Male birds confront a tradeoff between increasing the number of offspring they sire and providing parental care. This behavioral tradeoff may be manifested as variation in testis size: larger testes, producing more sperm and testosterone, are advantageous for sperm and mating competition, thus ensuring paternity, yet high levels of plasma testosterone also inhibit parental care. There is good evidence that relative testis size is greater in species in which males compete more intensely to fertilize females, but it remains unclear whether, in turn, smaller testes prevail in species with greater levels of paternal care. Cuckoos provide an opportunity to test for an effect of paternal care on testis size because of the diversity of breeding systems in this family: parasitic species lack parental care altogether, whereas some coucals (Centropodinae) show exclusively or predominantly male care. In addition, coucals have a reduced left testis, which Ligon (1997) suggested may promote male care. We tested the idea that species with more paternal care have smaller testes in a phylogenetic analysis of 18 parasitic and 15 nonparasitic species and, specifically, quantified the reduction of the mass of the left testis in the Pheasant Coucal (Centropus phasianinus). Contrary to expectation, nesting cuckoos had larger testes than parasitic species and coucals compensated the reduction of the left testis by an increase of the right. These findings suggest that plasma testosterone is regulated independently of testis size and paternal care is not associated with testis size in cuckoos.

Because reliable estimates of nesting success are very important to avian studies, the defnition of a “successful nest” and the use of different analytical methods to estimate success have received much attention. By contrast, variation in the criteria used to determine whether an occupied site that did not produce offspring contained a nesting attempt is a source of bias that has been largely ignored. This problem is especially severe in studies that deal with species whose nest contents are relatively inaccessible because observers cannot determine whether or not an egg was laid for a large proportion of occupied sites. Burrowing Owls (Athene cunicularia) often lay their eggs ≥3 m below ground, so past Burrowing Owl studies have used a variety of criteria to determine whether a nesting attempt was initiated. We searched the literature to document the extent of that variation and examined how that variation influenced estimates of daily nest survival. We found 13 different sets of criteria used by previous authors and applied each criterion to our data set of 1,300 occupied burrows. We found significant variation in estimates of daily nest survival depending on the criteria used. Moreover, differences in daily nest survival among populations were apparent using some sets of criteria but not others. These inconsistencies may lead to incorrect conclusions and invalidate comparisons of the productivity and relative site quality among populations. We encourage future authors working on cavity-, canopy-, or burrow-nesting birds to provide specific details on the criteria they used to identify a nesting attempt.

Despite the widespread use of stable isotopes in studies of avian movement, key assumptions on which the methodology is based remain unsubstantiated, including the assumption that measurements of stable hydrogen isotopes in feathers (δD_f) are consistent across time within the same laboratory or among laboratories using the same analytical protocols and keratin standards. We tested this assumption by remeasuring δD_f from 211 raptor feathers within and between laboratories. Initial and repeat samples were prepared and analyzed using identical protocols but analyzed in distinct automated runs with laboratory staff blind to sample identity. Reproducibility of δD_f measurements varied significantly and substantially among nine independent sample groups. Feather δD measurements among sample groups exhibited average isotopic shifts from -15.6%‰ to 27.5%‰ (an absolute difference of 43.1%‰), with standard deviations from 6.0%‰ to 12.4%‰. Therefore, despite existing analytical protocols to address issues of reproducibility, empirical data suggest that comparing δD_f measurements among studies or labs and pooling samples analyzed during different automated runs within a laboratory remain problematic. More importantly, poor reproducibility compromises the geographic assignment of origins based on δD_f , because the substantial differences in δD_f measurements between automated runs can result in spurious inferences regarding the origins of migratory birds. We caution against the continued use of δD_f for predicting geographic origin, and for addressing important conservation questions, until the factors affecting poor reproducibility are identified and improved reproducibility is demonstrated within and among laboratories across time and taxa.

Patterns of relatedness among males attending leks can provide insights into how this reproductive behavior has evolved. Past research on birds has found that lekking males show either elevated levels of relatedness, supporting a mechanism based on kin selection, or a lack of relatedness, supporting a direct-benefits mechanism. We show that males attending Blue Manakin (Chiroxiphia caudata) leks exhibit a third pattern, with leks consisting of mixtures of related and unrelated individuals. Kinship analyses of males sampled from 13 leks in three local populations showed that close male relatives (r = 0.5) were present, but only at half the leks sampled. Analysis of male relatedness among leks in each local population showed that overall levels of relatedness were not significantly different between males from the same lek and those at different leks and that no isolation-by-distance relationships were present. We argue that these patterns are most parsimoniously explained as a byproduct of limited dispersal rather than as direct selection operating via reproductive behavior to produce specific patterns of relatedness among lek attendees.

Many migratory birds use staging sites to gain essential resources to fuel their ongoing migration. Understanding staging strategies reveals much about migration systems and is essential if one is concerned with monitoring population trends and mass gains, two of the principal methods for assessing the “health” of a migratory population. In spring 2004, we investigated the staging behavior in Delaware Bay of Red Knot (Calidris canutus) using mark-recapture techniques and resightings of birds marked in the preceding spring. Individuals staged for 11–12 days, which declined to 8–10 days late in the season. Arrivals were asynchronous, but departures tended to be synchronized. A simple sensitivity analysis showed that the mark-recapture analysis estimated length of stay to within 10% and confirmed biases in monitoring trends and mass gains using peak counts and mass-on-date regressions. Alternative methods using staging duration to estimate passage population size and mass gains were shown to be unbiased. Using these methods, we estimated a passage population size in 2004 of 18,000 Red Knot that arrived at an average mass of 111 g and, on average, gained mass at 7.2 g day^-1. Thus, in 2004, the passage population was substantially smaller than the recent peak count of 50,360 in 1998, which confirms a significant decline in the number of Red Knot staging in Delaware Bay. Use of refined techniques such as these is essential if management decisions such as those in Delaware Bay are to be based on firm scientific advice.

Headwater forests serve many ecological functions and may be particularly responsive to changes in climate and land use. Riparian birds can serve as indicators of changes in their associated ecosystems. Little known, however, are combined influences of climate and land use on riparian birds and riparian ecosystems. We examined multiscale associations between these environmental conditions and reproduction of the Louisiana Waterthrush (Seiurus motacilla), a riparian-obligate songbird that breeds in the eastern United States. Specifically, we measured variables at multiple spatial and temporal scales to model crucial components of individual fecundity, using an information-theoretic approach. We monitored 190 nests in 139 territories within 13 drainages from 2002 to 2005. Daily nest survival reached a maximum when mean rainfall was intermediate (3–10 mm day^-1) during the nesting period. Nestling survival, by contrast, reached its maximum with high amounts of rainfall (>14 mm day^-1). Nestling survival declined with increasing territory size and was lowest in areas that were far from clearcuts and fields (=160 m) but were surrounded by large expanses of fields (=40% within 1.75 km). Urban land uses surrounding drainages, proximity to edges, measures of food availability, differences among years, and timing of nesting had weak, if any, effects on Louisiana Waterthrush reproduction. These findings indicate that reproduction by this riparian obligate is negatively associated with (1) rainfall extremes and agricultural land use and (2) size of the territory defended by the male.

Reliable information on demography is necessary for conservation of albatrosses, the most threatened family of pelagic birds. Albatross survival has been estimated using mark-recapture data and the Cormack-Jolly-Seber (CJS) model. However, albatross exhibit skipped breeding, violating assumptions of the CJS model. Multistate modeling integrating unobservable states is a promising tool for such situations. We applied multistate models to data on Grey-headed Albatross (Talassarche chrysostoma) to evaluate model performance and describe demographic patterns. These included a multistate equivalent of the CJS model (MS-2), including successful and failed breeding states and ignoring temporary emigration, and three versions of a four-state multistate model that accounts for temporary emigration by integrating unobservable states: a model (MS-4) with one sample per breeding season, a robust design model (RDMS-4) with multiple samples per season and geographic closure within the season, and an open robust design model (ORDMS-4) with multiple samples per season and staggered entry and exit of animals within the season. Survival estimates from the MS-2 model were higher than those from the MS-4 model, which resulted in apparent percent relative bias averaging 2.2%. The ORDMS-4 model was more appropriate than the RDMS-4 model, given that staggered entry and exit occurred. Annual survival probability for Greyheaded Albatross at Marion Island was 0.951 ± 0.006 (SE), and the probability of skipped breeding in a subsequent year averaged 0.938 for successful and 0.163 for failed breeders. We recommend that multistate models with unobservable states, combined with robust-design sampling, be used in studies of species that exhibit temporary emigration.

An understanding of individuality in animal vocalizations can assist in tracking individuals spatially and temporally, and is particularly useful for species of conservation concern. We determined whether fitz bew vocalizations of the endangered Southwestern Willow Flycatcher (Empidonax traillii extimus) showed vocal individuality, assessed the differences in vocal individuality among three populations, and tested the ability of predictive vocalization models to reidentify individuals. Fitz bew vocalizations were recorded from two populations in Arizona (Roosevelt Lake and San Pedro River) and one in California (Kern River). Individuality was determined using discriminant function analysis (DFA) and trained artificial neural networks (ANN). Southwestern Willow Flycatchers showed individuality in the fitz bew, with the models correctly classifying 81–86% of the vocalizations. We also found population-level variations: vocal structure differed substantially between Roosevelt Lake and Kern River, but vocal structure in the San Pedro River population overlapped with that of the other two populations. These population differences could be related to dispersal patterns of adults or offspring, patterns of territory establishment, or habitat structure differences. The ANN vocalization models reidentified an average of 81% of the individuals and were able to identify novel individuals. On the basis of these results, we recommend that acoustic tracking should complement rather than replace current monitoring practices, given its logistical limitations. We provide a basic understanding of vocal parameters that can be used in the future to study different aspects related to vocal individuality (e.g., taxonomic, seasonal, yearly, and sex differences).

Point counts are used widely to index bird populations. Variation in the proportion of birds counted is a known source of error, and for robust inference it has been advocated that counts be converted to estimates of absolute population size. We used simulation to assess nine methods for the conduct and analysis of point counts when the data included distance-related heterogeneity of individual detection probability. Distance from the observer is a ubiquitous source of heterogeneity, because nearby birds are more easily detected than distant ones. Several recent methods (dependent double-observer, time of first detection, time of detection, independent multiple-observer, and repeated counts) do not account for distance-related heterogeneity, at least in their simpler forms. We assessed bias in estimates of population size by simulating counts with fixed radius w over four time intervals (occasions). Detection probability per occasion was modeled as a half-normal function of distance with scale parameter σ and interceptg(0) = 1.0. Bias varied with σ/w; values of σ inferred from published studies were often <25 m, which suggests a bias of >50% for a 100-m fixed-radius count. More critically, the bias of adjusted counts sometimes varied more than that of unadjusted counts, and inference from adjusted counts would be less robust. The problem was not solved by using mixture models or including distance as a covariate. Conventional distance sampling performed well in simulations, but its assumptions are difficult to meet in the field. We conclude that no existing method allows effective estimation of population size from point counts.

Understanding sexual diferences in habitat use is important for effective conservation management, particularly with regard to polygynous species, the sexes of which may differ in their responses to land-use change. We examined sex-specifc habitat use in the critically endangered Bengal Florican (Houbaropsis bengalensis), a polygynous bustard whose most important population occurs in traditionally farmed grasslands in the Tonle Sap foodplain, Cambodia. Tis habitat is undergoing rapid conversion to intensive dry-season rice production. Using radiotelemetry, we compared male and female breeding-season habitat selection and home-range sizes and confgurations. Te sexes differed in their spatial use of the lek and their ability to utilize anthropogenic habitat features. Both sexes avoided intensive dry-season rice fields. Males selected habitats related to low-intensity human activity, chiefly burned grassland, whereas females selected unburned grassland but also used unburned, uncultivated grassland in dry-season rice head-ponds. Tese differences refect the species' breeding system, with males using open areas for display and females selecting cover. Our findings demonstrate the importance of the landscape heterogeneity associated with traditional human activity in maintaining the habitat mosaics necessary for the contrasting breeding-season requirements of male and female Bengal Floricans. Two-thirds of tagged females may have left the lek to nest elsewhere, which suggests that protecting habitat in which males display will not be a suffcient conservation response for such lekking species. Both sexes are detrimentally affected by agricultural intensification within the Tonle Sap, and encouragement of industrial rice production to spare more “natural” habitats elsewhere is likely to be counterproductive for this globally threatened flagship species.

Although egg size is a widely studied life-history trait in evolutionary ecology, it is largely unknown whether exposure to persistent organic pollutants (POPs) can influence the allocation of resources to avian eggs and, if so, how. It is well established that female birds exposed to POPs transfer these compounds to their eggs. However, little is documented with regard to contaminant-related changes in egg quality, such as egg mass, albumen mass, yolk mass, lipid, and water content. We report positive correlations between the concentrations of several major classes of POPs (organochlorines, brominated flame-retardants, and metabolically derived products) in plasma of Arctic-breeding Glaucous Gulls (Larus hyperboreus) and in the yolk of the last-laid egg of their clutches. The contributions of the different POP classes to the summed POP concentration were also positively correlated between female plasma and egg yolk. In addition, Glaucous Gulls with a relatively high concentration of sum (Σ) chlordanes and total-(α)-hexabromocyclododecane in their plasma laid smaller eggs. Eggs into which females had deposited a relatively low concentration of ΣPCB and a relatively high concentration of ΣDDT were also smaller. The POP patterns of yolk and maternal plasma were associated with changes in water and lipid content of the yolk. These results suggest that egg quality—and, thus, offspring performance—may be affected not only by the direct transfer of contaminants from the female to the egg, but also through associated changes in egg size and composition.

I report on the evolutionary loss of the sternotrachealis muscle (ST) in a vocal bird, the tinamou Darwin's Nothura (Nothura darwinii). Dissections of immature and adult individuals of two subspecies of Darwin's Nothura (N. d. agassizii and N. d. boliviana) and of immature and adult specimens of Ornate Tinamou (Nothoprocta ornata) showed absence of the ST in all the individuals of Darwin's Nothura. By contrast, this muscle was observed in all the specimens of Ornate Tinamou. I provide a description of the morphological organization of the syrinx and the extrinsic muscles of these two species. The presence of the ST in ratites and the Ornate Tinamou suggests that it is primitive to tinamous and a derived evolutionary loss within Darwin's Nothura. The absence of the ST in a vocalizing bird indicates the need to reconsider the function of the extrinsic muscles of the syrinx in phonation. Future research on the morphology of the syrinx of tinamous is required to establish where this loss occurred in tinamou phylogeny.

Birds generally begin incubation either before laying the last egg of a clutch or when the last egg is laid. We report a third incubation tactic, in which incubation onset is delayed beyond the laying of the last egg. In an Illinois population of American Robins (Turdus migratorius), ∼20% of females delayed the onset of incubation ≤4 days beyond clutch completion. Females that delayed incubation nested earlier and took longer to hatch their young than those that initiated incubation before or on the clutch completion date. Using a cost-beneft approach, we propose that predictably low levels of predation at the study site may have reduced the costs associated with delaying incubation. Females do not appear to pay any fitness costs associated with delaying incubation and may benefit by replenishing food reserves early in the season, when the energetic demands of incubation are higher. Alternatively, females may benefit by delaying incubation as a means of timing the hatching of young with availability of food resources. Although this delayed incubation may be attributable to the unique conditions of the study site, we suggest that this behavior may be found more widely, particularly in populations experiencing similar reductions in predation risk, such as populations in urban areas.

We studied 19 color-banded groups of the cooperatively breeding Superb Fairy-wren (Malurus cyaneus) to determine (1) the contributions of breeding and helper males to antipredator vigilance, (2) whether such vigilance reduces predation risk, and (3) the mechanisms by which it might do so. Time spent as a sentinel (perching and scanning from conspicuous locations within sight of the nest) increased with group size, but successful and depredated nests did not differ significantly in sentinel time, and sentinels did not appear to coordinate their vigilance. Both breeder and helper males acted as sentinels, and both were more vigilant when nests contained nestlings than when they contained eggs. Breeders with helpers spent more time as sentinels than those without helpers. Presence of a sentinel reduced the time feeding adults spent pausing to scan when approaching and leaving the nest. Thus, vigilance could enable a male to detect a predator and decoy it away from the nest site or prevent it from locating the nest by deferring feeding visits of other provisioners, but we could not demonstrate that it reduced nest predation by the major nest predator, the Pied Currawong (Strepera graculina).

Rearing of young has long been considered the energetically most demanding phase of the avian breeding cycle. Arctic-breeding shorebirds expend large amounts of energy during breeding. Because they are too small to carry sufficient stores to sit out the incubation period, they regularly interrupt incubation to feed and still can run short of energy, particularly in species in which one adult takes care of the eggs and chicks alone (uniparental). We measured daily energy expenditure (DEE) and time budgets during incubation and chick rearing in the smallest uniparental Arctic shorebird, the Little Stint (Calidris minuta). Daily energy expenditure decreased with increasing temperature but did not differ between the incubation and chick-rearing periods. Because of the increase in potential foraging time from incubation to the chick-rearing phase, the foraging intake rate required to balance the budget dropped by two-thirds. To evaluate the effect of uniparental care on energy budgets, we also measured DEE in the Dunlin (C. alpina), a sympatric congener in which both parents incubate but the female deserts the brood after hatching. Daily energy expenditure decreased with temperature, was the same during incubation and chick rearing, and was higher in males. Our results are discussed in relation to the timing of breeding of Arctic shorebirds with different systems of parental care.

Stable-isotope analysis of feathers is an increasingly important source of information on diet and movement of birds. Feathers are typically cleaned with a solvent before analysis, but the effects of this cleaning on the resulting data have not been examined critically. We conducted an experiment to determine whether a cleaning regime affected hydrogen (δD), carbon (δ¹³C), and nitrogen (δ¹⁵N) stableisotope ratios in feathers of Japanese Quail (Coturnix japonica). A paired design was used to clean feathers with 2:1 chloroform: methanol or detergent. Results after initial cleaning indicated enrichment of hydrogen by ∼40‱ in feathers treated with 2:1 chloroform: methanol-treated compared with other treatments but no correlation between treatments. We found a similar pattern among treatments for carbon, but the effect was on the order of 0.2‱. Nitrogen values showed no discernible correlation, but both uncleaned and 2:1 chloroform: methanol treatments had enriched values, on average, compared with detergent treatments. Further, variance among samples was high for hydrogen and nitrogen measurements. After recleaning with alternate treatments, differences in mean hydrogen-isotope ratios were no longer evident, data for hydrogen and carbon became less variable, and carbon maintained its initial pattern. We suggest a standard method of cleaning feathers, first with a dilute detergent solution, then with 2:1 chloroform:methanol solvent. This study has implications for increasing repeatability of hydrogen, carbon, and nitrogen stable-isotope measurements, which would increase the validity of inter-laboratory comparisons and the utility of large-scale projects using compiled data sets.

Most frugivorous birds must complement their diet with insects to fulfill their protein requirements; species that rely almost exclusively on fruits are rare. We used nitrogen (¹⁵N:¹⁴N) stable-isotope analysis of whole blood to quantify and compare the use of insects and fruits as sources of assimilated nitrogen in a specialized frugivorous bird, the Yellow-throated Euphonia (Euphonia hirundinacea). Nitrogen stable-isotope analysis is particularly useful for examining the relative contribution of animal and plant products as sources of assimilated nitrogen, because there is trophic enrichment of the heavier isotope in higher trophic levels of food webs. We found that most assimilated nitrogen was derived from fruits (76–100%), with a slight increase in the contribution of fruits as their abundance increased. In comparisons of bird species, δ¹⁵N values of Yellow-throated Euphonia were lower than those of insectivorous and piscivorous species but similar to the values found in seed-fruit eaters. Our results suggest that the dependence on fruits as a source of assimilated nitrogen in Yellow-throated Euphonia ranged from predominant to almost exclusive during the period of our study (February–August). Total dependence on fruits as a source of assimilated nitrogen is not a common phenomenon among birds, but it may be favored in the tropics, where fruits are more abundant and diverse.

A previous study reported that climate-mediated increases in the length of the breeding season produced increasingly female-biased fledging sex ratios in Red-winged Blackbirds (Agelaius phoeniceus). Using those same data plus one additional year (11 years in total), I found that this phenomenon was not a result of greater production of females early and late in the season, contrary to what had been proposed. Instead, seasonal sex-allocation patterns interacted with season length. Early and midseason sex ratios became more female-biased as breeding seasons became longer, whereas late-season sex ratios tended to vary in the opposite manner, albeit weakly. Thus, the discrepancy between sex ratios late in the season and those earlier (early plus midseason) was a strong function of season length. Because fledging sex ratios did not vary with nestling mortality, these patterns appear to be a consequence of nonrandom sex-allocation rather than sex-biased survival. It is unclear whether these sex-allocation patterns are adaptive. Because the climatic factor (the North Atlantic Oscillation) associated with longer breeding seasons is also associated with higher winter mortality, however, it is possible that female Red-winged Blackbirds change how they allocate sex in response to changes in the breeding sex ratio. If climate change continues to alter these patterns, documenting how individuals and populations respond will be informative, from both basic and applied perspectives.

Most scrub-shrub bird species are declining in the northeastern United States, and these declines are largely attributed to regional declines in habitat availability. American Beaver (Castor canadensis; hereafter “beaver”) populations have been increasing in the Northeast in recent decades, and beavers create scrub-shrub habitat through their dam-building and foraging activities. Few systematic studies have been conducted on the value of beaver-modified habitats for scrub-shrub birds, and these data are important for understanding habitat selection of scrub-shrub birds as well as for assessing regional habitat availability for these species. We conducted surveys in 37 beaver meadows in a 2,800-km² study area in western Massachusetts during 2005 and 2006 to determine the extent to which these beaver-modified habitats are used by scrub-shrub birds, as well as the characteristics of beaver meadows most closely related to bird use. We modeled bird abundance in relation to microhabitat-, patch-, and landscape-context variables while adjusting for survey-specific covariates affecting detectability using N-mixture models. We found that scrub-shrub birds of regional conservation concern occupied these sites and that birds responded differently to microhabitat, patch, and landscape characteristics of beaver meadows. Generally, scrub-shrub birds increased in abundance along a gradient of increasing vegetation complexity, and three species were positively related to patch size. We conclude that these habitats can potentially play an important role in regional conservation of scrub-shrub birds and recommend that conservation priority be given to larger beaver meadows with diverse vegetation structure and composition.

We investigated the genetic population structure of the Black-throated Blue Warbler (Dendroica caerulescens), a Nearctic-Neotropic migrant passerine that breeds in cool mixed deciduous-coniferous forests in eastern North America. A cline in plumage color in breeding populations in the central Appalachian Mountains suggests either a contact zone between two formerly allopatric populations or the presence of a strong contemporary selection gradient. Analysis of 333 base pairs of the mitochondrial control region from 287 individuals sampled from 14 populations revealed relatively high haplotype diversity, low nucleotide diversity, and limited but significant phylogeographic structure across the breeding range (analysis of molecular variance [AMOVA], variation among populations = 2.7%; P < 0.01) and between northern and southern population groups (AMOVA, variation among groups = 2.9%; P < 0.01). Genetic differentiation among populations did not conform to an isolation-by-distance model. Nucleotide diversity was generally highest in the central Appalachians and lower in geographically peripheral populations. Populations from the northwestern periphery of the breeding range in Michigan had the lowest haplotype diversity and were genetically distinct from populations in the southern Appalachians. The star-shaped haplotype network, extensive sharing of common haplotypes among populations, and the haphazard distribution of rare haplotypes are most likely attributable to the combined effects of postglacial expansion from a single refugium (12,000-84,000 years ago) and long-distance dispersal events. The existence of a cline in plumage color, in the face of inferred recent gene flow, suggests that a strong selection gradient is operating, perhaps related to the migratory divide postulated from stable-isotope data.

Avian researchers often uniquely mark birds, and multiple estimators could be used to estimate population size using individually identified birds. However, most estimators of population size require that all sightings of marked birds be uniquely identified, and many assume homogeneous detection probabilities. Bowden's estimator can incorporate sightings of marked birds that are not uniquely identified and relax assumptions required of other estimators. I used computer simulation to evaluate the performance of Bowden's estimator for situations likely to be encountered in bird studies. When the assumptions of the estimator were met, abundance and variance estimates and confidence-interval coverage were accurate. However, precision was poor for small population sizes (N < 50) unless a large percentage of the population was marked (>75%) and multiple (≥8) sighting surveys were conducted. If additional birds are marked after sighting surveys begin, it is important to initially mark a large proportion of the population (p_m ≥ 0.5 if N ≤ 100 or p_m > 0.1 if N ≥ 250) and minimize sightings in which birds are not uniquely identified; otherwise, most population estimates will be overestimated by >10%. Bowden's estimator can be useful for avian studies because birds can be resighted multiple times during a single survey, not all sightings of marked birds have to uniquely identify individuals, detection probabilities among birds can vary, and the complete study area does not have to be surveyed. I provide computer code for use with pilot data to design mark-resight surveys to meet desired precision for abundance estimates.