A recent study of New World orioles (Icterus spp.), which traced a large number of plumage characters onto a mitochondrial DNA phylogeny, reported high frequencies of evolutionary convergence and reversal of plumage characters (Omland and Lanyon 2000). Although those results are consistent with other smaller scale studies that have documented plumage homoplasy, the mitochondrial genome is inherited as a single linkage group, so mitochondrial data represent only one gene tree. The mitochondrial (mt) DNA tree may not reflect the true evolutionary history of a lineage; therefore, it remains possible that the plumage characters could reflect the true species phylogeny. Other rapidly evolving regions of DNA can provide independent phylogenetic hypotheses useful for evaluating mitochondrial gene trees. A novel phylogenetic marker, a region of the nuclear gene ornithine decarboxylase (ODC) spanning from exon 6 to exon 8, was sequenced in 10 oriole species. The resultant nuclear gene tree reconstructs the same three major oriole clades as the mtDNA tree (Omland et al. 1999), supporting the conclusion that plumage evolution in the New World orioles has been highly homoplastic. Although most phylogenetic studies that have employed introns report greatest resolution at the genus or family level, ODC appears to offer some degree of phylogenetic resolution for infrageneric analyses. However, that intron has clearly not sorted to monophyly within or between closely related species.

We describe a new species of drepanidine bird from a fossil found in a lava tube cave on the island of Hawaii. The bill of the new species combines a long, scimitar-like maxillary rostrum with a much shorter mandibular rostrum, giving the bird a most unusual appearance. The general bill form is shared with members of the drepanidine genus Hemignathus, to which the new species is referred, although it is quite distinct from other species of Hemignathus in aspects of its bill morphology and in its much larger body size. The scimitar-like maxilla appears to be adapted to probing in cracks or crevices and possibly to moving loose material, such as leaf detritus, to obtain invertebrate prey. The species became extinct <3,000 years ago.

We address the problem of microsatellite genotyping errors associated with polymerase chain reaction (PCR) amplification from degraded and dilute template DNA and provide suggestions for improving the accuracy of genotype data in studies using older museum specimens as a source of DNA. In the course of a population genetics study of African indigobirds (Vidua spp.), we used replicate PCR to evaluate genotyping reliability for nine microsatellite loci in relation to PCR fragment length and DNA template concentration (DNA extracted from the calamus of one vs. two wing feathers). Complete amplification failure and the dropout of one allele from heterozygous genotypes were the predominant problems encountered. For samples with heterozygous genotypes, allele dropout occurred in 19.2 and 12.1% of PCR using extracts derived from one and two feathers, respectively. The amplification of artifact bands was less frequent (affecting 4.9 and 1% of positive PCR reactions with one- and two-feather extracts, respectively). Those results indicate that multiple replicates per sample and locus are required to obtain accurate genotype data from museum feather samples. Although higher DNA concentration improved success, PCR fragment size had a much stronger influence on the success and repeatability of microsatellite amplification, which suggests that the accuracy and efficiency of genotyping can be improved most easily by designing primers that amplify smaller DNA fragments.

Multibrooded species that undertake more than one nesting attempt per breeding season and individuals that breed over multiple years (breeding seasons) must decide whether to return to (or remain at) their former breeding site and social mate (fidelity) or to relocate (dispersal). During three breeding seasons (1998–2000), we examined breeding-site (territory and nest) fidelity and social-mate fidelity of Eastern Phoebes (Sayornis phoebe) (n = 435 adults captured and color-banded, n = 198 males, n = 237 females) both within years and between years. We also examined the influence of sex and previous reproductive success on breeding-site and social-mate fidelity decisions. Field research was conducted at Crane Naval Surface Warfare Center, Martin County, Indiana. Breeding-site (territory and nest) and social-mate fidelity were extremely high both within and between years. Only 23 instances of breeding dispersal to new territories were documented. Within years, Eastern Phoebe adults rarely dispersed to new territories; but after an initial nest failure, they were more likely to change nests within a territory for their second breeding attempt. Males were more likely to change territories between years; however, the distance dispersed between territories did not differ between sexes. Within-year social-mate fidelity was nearly universal with 85.5% of all males and 92.7% of females mating with the same mate during multiple breeding attempts. Divorce was uncommon and mate replacement usually occurred following mate disappearance and probable death. Within years, 2.4% of females and 4.8% of males divorced and paired with new mates for their next breeding attempt. Between-year divorce rates were low; of those birds for which the original mate was known to be alive, only 3.0% of females and 4.3% of males changed mates. The probability of divorce was not influenced by sex or previous reproductive success.

We quantified foraging rates and foraging visibility metrics for four Neotropical warblers—Slate-throated Redstart (Myoborus miniatus), Golden-crowned Warbler (Basileuterus culicivorus), Wilson's Warbler (Wilsonia pusilla), and Black-and-White Warbler (Mniotilta varia)—under flocking and solitary conditions in western Panama to test hypotheses regarding the relative influences of predation pressure and social facilitation on foraging behavior. We also compared foraging behavior in primary forests and in traditionally managed shade coffee fields for two species (Slate-throated Redstart and Wilson's Warbler) to estimate spatial variation in foraging behavior and compare it to variation due to social situation (flocking or solitary). We then assessed the contribution of spatial variation in flocking propensity to the total spatial variation in foraging rates within species.

We observed very little overall within-species variability in foraging behavior between social situations or study locations. Only Slate-throated Redstart's behavior was consistent with the hypothesis that flock membership reduces predation pressure and therefore reduces the amount of foraging time spent being vigilant against predators, allowing birds to forage more quickly and find more prey items per minute. No species' behavior supported the hypothesis that flocking birds forage more efficiently than solitary birds by obtaining useful information from flock mates about the location or suitability of foraging resources or techniques.

The effort required to find prey items did not vary between study locations (forest and coffee field plots) for Wilson's Warbler. Because flocking also had no effect on foraging behavior of Wilson's Warbler, a reduction in flocking propensity in coffee habitat, relative to forest, did not cause further foraging behavior differences between study locations. Spatial variation in Slate-throated Redstart's foraging behavior independent of a flocking effect was minor; but flocking affected foraging rates, and flocking propensity was lower in coffee fields than in forest, so that location and flocking effects combined to widen foraging rate differences between locations. Thus, variations in flocking behavior and foraging behavior interacted differently for those two species.

We used data from statewide surveys of riparian birds in Utah, 1992–1998, to compare relative-abundance and distance-sampling methods. By generating relative-abundance indices with point-count methods and density with point-transect sampling methods, we examined whether the assumptions underlying each method were met during field surveys for four bird species (Brown-headed Cowbird [Molothrus ater], Bullock's Oriole [Icterus bullockii], Warbling Vireo [Vireo gilvus], and Yellow Warbler [Dendroica petechia]). Point-count methods failed to reasonably meet the fundamental assumption of constant proportionality, with estimated detectability varying 3- to 5-fold despite the use of widely accepted and well-standardized methods. Population trends based on relative abundance were subsequently unstable, often varying in both magnitude and direction with the survey plot radius used (25 m, 50 m, or unlimited distance). Distance-sampling methods appeared to meet critical assumptions, were robust to assumption violations, allowed methodological self-assessment, and were demonstrably efficient in a large-scale, multispecies survey setting. Our data show surveys of birds without estimations of detectability are likely biased because the assumption of constant proportionality is violated to a degree that precludes strict inference and may confound trend analyses.

Secondary cavity nesting birds have been predicted to switch their nesting location when the quality of the nest site declines such as from accumulation of soiled nest material and parasites. We hypothesized that nest-site switching in Eastern Bluebirds (Sialia sialis) should depend not only on the condition of the original nest, but also on quality of alternate nest cavities. We tested that hypothesis experimentally by providing Eastern Bluebirds with attractive and unattractive nest boxes (as determined from a choice experiment). In one experiment, bluebirds were forced to choose between their soiled box of the preferred type and a clean box of the less-preferred type. Faced with that decision, a significant proportion of pairs opted to reuse their nest cavity, despite the ectoparasitism costs of that option. When given the choice between their soiled box of the preferred type and an identical but clean box, a significant proportion switched to the clean box, which suggests that soiled nests present some cost. By manipulating box type, we were able to decrease and increase, respectively, the costs of nest-site fidelity. Thus, bluebirds do not simply operate under a rule of thumb “switch nest sites when nest quality falls below point x.” Rather, they must weigh the declining quality of their current nest against the relative quality of all other available nest sites.

We investigated the function of Red-tailed Tropicbird (Phaethon rubricauda) tail streamers by quantifying patterns of variation in streamers and other measurable traits on the basis of measurements of 659 individuals, including 422 of known age and 459 of known sex, measured in the field from 2000 to 2002. Our data were consistent with the idea that Red-tailed Tropicbirds' tail streamer ornaments function for mate attraction, but it suggested that variability in streamer expression is arbitrary and unlikely to provide a meaningful signal of individual quality during mate choice. The two elongated red tail streamers are composed of bilaterally symmetrical filamentous central rectrices with a black rachis and narrow red vane averaging 399 ± 1.8 mm (SE) in length when fully grown. Prior to breeding, individuals of opposite sex conspicuously display elongated red tail streamers during complex aerial courtship. Streamers exhibited measurement asymmetries (the difference between new and old fully grown tail streamers) of up to 144 mm because of wear at the tip of the older streamer, which accounts for most of the difference in the lengths of two fully grown streamers in individual birds. As in other putative sexually selected traits, tail streamers were more variable than nonornamental traits across individuals. Males were slightly larger than females in length of fully grown streamers (ratio 1.04), culmen length (ratio 1.02), and tarsal length (ratio 1.01). There was no correlation between fully grown streamer length and body size (score on first principal component) (r = 0.004), wing length (males, r = 0.05; females, r = 0.10), or mass (males, r = 0.10; females, r = 0.04), which is consistent with the hypothesis that streamers have an ornamental rather than aerodynamic function. There was a significant correlation between the ratio of streamer lengths (growing vs. fully grown, r = 0.50) of male and female pair members, indicating that at least the timing of ornament development was coordinated within pairs. However, tail streamers did not appear to be good indicators of an individual's “quality;” on the basis of 372 adults of known age (3–22 years), streamer length did not increase with age (r = 0.30) and was not correlated with an index of body condition (r = 0.03). The streamer length of pair members was not correlated with chick asymptotic body mass or chick fate, nor was female streamer length with egg size.

Although multiple male feeders and multiple paternity for a single brood are taxonomically widespread among nonmigratory birds, they appear to be exceedingly rare among migrants. During a demographic study of Bicknell's Thrush (Catharus bicknelli) in Vermont, we observed groups of 2–4 males and one female feed each of 14 broods (78% of 18 broods observed). One male and one female fed each of the remaining four broods. Three males fed broods of two females concurrently or consecutively. Genetic analysis using microsatellite markers revealed multiple paternity in 9 of 13 broods (69%). Four males had offspring in more than one brood in the same year, but no females did. Ten of 17 males (59%) sired offspring in the broods they fed, and 10 of 13 sires (77%) fed the broods in which they sired young. Females fed nestlings more than twice as often as males. Both males and females tended to increase feeding rates as brood size increased. Possible factors influencing the reproductive behavior of Bicknell's Thrush include harsh montane weather, food limitation, a male-biased sex ratio, and reproductive synchrony. Additional research is needed to examine the interaction of ecological and demographic variables that shape the complex breeding ecology of Bicknell's Thrush.

We examined prevalence of extrapair young (EPY) between first and second broods of a multibrooded passerine, Eastern Phoebe (Sayornis phoebe). During the 1998–2000 field seasons, we conducted behavioral observations to assign social parentage to offspring in nests and then conducted paternity analysis on a subset of social families where (1) the male and female maintained their pair bond for all broods within the breeding season, and (2) adults successfully fledged their first brood and subsequently attempted a second brood within the same breeding season. We used three hypervariable microsatellite loci to document the presence and frequency of EPY in first and second brood offspring from 87 social family units where all individuals had been sampled (n = 174 broods, n = 81 social males, n = 82 social females, n = 769 offspring). Although the majority of pairs were both socially and genetically monogamous within a breeding season, 17.2% (15 of 87 families) of all families had EPY in at least one brood and we found two cases of intraspecific brood parasitism. Overall, 9.2% of all broods (16 of 174 broods) contained EPY and 5.1% of all nestlings that hatched were EPY (39 of 769 nestlings). Second broods were more likely to contain EPY than first broods (4.6% first broods with EPY [4 of 87], 13.8% second broods with EPY [12 of 87]). The total number of EPY was greater in second broods than in first broods (1.0% EPY [4 of 411 nestlings] in first broods, 9.8% EPY [35 of 358 nestlings] in second broods).

Although some birds can detect wavelengths in the infrasound range, there has been litle evidence that birds produce very low frequencies. We made nine recordings of a captive Dwarf Cassowary (Casuarius benneti) and one recording of a wild Southern Cassowary (C. casuarius) near Crater Mountain, Papua New Guinea. Both species produced sounds near the floor of the human hearing range in their pulsed booming notes: down to 32 Hz for C. casuarius and 23 Hz in C. benneti. Recordings of C. benneti indicate four levels of harmonics with the 23 Hz fundamental frequency. Such low frequencies are probably ideal for communication among widely dispersed, solitary cassowaries in dense rainforest. The discovery of very low-frequency communication by cassowaries creates new possibilities for studying those extremely secretive birds and for learning more about the evolution of avian vocalizations.

Effects of variable energy intake on chick growth, organ development, and gut-passage time in seabirds were investigated by raising Elegant Tern (Sterna elegans) chicks in the laboratory on three diets involving a major prey species, northern anchovy (Engraulis mordax), and a minor prey species, topsmelt (Atherinops affinis). Anchovies are ∼25% higher in energy content than topsmelt and represent a more abundant but highly fluctuating prey resource. Chicks were raised from age 15 to age 35 days posthatch on one of three diets (n = 8): (1) high-energy anchovy at the average daily intake rate, (2) low-energy topsmelt at the same intake rate, and (3) high-energy topsmelt (i.e. at a biomass equal in energy content to the anchovy diet). Chicks raised on the high-energy anchovy diet had a significantly faster gain of body mass and wing length. All three groups, however, had attained a statistically similar wing length at 35 days posthatch and did not differ in lean dry mass or pectoral muscle mass, indicating that energy was allocated preferentially toward wing development and flight capacity. Most digestive organs were heavier and gut-passage rates faster for chicks fed topsmelt. Bill dimensions and tarsus length showed little difference among chicks on the three diets. Lipid content of chicks that were fed anchovy was twice that of those fed low-energy topsmelt and one-third higher than that of chicks on the high-energy topsmelt diet. Our results indicate that Elegant Terns have evolved certain capacities for growth and digestion in response to variable prey quality that may increase the probability of chick survival. Nevertheless, if Elegant Tern chicks were switched to a lower quality, primarily topsmelt diet, they would be underweight at fledging with heavier digestive organs, lower lipid reserves, and faster gut-passage times, which would place added provisioning demands on the parents. Under that scenario, the prospects for survival and long-term reproductive success might diminish for such an Elegant Tern colony.

Effects of deployment of miniaturized transmitters and loggers have been well studied in penguins, but much less so in flying seabirds. We examined the effects of satellite tag (platform terminal transmitter, PTT) deployment in Black-browed (Thalassarche melanophris) and Gray-headed (T. chrysostoma) albatrosses at South Georgia and reviewed the recent literature for other albatrosses and petrels. In our study, although a few individuals may have slightly extended their foraging trips, overall there was no significant difference in trip duration, meal mass, breeding success, or rate of return in the next season between birds with PTTs and controls. By comparison, most other studies of albatrosses and petrels recorded extended trip durations and, in some cases, high rates of nest desertion following PTT attachment. That occurred particularly where transmitter loads exceeded 3% of adult mass. Extended trip durations may result from reduced flight efficiency, as well as the effect of capture and temporary restraint, but affected birds seem nonetheless to commute to representative foraging areas. To minimize device effects, we suggest that transmitter loads be reduced to a minimum, use of harnesses be avoided (particularly for breeding season deployments when tape attachment to feathers is an effective alternative), and careful attention be given to limiting handling times during incubation when some species are particularly sensitive to disturbance.

Degradation of urinary nitrogen-containing compounds by bacteria in the ceca of birds occurs in a number of herbivorous and omnivorous species, and cecal absorption of the products of that degradation has been reported in chickens. This recycling of nitrogen may play an important role in nitrogen balance, especially in those species with low dietary nitrogen intake. We report, for the first time, degradation of nitrogenous compounds by intestinal bacteria in a bird that is nectarivorous and lacks ceca, Anna's Hummingbird (Calypte anna). Hummingbirds subsist year-round on a liquid diet with an exceptionally low-nitrogen content. Ureteral urine containing ammonia, urea, and uric acid has been observed in the lower intestinal tract of Anna's Hummingbird. Bacteria obtained from intestinal contents and homogenates of the anterior and posterior intestine of this species were able to break down uric acid, urea, and potassium urate, but not sodium urate. This degradation is the necessary first step in the recycling of nitrogen. Assessing its significance will involve determining whether the products of microbial breakdown are subsequently absorbed across the intestinal walls of these unique animals.

Previous studies have shown Olive-sided Flycatchers (Contopus cooperi) to be associated with burned forest, which suggests that wildfire is beneficial to the species. To examine that more closely, we studied the short-term effects (first two years after disturbance) of moderate- to high-severity wildfire on Olive-sided Flycatchers breeding in northwestern California. During summers of 2000 and 2001, we investigated distribution of and compared the relative nest loss, foraging rates, and aerial arthropod biomass at Olive-sided Flycatcher territories in burned and adjacent unburned forest. The probability of postfire site occupancy was best predicted by the presence of pre-existing forest edges (odds ratio = 8:1). Probability of relative nest loss was much higher in the presence of fire (odds ratio = 9:1). Adult female peak foraging rates were nearly twice as high in unburned (2000 = 2.1 attacks min⁻¹, 2001 = 2.5) as in burned (2000 = 1.0, 2001 = 1.5) territories, and relative aerial arthropod biomass was nearly twice as high in unburned (2000 = 1,909 mg 2 m⁻² 40 days⁻¹, 2001 = 3,200) as in burned (2000 = 1,105, 2001 = 1,751) territories. Although Olive-sided Flycatchers occupied recently burned areas, fire had apparent negative effects on reproduction. Poor reproduction appeared to be partially related to reduced food availability in recently burned areas. Our data suggest a need for detailed investigations of the relationship between Olive-sided Flycatchers and wildfire as postfire forest regeneration progresses.

Timing of breeding in Florida Scrub-Jays (Aphelocoma coerulescens) varies both within and between years. Social status and breeding experience may explain much of the within-year variation, but the availability of certain foods may partially explain between-year patterns. Scrub-jays in suburban habitats with access to unlimited human-provided foods breed earlier and with less between-year variation in timing of breeding than jays in wildland habitats. We hypothesized that those differences in timing of breeding result from access to human-provided foods in the suburban site. Human-provided food may influence timing of breeding by improving the overall body condition of females, or it may influence breeding by providing nutrients essential for breeding. If condition mediated, breeding females in the two habitats should differ in certain physiological parameters relative to time before egg laying and calendar date. If the effect is not related to body condition, we expect differences in prebreeding females relative to calendar date, but not in relation to time before egg laying. To test those predictions, we measured plasma levels of total protein, calcium, luteinizing hormone, and estradiol. We also measured variables associated with body condition—body mass, a size-corrected condition index, and total body lipids. Most variables tended to increase with both days before laying and calendar date, except total body lipids, which decreased. Suburban females had higher levels of plasma protein relative to both days before egg laying and calendar date than female breeders in the wildland habitat. Luteinizing hormone differed between sites relative to calendar date but not days before laying. Our data suggest that suburban scrub-jays with access to predictable sources of high-quality human-provided foods accumulate endogenous protein that can be used to breed earlier.

Shiny Cowbirds (Molothrus bonariensis) often parasitize larger hosts. It has been proposed that larger hosts are preferred by that parasite because they provide higher reproductive success, but available data are quite variable. We studied the reproductive success of Shiny Cowbirds in nests of Brown-and-yellow Marshbirds (Pseudoleistes virescens), a larger and often multiply parasitized host. To estimate the extent of interspecific competition, we compared the hatching success of parasite eggs in nests with and without reduction of the clutch size of the host as a result of egg punctures inflicted by the parasite, and the survival and growth of parasite chicks reared with and without host chicks. To estimate the extent of intraspecific competition, we compared Shiny Cowbird egg losses, hatching success, and chick survival in singly versus multiply parasitized nests. Reproductive success of Shiny Cowbirds was 8% with depredation causing 80% of losses. Clutch reduction due to egg punctures were higher in multiply than in singly parasitized nests, but it did not improve hatching success of parasite eggs. Neither survival nor growth of parasite chicks was affected by the presence of host chicks. Shiny Cowbird hatching success and chick survival did not differ between singly and multiply parasitized nests. Parasite chicks were smaller than same-age Brown-and-yellow Marshbird chicks. However, because parasite chicks hatched one or two days before host chicks and had a higher growth rate, they were the larger chicks in the nest. Overall Shiny Cowbird reproductive success in Brown-and-yellow Marshbird nests was apparently higher than that reported in other smaller or similar-sized hosts. We think that host life-history traits like large clutch size, a longer incubation period, and slower growth rate of chicks are responsible for the high reproductive success of Shiny Cowbirds with Brown-and-yellow Marshbirds.

Modulation of the adrenocortical stress response with respect to the degree of parental activity was investigated in three Arctic-breeding species of songbirds faced with limited opportunities to breed. The hypothesis that the strength of the response can be lowered when reproductive effort or investment is greatest was tested by measuring the adrenocortical response to handling stress during two breeding stages that represented different levels of reproductive effort (i.e. before young were present [preparental] and while feeding nestlings [parental]). Comparisons of the corticosterone stress response (baseline at capture and subsequent samples 5, 10, 30, and 60 min after capture) were made within and between both sexes of American Tree Sparrows (Spizella arborea), White-crowned Sparrows (Zonotrichia leucophrys gambelii), and Savannah Sparrows (Passerculus sandwichensis) breeding above the Arctic Circle at Toolik Lake, Alaska. In general, body mass and baseline corticosterone did not differ between sexes within each of the three species, nor did they change during the two stages of breeding (tree and White-crowned sparrows only). In all three species, males had stronger adrenocortical responses than females during the preparental period, a time when males may expend less in reproductive effort than females. However, during the parental stage (tree and White-crowned sparrows only), the stress response of males declined and became similar to that of females because both sexes fed young. Females of both species (having considerable reproductive effort throughout both stages via egg laying or incubation and feeding young) showed no change in stress response with breeding stage. These results support the hypothesis that individuals with limited opportunities to breed can modulate the adrenocortical stress response when reproductive effort or investment is greatest as a way to maximize breeding success.

Capture-mark-recapture studies provide a useful mechanism for estimating the components of the population dynamics of birds, especially survival. In such studies, it is important that the population being captured matches the population of interest. In many studies, transients are captured along with the population of interest (e.g. resident breeders). Ignoring that phenomenon produces negatively biased survival estimates, because transients do not return. Although transients cannot be distinguished from residents in the hand, previous methods have adjusted for transience by relying on those captured in more than one year to provide direct estimates of survival rate for residents. Here, we extend that approach by supplementing that cohort of known residents with those previously unmarked birds captured twice or more, at least d days apart, within a season. We provide an ad hoc approach to that extension in detail and outline two more formal approaches. That extension increases the precision of survival estimates.

We examined effects of movement patterns and habitat use of female Wood Ducks (Aix sponsa) during incubation on incubation constancy and recess frequency. Incubating females (n = 41) were equipped with subcutaneous radiotransmitters and subsequently located during daily recess events. Using compositional analysis, we determined beaver ponds, creeks, ephemeral wetlands, and lake-influenced habitats ranked higher in preference than other available aquatic habitats (i.e. managed impoundments, farm pond, and lake habitats). An inverse relationship between female use of the top four ranked habitats and recess range size suggested that those were high-quality habitats. Mean (±SE) incubation constancy (n = 40 nests) was 81.3 ± 0.8%, and females took an average of 2.2 ± 0.3 recesses day⁻¹. Incubation period averaged 31.8 ± 0.3 days, and there was a weak inverse relationship between incubation period and incubation constancy. Incubating females lost 3.9 ± 0.8% of early incubation body mass, but body-mass changes were not associated with use of preferred habitats (i.e. beaver ponds, creeks, ephemeral wetlands, and lake-influenced areas). Initiation date of incubation and percentage use of preferred habitats were the most important variables describing variation in incubation constancy. Constancy declined later in the breeding season and with increased use of preferred habitats. Recess frequency decreased with increasing variation in distances that females traveled from the nest. Wood Ducks nesting at southern latitudes generally are not energetically constrained during incubation, and nest attentiveness is only weakly associated with incubation period. We would expect stronger relationships between habitat use, body-mass dynamics, and incubation behavior under environmental conditions that are more severe or less predictable.

Differences among observers in ability to detect and identify birds has been long recognized as a potential source of error when surveying terrestrial birds. However, few published studies address that issue in their methods or study design. We used distance sampling with line transects to investigate differences in detection probabilities among observers and among three species of grassland songbirds: Henslow's Sparrow (Ammodramus henslowii), Grasshopper Sparrow (A. savannarum), and Savannah Sparrow (Passerculus sandwichensis). Our review of 75 papers published in 1985–2001 found that the most commonly used methods were fixed-width transects (31%, 23 papers) and fixed-radius point counts (20%, 15 papers). The median half-width of fixed-width strip transects used by researchers was 50 m, but our results indicated detection probabilities were <1.0 at distances >25 m for most observers and species. Beyond 50 m from the transect line, we found that as many as 60% of birds were missed by observers and that the proportion missed differed among observers and species. Detection probabilities among observers ranged from 0.43 to 1.00 for Henslow's Sparrow, from 0.44 to 0.66 for Grasshopper Sparrow, and from 0.60 to 0.72 for Grasshopper Sparrow for birds detected within 58–100 m of the transect line. Using our estimates of detection probabilities for Henslow's Sparrows among six observers in a computer simulation of a monitoring program, we found that bird counts from fixed-width transects required an additional 2–3 years of monitoring to detect a given decline in abundance compared to density estimates that used a method to correct for missed birds. We recommend that researchers employ survey methods that correct for detection probabilities <1.0.

Nest predation is the primary cause of nest failure among birds. As such, it has large consequences on avian populations and is believed to be an important force in the evolution of avian life-history traits. Therefore, using a combination of laboratory and field research, we investigated the potential of northern flying squirrels (Glaucomys sabrinus) and two species of deer mice (Peromyscus maniculatus and P. keeni) to be predators on eggs and nestlings of birds, particularly the threatened, canopy nesting Marbled Murrelet (Brachyramphus marmoratus). In captivity, both mice and squirrels atempted to prey on eggs and live nestlings of various sizes. Mice atempted to prey on eggs more than nestlings, were more likely to atack nestlings when hungry than when sated, and were more likely to atack small than large nestlings. Individual flying squirrels varied in their propensity to atack but generally were more likely to atempt to open eggs when hungry than when sated. Opening of eggs by both mice and squirrels was limited by egg size. Video monitoring of artificial nests containing live nestlings confirmed that mice prey on large nestlings at canopy nests in Washington State's temperate rainforest. We conclude that mice and flying squirrels are predators of canopy nesting passerines, and their potential as nest predators must be considered to understand the consequences of nest predation.

We estimated annual rates of survival for juvenile and adult Swainson's Thrushes (Catharus ustulatus) using capture-recapture analyses from 22 years of mist-neting data in coastal California (n= 2,651 individual captures). Our apparent survival estimate was 56% for adults and 25% for juveniles. We are the first to estimate an annual juvenile survival rate for a Neotropical migrant using capture-recapture probability estimates. Like most estimates of annual survival, we could not distinguish between dispersal away from our study area (which is likely high for juveniles) and mortality. Hence, survival is underestimated. However, our juvenile survival estimate did not include the period from fledging to independence, a time when mortality can be high. Many researchers have assumed juvenile survival to be half that of adult survival in population models (e.g. source-sink). Our juvenile to adult survival ratio was 45% (95% CI = 27 to 65%). We caution researchers from simply assuming that juvenile survival approximates half of adult survival when modeling populations and suggest using a range of values. Using a range of values is prudent because of the potential for annual variation, site-specific variation, and especially because estimates are imprecise or completely lacking.

The following critiques express the opinions of the individual evaluators regarding the strengths, weaknesses, and value of the books they review. As such, the appraisals are subjective assessments and do not necessarily reflect the opinions of the editors or any official policy of the American Ornithologists' Union.