Our knowledge of avian behaviors during the nonbreeding period still lags behind that of the breeding season, but the last decade has witnessed a proliferation in research that has yielded significant progress in understanding migration patterns of North American birds. And, although historically the great majority of migration research has been conducted in the eastern half of the continent, there has been much recent progress on aspects of avian migration in the West. In particular, expanded use of techniques such as radar, plasma metabolites, mist-netting, count surveys, stable isotopes, genetic data, and animal tracking, coupled with an increase in multi-investigator collaborations, have all contributed to this growth of knowledge. There is increasing recognition that migration is likely the most limiting time of year for migratory birds, increasing the importance of continuing to decipher patterns of stopover ecology, identifying critical stopover habitats, and documenting migration routes in the diverse and changing landscapes of the American West. Here, we review and briefly synthesize the latest findings and advances in avian migration and consider research needs to guide future research on migration in the West.

Birds of the forest canopy are important components of tropical forest ecosystems, but difficulty of access or viewing into the canopy complicates their study. If ground methods are biased against canopy birds, as has been suggested, this bias could affect our understanding of forest ecology as well as biological monitoring and conservation practices. This study is the first to quantitatively compare results from ground- and canopy-based methods of censusing canopy birds. I used three methods to assess differences in ground-based and canopy-based methods for detecting forest birds in a 100-ha plot of lowland forest in northern Honduras: (1) point counts from the ground, (2) 22 repeat censuses from two canopy trees, and (3) single censuses from 22 canopy trees. I counted birds for a full annual cycle from April 2006 to April 2007 and recorded 157 species in over 4000 individual detections. Ground methods significantly underestimated species and familial richness as well as abundance of individuals in the canopy stratum. On the basis of these results, I predict that the use of ground methods alone misses 25 to 50% of the species richness for some migrant and resident families and underestimates the density of some species by as much as 25%. These findings highlight the risk of relying on ground-based methods for bird studies in structurally complex tropical forests; reliance on ground-based methods may negatively affect long-term biological monitoring and the setting of conservation priorities for tropical forests.

In eastern North America, most early-successional woody habitats are ephemeral and succeed to forests within a few decades. Consequently, for shrubland birds patches of habitat are generally suitable for breeding for only a short time. This has led some authors to suggest that shrubland birds should show little fidelity to former breeding sites and frequently disperse to new, more suitable patches. Similarly, one would expect birds of mature forests to have greater site fidelity because their habitats are more stable. Understanding the dispersal strategies of shrubland birds has important implications for the management and conservation of these declining species. Therefore, I used meta-analysis to compare rates of site fidelity of migratory shrubland and forest passerines that breed in eastern North America. For adult birds, site fidelity of shrubland (estimate ± SE = 0.353 ± 0.022) and forest species (0.364 ± 0.036) was similar. Philopatry of yearling birds to their natal site was lower but similar for shrubland (0.048 ± 0.014) and forest birds (0.028 ± 0.019). I conclude that dispersal rates of shrubland birds are not unusually high. Rather, both forest and shrubland species appear to follow decision rules that are common to passerines, with adults frequently returning to former breeding sites and yearlings dispersing away from their natal sites. For management, these results are encouraging, as populations of shrubland birds should persist in highquality habitats maintained in an early-successional state.

After spreading across North America, West Nile virus (WNV) arrived in the Sacramento Valley of California in 2004 and began killing many corvids. To estimate the regional effect of WNV on corvids and other birds, we reinitiated a road survey along six routes totaling 203 km in the Sacramento Valley. We surveyed these transects 30 times in fall and winter from 1990 to 1995 and repeated the surveys each fall and winter from 2005 to 2008. By 2007–08, annual maximum counts of the Yellow-billed Magpie, American Crow, and Loggerhead Shrike had declined 83%, 63%, and 63%, respectively, from those of the 1990s. These species declined in riparian and rice-cultivation areas, most substantially outside Yolo County. The magpie declined 90% along our routes north of Yolo County, causing us concern for the viability of the species. After a lag, the crow began declining quickly in 2007. We recommend the Yellow-billed Magpie be given special status. Also, searches for Yellow-billed Magpies should be extended across the species' range to find locations with sizable numbers, and experimentally designed mosquito control should be considered in breeding areas, especially in areas of high densities of Culex mosquitoes.

The use of hydrogen isotopes to delineate origins of migratory birds relies on predictable relationships between levels of deuterium (δD) in tissue and those predicted from long-term precipitation (δD_p). Variance in deuterium associated with the year of interest, the long-term isotopic database, and in feathers (δD_f) of waterbirds occupying small wetlands is an issue confronting isotopic comparisons. We examined the factors that influence isotopic variation among feathers of known-origin Mallards (Anas platyrhynchos) from breeding locations in north-central North America. We evaluated temporal variability in δD_f values at two spatial scales. At scales >500 km, annual differences accounted for 0–45% of variation in δD_f values of feathers from the North American Boreal Forest, Peace Lowlands, Aspen Parkland, and Prairie ecoregions; annual variability was greatest in the Aspen Parkland. At scales <50 km, differences among and within years contributed similarly and together accounted for 93–95% of variation in δD_f values of Mallard broods at two Canadian prairie sites. Variability in δD_f among Mallards from one small wetland complex in prairie Canada was best explained by variability in δD_p values that represented the period of feather synthesis through the beginning of the previous growing season >12 months earlier. These annual and seasonal shifts in δD_f values may help to explain why assigning origins of wetland birds on the basis of deuterium levels can be more uncertain at finer spatial scales, particularly in regions of complex wetland hydrology.

Approximately 70–80% of the entire population of the Trumpeter Swan (Cygnus buccinator) depends for reproduction on wetlands in Alaska. This makes the identification of important habitat features and the effects of human interactions important for the species' long-term management. We analyzed the swan's habitat preferences in five areas throughout the state and found that swan broods occupied some wetland types, especially larger closed-basin wetlands such as lakes and ponds, at rates much higher than they occupied other wetland types, such as shrubby or forested wetlands. We also found a negative effect of transportation infrastructure on occupancy by broods in and around the Minto Flats State Game Refuge, Kenai National Wildlife Refuge, and Tetlin National Wildlife Refuge. This finding is of particular interest because much of the Minto Flats refuge has recently been licensed for oil and gas exploration and parts of the Kenai refuge have been developed in the past. We also investigated the potential effects of the shrinkage of closed-basin ponds on habitat occupancy by nesting Trumpeter Swans. We compared nesting swans' use of ponds with changes in the ponds' size and other characteristics from 1982 to 1996 and found no relationships between occupancy and changes in pond size. However, we believe that the recent and rapid growth of Trumpeter Swan populations in Alaska may become limited by available breeding habitat, and anthropogenic and climate-induced changes to the swan's breeding habitats have the potential to limit future production.

Some Canada Geese (Branta canadensis) raise their broods by themselves (two-parent families), while others raise them in gang broods, defined as two or more broods amalgamated into a single cohesive unit and shepherded by four or more parents. From 1984 to 2005, I individually marked Canada Geese in New Haven County, Connecticut, so that I could compare the characteristics of adults that raise their goslings in gang broods to those of adults that raised their goslings in two-parent families. I wanted to determine if a parent's decision to form a gang brood was influenced by its age or body mass, its own parents (indicating either that the behavior has a genetic component or that the behavior is learned while a gosling), its prior experiences raising broods, or the loss of its mate. Parents tended to use the same brood-rearing approach from one year to the next: 61% of parents of gang broods (i.e., gang-brooders) during one year also were gang-brooders the next year they had goslings; likewise, 65% of parents in two-parent families during one year raised their next brood in a two-parent family. Geese that changed mates from the previous year were more likely to switch brood-rearing approaches than those that stayed with the same mate. As geese gained more years of experience raising goslings, their propensity to form a gang brood increased; only 29% of geese raising broods for the first time formed a gang brood versus 80% for geese with 5 or more years of experience. Geese raised in gang broods themselves were no more likely than geese raised in two-parent families to form gang broods once they became adults and had their own broods. These results indicate that gang brooding is a behavior learned as an adult. I tested the hypothesis that adult geese attending the same gang brood are members of the same extended family but found that geese were as likely to form a gang brood with unrelated individuals as with siblings or parents.

Quantifying population genetic heterogeneity within nonbreeding aggregations can inform our understanding of patterns of site fidelity, migratory connectivity, and gene flow between breeding and nonbreeding areas. However, characterizing mechanisms that contribute to heterogeneity, such as migration and dispersal, is required before site fidelity and migratory connectivity can be assessed accurately. We studied nonbreeding groups of Common Mergansers (Mergus merganser) molting on Kodiak Island, Alaska, from 2005 to 2007, using banding data to assess rates of recapture, mitochondrial (mt) DNA to determine natal area, and nuclear microsatellite genotypes to assess dispersal. Using baseline information from differentiated mtDNA haplogroups across North America, we were able to assign individuals to natal regions and document population genetic heterogeneity within and among molting groups. Band-recovery and DNA data suggest that both migration from and dispersal among natal areas contribute to admixed groups of males molting on Kodiak Island. A lack of differentiation in the Common Merganser's nuclear, bi-parentally inherited DNA, observed across North America, implies that dispersal can mislead genetic assessments of migratory connectivity and assignments of nonbreeding individuals to breeding areas. Thus multiple and independent data types are required to account for such behaviors before accurate assessments of migratory connectivity can be made.

Theory suggests habitats should be chosen according to their relative evolutionary benefits and costs. It has been hypothesized that aspen (Populus spp.) forests provide optimal habitat for Ruffed Grouse (Bonasa umbellus). We used the low phase of a grouse population's cycle to assess the prediction that grouse should occupy aspen and avoid other forest types at low population density because of the presumptive fitness benefits of aspen. On the basis of our observations, we predict how the Ruffed Grouse population will increase in different forest types during the next cycle. In conifer (Pinus spp., Abies balsamea, Picea spp.)-dominated and mixed aspen—conifer landscapes, grouse densities were highest where forest types were evenly distributed. Within these landscapes, male Ruffed Grouse selected young aspen stands that were large and round or square. Although Ruffed Grouse selected young aspen stands strongly, contrary to prediction, they also used other forest types even when young aspen stands remained unoccupied. The relative densities of Ruffed Grouse in aspen and conifer forests indicated that the aspen forest's carrying capacities for grouse was higher than the conifer forest's at least during the low and declining phases of the grouse's cycle. On the basis of our observations, we predict that Ruffed Grouse populations in aspen-dominated landscapes will have higher population densities and fluctuate more than will populations in conifer-dominated landscapes. We suggest that studies of avian habitat selection would benefit from knowledge about the relative densities among habitats at differing population sizes because this information could provide insight into the role of habitat in regulating populations and clarify inferences from studies about habitat quality for birds.

Resource availability in a heterogeneous environment and density-dependent processes may influence the spatial distribution of individuals among habitats. The distribution of nests of secondary cavity nesters is rarely clumped because the birds are constrained by the distribution of existing cavities as nest resources. In this study, to evaluate the interplay of environmental and behavioral processes in the spacing of parrot nests, we compared the spatial distribution of active Lilac-crowned Parrot (Amazona finschi) nests with that of all cavities used as nests over 14 years. Parrots reused 42% of cavities, and the frequency of reuse was significantly associated with a previously successful nesting attempt. Positive fitness benefits of cavity reuse may indicate high-quality nest sites that are used more intensively by resident breeding pairs. Spatial-point-pattern analysis indicated that trees used as nests were significantly clustered within 60 m in the three nesting areas, with average distance of 100–200 m between nest trees. In a given breeding season, active parrot nests were separated by a mean 950 ± 890 m. Parrot nests were also located significantly closer to a tree used as a nest in the previous breeding season than the distance between nearest nesting conspecifics. This pattern suggests that conspecifics influence the spatial distribution of reproductive pairs breeding simultaneously, with nesting pairs occupying areas where suitable cavities are more numerous. The behavioral spacing requirements of nesting parrots may limit breeding densities and restrict management strategies to increase numbers of nesting pairs within protected areas.

The consequences of forest harvest to birds nesting in spatially and temporally dynamic landscapes are poorly understood. The boreal forests of Newfoundland have a low density of nesting birds, are naturally heterogeneous, and experience extreme annual variation in weather. Against this backdrop, we tested whether breeding success of passerines was affected by forest harvest or whether natural heterogeneity masked potential consequences of harvesting. During 2004 and 2005, we monitored 98 nests and banded 439 hatch-year (HY) birds of three migratory passerines in landscapes that varied in the extent of natural or human-induced heterogeneity: the White-throated Sparrow (Zonotrichia albicollis), Yellow-rumped Warbler (Dendroica coronata), and Blackpoll Warbler (Dendroica striata), We monitored nest-initiation date, clutch size, hatching success, nests' daily survival rates, fledging success, and productivity (ratio of HY to adults captured) relative to proportion of forest harvested within radii of 20 m (local scale), 115 m (neighborhood scale), and 1250 m (landscape scale). Local habitat and year significantly predicted nest-initiation date. Hatching success, fledging success, and productivity were significantly influenced by year and proportion of harvest at all scales, although associations varied by species. Nests' daily survival rates were significantly related to proportion of harvest at all three scales for the White-throated Sparrow; for all species they were consistently higher in 2005, and the direction of the harvest's effect differed by species. Our results reveal that larger scales are important later in breeding and that spatial and temporal heterogeneity may not only conceal consequences of forest harvest, they may also have complex interactions that make predictions difficult in these dynamic landscapes.

Clark's Nutcrackers (Nucifraga columbiana) are important seed dispersers for at least ten species of conifer in western North America and are obligate mutualists for the whitebark pine (Pinus albicaulis), a subalpine tree. Despite the important role they play in forest regeneration, space use by nutcrackers has not been formally studied. Several hypotheses exist to explain their year-round patterns of space use. We tested the hypothesis that one population in the Cascade Range, Washington, migrates altitudinally between summer and autumn. In 2006 and 2007, we compared seasonal differences in summer and autumn space use by 26 radio-tagged nutcrackers. Five nutcrackers remained as year-round residents on their home ranges; 21 emigrated from the study area in summer. Among residents we found summer and autumn ranges overlapped and summer ranges were contained within autumn ranges. Residents increased their use of low-elevation habitats as autumn progressed, but rather than migrating from summer ranges, they used low-elevation forests only for seed harvesting. High-elevation portions of the summer range were used for all other activities including seed storage even though this required residents to transport seeds from source trees up to 29 km in distance and 1007 m in elevation. We were unable to test hypotheses regarding space use by emigrants. However, our results suggest that emigrants in this study did not migrate altitudinally because they showed no seasonal trend in movements either upslope or downslope.

We studied the nesting of the Louisiana Waterthrush (Seiurus motacilla) in western Pennsylvania from 1996 to 2008. Eight of 143 pairs (5.6%) that successfully fledged young from their first nest attempted a second brood, the first cases of double brooding reported for this species. Given the potential for double brooding to increase annual productivity, its infrequency suggests strong costs offsetting this life-history strategy. Molting is a late-season constraint that may influence the occurrence of double brooding in this migratory species. The waterthrushes' nesting season extended from 14 April to 30 July. A single nesting cycle, from clutch initiation through post-fledging care, encompassed 48–55 days. The mean date of clutch initiation for first attempts of single-brooded pairs was 5 May, with at least two thirds of pairs renesting if their first nest attempt failed; the mean date of initiation of second clutches was 25 May. The mean dates of first and second clutches of eight double-brooded pairs were 29 April and 4 June, respectively. The average date of onset of molt was 26 June, and molt was completed in about 40 days, or by early August in most birds. Double-brooded and very late-renesting single-brooded birds delayed molt by up to 3 weeks later than average, and their molt and breeding overlapped by up to 4 weeks. Delayed molt and migration associated with late nesting may be an especially significant cost of double brooding for the Louisiana Waterthrush because it is among the earliest migrants returning to its wintering grounds, where the birds compete strongly for optimum territories.

Each record of a bird on a survey is the result of three processes: (1) a bird being physically present, (2) this bird making itself available for detection, given that it is present, and (3) the bird being detected given that it has made itself available for detection. We employ a novel approach to examine the variation in availability for detection of the endangered Florida Grasshopper Sparrow (Ammodramus savannarum floridanus). Analyzing multi-day acoustic recordings, we quantified the effects of four sources of variation in the probability of singing: consistent variation among birds, day-to-day variation that was consistent from individual to individual, withinmorning variation consistent from individual to individual, and short-term variation related to birds' immediately previous state of singing (whether a bird had been singing in the immediate past). The two most important sources of variation were changes in singing probability with time of day and short-term differences due to an individual's intrinsic state, with birds currently singing being more likely to sing in the immediate future. The latter effect was not constant because nonsingers were more likely to start singing at morning civil twilight and singers were more likely to stop singing later in the morning. Monitoring Florida Grasshopper Sparrows needs to account for sharp drops in the probability of singing at times away from the daily window of peak singing activity. Additional analyses indicate that this conclusion holds across the species' range. We suggest that our findings have even wider applicability among birds.

Stable isotopes have become an accepted method to track resource acquisition and nutrient utilization by birds. Many studies have used these methods to examine nutrient allocation and utilization during egg formation. None, however, has addressed the potential influence of nutrient utilization and movement during embryo development on the isotopic signature of egg components or its implications for sampling protocols. Such fractionation would distort the isotopic signature in incubated eggs, resulting in conclusions based on eggs that may not reflect resource allocation during formation. Using incubated domestic chicken (Gallus gallus) eggs, we examined how embryo development influences δ¹³C and δ¹⁵N signatures in albumen, yolk protein, and yolk lipid. Embryo development significantly lowered δ¹⁵N by 1.0‰ in yolk protein after day 15 and depleted δ¹³C by 0.2‰ in albumen after just 3 days. Future studies examining resource allocation to eggs must control for the influence of embryonic development on isotopic signatures in eggs.

Although females' mating with multiple males is widespread in socially monogamous species, its evolutionary significance is poorly understood. Tests of the hypothesis that socially monogamous females seek extra-pair copulations to increase the heterozygosity of their offspring have produced mixed results. Some of the inconsistency may be the result of technical limitations of the molecular analyses used. In a previous analysis using five microsatellite loci, we showed that in the House Wren (Troglodytes aedon) extra-pair sires had fewer alleles common to the population than did other nearby males that could have sired offspring but did not, suggesting a “rare male” effect (Masters et al. 2003, Proceedings of the Royal Society of London, Series B 270:1393–1397). We repeated the previous analysis, including an additional set of seven microsatellite loci. An analysis that used all 12 loci (both the original and additional loci) produced results suggesting that genotype affects extra-pair paternity. By contrast, an analysis using only the seven new loci alone showed no significant effects. We conclude that studies of this type are likely to be sensitive to the loci employed, particularly when relatively low numbers of loci are analyzed.

Wildfire and conversion of sagebrush (Artemisia spp.) shrublands to cheatgrass (Bromus tectorum) grasslands is a serious threat to the shrubsteppe ecosystem, but few studies have documented wildfire's effects on birds with multiple years of pre-and post-fire data. Using data from avian point counts recorded 4 years before and 7 years after a large-scale, severe wildfire in the Columbia Basin of south-central Washington, we found significant effects of fire on population trends or mean abundance of nearly all species investigated. The Sage Sparrow (Amphispiza belli), a sagebrush obligate, was decreasing at a high rate both pre- and post-fire. Among species inhabiting more open shrubsteppe or grasslands, the mean abundance of three (Grasshopper Sparrow, Ammodramus savannarum; Western Meadowlark, Sturnella neglecta; Vesper Sparrow, Pooecetes gramineus) was lower post-fire and one (Lark Sparrow, Chondestes grammacus) showed an initial, but short-lived, increase post-fire before dropping below pre-fire levels. Only one (Horned Lark, Eremophila alpestris) increased steadily post-fire and had higher post-fire mean abundance.

We examined the utility of the maximum Euclidean distance (MED) method, which was developed for the Common Goldeneye (Bucephala clangula) and is based on egg morphology, to detect parasitism in the Wood Duck (Aix sponsa). We used five polymorphic microsatellite loci to identify parasitized clutches and contributions by multiple females. Three-egg clutches randomly assembled from eggs of one female were less variable than those of three females, indicating that variation within females was less than variation among females. Although variation in egg morphology in parasitized clutches was greater than among eggs laid by one female, extensive overlap in MED values precluded the identification of a clear boundary to distinguish between parasitized and unparasitized clutches. The best MED criterion misclassified 28% of nests. Our results suggest that egg morphology should not be used to detect parasitism in Wood Ducks.

We obtained 1403 base pairs of mtDNA sequences of cyt b and ND2 from four specimens of the Pale-faced Bareeye (Skutchia borbae, representing a monotypic genus of the Thamnophilidae) and evaluated for the first time the species' phylogenetic position among core obligate army-ant-following antbirds. All trees placed Skutchia borbae consistently and with high statistical support as sister to the Black-spotted Bare-eye (Phlegopsis nigromaculata) in a clade with the two known species of Phlegopsis. This result supports the return of S. borbae to the genus Phlegopsis, where it was originally placed. When the plumage characters originally used to diagnose Skutchia are mapped onto the phylogeny, it is evident that they have evolved convergently multiple times in core obligate army-ant-following antbirds. This discovery further supports merging Skutchia with Phlegopsis.

The general relationship between extrapair copulations (EPC) and extrapair paternity (EPP) in wild birds is unclear because relatively few studies have collected both types of information from a single population. I compared observed copulatory behavior with genetic paternity in a population of the American Crow (Corvus brachyrhynchos). For each group of nesting crows, the proportion of extrapair young in a brood was higher when EPC attempts were observed in the group that year. The overall proportion of broods with extrapair young was identical to the proportion of focal group-years in which EPC attempts were observed (32%). In a given brood, however, observed EPC attempts did not always predict EPP, and failure to observe EPCs did not always predict monogamy. Furthermore, males observed attempting EPCs often differed from the males gaining EPP, suggesting that EPCs were attempted by multiple males with certain females in certain years. Observed EPC attempts were initiated by males, and most appeared to be resisted by females.

Earlier initiation of nests by breeding birds may reflect an adaptive response to changes in food availability or warming of spring temperatures, but the consequences of initiating nests too early may be severe, particularly at high elevations. A rare snowstorm in late May 2008 resulted in nest abandonment by 68% of Red-faced Warblers (Cardellina rubrifrons) breeding in a high-elevation riparian ecosystem of southeastern Arizona. In addition, climate data from our study site from 1950 to 2008 revealed higher-than-average springtime temperatures during the past 10 years. If birds respond to this increase in springtime temperatures by nesting earlier their vulnerability to spring snowstorms may increase.

Orientation of the entrances of bird nests may be especially important in grasslands, where protective cover from solar radiation and wind is minimal. We examined orientation patterns of nest-dome entrances in two grassland bird species, the Grasshopper Sparrow (Ammodramus savannarum) and the Eastern Meadowlark (Sturnella magna). We noted how these patterns changed over the nesting season and how they related to prevailing wind direction. We found that Grasshopper Sparrow (n = 333) and Eastern Meadowlark (n = 272) nests were oriented nonrandomly, toward the northeast (ā = 33.4° and 52.9°, respectively). Prevailing wind in the study region was approximately from the south (ā = 171.1°); therefore, nests of the two species were generally oriented downwind. Nest orientation of the Eastern Meadowlark shifted northward as the nesting season progressed, coinciding with a southeastward shift in prevailing wind direction. Conversely, in one year we observed a seasonal shift toward the east in nest orientation of the Grasshopper Sparrow. Nest orientation in these species may represent a trade-off between various factors, including wind and solar radiation.