stable over time. Variability within males over time makes re-identification of individuals on the basis of vocalizations difficult. The high degree of uncertainty in recognizing individuals limits the usefulness of vocalizations for censusing of bitterns.

The Akiapolaau (Hemignathus munroi), an endangered Hawaiian honeycreeper, drills 3–5 mm deep holes in particular ohia trees (Metrosideros polymorpha) and drinks the sap that emerges, a remarkable example of convergent evolution in sap-feeding behavior with mainland woodpeckers and Australian sugar-gliders. There has been little research on how this species selects sap trees (“Aki trees”) and what advantages they confer. We marked the locations of and collected sap samples and microhabitat data from 101 Aki trees and 73 randomly selected control trees in Hakalau Forest National Wildlife Refuge, Hawaii. Aki trees were rare (2 ha⁻¹), spatially clustered, and defended by Akiapolaau. Sap flow volume and speed were substantially greater in Aki trees than in controls. Aki trees also were larger, had thinner bark, and were more likely to be located on convex east-facing slopes where more light is available. Those results support the hypothesis that Aki trees are selected on the basis of high sap flow and a suite of unique microhabitat and tree characteristics. Sap may be an important energy source in times of low insect availability and a potent alternative to nectar for the Akiapolaau. Aki trees are both a fascinating example of niche specialization and a factor that should be considered when conserving or restoring habitat for this endangered species.

Food abundance influences various aspects of birds' breeding ecology, such as onset of laying, clutch size, and reproductive success. Here, we examine the effects of a natural superabundance of food—cockchafers (Melolontha melolontha, Coleoptera)—on nesting success of a monogamous long-distance migrant, the Lesser Gray Shrike (Lanius minor). In that species, cockchafers make up 88% of adult and 48% of nestling diet in years with cockchafer outbreaks. We compared timing of egg laying, clutch size, and fledging success in three years and chick development in two years with and without cockchafer outbreaks. In cockchafer years, laying date was advanced by about one day, clutch size increased by about one egg, and heavier chicks were produced. Fledging success, however, did not change (fledgling number in non-cockchafer years: 5.3 ± 0.2, 5.0 ± 0.2, and 4.0 ± 0.5; in cockchafer years: 4.1 ± 0.7, 5.4 ± 0.2, and 4.2 ± 0.5), because more eggs failed to hatch during cockchafer years. Thus, increased clutch size in periods of superabundant food do not always result in increased fledgling production. Limited incubation ability or intrinsic physical egg properties, resulting in inefficient incubation, are the most likely explanations for increased hatching failure in years of food superabundance in our study population of Lesser Gray Shrikes.

The distributions of southern African (Tockus erythrorhynchus rufirostris) and Damaraland (T. e. damarensis) Red-billed Hornbills overlap in northern Namibia. Allopatric populations of the taxa have diagnosable differences in habitat, morphology, vocalizations, and displays. We investigated the structure of the hybrid zone using data from morphology, behavior, and breeding biology. The morphological characteristics—eye color and facial plumage color—were summarized as hybrid index scores, which showed a significant positive regression against distance from southwest to northeast across the hybrid zone. Vocalizations also showed a positive relationship between the first principal component (extracted from 12 call variables) and distance across the hybrid zone. However, there appears to be introgression of a T. e. damarensis call into T. e. rufirostris, but not vice versa. In addition, female T. e. damarensis-male T. e. rufirostris breeding pairs occur more frequently than male T. e. damarensis-female T. e. rufirostris pairs. The asymmetrical call introgression may result either from asymmetry in mating or from genetic control of call inheritance. Finally, heterospecific pairs show lower fitness, in the form of reduced hatching success, even when female fitness attributes are included as covariates. Although we are uncertain whether the Red-billed Hornbill hybrid zone is stable, the apparent biological processes operating within it conform to predictions of both the “mosaic” and the “tension zone” models, because both habitat characteristics and a balance of dispersal and selection appear to determine its structure.

We used microprocessor data loggers to document patterns of nest attendance during the laying stage and to quantify temperatures of dummy eggs during laying for Mallard (Anas platyrhynchos), Blue-winged Teal (A. discors), Northern Shoveler (A. clypeata), Northern Pintail (A. acuta), Gadwall (A. strepera), Green-winged Teal (A. crecca), American Wigeon (A. americana), and Lesser Scaup (Aythya affinis) nesting in southern Manitoba in 1994 and in northeastern North Dakota in 1995–1997 and 2000–2002. Females of all species increased the time they spent on the nest as laying progressed, but species differed in their pattern of increased attendance. Female Blue-winged Teal and Northern Shoveler that laid smaller clutches increased the time they spent on the nest more rapidly than conspecifics that laid larger clutches, but large- and small-clutch conspecifics had similar attendance at the end of the laying period. Attendance during laying was not influenced by low ambient temperature, precipitation, or nest initiation date. For all species combined, maximum egg temperatures increased as laying progressed. Eggs were heated to temperatures sufficient for embryonic development as early as the day that the second egg was laid. Our findings contradict the prevailing paradigm that incubation in waterfowl begins after clutch completion and raise questions about how hatching synchrony is achieved. We relate our findings to two hypotheses (nutrient limitation and viability–predation) that have been proposed to explain the limits to clutch size in ducks.