I investigated the relative importance of floristics and physiognomy in determining community organization of autumn-migrating landbirds in a riparian corridor in New Mexico invaded by Tamarisk (Tamarix ramosissima). All six avian measures were associated with floristics, physiognomy, or both. However, usefulness in predicting migrant parameters differed between floristics and physiognomy, and depended on the vegetation measures used (direct measures vs. plant community-structure indices) and the scale investigated (micro- vs. macrohabitat). Using direct vegetation measures, migrant abundance, energy consumption, and evenness were more strongly associated with floristics than with physiognomy at all scales. Contrastingly, migrant species richness and diversity were more strongly associated with physiognomy than with floristics at the microhabitat scale, and appeared to be unrelated to vegetation measures at the macrohabitat scale. Migrant species composition was similar among floristically similar macrohabitats, but it was equally correlated with floristics and physiognomy at the microhabitat scale. Using plant community-structure indices, migrant species composition and evenness remained strongly associated with the floristic measure (plant species diversity). However, floristic diversity was most important in predicting migrant abundance and diversity, whereas both floristic and physiognomic (horizontal structure) diversity were important in predicting migrant energy consumption. Migrant species richness was not associated with plant community structure. Respective relationships of floristics and physiognomy to food resources and foraging substrates might explain observed bird–vegetation associations. The results indicated that floristics and physiognomy are both useful in predicting avian community organization in exotic vegetation, and such information can guide conservation and management strategies that seek to control Tamarix while protecting migrant landbirds and their stopover habitats.

The function of nonvocal sounds in avian communication has rarely been investigated. I used playback of natural and digitally altered wing sounds from both sexes of Calliope Hummingbird (Stellula calliope) and Rufous Hummingbird (Selasphorus rufus) to test whether these stimuli altered their behavior. Stimuli played from behind target birds at artificial feeders were used to study responses that characterized the level of threat associated with each wing-sound stimulus. I classified the behaviors into one of five response categories and analyzed the data using log-linear (Poisson) models. I found that the wing-trill signal of males strongly altered the behavior of both conspecific and heterospecific recipients. Females responded more strongly than males to male stimuli, and stronger responses were elicited by male Rufous Hummingbird than by male Calliope Hummingbird stimuli. I used digitally altered wing-sound stimuli to investigate further which sound components are used in communication. The results, in conjunction with previous research that has shown fitness benefits to the sender of the signal, lead me to conclude that male wing trill is an important component of hummingbird communication. Female wing sounds elicited stronger responses than control sounds, but the base wing-hum sound itself appears to be a simple by-product of flight rather than a communication signal. These results of the first playback study using nonvocal avian sounds suggest that further research to identify which nonvocal sounds are communication signals is needed.

Several sources of data suggest that the Yellow-billed Magpie (Pica nuttalli), a corvid endemic to California, is extremely susceptible to West Nile virus (WNV) and that its abundance has decreased since the establishment of WNV throughout California in 2004. From 2004 to 2006, 12,211 Yellow-billed Magpie carcasses were reported to the California Department of Health Services. Seventy-eight percent of the 1,007 Yellow-billed Magpie carcasses tested were WNV-positive, and this was the highest proportion of WNV-positive carcasses of all California bird species with reasonable sample sizes (>20). Assuming a starting population size of 180,000 in 2003, California Department of Health Services data suggest that Yellow-billed Magpie populations may have been reduced by 49% in just two years. Breeding Bird Survey (BBS) data show a 22% decline as of 2005, and Christmas Bird Count (CBC) data show a 42% decline as of 2006. Furthermore, flock size at three traditional urban communal roosts monitored in Sacramento, California, decreased dramatically after the establishment of WNV, with two becoming vacant by summer 2005 and the third declining precipitously into 2006. Of 38 serum samples obtained from 21 Yellow-billed Magpies in Davis, California, in 2006, only one individual was found to produce WNV-specific antibodies. Range-wide monitoring is warranted to detect and track population trends of this species. Population size, genetic diversity and population structure, cause-specific mortality, and population viability should be evaluated.

Studies of reproduction and habitat use are essential for any species assessment, especially for species with declining populations. We compared habitat in nest sites and randomly selected sites within Golden-winged Warbler (Vermivora chrysoptera) territories. We also modeled the effects of temporal and biotic factors on daily nest survival in relation to the constant-survival model. The percent cover of herbaceous vegetation was greater at nest sites, and that of woody vegetation was greater at non-nest sites. There was support for models with annual variation and a decline in nest survival throughout the nesting season, but the constant-survival model performed equally well. One parameter performed marginally better than the constant-survival model: nests with a woody stem in the substrate had lower nest-survival rates. We conclude that nest-site selection was nonrandom, such that females use specific criteria to select nest sites. However, habitat characteristics did not appear to significantly affect daily nest survival or, therefore, predation rates. Until factors that affect predation rates are better understood, conservation strategies that increase breeding habitat with specific nest-site features may be more successful than attempts to directly control nest survival.

Ossuaries, or bone-breaking sites, are used by Bearded Vultures (Gypaetus barbatus) to prepare and store bone remains. The different nutritive values of different parts of the skeleton and bones and the fact that many remains stay in the ossuary for long periods without being consumed suggest that they may have another use besides storage. I tested whether the presence of bone remains in ossuaries may result from selection ("nutrient concentration" hypothesis) and rejection of bone remains on the basis of nutritive value. Of the remains found at the study sites, 84.9% belonged to medium-sized ungulates, 11.6% to large mammals, 2.5% to carnivores, and 1% to Suidae. Bone remains found were principally scapulas (14.9%), vertebrae (13.2%), skulls (12.5%), tibias (10.7%), mandibles (9.3%), ribs (8.3%), and humeri (7.2%). The larger proportion of less-nutritious skeletal parts (i.e., containing less oleic acid) and the significantly smaller proportion of distal epiphyses, which are more nutritious, support the nutrient concentration hypothesis. On the other hand, the scarce presence of remains of large mammals and Suidae and the high presence of scapulae, vertebrae, and skulls suggest that handling efficiency can also influence food selection. Bone selection based on nutritive value may allow Bearded Vultures to optimize parental foraging effort and maximize fitness.

As a result of changes in climate over the past 100 years, many birds are arriving at points along their migration routes earlier in the spring now than they did in the past. Increasingly, researchers are relying on a variety of data sources, such as naturalist journals and bird-club records, to document migration times. However, it is not clear whether researchers can successfully use different sources of data to compare changes in migration times. We examined 25 years of changes in migration times for 30 species of birds at Mt. Auburn Cemetery in Cambridge, Massachusetts, as documented by bird-club members and published in a regional bird journal. We found that, overall, birds arrived earlier in warmer springs in eastern Massachusetts. We compared our findings with those of previous studies in Massachusetts, which included data from a standardized bird-banding station and observations from a naturalist's journal and bird-club records. On a species-by-species basis, changes in migration times were not correlated among the studies. We believe that local changes in population sizes and sampling effort at some of the sites may have contributed to the lack of correlation. For the purpose of comparing changes in migration times across species and locations, standardized bird-banding data are preferable to data collected by volunteer naturalists. However, naturalist data sources are useful and reflect the widely observed trend toward earlier migrations in warm springs.

Costa Rican hummingbirds and Australian honeyeaters respond to an increase in the volume of nectar made available in tubular flowers by increasing the duration of foraging bouts, the rate at which nectar is ingested, and the energetic efficiency of that process. Enhanced intake is the result of increased nectar capture by the tongue during each lick rather than of any significant change in licking rate. All species react to an increase in floral length by spending more time foraging and reducing nectar intake, short-billed species being most affected. Decreased nectar capture per lick, rather than a change in licking rate, is responsible for this response. Honeyeater foraging times increase and nectar-intake rates decrease when the curvature of flowers is increased, though all but one of the short-billed hummingbird species were relatively insensitive to this change. Hummingbirds harvest nectar with equal proficiency whether foraging at erect or at pendulous flowers, whereas the bouts of honeyeaters are longer, and their nectar-uptake rates lower, when they visit pendulous flowers. Overall nectar-extraction rates of hummingbirds, as measured in the laboratory, were greater than those of honeyeaters; values for both groups were generally higher than rates recorded in the field. Hummingbird and honeyeater tongues are equally adept at extracting nectar from tubular flowers, though my results suggest that honeyeater tongues would be more effective in situations where nectar is thinly and widely dispersed.

Both sexes of central-place-foraging seabirds usually share the task of incubation and alternate fasting bouts on the egg with foraging trips at sea. Because foraging strategies during incubation are poorly known, compared with strategies during chick rearing, we examined the foraging behavior of incubating Little Penguins (Eudyptula minor), together with nest-attendance behavior. The duration of foraging trips varied greatly (1–9 days). Birds with lower initial body condition made longer foraging trips, and the increase in body condition after multi-day trips was higher than that after single-day trips. During trips of >1 day, females dove more times each day but total underwater time did not differ between the sexes. By contrast, during one-day trips, foraging males made as many dives as females and spent more time underwater. Birds making longer trips spent more time diving on the second day than on the first day. The proportion of dives in which prey was encountered was lower during single-day than multi-day trips; during the latter, the proportion was lower on the first day than on the second and subsequent days. Body condition of Little Penguins seems to be an important factor influencing trip duration during incubation. Little Penguins apparently undergo long trips to target more profitable, distant prey patches. Incubating Little Penguins benefit from combining short and long trips at sea to optimize both reproduction and survival.

In oviparous reptiles, incubation temperature has been shown to have profound effects on embryonic development and hatchling phenotypes. However, these effects are not well studied in birds, because they typically brood their eggs within a narrow range of temperatures. The Australian Brush-turkey (Alectura lathami) is a megapode that constructs incubation mounds and relies on the heat produced by respiring microorganisms in these mounds to incubate its eggs and is, therefore, a useful comparative model. We developed a new method for monitoring mound and egg temperature to determine both mound thermal variability and the thermal tolerance of embryos. All mounds exhibited greater temperature fluctuations than previously reported or predicted by modeling. Furthermore, all Australian Brush-turkey embryos were exposed to suboptimal temperatures for prolonged periods during development, some experiencing temperatures 6°C above or 9°C below the optimum (34°C) for 12 h. This is the first evidence of bird embryos developing during long-term exposure to suboptimal temperatures. Notably, natural incubation periods were 2–6 days shorter than previously reported for this species.

We used a bird-song simulation system to experimentally assess the effects of habitat, vegetation structure, and background noise on detection probability in aural avian point counts. We simulated bird songs of seven species in two habitats (mixed pine–hardwood forest and deciduous forest) and two leaf conditions (leaves on and leaves off) with two levels of background noise (~40 dB and ~50 dB). Estimated detection probabilities varied greatly among species, and complex interactions among all the factors existed. Background noise and the presence of leaves on trees decreased detection probabilities, and estimated detection probabilities were higher in mixed pine–hardwood forest than in deciduous forest. At 100 m, average estimated detection probabilities ranged from 0 to 1 and were lowest for the Black-and-white Warbler (Mniotilta varia) and highest for the Brown Thrasher (Toxostoma rufum). Simulations of expected counts, based on the best logistic model, indicated that observers detect between 3% (for the worst observer, least detectable species, with leaves on the trees and added background noise in the deciduous forest) and 99% (for the best observer, most detectable species, with no leaves on the trees and no added background noise in the mixed forest) of the total count. The large variation in expected counts illustrates the importance of estimating detection probabilities directly. The large differences in detection probabilities among species suggest that tailoring monitoring protocols to specific species of interest may produce better estimates than a single protocol applied to a wide range of species.

Habitat models are often used to describe species distributions, but they need to be tested to evaluate their predictive performance. We investigated the importance of model evaluation in a study of habitat selection by Saltmarsh Sharp-tailed Sparrows (Ammodramus caudacutus), a species of conservation concern in eastern North America. We estimated the number of birds, nests, and fledglings produced in thirty 1-ha study plots spread across multiple marshes and used an information-theoretic approach to select among explanatory habitat models. Model performance was evaluated using both the original data set and data from another 30 plots from the same set of marshes. Our models indicate that both female and male Saltmarsh Sharp-tailed Sparrows increase in abundance as one moves away from the marsh's upland edge and in areas where there is deep thatch and uniform vegetation height. In contrast to the results for adult birds, number of nests and production of fledglings were positively associated with Saltmeadow Rush (Juncus gerardii). These models suggest that where adults spend the most time is influenced by the vertical structure of the vegetation but that nesting activity is determined more by plant compositions that indicate subtle variations in marsh elevation. Despite the fact that we found good internal consistency for our models during model evaluation, model performance worsened considerably when used to make predictions about new sites. Thus, although our study identifies several new factors influencing habitat selection in Saltmarsh Sharp-tailed Sparrows, it also highlights the need to be cautious when making predictions from habitat models.

We explored predictive models relating body condition and age to nesting propensity, timing of nest initiation, clutch size of first nests, aggregated nest survival, hatching success, and timing of hatch in Mallards (Anas platyrhynchos). Nesting propensity had a positive linear relationship with body condition, and second-year (SY) females had a lower probability of nesting than after-second-year (ASY) females (84% and 94%, respectively, at average body condition). Females in better body condition initiated nesting ∼15 days earlier than those in poor condition, and SY females nested ∼4 days later than ASY females at average body condition. Clutch size of first nests exhibited a curvilinear decline with body condition, such that large clutches were characteristic of females in the best condition that nested early. Nest survival and hatching probability were unaffected by body condition. Younger females had somewhat lower nest survival (11%) than older females (14%), which, in combination with renesting effort, resulted in an age difference in hatching probability (22% and 33%, respectively). Females in better condition hatched nests ∼15 days earlier than those in poor condition, and SY females hatched nests ∼4 days later, on average, than ASY females. Our results indicate that factors influencing the body condition of female Mallards arriving on breeding areas could influence subsequent reproductive investment and success. Condition effects are primarily through the mechanisms of nesting propensity, clutch size, and timing of nest initiation and hatch. Additionally, we provide evidence that Mallards in their first breeding season have lower reproductive potential than older females.

In dominance-structured animal societies, variation in individual fitness is often related to social status. Like many passerine birds, Black-capped Chickadees (Poecile atricapillus) have a short average adult life-expectancy (∼2 years); however, the maximum recorded life span is >5× as long. Enhanced annual survival could contribute to greater lifetime reproductive success for male Black-capped Chickadees with high social rank. We used multistate capture–mark–recapture models to estimate annual survival of male Black-capped Chickadees in Ontario using resighting and recapture data collected from 1997 to 2002. Our goal was to evaluate support for an influence of rank on annual survival and estimate its effect size for a food-supplemented study site. We also statistically modeled the probability of between-year rank transitions. Model selection based on Akaike's information criterion provided support for an effect of rank on survival. However, multimodel inference revealed that the size of the effect was rather small. Over the six study years, model-averaged estimates of the survival benefit of high versus low rank ranged from 5.0 to 7.3%. As expected, survival was strongly year-dependent, with model-averaged estimates of annual survival probability varying between 0.36 and 0.73. Age was an important predictor of the probability of rank transitions. Low-ranked second-year birds were less likely than older low-ranked birds to advance to high rank between years; likewise, high-ranked after-second-year birds were less likely to drop in rank. Other studies have found larger effects of rank on survival than we observed here. Future research should consider how interactions between social and environmental factors influence annual survival.

Most male passerines do not develop brood patches. Despite this, some, including Barn Swallows (Hirundo rustica), apparently incubate. Male incubation should stabilize and enhance average egg temperature over the course of embryonic development and allow females more time to forage before eggs cool to suboptimal temperatures. We recorded egg temperatures and monitored incubation behavior in three Barn Swallow colonies. Female incubation and male nest attendance produced higher average egg temperatures than periods of unattended egg cooling. Females reheated eggs at significantly higher rates than males. Eggs normally cooled during male on-bouts and when unattended, though male nest attendance slowed cooling significantly. Incubation cycles with male nest attendance had less thermal variation than those that lacked male assistance. Embryonic development time was not correlated with male nest attendance. Although male nest attendance is unlikely to enhance embryonic development, it appears to play a significant role in enabling females to forage longer when off nests. Our observations suggest that male incubation in Barn Swallows most likely serves to reduce the probability of nest desertion by females and to increase the male's reproductive output.

Predator deterrence has been widely studied as a potential advantage of colonial breeding. We extend the predator-deterrence hypothesis to the Least Flycatcher (Empidonax minimus), a noncolonial species that clusters its all-purpose territories, leaving apparently suitable habitat unoccupied. Under the hypothesis that Least Flycatchers' alarm calls deter some predators from hunting inside their nesting clusters, we predicted that the rate of nest predation would be lower for interior nests than for those on the periphery. In 1995 and 1996 in north-central Minnesota, we monitored 157 Least Flycatcher nests from nine nesting clusters, with locations ranging from directly on the edge to 170 m in from the edge. Using proportional hazards regression, we assessed the effect of distance to cluster edge on nest success. The models best supported by the data all indicated higher success for interior nests, with 34–38% lower predation hazard. This result is the first evidence of reduced predation within nesting clusters of a species that defends all-purpose territories. Combined with earlier results demonstrating a dramatic response by Least Flycatchers to a live predator, our results lend substantial support to the predator-deterrence hypothesis.

Two morphologically distinct subspecies of the Australian Ringneck Parrot (Platycercus zonarius) meet in a zone of hybridization in southwestern Western Australia. Individuals produce a flight call, a learned vocal signal used by a mated pair to maintain contact and coordinate their movements. I asked how the learned vocal signal covaried geographically with morphology. Across the distributions of the parental taxa and within the hybrid zone, I tape-recorded 398 birds in 38 locations and scored plumage traits. I found that the parental taxa exhibit a discrete difference in their flight calls, but within each of the parental taxa there also were local dialects. There were dialects in the hybrid zone as well, where individuals at a site shared the same type of flight call whether they displayed plumage phenotypes of parental taxa or of hybrids. In the hybrid zone, populations tended to have a form of the flight call intermediate between parental taxa, though the form of the call was more strongly influenced by introgression of call characteristics of one of the parental taxa. These results support both a cultural-dominance model and a blending model of cultural interchange. The parental taxa are hypothesized to have resulted from Pleistocene isolation in refugia during a severe arid period about 25,000–15,000 years ago, with subsequent expansion to create the observed overlap zone. My data suggest that the phylogenetic trace, evident in the culturally transmitted vocal differences of the contemporary parental taxa, originated in the remote past and has been retained for many generations.

Costa's Hummingbird (Calypte costae) is a North American species that breeds in desert scrub in the southwestern United States. Males sing a whistled song that is relatively simple compared to the complex learned song of the species' congener, Anna's Hummingbird (C. anna). Because hummingbirds are one of only three groups of song-learners separated by intervening taxa of non-song-learners, this family is an important group in the study of song evolution. We characterize the structure of Costa's song and identify song features that vary among males. More than 300 songs from 26 individual male Costa's Hummingbirds were recorded during the 2006 spring breeding season in Anza Borrego State Park. We found that the song, which is, on average, 2.5 s in length, has a stereotyped structure consisting of four elements in an invariant sequence. The song can occur singly or be repeated multiple times in a bout. All song features measured show significant variation among individuals; however, it is not known whether the variation found is sufficient to allow individual recognition. The ability to identify individuals vocally is a function of song that may differ between Costa's and Anna's hummingbirds. Further behavioral studies of the differences in structure, function, physiology, and development of song in these two species will contribute to our understanding of the evolution of avian song.

Provisioning calls given by nest attendants immediately before or while they feed nestlings have been recorded in many avian species. Although the adaptive significance of these vocalizations has rarely been examined, their most obvious function seems to be to stimulate begging in blind altricial nestlings. Bell Miners (Manorina melanophrys), cooperative Australian honeyeaters, give provisioning "mew" vocalizations that are relatively unusual in being individually distinctive and given during both feeding events and as attendants leave the nest. We show that mew calls stimulated begging during playbacks and that more calls were given if the brood initially did not beg, if the prey was of a type that was difficult to transfer, or both. This is consistent with mew calls being aimed at the nestlings to stimulate begging and, thereby, improve the efficacy of food transfer. However, mew calls were given in 52% of visits as attendants left the nest area, and the probability of calling in this context increased if another group member was nearby. Furthermore, mew call rate per visit increased throughout the nestling period as provisioning rates increased, despite nestlings being increasingly able to attend to other (e.g., visual) cues of impending food delivery. Together, these results suggest that mew vocalizations also have a role in communication between nest attendants. By improving the coordination and social cohesion of helpers and parents around a nest, mew calls may facilitate cooperative activities by the same group of birds away from the nest, such as during dangerous predator-mobbing events.

Distributing eggs among multiple nests may have a selective advantage over laying eggs in one nest when stochastic events, such as predation, affect individuals of the same phenotype differently. However, an earlier analysis revealed that the mean fitness of such an egg-spreading strategy is equal to putting all eggs in one nest when predation destroys entire clutches. However, if predation typically results in partial clutch loss, distributing eggs among multiple nests may provide a selective advantage. We investigated the possibility that partial clutch loss could favor egg-spreading strategies by modeling mean fitness under a variety of egg-distribution strategies with partial nest predation. We found that higher fitness resulted from distributing eggs among multiple nests that contained at least as many eggs as a single nest containing the eggs of one female. The highest fitness resulted when eggs were in large clutches, because of predator-dilution effects. The fitness differences among egg-distribution strategies increased as predation rates, frequency of partial clutch loss, and the number of eggs destroyed in each partial predation event increased. We also examined the invasibility of pure and mixed parasitic and nesting strategies. Nest parasites may increase their fitness by spreading eggs among multiple nests that contain more eggs than would be present if they were nesting alone, but only a pure parasitic strategy can invade a population of nonparasites when the number of eggs laid is constrained.

There are many causes of nest failure in birds. Although partitioning the risk of nest failure among causes has long been of interest to ornithologists, application of formal methods for estimating competing risks has received little attention in the literature. We describe how evidence collected at nests can be formally incorporated into likelihood functions for competing risks to control classification uncertainty. We briefly review estimators for an idealized case in which all fates are known with certainty, and then we introduce new estimators for four cases in which evidence is used. In the evidence-based models, we consider several distinct types of evidence, including videographic evidence, static ecological evidence, and ecological evidence that decays over time. For each of the four cases using evidence, we compare the asymptotic sampling variance to the ideal case in which fates are always known. We also develop closed-form expressions for expected bias when assumptions underlying the estimators are not met. In all cases, use of evidence results in larger sampling variances for the failure probabilities than when fates are known with certainty. Typically, the magnitude of increase in sampling variance depends on the inverse of the evidence probabilities. We also show that disjoint evidence does not reduce sampling variance and should be ignored. Finally, we show that violations of underlying assumptions cause bias, though the bias may be tolerable in some cases.

In hay fields in the northeastern United States, Savannah Sparrows (Passerculus sandwichensis) whose first nests fail as a result of the harvesting of hay renest in the same field in a dramatically altered habitat. We evaluated availability of invertebrate prey in two treatments (harvested and unharvested hay fields) in Vermont's Champlain Valley and assessed potential effects of food resources on clutch size, food provisioning by adults, and growth of nestling Savannah Sparrows. A relative measure of invertebrate biomass (sweep-net samples) showed a 36–82% decline after harvesting, compared with continual increases throughout the nesting season on unharvested fields. Clutch sizes were not significantly different between treatments. Nestling provisioning rates obtained through video observations differed between treatments, with birds on unharvested fields delivering 73% more food than those on harvested fields (P = 0.02). However, food provisioning differences did not translate into differences between treatments in either average nestling mass or the mass of the lightest nestlings within nests. A measure of total biomass (vacuum samples) on harvested fields showed a 28–56% decline after harvesting; this reduction was insufficient to induce food limitation based on the energetic requirements of Savannah Sparrows. Our results suggest that adult Savannah Sparrows must compensate for reduced food availability on harvested hay fields, possibly by increasing the total time spent foraging.

The level of site fidelity in birds is often characterized as "high" on the basis of rates of return or homing from mark–recapture data. For species that exhibit site fidelity, subsequent biological assumptions have included population structure, demographic independence, and that the extirpation of a site-faithful group might be irreversible because of low immigration. Yet several genetic studies have observed patterns of population differentiation that are incongruous with strong site fidelity, which suggests recent isolation, gene flow, or both. Using a 13-year live-recapture and dead-recovery data set, as well as nuclear and mitochondrial DNA collected across the range of the Hooded Merganser (Lophodytes cucullatus), an obligate cavity-nester endemic to North America, we found evidence that gene flow persists across portions of the species' range even though the probability of female breeding-site fidelity is high (0.92; 95% confidence interval [CI]: 0.64–0.98) and disjunct breeding ranges of this species have been isolated for ≥10,000 years. By combining inferences from genetic, band-recovery, mark–recapture, and comparative data from another cavity-nesting species of waterfowl, we conclude that a high level of site fidelity should not be considered a universal proxy for population structure and demographic independence. Our results also suggest that an accurate assessment of site fidelity—and its implications for population dynamics and delineation—requires cross-species comparisons and multiple data types, such as mark–recapture and genetic information, to best infer patterns across a range of geographic and temporal scales.

Survival from fledging to maturity is an important life-history parameter in long-lived species such as seabirds. However, because of the long period of unobservability following fledging, few studies have reported reliable estimates of survival rates for immatures. We estimated survival to maturity of two cohorts of Atlantic Puffin (Fratercula arctica) fledglings from Hornøya in northern Norway using capture–mark–recapture methodology. By considering only juveniles that actually left their nest burrows, we arrived at unbiased estimates of survival rates for immatures. Contrary to many previous studies, annual survival of immatures was not depressed in relation to adult survival. By the age of five years, more than two-thirds of all fledglings are still estimated to be alive. Averaged over this period, annual survival of immatures is estimated as 0.933 (95% confidence interval: 0.806–0.993). This compares to an annual adult survival of 0.943 (0.909–0.965) during the same period. The survival estimates also imply that the cohorts studied are overwhelmingly philopatric. Dispersal of immatures must be extremely rare or absent. The annual estimates of resighting reveal a clear age-related pattern, including a peak at three years of age and a subsequent minimum at six years of age. Possible biological explanations for this behavior are given.

We conducted dual-observer trials to estimate detection probabilities (probability that a group that is present and available is detected) for fixed-wing aerial surveys of wading birds in the Everglades system, Florida. Detection probability ranged from <0.2 to ~0.75 and varied according to species, group size, observer, and the observer's position in the aircraft (front or rear seat). Aerial-survey simulations indicated that incomplete detection can have a substantial effect on assessment of population trends, particularly over relatively short intervals (≤3 years) and small annual changes in population size (≤3%). We conclude that detection bias is an important consideration for interpreting observations from aerial surveys of wading birds, potentially limiting the use of these data for comparative purposes and trend analyses. We recommend that workers conducting aerial surveys for wading birds endeavor to reduce observer and other controllable sources of detection bias and account for uncontrollable sources through incorporation of dual-observer or other calibration methods as part of survey design (e.g., using double sampling).