In contrast to diurnal songs and calls, avian nocturnal vocalizations are understudied, and their occurrence and function are poorly understood. Here, using primarily the Birds of North America species accounts, I systematically examine the occurrence and potential factor(s) that contribute to nocturnal vocalizing across 749 species of breeding birds in North America and review proposed hypotheses on its function(s). Nocturnal vocalizations are reported from at least 30% of North American birds, across 18 of 22 orders, of which over 70% are considered diurnal. This indicates that nocturnal vocalizations are a taxonomically widespread behavior and are not restricted to nocturnal species as traditionally believed. Furthermore, it indicates that diurnal birds are extending activities into night-time hours, which may influence energy dynamics and reproductive success. Lack of significant phylogenetic signal suggests that nocturnal vocalizations are not merely a result of phylogeny, which leaves ecological factors such as elevated light levels and mated status as potential promoters of its occurrence. With less than 4% of avian vocalization literature concentrating on nocturnal vocalizations, the goal of this paper is to synthesize empirical knowledge and to stimulate more research in this field.

Over long time periods, urbanization is expected to have a negative effect on species diversity. Predicted effects generally follow one of three competing paradigms: diversity decay, homogenization, or community-composition turnover. However, it has been hypothesized that urban green spaces may provide a means by which urban areas can maintain or increase their species diversity over time. We used surveys conducted in 1913–18,1938– 39, and 2006–07 on the campus of the University of California, Berkeley, to evaluate how an avian community has changed over time in the context of urban growth. In each of the three periods the community differed greatly, yet we found no evidence for a decline in species or functional diversity. Despite the birds of the 1913–18 community having a greater affinity for native habitats than birds of later periods, we found no further evidence that specialists were being replaced by generalists. Of the three paradigms, our results strongly supported community-composition turnover. Parsimoniously, the habitat preferences of groups of species that changed over time were concordant with known changes in landscaping. While urbanization often does result in decreased biodiversity, our results provide an example of how an urban green space can mitigate and potentially reverse this trend within the context of dynamic community change. Our results are concordant with the view that urban green spaces can maintain original bird communities and disturbance-sensitive species can reestablish themselves given appropriate conditions.

Populations of many shrubland bird species are declining in the eastern United States. Efforts to restore shrubland and early-successional forest may help to ameliorate these declines. However, uncertainty remains about how the size and shape of habitat patches and the surrounding habitat matrix affect patch occupancy by shrubland passerines. Our objectives were to determine if shrubland birds avoid small or irregularly shaped habitat patches and to identify minimum area requirements for area-sensitive species. Additionally, we sought to determine if the proportion of mature forest cover in the landscape influences patch occupancy. We surveyed 35 individual habitat patches in 2007 and 43 in 2008 for the presence of eight shrubland birds. Then, we modeled the probability of five of these species occupying an individual patch relative to patch area, patch shape, and percent forest cover within 1 km of the patch. We documented evidence of area sensitivity for the Yellow-breasted Chat (Icteria virens) and Prairie Warbler (Setophaga discolor) and estimated their minimum area requirements at 2.3 and 1.1 ha, respectively. The Blue Grosbeak (Passerina caerulea) also was area-sensitive in irregularly shaped patches. Predicted patch-occupancy probability was >0.9 in patches ≥5.5 ha for all area-sensitive species. Patch shape alone and proportion of forest cover were not important predictors of occupancy for these shrubland birds. Restored shrubland and early-successional forest in agricultural landscapes can provide habitat for many shrubland birds, but patches should be >5 ha to maximize shrubland bird diversity.

Despite high raptor diversity and species of conservation importance, little is known about the structuring of raptor communities in tropical regions. We examined diversity across land uses, spatial-niche overlap among species, community structure, and relationships between abundance and niche position/width of diurnal raptors in Peru. Between April and December in 2008 and 2009, we surveyed raptors by distance sampling along transects, and recorded associated habitat data, in 70 randomly selected plots of 1 km² in Cerros de Amotape National Park, the Tumbes National Reserve, and its buffer areas. We recorded 563 sightings of 19 species of diurnal raptors. Abundance and richness were highest in the buffer zone and lowest in the national park. Mantel tests revealed no correlation between the species' spatial-niche overlap and body-size differences, but there was a near-significant relationship between spatial-niche overlap and dietary overlap. A canonical correspondence analysis (CCA) of raptor species and habitat variables ordinated species according to latitude, elevation, percentages of vegetation cover, and, in some cases, individual tree species. Abundance was negatively correlated with habitat-niche position (rarer species used “more extreme” habitats) and positively correlated with niche width (standard deviations of CCA axis scores). There was, however, considerable variation in the abundance—niche width relationship, and we were able to identify species with niches narrower than expected. We then calculated “niche bottlenecks” for each species. There was a strong negative relationship between degree of bottleneck and abundance, with the small rare species having particularly narrow bottlenecks.

Kleptoparasitism in birds has been the subject of much research, and the Bald Eagle (Haliaeetus leucocephalus) is a known kleptoparasite. It has been reported to pirate ducks captured by Peregrine Falcons (Falco peregrinus), but ours is the first study to examine the effect of kleptoparasitic Bald Eagles on the kill rate of shorebird-hunting Peregrines and indirectly on a population of Dunlins (Calidris alpina) wintering in coastal British Columbia. Bald Eagles increased seasonally and yearly from October 2008 to January 2011. When eagles were scarce, Peregrines hunted ducks as well as Dunlins. Conversely, when eagles were numerous Peregrines hunted Dunlins only. In 56 instances, one or more eagles closely followed hunting Peregrines and retrieved 13 Dunlins dropped or downed by the falcons. The Peregrines were also kleptoparasitized by Gyrfalcons (Falco rusticolus), which pirated 11 Dunlins from Peregrines. Observed losses to kleptoparasites amounted to 24 (36%) of 67 Peregrines' captures. The kill rate per hour of observation was 0.05 hr^-1 in October and November when eagles and Gyrfalcons were few but significantly higher at 0.18 hr^-1 during January and February. In January 2011, when intraguild kleptoparasites were most abundant, the Peregrine's kill rate was 0.30 hr^-1. These results support the hypothesis that kleptoparasites had an indirect effect on a population of wintering Dunlins because Peregrines compensated for prey lost to kleptoparasites by increasing their kill rate.

Many birds do not breed in the year(s) immediately following independence from parental care. Instead, they spend time as immatures attaining adult plumage and spend time as floaters searching for an opportunity to breed. Floaters are nonbreeding adults. Survival during this period often is poorly understood because immatures and floaters can be secretive and range widely, making them difficult to track. From July 2006 through March 2009, we used radio-tracking data collected by aerial telemetry to estimate survival of 58 nonbreeding Crested Caracaras (Caracara cheriway). Based on an information-theoretic approach, the best-supported models indicated differences in monthly survival, which was lowest (0.953) during the peak of breeding (December–January), slightly higher (0.984) during the remainder of the breeding season (October, November, February, March), and highest (0.995) during the nonbreeding season (April–September). We identified “life stage” as juvenile, immature, or floater on the basis of plumage. We found no effect of sex or life stage on monthly or annual survival, and annual survival was intermediate (0.826) between existing estimates for breeding caracaras (0.876 for males and 0.906 for females) and the dependent juveniles (0.694) of breeding caracaras. None of the birds we tracked nested during our 33-month study. Our findings provide unique insight into reduced survival of nonbreeding individuals during the period when the remainder of the population breeds, and the long-term persistence of individual floaters supports the assertion of previous authors that all breeding habitat is occupied.

Surveys and banding records of Calidris canutus rufa indicate that Red Knots migrate mainly north and south through Massachusetts, Delaware Bay, and Virginia, and winter in Florida and South America. We fitted 40 adult Red Knots with geolocators at Monomoy National Wildlife Refuge, Massachusetts, during fall migration (2009), and in this paper report on the locations of migration and wintering along the Atlantic coast of the United States of eight recaptured knots. The knots' migration patterns varied: four birds wintered along the U.S. Atlantic coast, and the rest went to the Caribbean islands or the northern edge of South America. Knots spent 58 to 75 days in Monomoy Refuge before migrating south in November. Seven of the eight stopped along the U.S. Atlantic coast for relatively long periods. For the six with complete yearly cycles, the total time spent along the Atlantic coast averaged 218 days (range 121–269 days). All eight knots crossed the Atlantic outer continental shelf from two to six times. Areas of use were Monomoy, Long Island, New Jersey, Maryland, the Outer Banks of North Carolina, South Carolina, and Florida. These data indicate that Red Knots moving through Massachusetts in the fall had variable migration patterns, spent considerable periods of their life cycle along the Atlantic coast, and each knot followed a separate and distinct path, which suggests that knots can be at risk along the Atlantic coast for a substantial period of their life cycle.

We explored the breeding biology of the Northern Pygmy-Owl (Glaucidium gnoma) from 2007 to 2009 in a forested reserve in Portland, Oregon. Large body size is often assumed to give animals reproductive advantages, and we tested whether body size affected timing of breeding and examined variation in diet, breeding date, clutch size, and reproductive success to explore whether the presumed benefits of large body size are evident in this species. The average size of 13 clutches was 5.8, and nest success was high (92%); 22 successful nests fledged an average of 5.2 young. Dates of first laying varied over an 18- or 19-day period in each year and averaged 3 weeks earlier in 2008 than in 2009. Early breeders laid larger clutches. After the effect of breeding site was controlled for, small rather than large female pygmy-owls bred earliest. The same pattern of small size was evident in all years. Diet varied by year in regard to whether mammals (2008) or birds (2007 and 2009) were the dominant prey taken, and the owls bred earlier in 2008 occurred when mammals dominated their diet. Although small females tended to breed earlier in all years, it was only in 2009 when pairs bred very late and birds dominated their diet that small females also laid larger clutches and fledged more young. These data suggest that the merits of small or large body size may vary with stages of the breeding cycle and ecological conditions.

Numerous species use socially derived information from conspecifics to evaluate the quality of potential habitat. We examine whether conspecific cues influence Chimney Swift (Chaetura pelagica) behavior at uninhabited provisioned habitat, and whether their response in the pre- and post-breeding seasons differs. We used conspecific playbacks and decoys at 19 towers designed for the swift's nesting in southern Ontario, Canada, and monitored response before, during, and after the experiment. In the pre-breeding season Chimney Swifts spent more overall time within 25 m of the towers regardless of experimental treatment. The length of time individuals spent in range of the towers increased when conspecific cues were deployed. In the pre-breeding season this effect ceased with the removal of cues, while in the post-breeding season the time spent in range increased following the removal of cues. We assert that conspecific cues influence Chimney Swift behavior, particularly in the post-breeding season when juveniles are likely prospecting for future nesting sites. Settlement in the towers did not improve during the years of this study, which may be because (1) provisioned habitat did not meet other requirements for settlement, (2) conspecifics influence behavior but they are not prerequisites for habitat selection, or (3) conspecific cues must be present for longer or more frequent periods to elicit settlement. However, Chimney Swifts showed a strong behavioral response to treatment which, provided all other cues for settlement are fulfilled, indicates that conspecific cues may encourage Chimney Swifts to settle in provisioned habitat.

We describe the courtship displays and sonations of a male hybrid Broad-tailed × Black-chinned Hummingbird (Selasphorus platycercus × Archilochus alexandri). The hybrid performed shuttle and dive displays similar to the displays of the parent species. His wing and tail morphology were intermediate between those of the parental species. The hybrid produced dive sounds with rectrix 5 (R5), matching the mechanism of the tail-generated portion of the dive sound of the Black-chinned Hummingbird, and not matching that of the Broadtailed Hummingbird, which uses rectrix 2 (R2). The hybrid's R2 was capable of fluttering at a frequency and mode similar to those of the Broad-tailed's R2, but unlike the Broad-tailed's R2, the hybrid's R2 produced little sound. During displays, but not during ordinary flight, the hybrid's wing trill was higher pitched than that of either parental species. These results indicate that small changes in feather morphology can result in comparatively large changes in sound production. All of the hybrid's morphological characters and most of the display characters were intermediate between those of the parental species; at least one behavioral character was transgressive, suggesting that some behavioral display characters may be under the control of comparatively few genes.

Accurate estimates of juvenile survival are critical to understanding population processes. However, information about post-fledging vital rates is lacking for most avian species because of the difficulty of following individuals after they leave the nest. We radio-tagged 43 Red-bellied Woodpeckers (Melanerpes carolinus) as nestlings. We tracked the birds for 5 months after fledging, during exploratory forays and after natal dispersal. We modeled the influence of intrinsic, temporal, social, and landscape factors with the potential to affect survival during the post-fledging period. Estimates of post-fledging survival were best explained by fledgling age. Predictions of weekly survival rates were 0.94 for birds 1 week after fledging, then quickly increased to over 0.99 for birds 7–22 weeks after fledging. We calculated period survival for the entire 5 months as 0.80 (95% CI: 0.65–0.90). We observed no mortalities after the birds departed natal territories, suggesting that exploratory and dispersal behaviors are not costly in this species.

We examined foraging-habitat selection of Black-backed Woodpeckers (Picoides arcticus) in burned forests of southwestern Idaho during 2000 and 2002 (6 and 8 years following wildfire). This woodpecker responds positively to large-scale fire disturbances and may be at risk from logging and post-fire management. With 100 radio-locations of four adult males, we used resource-selection probability functions in logistic form in an information-theoretic framework to model the Black-backed Woodpecker's selection of foraging habitat at fine and coarse spatial scales. Fine-scale data included characteristics of the foraging tree (tree level) and local habitat surrounding foraging trees (plot level, 0.04 ha), whereas coarse-scale data (224–778 ha) included patch characteristics within home ranges. Model selection by Akaike's information criterion identified a multi-scale model containing tree- and plot-level covariates, and their interaction, as the best model to characterize foraging trees. The positive effect of interaction between foraging-tree diameter and plot-level tree density suggested that foraging Black-backed Woodpeckers select both patches with dense trees and larger-diameter trees. Fire severity was not important, possibly because of the time since fire and the birds' habit of foraging on recently dead trees in adjacent unburned forests. Salvage logging that retains large-diameter trees in clumped distributions is most likely to provide long-term foraging habitat for Black-backed Woodpeckers in dry coniferous forests of the interior western U.S. Following wildfire, conservation of forest patches containing weakened trees may extend the suitability of habitat for foraging Black-backed Woodpeckers by up to 8 years.

For birds, risk of nest predation can vary within a breeding season, but few data exist that explain why such variation occurs. We investigated intraseasonal variation of nest survival of the Acadian Flycatcher (Empidonax virescens) in Midwestern forests and tested whether four of the adults' reproductive strategies (clutch size, nest concealment, nest visitation rates, nest height) explained trends in survival across the breeding season. We also used video cameras to identify predators at 40 nests, which allowed us to determine whether variation in predation rates by category of predator (e.g., birds, mammals, snakes) explained overall seasonal variation in predation rates. The flycatchers' nest survival had a quadratic relationship with Julian date but generally increased through the breeding season. Nest height increased as the breeding season progressed but did not explain any variation in nest survival. No other reproductive trait exhibited significant intraseasonal variation. Overall, predator-specific predation rates did not vary seasonally, but there was a marginal decline in the risk of failure from avian predators as the season progressed. Of the explanations we considered, changes in predator abundance or activity were likely the primary contributor to intraseasonal variation in survival of Acadian Flycatcher nests.

The effects of global climate change have attracted increasing attention, especially concerning the Arctic, and Antarctic. However, montane/alpine areas are also quite sensitive to climate change. Animals endemic to these areas are distributed within restricted elevational ranges, and many of them are also reliant on the harsh climate, a change of which may affect them as disastrously as it may affect polar species. Here we used MaxEnt software to construct models and make predictions for the rare Sichuan Jay (Perisoreus internigrans), which is known only from isolated fragments of high-elevation coniferous forest on the Qinghai—Tibet plateau of west-central China. Our model suggests that potentially suitable areas are concentrated in northern Sichuan and southern Gansu provinces, and they are fragmented generally, because of the mountainous terrain. It also predicts severe risks from climate change, even more than for the other two species of the genus, P. canadensis and P. infaustus: (1) both of the extent of suitable habitat and the suitability of that habitat will decline significantly under climate change; (2) climate change will compel this bird to shift northward and upward, but areas left for such compensatory extension are quite limited, and (3) the suitable habitat will become much more fragmented, which may exacerbate the effects of climate change indirectly by slowing or halting gene flow and increasing the rate of extinction of isolated local populations.

Within a population, the sizes of eggs and clutches vary, and the combination of both determines a female's reproductive investment. We investigated females' investment in clutches of the Chilean Swallow (Tachycineta meyeni) at the southern limit of its range, where it breeds in an extreme climate. We analyzed variation in clutch, egg and yolk size in relation to the female's condition, date of laying, and position in the sequence of laying. As predicted by energy/nutrient constraints, clutch size and yolk size decreased over the breeding season, though egg mass increased. Females' investment strategy differed with clutch size: their investment in eggs increased with each successive egg in clutches of 4 and 5 eggs but decreased with each successive egg in clutches of 3 eggs. Eggs that were heavier for their size were more likely to hatch than eggs light for their size. Females may make a strategic decision, with high investment in eggs laid early resulting in a short sequence (small clutch) and delayed investment resulting in a long sequence (large clutch). Alternatively, the shift in clutch investment may simply be a consequence of physiology. Better estimates of female body condition are needed for these options to be distinguished.

The lining material is a key element of bird nests, serving primarily as insulation for the adult, eggs, and/or chicks, but collection of such material has an energetic cost. Our study investigated the nest-building effort of four species of tit (Paridae) in an English wood by quantifying the use of colored wool-like artificial material in nest lining from 2000 to 2010. We recorded the distances that birds carried the material from source to nest for each nest as an indirect measure of the energetic cost of collecting nest material to individual birds. Birds did not always use nest material from the nearest source to their nest, and some birds collected material from two, three or four well-separated sources. There was no detectable color preference in choice of material, and few birds traveled more than 200 m to gather the material. Use of the material appeared to depend on the species. Within defined areas around material dispensers not all individual Great Tits (Parus major) used the artificial material, and, for all species examined, the proportion of birds using the material declined with increasing distance between source and nest. Use of artificial material suggested that selection of nest materials was probably opportunistic but also reflected the preference of these species for a wool-like nest lining.

Molecular analyses have confirmed that the majority of socially monogamous birds follow a genetically promiscuous reproductive strategy. Most such studies, however, have addressed species of the North Temperate Zone; tropical species are grossly underrepresented, although most of Earth's biodiversity is concentrated in the tropics. In this study, we describe the genetic mating strategy of the Rufous-and-white Wren (Thryothorus rufalbus), a socially monogamous duetting neotropical songbird. Over 8 years of studying a marked population in Costa Rica, we recorded genetic data from 51 broods. Microsatellite analysis of four variable loci revealed that the Rufous-and-white Wren follows a mixed reproductive strategy, where extra-pair young are found in a small minority of broods. Three of 158 nestlings (2%) were the result of extra-pair fertilizations; three of the 51 broods (6%) contained a nestling with alleles mismatched to its social father. We assigned paternity of two of the extra-pair nestlings to males in territories adjacent to the cuckolded males. During behavioral observations, we observed within-pair copulations rarely and extra-pair copulations never. The rate of extra-pair paternity we report here is lower than the average reported for socially monogamous birds in the North Temperate Zone but comparable to rates in three closely related tropical wrens. Rufous-and-white Wrens are renowned for their coordinated vocal duets. We compared rates of extra-pair paternity among socially monogamous tropical birds, contrasting four duetting species against twelve nonduetting species and found lower levels of extra-pair paternity in the former group, suggesting that duetting and low levels of extra-pair paternity are related.

For most bird species, biparental care is expected to play an integral role in offspring survival. Nevertheless, relatively few studies have simultaneously examined male and female investment into nest attendance, the prevalence of nest attendance through the nesting cycle, or the relationship between nest-attendance effort and nesting success. Here, in a monogamous passerine, the Wood Thrush (Hylocichla mustelina), we use radiotracking to examine nest-attendance behaviors of males and females during the laying, incubation, and nestling stages, and the relationships between nest attendance and nesting success. Across nesting stages, males spent between 14–38% of their time <5 m and 21–58% of their time 5–25 m from the nest, and the time males spent near the nest was positively associated with nesting success. During the incubation stage, the amount of time males spent <5 m from the nest depended upon the female's presence on or off of the nest, as males appear to coordinate their nestattendance behaviors with females. Overall, our results indicate that male Wood Thrushes invest extensively into indirect parental-care behaviors throughout the nesting cycle and that increased nest attendance translates into improved offspring survival.

Polymorphisms of the juvenal plumage in birds have received little study in comparison to other plumages. We investigate a polymorphism in the juvenal plumage of the Yellow Warbler (Setophaga petechia) in southeastern Ontario, Canada. Yellow Warblers in juvenal plumage show either yellow or white plumage on their lower ventral surface of the neck, breast, and belly, and these differences have been speculated to be associated with sex. We tested the hypothesis that juvenal plumage color varies with sex by using blood samples to molecularly sex 10 yellow and 14 white nestlings. We found no relationship between plumage color and sex (yellow nestlings: 70% male, 30% female; white nestlings: 64% male, 36% female). Using the same 24 nestlings that we sexed, we measured feather color with a spectrometer and found that white and yellow morphs differ significantly in reflectance spectra of red and yellow chroma. Of 66 nestlings whose plumage color we visually inspected in the wild, 73% were white and 27% were yellow, showing that white nestlings are more common than yellow in our study population. We propose alternative explanations for the possible significance of yellow and white polymorphism in the juvenal plumage of the Yellow Warbler.

Within bird populations, eggs vary extensively in size, shape, and color, but individual females tend to lay eggs that are relatively consistent in most traits. We measured all eggs laid by individual female Savannah Sparrows (Passerculus sandwichensis) breeding on Kent Island, New Brunswick, comparing subsequent clutches within the same year and in successive years. Repeatability was high for egg size and shape (0.78 and 0.72, respectively). Conversely, the repeatability of intensity of spotting was only moderate (0.46), and the background color of eggs varied from clutch to clutch and even within a clutch. Egg size increased slightly within a year from a female's first to subsequent clutch, but egg size was independent of the female's body size, the age or size of her mate, or weather conditions during clutch formation. Ranking of individual females' eggs by size and shape remained almost the same from clutch to clutch. Although laying eggs that are relatively consistent and individually distinctive in size, shape, and spotting could be an adaptation to allow females to discriminate their own eggs from those of brood parasites, this explanation does not apply on Kent Island, where neither intra- nor interspecific brood parasitism occurs. We found no evidence of short-term effects of egg size on the size of 7-day-old nestlings or of long-term effects on adults' survival or lifetime reproductive success. High repeatabilities suggest a substantial genetic component to variation in certain egg traits, which could limit females' ability to modify their eggs in response to environmental changes.

Three species of coastal sparrows (Ammodramus nelsoni, Nelson's Sparrow; A. caudacutus, Saltmarsh Sparrow; and A. maritimus, Seaside Sparrow) reside in North Carolina salt marshes in winter during their nonbreeding periods. We analyzed the timing of migration, survivorship, and site fidelity of these species with mark—recapture data from five winters (2006–2010). By determining the percentage of individuals captured more than once, we documented a shift from transient to settled individuals during and following migration and used linear regressions to test whether this shift was related to mean monthly minimum temperatures. We also used MARK and capture histories over five winters to estimate probabilities of apparent survival and capture. On the basis of recapture data, the three species' populations were composed largely of transient individuals from October until the sparrows settled for the winter by late November. Our recapture data indicate that when coastal sparrows settle for the winter or return to the region in a subsequent year, they do so with high site fidelity. We found that the percent of Nelson's and Seaside sparrows captured more than once had a negative relationship with mean monthly minimum temperature. We estimated survival of Nelson's, Saltmarsh, and Seaside sparrows at 0.673, 0.520, and 0.483, respectively. Our data indicate that survival of these coastal sparrows through the nonbreeding season is comparable to existing estimates for their breeding populations. Surveys in the nonbreeding season and management plans should take into account the likely presence of a large proportion of transient individuals during migration.