Rebstock and Boersma (2011) recently explored variation in the temperature and incubation period of eggs within clutches of the Magellanic Penguin (Spheniscus magellanicus). They defined incubation period as “the time from the laying of an egg to its hatching” and concluded that parental behavior explained why the incubation period of second eggs was shorter than that of first eggs and controlled asynchronous hatching. While we agree that parents influenced asynchronous hatching by delaying the onset of incubation, we argue that their conclusions are based on an unconventional definition of incubation period. They included the period before the delayed onset of incubation in the incubation period, which leads to confusion. We state that the incubation period cannot include the time before the (delayed) onset of incubation when parents are not warming the eggs. As regards this latter and widely accepted definition, Rebstock and Boersma (2011) provided a large dataset showing that incubation consistently lasted for 39 days, whenever the onset of incubation, for both first and second eggs. The divergence in the definition of “incubation period” and the failure to consider the “onset of incubation” for a species in which the first egg is not incubated immediately after laying led to confusion in the interpretation of the results and conclusions from Rebstock and Boersma (2011).

We defined incubation period as the time from the laying of an egg to its hatching (Rebstock and Boersma 2011) because this full period is ecologically important and matters to both parents' and offspring's fitness. Birds have many patterns of incubation onset and various degrees of egg neglect following onset of incubation. Onset of incubation is difficult to measure in the field and even if known, ignoring the period before onset of incubation misses many of the selective forces acting on incubation patterns and periods.

A combination of elements (e.g., crops and pasture lands, strips of roadside vegetation, woodlots, temporary wetlands) increases the heterogeneity of rural landscapes. Agricultural landscapes range from homogeneous, dominated by a single element (i.e., pure cropland or pure pastoral farming) to heterogeneous, dominated by two or more elements (i.e., mixed farming). In this study we characterized landbird assemblages in various agricultural landscapes (cropland, pastoral, and mixed landscapes) in the Pampas of central Argentina, surveying along transects to quantify species richness, composition, and abundance. Mixed landscapes were more heterogeneous than pastoral areas and cropland. Species richness, particularly of generalists, was greater in mixed landscapes. Richness of grassland specialists (species of increased conservation concern in the Pampas) was lower in croplands than in pastoral and mixed landscapes. An indicator-species analysis supported the association of some grassland specialists (Rhea americana, Asthenes hudsoni, Embernagra platensis, Pseudoleistes virescens) with pastoral landscapes. Our results suggest that maintaining landscape heterogeneity throughout the Pampas (i.e., mixed landscapes) is important for preserving species richness of birds. But several threatened grassland specialists inhabiting the Pampas, such as Rhea americana and Asthenes hudsoni, are found exclusively in pastoral landscapes, so the long-term survival of these species will depend on the conservation of this landscape type.

After a severe population reduction during the mid-20^th century, the endangered Hawaiian Goose (Branta sandvicensis), or Nēnē, has only recently re-established its seasonal movement patterns on Hawai‘i Island. Little is currently understood about its movements and habitat use during the nonbreeding season. The objectives of this research were to identify habitats preferred by two subpopulations of the Nēnē and how preferences shift seasonally at both meso-and fine scales. From 2009 to 2011, ten Nēnē ganders were outfitted with 40-to 45-g satellite transmitters with GPS capability. We used binary logistic regression to compare habitat use versus availability and an information-theoretic approach for model selection. Meso-scale habitat modeling revealed that Nēnē preferred exotic grass and human-modified landscapes during the breeding and molting seasons and native subalpine shrubland during the nonbreeding season. Fine-scale habitat modeling further indicated preference for exotic grass, bunch grass, and absence of trees. Proximity to water was important during molt, suggesting that the presence of water may provide escape from introduced mammalian predators while Nēnē are flightless. Finescale species-composition data added relatively little to understanding of Nēnē habitat preferences modeled at the meso scale, suggesting that the meso-scale is appropriate for management planning. Habitat selection during our study was consistent with historical records, although dissimilar from more recent studies of other subpopulations. Nēnē make pronounced seasonal movements between existing reserves and use distinct habitat types; understanding annual patterns has implications for the protection and restoration of important seasonal habitats.

Since the late 18^th century bird populations residing in the Aleutian Archipelago have been greatly reduced by introduced arctic foxes (Alopex lagopus). We analyzed data from microsatellite, nuclear intron, and mitochondrial (mtDNA) loci to examine the spatial genetic structure, demography, and gene flow among four Aleutian Island populations of the Common Eider (Somateria mollissima) much reduced by introduced foxes. In mtDNA, we found high levels of genetic structure within and between island groups (Φ_ST = 0.643), but we found no population subdivision in microsatellites or nuclear introns. Differences in genetic structure between the mitochondrial and nuclear genomes are consistent with the Common Eider's breeding and winter biology, as females are highly philopatric and males disperse. Nevertheless, significant differences between islands in the mtDNA of males and marginal significance (P = 0.07) in the Z-linked locus Smo 1 suggest that males may also have some level of fidelity to island groups. Severe reduction of populations by the fox, coupled with females' high philopatry, may have left the genetic signature of a bottleneck effect, resulting in the high levels of genetic differentiation observed in mtDNA (Φ_ST = 0.460–0.807) between islands only 440 km apart. Reestablishment of the Common Eider following the fox's eradication was likely through recruitment from within the islands and bolstered by dispersal from neighboring islands, as suggested by the lack of genetic structure and asymmetry in gene flow between Attu and the other Near Islands.

Prey selection of migrating raptors has been documented only rarely. Here we used a genetic approach to identify avian prey of Sharp-shinned Hawks (Accipiter striatus) migrating through central New Mexico. We identified species by comparing profiles of a section of the 16S rRNA mitochondrial gene extracted from feathers of prey of known species to profiles from feathers of prey found on the feet and beaks of migrating hawks. We also quantified prey availability along the migration route with multi-year sampling by mist net at two sites near the raptor-sampling site. Sharp-shinned Hawks took most prey species in proportion to their availability, but they took some species, particularly medium-sized species, more frequently than expected. This pattern may indicate selection for energetically rewarding prey, or the pattern also could arise from differences between our sample of potential prey and the potential prey as viewed by the hawks themselves. The co-occurrence of migrating predators and their prey suggests interesting feedbacks that likely influenced the evolution of migration strategies of both hawks and songbirds in this area.

Few studies have examined raptor reproduction in response to land-use change in sub-Saharan Africa, hampering conservation efforts to address regional declines. To further our understanding of mechanisms underlying the dramatic declines of West African raptors, we examined the relationship between environmental conditions, nest density, and measures of reproduction in the Grasshopper Buzzard (Butastur rufipennis). Analyses were based on 244 nest sites divided between transformed and natural habitat in northern Cameroon. At the landscape scale, nest density increased with the density of preferred nest trees. Nests were more widely spaced in transformed than in natural habitat. Dispersion was adjusted to differences in availability of small mammals, which was negatively associated with distance to nearest neighbor, and in the area under cultivation, which was positively associated with distance to nearest neighbor. Productivity was positively associated with rainfall, canopy shielding the nest, availability of grasshoppers, and the nest's visibility from ground level; canopy shielding, grass cover, rainfall, and distance to nearest neighbor were positively associated with nest success. In natural habitat, losses of eggs and nestlings to natural predators were greater than in transformed habitats, while losses through human predation were small. Productivity and nest success were unaffected by land use because of the opposing effects of greater predation pressure, closer spacing of nests, and more food in natural habitat than in transformed habitat. Thus transformed habitat may provide adequate breeding habitat for the Grasshopper Buzzard, but declining rainfall and intensifying anthropogenic land use are likely to affect future reproductive output.

Conversion of natural grassland to cropland has been postulated as a cause for population declines among grassland birds. We evaluated nest-site habitat characteristics and landscape composition for three species of prairie-breeding shorebirds nesting across the agricultural landscape of prairie Canada. Nests of the Upland Sandpiper (Bartramia longicauda) and Willet (Tringa semipalmata) were found disproportionately in natural grazed (57%) or natural idled (21%) patches, whereas Marbled Godwit (Limosa fedoa) nests were in habitats in proportion to their availability on the landscape. We examined multiple landscape variables (proportions of crop, natural idled, natural grazed, and wetland habitats, edge density, and patch area) across a broad geographic scale, using relatively large samples of nests, and found no strong relationships. Neither nest-site habitat characteristics nor landscape-level effects influenced daily survival rates of Upland Sandpiper or Willet nests. Variation in landscape composition at three different spatial scales (200, 600, and 2000 m) also did not influence daily nest-survival rates. To adequately inform land-use management programs aimed at shorebird conservation, further research should examine site-selection patterns and characteristics of nest sites that maximize survival of chicks and adults during subsequent stages in reproduction.

Coastal urban environments provide a potentially diverse source of food for gulls, including items of marine, terrestrial, and anthropogenic origin. Our objective was to examine variation in the diet and use of feeding habitat of four species of gulls, the Laughing (Leucophaeus atricilla), Herring (Larus argentatus), Great Blackbacked (L. marinus), and Ring-billed (L. delawarensis), at a coastal—urban interface. We necropsied, identified the sex and age class, and quantified the stomach contents of 1053 Laughing, 249 Herring, 67 Great Black-backed, and 31 Ring-billed Gulls collected near the New York City metropolitan area in 2003 and 2004. Great Black-backed Gulls specialized on marine foods, whereas Ring-billed Gulls were generalists. Laughing Gulls and Herring Gulls favored marine foods and foraged in marine habitats but also used terrestrial and anthropogenic food sources. We found evidence that demographics influenced the gulls' choice of diet and use of feeding habitat. Laughing Gulls and Herring Gulls switched their use of feeding habitats at various stages of breeding, exploiting terrestrial prey and feeding habitats most during chick rearing. Interspecific and intraspecific differences in the four species' diet and use of feeding habitat apparently allow for their coexistence at this coastal—urban interface.

A fossil from the Middle Miocene Rosarito Beach Formation of Baja California represents a previously undescribed, auklet-sized species of wing-propelled diving Pan-Alcidae (Aves, Charadriiformes). This new taxon, Divisulcus demerei, is recognized from the presence of a bifurcated scapulotricipital sulcus of the distal end of the humerus, a potentially neomorphic character within Aves. Additionally, the degree of compression of the humeral shaft of this new species is less than that of other pan-alcids. These characters may represent retention of ancestral character states that are associated with the transition to wing-propelled diving from nondiving Charadriiformes. This discovery provides further information regarding paleodiversity in this clade, extends the geographic range of Miocene pan-alcids, and may represent the oldest record of the clade from the Pacific Ocean basin, as previously reported unambiguous records are from Late Miocene or younger deposits (∼10–1.6 Ma). Moreover, the age of this new pan-alcid (14–16 Ma) corresponds with the timing of the Middle Miocene climatic optimum, a time for which previous records of Pacific Ocean basin pan-alcids were lacking. Because of the relative incompleteness of the specimen, the systematic position of this new taxon within the Pan-Alcidae from a phylogenetic analysis is not strongly supported. Until additional remains of D. demerei are recovered that can provide additional character data, the affinities of this new taxon within the Pan-Alcidae are uncertain.

In this study we measured two physiological traits (levels of corticosterone and immunoglobulin) in two species of landbirds, the Canyon Towhee (Melozone fusca) and Inca Dove (Columbina inca), occupying three degrees of human alteration of a subtropical mountain landscape: forest edges, croplands, and urban sites. We found that both physiological variables differed by species and habitat condition. In both species, corticosterone concentration was significantly higher in croplands. But immunoglobulin concentration behaved differently, in C. inca being highest at urban sites, where in M. fusca it was lowest. Contrary to expectation, we only found one strong significant relationship between both physiological variables: M. fusca in urban areas. Our results suggest that 30% of the towhees captured in urban areas are under chronic stress. Results for body condition support this hypothesis, as the condition of towhees in urban areas was poorer, suggesting physiological vulnerability. Although we expected the density of both species to be high in urban areas because of the amount and predictability of resources, we found a significantly lower density of M. fusca in urban areas, suggesting that the habitat variables influencing the physiological condition of M. fusca affected its population density. In summary, our results suggest that a substantial proportion of Canyon Towhees in the urban area studied have physiological limitations, while the Inca Dove seems to have an appropriate physiological response despite low values for body condition in urban areas.

The White-fronted Woodpecker (Melanerpes cactorum) drills holes in branches and trunks to feed on sap flows, providing an energy-rich food resource for other birds. Here we describe ecological and behavioral traits of the White-fronted Woodpecker related to its sap-feeding habits in the semiarid Chaco of Argentina and explore the structure of the avian assemblage in relation to the sap resource. Sap consumption by the White-fronted Woodpecker and other sap-feeding species was strongly seasonal and positively associated with periods of resource scarcity. The White-fronted Woodpecker actively defended the sap wells from smaller birds. Specialist and facultative nectarivores that assimilate sucrose at a high rate represented an important proportion of sap-feeding birds. In this system of woodpecker, sap, and other sap-feeding species, each species' consumption depends on its physiological and behavioral characteristics as well as on the availability of other food in the surrounding environment.

Little is known about juvenile birds' movements during the post-fledging stage of development, especially in urbanizing landscapes where novel ecological factors such as invasive plants and altered densities of conspecifics might influence fledglings' use of space. In 2008 and 2009 we used radio telemetry to track movements of fledgling Northern Cardinals (Cardinalis cardinalis; n = 45) and Acadian Flycatchers (Empidonax virescens; n = 31) in a network of riparian forests embedded within a rural-to-urban gradient of landscapes in central Ohio. A subset of 20 cardinals and 11 flycatchers survived sufficiently long for subsequent analyses of their movement. Natal ranges of juvenile cardinals decreased in size with proximity to fragment edge, and fledglings moved less from nests surrounded by extensive cover of the Amur honeysuckle (Lonicera maackii). Conversely, the size of natal ranges of juvenile flycatchers was positively related to honeysuckle cover. During the study period, 70% of the cardinals dispersed from natal sites at an average of 47 ± 2 days after fledging. Dispersal patterns of individual cardinals varied; birds dispersed locally within their natal forest fragment or made extended movements into the surrounding landscape matrix. In our study area the density of cardinals increased with urbanization, and fledglings tended to disperse later from sites of high densities of conspecifics. Collectively, our results suggest that while novel ecological factors associated with urbanization may influence fledglings' movements, patterns are likely species-specific.

The Upper Mississippi River is thought to provide important stopover habitat for migrating landbirds because of its north-south orientation and floodplain forests. The river flows through the Driftless Area of southwestern Wisconsin and southeastern Minnesota where forests are plentiful, yet forests of the floodplain and Driftless Area uplands differ greatly in landscape setting, tree species composition, and topography. We compared landbird assemblages in these upland and floodplain forests over three springs, 2005–2007, using line-transect surveys at randomly selected areas in and within 16 km of the floodplain. We found more species of both transient and locally breeding migrants per survey in floodplain than in upland forest. Detections of transient neotropical migrants did not differ statistically by habitat. Detections of locally breeding neotropical and temperate-zone migrants and transient temperate-zone migrants were greater in floodplain than in upland forest. Between floodplain and upland forest, assemblages of locally breeding species, including neotropical and temperate-zone migrants (of which some individuals were in transit), differed substantially, but assemblages of transients (including both neotropical and temperate-zone migrants) did not differ as much. Only two species of transient migrants had clear affinities for floodplain forest, and none had an affinity for upland forest, whereas most locally breeding migrants had an affinity for either upland or floodplain forest. Within each spring, however, detections of transient neotropical migrants shifted from being greater in floodplain to greater in upland forests. This intraseasonal shift may be related to the phenology of certain tree species.

The Buff-breasted Earthcreeper (Upucerthia validirostris) is endemic to western Argentina, and the Plain-breasted Earthcreeper (U. jelskii, including subspecies saturata in the north and pallida in the south), ranges from northern Peru to northwestern Argentina. They have been considered subspecies, as constituents of a superspecies, and as different species. From north to south, a morphocline, involving an increase of rustiness of the plumage and of ∼15% in bill length, 10% in wing length, and 20% in tail length, links jelskii to validirostris. The cline linking jelskii and pallida is gradual, over ∼1800 km; that between pallida and validirostris is steep, over ∼80 km. The northernmost record of validirostris is from the northern Calchaquies Valley, Salta, northwestern Argentina, a valley surrounded by mountains of up to ∼6300 m above sea level through which the lowest pass is at over 4900 m, forming a barrier between validirostris and the southernmost record of pallida to the north. The song, continuous song, duet, and call of validirostris are structurally indistinguishable from those of jelskiilpallida and from the single available recorded song of saturata. In all playback experiments, validirostris answered by approaching and vocalizing to voices of validirostris and jelskii /pallida and vice versa. Treatment of validirostris as a single species is warranted, and three subspecies can be tentatively recognized: southern validirostris (large, rufescent birds with buff bellies restricted to Argentina), central and northern jelskii (small, pale birds ranging from northwestern Argentina to central Peru), and northern saturata (small, dark, and brownish birds in northern central Peru).

We describe a new species of softtail, genus Thripophaga, from the southern portion of the delta of the Orinoco River in Venezuela. In plumage the new species is most similar to the Orinoco Softtail (T. cherriei) from the upper Rio Orinoco and to the Striated Softtail (T. macroura) of southeastern Brazil. It differs from either in voice, plumage, and mensural characters, but, like these two species, it has a small and geographically isolated range. The new taxon, as far as is currently known, is restricted to seasonally flooded forest along streams and rivers in the vicinity of the Brazo Imataca, a closed loop branch of the Rio Grande, which is the largest branch of the Rio Orinoco passing through the southern part of the Orinoco delta. We also present notes on the behavior, ecology, and conservation of this species.

Predation is the leading cause of nest failure for many bird species. Most studies associate risk of predation with vegetation characteristics of the nest site. Alternatively, the Skutch hypothesis suggests that adults' activity at the nest can attract the attention of predators and lead to an increased risk of predation. We investigated whether vegetation characteristics surrounding nest sites affected nest attentiveness and visitation and if these behaviors affected nest survival. We used 1-hr nest observations and 8-hr video observations at Black-capped Vireo (Vireo atricapilla) nests in three regions of Texas to quantify nest attentiveness and visitation during incubation and the nestling stage. Females spent 80% more time on nests during incubation and 250% more time on nests during the nestling stage than did males, but visitation was similar for each sex. In general, nest behavior did not appear to be affected by vegetation characteristics, except males' attentiveness during incubation increased as average cover from 0 to 2 m increased. Adults' activity did not appear to increase the risk of nest predation. Despite visitation being more frequent during the nestling stage than during incubation, visitation during either stage did not affect nest survival. Overall, nest survival improved with attentiveness during incubation.

Estimates of survival of nearctic—neotropic migrants have broadened our understanding of lifehistory variation across taxa and latitudes. Despite the importance of assessing migrants' survival through all phases of their life-cycle, data from their tropical winter ranges are few. In this study we used 14 years of data on captured birds to quantify the influence of mass on the annual survival of the Prothonotary Warbler (Protonotaria citrea) in northeastern Costa Rica and compared our results to survival estimates generated from the breeding grounds. Furthermore, from estimates of population growth (λ) based on marked individuals, we projected the Prothonotary Warbler's demographic trajectory at our study site. Our results suggest that heavier individuals had higher rates of annual survival. Population growth at our study sites was stable, punctuated by swings in growth and decline. We believe the benefits of weight gain (preparation for migration and intraspecific competition for territories) outweigh inherent costs (greater susceptibility to predation).

The Connecticut Warbler (Oporornis agilis) is a rare and declining neotropical migrant that breeds in the north-central United States and south-central Canada. To better understand the species' habitat needs, we analyzed 371 observations of the Connecticut Warbler over 18 years at 86 sites in 28 stands of forest in northern Minnesota. We considered the habitat and landscape at three spatial scales (buffer radii of 100, 500, and 1000 m) and regressed combinations of habitat variables with two response variables, the Connecticut Warbler's abundance (the total number of individuals ever recorded at a site or stand, with a zero-inflated negative binomial distribution) and frequency (the number of years recorded out of 18, with logistic regression). From a subset of models retained on the basis of Akaike's information criterion, we calculated model-averaged predictions for each combination of buffer size and response variable. Models based on Connecticut Warbler frequency at the 1000-m buffer performed best in comparisons of model-averaged predictions to observed data. At the 1000-m scale, Connecticut Warblers were positively associated with a combination of large patches of upland coniferous and lowland black spruce forest and were negatively associated with upland deciduous forest. From these models, we mapped predicted breeding habitat for the Connecticut Warbler in the areas sampled in northern Minnesota.

The Cerulean Warbler (Setophaga cerulea) is one of the most rapidly declining warblers in North America. Our previous genetic work suggested that this migratory songbird has no significant population genetic structure in the northern and western parts of its breeding range, and for conservation purposes we assigned all sampled populations to a single genetic management unit. Here, we expand this work to include the entire breeding range of the Cerulean Warbler, given recent evidence for morphological and ecological differentiation between the northern and southern sections of that range. We assayed variation in four microsatellite loci and an 841-base-pair fragment of the mitochondrial control region, finding support for low but significant population-genetic structure in the mitochondrial marker. Estimates of population-genetic structure for pairs of sampling locations did not detect a clear geographic pattern of differentiation, and a hierarchical AMOVA did not reveal significant structure between northern and southern locations. These findings, together with previously published evidence for high rates of contemporary dispersal among breeding locations, may support the hypothesis of a long history of gene flow among ecologically distinct Cerulean Warbler populations or may suggest that more recent anthropogenic dispersal has homogenized the genetic signature of differentiation that may have existed in pre-settlement populations.

Henslow's Sparrows (Ammodramus henslowii) are distributed in tallgrass prairies in central North America; however, this species is restricted further to specific habitats within these prairies—large expanses with relatively little woody vegetation but an accumulation of standing grasses and forbs, conditions that result from infrequent disturbances by fire, mowing, or grazing. Henslow's Sparrows have been documented to be unpredictable at breeding sites from year to year, but studies to date have considered only local spatial scales. We compared resettlement behavior (prevalence of occurrence and variation in abundance) of Henslow's Sparrows to that of two other grassland sparrows, Grasshopper Sparrows (A. savannarum) and Savannah Sparrows (Passerculus sandwichensis), across multiple spatial resolutions. In Henslow's Sparrows, prevalence was lower and variation in abundance was greater than in the other two species. Indeed, Henslow's Sparrows do not occur consistently at extents of less than 120 000 km², suggesting nomadic characteristics of where they breed from year to year. We suggest that these patterns reflect Henslow's Sparrows' responses to frequently changing habitat, such that this species is tracking spatiotemporal changes in optimal habitat that result from disturbances broadly across regional landscapes.

Nestlings communicate with parents via begging, but what does begging signal and how do parents allocate food to their nestlings? We tested the signal-of-need (SoN) and signal-of-quality (SoQ) hypotheses for nestling begging in the Red-winged Blackbird (Agelaius phoeniceus) by attempting to determine whether begging is negatively (SoN) or positively (SoQ) condition dependent, and by attempting to identify the attributes of nestlings that parents use to allocate food within broods. We quantified begging by its mean intensity (scale 0–7) and mean duration and parental allocation by the number of times each nestling was fed. We found that the intensity and duration of begging were not correlated with nestlings' size (estimated by body mass and tarsus length), condition (estimated from the residual of mass regressed on tarsus length), age, sex, or testosterone concentration, so begging did not appear to be negatively or positively condition dependent. A generalized linear model showed that mean intensity of begging, body condition, and log testosterone concentration were significant predictors of the number of feedings. These results are consistent with parents using begging intensity and nestling quality, but not long-term need, to allocate food within broods.