The San Pedro River in southeastern Arizona is one of the last free-flowing rivers in the southwestern United States that maintains significant stretches of perennial water. While critical for birds, this river is vulnerable to salt cedar (tamarisk, Tamarix spp.) invasion, woody encroachment into grassland, and alteration of hydrologic regime resulting from groundwater pumping. Bird species richness and community composition metrics provide a means to assess effects of management or conservation efforts. To estimate these metrics, we used methods that incorporated species detection probabilities from data collected at 160 points at 23 sites on the San Pedro River during 1998–2001. Species richness, co-occurrence, and uniqueness were estimated as a function of four riparian vegetation types (cottonwood-willow [Populus-Salix], salt cedar, mesquite [Prosopis spp.], and grassland), three hydrologic regimes (perennial, intermittent, and ephemeral), and riparian location (floodplain and terrace). We found significantly higher species richness in cottonwood and mesquite compared with salt cedar and grassland. Intermittent and perennial flow sites had higher species richness compared with ephemeral. Cottonwood and mesquite supported more unique species compared with grassland and salt cedar, and cottonwood or perennial sites supported canopy or water-dependent species, for which habitat is rare on the landscape. Within the intermittent class, salt cedar maintained an estimated 0–2 unique species compared with native woody vegetation types, while cottonwood and mesquite contributed an estimated 20–21 unique species compared with salt cedar. Thus, while maintaining relatively high species richness, salt cedar contributed little to regional avian diversity compared with native woody riparian vegetation. This research has important implications for regional conservation planning and riparian restoration efforts.

High annual variation in grassland bird populations in the Great Plains has often been attributed to changes in moisture levels, but most previous assessments of variation in grassland bird numbers have been of short duration, have occurred during a limited range of moisture levels, have been limited in geographic scope, have considered few species, or have sampled only one or few habitat types. Data from the long-term North American Breeding Bird Survey have the potential to overcome some of these shortcomings. We used linear models and information-theoretic methods to examine associations between moisture levels and populations of 17 species of grassland passerine and two species of wetland passerine in northern North Dakota from 1980 to 2004. We used data from 13 Breeding Bird Survey routes to provide indices of bird abundance and regional dispersion; we used numbers of ponds containing water identified on annual May waterfowl surveys and the Palmer Drought Severity Index (PDSI) as regional moisture indices. Responses varied among species, but the data indicated substantial support for moisture influencing the abundance of 17 of the 19 species we considered. Models including same-year pond numbers generally received more support than models including PDSI data. Dispersion of seven species throughout the study area was influenced by moisture levels, although the response was not as universal and support was not as strong as it was with abundance. Associations between grassland birds and moisture levels suggest the value of regional moisture indices to interpreting studies and surveys of grassland birds in the northern Great Plains.

Urbanization leads to the biotic homogenization of global avifauna. We hypothesized that urbanization acts as a filter on species traits and, therefore, that urban passerines share biological traits explaining their capacity to tolerate urban constraints. We investigated 18 biological traits of passerines related to their general biology, distribution, breeding, and morphometry. In a regional analysis conducted on passerine data from one Swiss and 11 French cities (regional analysis), we identified urban adapters (tolerant species) and urban avoiders (intolerant species), and compared their traits. In a local analysis conducted on passerine data of 13 woodlands located along a short rural-urban gradient, we identified groups of species associated with particular vegetation structures within or particular landscape structures around woodlands. We associated each of these species groups with a tolerance level to urbanization and compared their traits. Regional analysis revealed that urban adapters prefer forest environments, are sedentary, omnivorous, widely distributed, high-nesters with large wingspans. Urban avoiders seem to allocate more energy to reproduction than do urban adapters, to the detriment of adaptation to new environments such as urban areas. Local analysis did not reveal any link between traits and species tolerance levels. At large spatial scales, urbanization seems therefore to act as a filter on species traits. However, the urban constraints that filter species at such large scales do not seem to be the same ones that determine species distribution at local scales. Analyses of traits are powerful tools to understanding regional community composition between urban and rural areas.

I investigated survival, recruitment, and dispersal in the Hawai'i 'Elepaio (Chasiempis sandwichensis sandwichensis), a territorial, nonmigratory monarch flycatcher endemic to the island of Hawai'i. I color-banded and resighted 137 individuals from 1991–2000 and collected longevity data until 2008. The oldest known 'Elepaio was at least 17 years and 10 months old. I used multistate models to examine variation in survival and recruitment, with different states for territory holders and floaters. I classified birds into eight age-sex groups, with individual body size and annual reproduction as covariates. Territory holders of all ages had higher survival than floaters. Survival of territory holders was higher in years with low reproduction and was consistently higher in males (0.87 ± 0.02) than in females (0.81 ± 0.03) due to costs of reproduction. Larger body size was associated with higher survival in males but not in females because males engage in more intense physical competition. Survival and recruitment of floaters were influenced by different factors. Survival of floaters was not related to sex or size and may depend on foraging proficiency and avoiding aggression from dominant adults. Older and larger floaters were more likely to recruit. Natal dispersal distances were short but were longer in males (539 ± 68 m) than in females (357 ± 82 m), and this difference was due to higher survival of adult males. Accurate estimates of survival and recruitment are crucial for understanding population dynamics and designing effective conservation strategies.

We used mark-recapture and information-theoretic model selection methodologies to estimate survival and recapture probabilities for the federally endangered Black-capped Vireo (Vireo atricapilla) at Fort Hood Military Reservation, Texas, during 1997–2006. Adult survival was time-dependent and ranged from 0.36 to 0.60. Although we found no support for sex-specific differences in adult survival, recapture probability was greater for males (0.83) than females (0.58). Adult survival differed among three study areas, which could be indicative of site-specific differences in habitat quality. Survival of juveniles from their hatching year to the following spring was dependent on age at banding. Survival of juveniles banded as nestlings or soon after fledging was low (0.10). The survival estimate for juveniles banded after postfledging independence was substantially higher (0.42). Because juvenile survival is difficult to estimate for passerines, it is often set at an arbitrary value such as one third or half of adult survival. Our survival estimate for juveniles banded after postfledging independence was higher than suggested by either of these commonly used guidelines. We acknowledge that our survival estimates are probably biased low because we could not differentiate between dispersal and mortality. Adoption of a study design that includes core areas where vireos are marked and resighted in subsequent years as well as surrounding resight-only areas would presumably improve survival estimates for both adults and juveniles. More robust estimates of survival could greatly improve population viability analyses for this endangered species.

Despite their likely ecological importance, the basic biology of Cooper's (Accipiter cooperii) and Sharp-shinned (A. striatus) Hawks remains poorly understood. This is particularly true during the winter, when even basic information on the spatial ecology of these species is largely unknown. Thus, we characterized the home range size and habitat chosen by these species as part of a larger study on wintering Accipiter hawks. We also compared our findings of bird feeder use by Cooper's Hawks to our previously published study on Sharp-shinned Hawks. During the winters of 1999–2004, we intensively radio-tracked 21 Sharp-shinned Hawks and six Cooper's Hawks in rural areas, and eight Cooper's Hawks in urban areas. We found that Sharp-shinned Hawks and Cooper's Hawks in rural areas used significantly larger areas than did Cooper's Hawks in urban areas, and that adult hawks generally used smaller areas than immature individuals. Habitat use by Cooper's Hawks and Sharp-shinned Hawks in rural areas was nearly identical and focused mostly on forested and grass habitat types. Cooper's Hawks in urban areas focused disproportionately on grassy areas such as parks in addition to residential areas. All hawks avoided very open areas such as fallow agricultural fields. We observed no systematic use of bird feeders by Cooper's Hawks. In fact, visits by Cooper's Hawks to feeders were not statistically different from that expected by a null model based on random feeder visitations, a result consistent with our work on Sharp-shinned Hawks and the idea of "prey management" by Accipiter hawks.

Environmental light intensity is known to exert a strong influence on antipredation behavior by influencing prey vulnerability. However, an association between low light levels and increased predation risk is not well established empirically. For species that rely on visual detection of their predators, low light levels can hinder predator detection and thus increase predation risk. We examined the foraging behavior of migrating Semipalmated Sandpipers (Calidris pusilla) on a mudflat in the Bay of Fundy in New Brunswick, Canada as a function of time of day from dawn to dusk. Time of day was used as a surrogate for light intensity, assuming that, on average, light levels would be lower near sunrise and sunset. Sandpipers forage both day and night at low tide, which occurs at different times each day, thus disentangling the effect of light intensity from energy levels. Falcons make surprise attacks on sandpipers by leaving forest cover and flying low over the mudflat, rendering detection difficult against the dark forest background. The propensity for sandpipers to leave a foraging patch by taking flight was higher earlier and later in the day, controlling for temperature and sandpiper density. Pecking success was similar whether a focal sandpiper stayed in the current patch or took flight at the end of a focal observation, suggesting that the choice to leave abruptly was not related directly to food availability. We conclude that increased flightiness likely represents a response by sandpipers to a perception of higher predation risk from falcon attacks at low light levels.

Brain-size reduction in domesticated forms of mammals in comparison to their wild ancestors is well documented in numerous species. Although it does not involve intentional artificial selection for traits such as meat production, captive breeding also causes a reduction in brain size in some mammalian species. In birds, domestication results in a reduction in brain size as well, but whether captive breeding causes a similar effect is unknown. Given the increasing number of avian captive breeding programs, it is important to assess whether captive breeding affects the behavior and morphology of a species. Here we investigated whether relative and absolute brain volume differs between wild and captive-bred stocks of 21 species of waterfowl (Anseriformes). Absolute brain volume of captive-bred specimens was lower than in wild specimens for most (16 of 21) of the species examined, and the decrease varied from 1% to 33% (mean: 4.7%). Similarly, all but one species showed relative brain-volume decrease that varied between 2% and 30% (mean: 7.7%). Overall, these reductions in absolute and relative brain volume are smaller than that caused by domestication in ducks (Anas platyrhynchos) and geese (A. anser) but are larger than the decreases observed in captive-bred mammals. Thus, captive breeding appears to result in a decrease in both absolute and relative brain volumes in waterfowl. How this reduction reflects changes in behavior or brain composition is unknown, but it may nevertheless have important implications for the successful reintroduction of captive-bred individuals in the wild.

Past studies of the marine diets of Surf Scoters (Melanitta perspicillata) and White-winged Scoters (M. fusca) have reported that they eat mostly bivalves, but deviations from well-established methods by most studies suggest that the importance of soft-bodied prey has been underestimated for both species. Methods needed to reduce bias in diet estimates include collecting birds that are feeding, immediately preserving gut contents, excluding gizzard contents, averaging food-item percentages across birds versus pooling gut contents for all birds, and using energy or ash-free dry mass versus wet mass values of foods. For Surf Scoters collected in northern Puget Sound, Washington during 2005–2006, adherence to the latter three methods alone resulted in the assessed bivalve component of diet declining by over half and a near doubling of soft-bodied prey (i.e., crustaceans, polychaetes). Diets of Surf Scoters differed among three heavily used bays with distinct benthic habitats, yet 67%–86% of the ash-free dry mass of esophagus contents from each bay was nonbivalve prey. A synthesis of previous and new diet data revealed differences between scoter species: relative to White-winged Scoters, Surf Scoters consume smaller bivalves, a smaller and more variable percentage of mollusk prey (including bivalves and gastropods), and a declining percentage of bivalves as winter progresses. Past diet studies for scoters may provide misleading guidelines to conservation efforts by implying that only standing stocks of bivalves require consideration when prioritizing critical foraging sites.

Understanding the patterns, extent, and phenology of migration is important for estimating potential influences of habitat or climate changes on populations of migratory birds. We used satellite telemetry of >100 individual King Eiders (Somateria spectabilis) tagged in northwestern North America in 2002–2006 to describe the timing and extent of their migration and winter movements in the Bering Sea. We found high variability in timing of migration events and distances flown. Arrival on breeding grounds and onset of molt migration were the least variable events in duration. Fall migration was extremely variable, ranging from less than a week to several months. More than a third of King Eiders did not migrate after wing molt and wintered on or near wing-molting areas. We found diffuse migratory connectivity between breeding and wintering areas, and low intrayear fidelity to 25 km radius wintering sites. More than half of the King Eiders used several wintering sites in a given year, and their winter ranges were considerably larger than those of other sea duck species. We identified three distinct wintering regions in the Bering Sea that were several hundred km apart, among which no movements occurred from late December until April. The onset of spring migration was earlier for birds wintering farther south, but arrival time on breeding grounds was not correlated with wintering latitude. We conclude that high phenotypic plasticity in migratory traits may render King Eiders more likely to respond to environmental shifts than sea duck species that show stronger migratory connectivity.

We examined the marine distribution and behavior of newly fledged juvenile (hatching year; HY) and adult (after hatching year; AHY) Marbled Murrelets (Brachyramphus marmoratus) off southwest Vancouver Island, British Columbia, to test whether assumptions associated with estimating productivity are met in this area. Productivity estimates for murrelets use HY:AHY ratios from marine surveys, which assume limited emigration and that juvenile and adult birds are similarly distributed. We examined observations from June–August, 1994–2005. Behavioral data were collected from land-based surveys via instantaneous scan sampling. Locations of murrelets at sea were mapped from cliff-top vantage points using a theodolite; Geographic Information Systems (GIS) was then used to compare the distances from shore of juveniles and adults. Data from boat surveys were analyzed using GIS kernel density analysis to compare adult and juvenile murrelet distributions at sea. At fine scales (1–100 m), juveniles were associated with adults; however, they were found significantly closer to shore than adults. At coarse scales (1–10 km), juvenile and adult distribution overlapped on a daily basis but showed less overlap with annually averaged distributions. Juveniles typically were solitary foragers, whereas adults often foraged in pairs or larger groups. Our results indicate that monitoring HY:AHY ratios using boat transects off southwest Vancouver Island as an indicator of breeding success need not take into account possible "nursery areas," although the proximity of juveniles to the shoreline means that monitoring must consistently include waters closest to the shore. Sequential ratios should be used to account for emigration of adults due to postbreeding dispersal.

Changes in capelin (Mallotus villosus) biology since the 1990s have directly or indirectly induced variable breeding conditions for many seabirds in the Northwest Atlantic. Time budgets of the same individual Common Murres (Uria aalge) were examined in relation to annual variations in the arrival of inshore spawning capelin during three consecutive chick-rearing periods (1998–2000) on Great Island in the Witless Bay Ecological Reserve, Newfoundland, Canada. Despite high foraging effort (longer provisioning trips, lower co-attendance time, and faster colony departure after a brooding bout), chick-feeding rates were low during early chick rearing in 2000 due to a mismatch between early egg hatching and the later inshore arrival of spawning capelin. Time budgets of murres breeding on Great Island were examined in relation to those of murres in other nearby colonies and to long-term changes in capelin spawning behavior across decades (1982–1985 versus 1998–2000). Recent overall provisioning rates on Great Island were comparable to those of other nearby colonies during the same time period (with the exception of Funk Island) and to those reported during the 1980s. However, murres breeding in recent years in the reserve exhibited higher foraging effort, which is likely linked to recent changes in the availability of capelin as a result of later spawning, changes in capelin distribution, and their overall smaller size. Murres currently may be constrained to timing their egg laying such that hatching coincides with the arrival of inshore capelin rather than peak capelin abundance and, thus, are vulnerable to sudden changes in the ecosystem.

To assess potential changes in tundra-nesting bird populations relative to increased herbivory by growing Lesser Snow Goose (Chen caerulescens caerulescens) and Ross's Goose (C. rossii) populations, we estimated avian population densities in coastal tundra near Cape Churchill, Manitoba, Canada in June 1984, 1999, and 2000. We also compared bird abundance in altered and intact freshwater sedge (Carex spp.) meadows to assess bird response at a smaller spatial scale, the habitat patch. At the landscape scale, Herring Gull (Larus argentatus) densities were significantly greater in both 1999 and 2000 than 1984, and Semipalmated Sandpiper (Calidris pusilla) and Savannah Sparrow (Passerculus sandwichensis) densities were greater in 2000 than 1984. As a group, tundra-nesting passerine densities were significantly greater in 1999 than 1984. Dunlin (Calidris alpina) densities were significantly lower in 1999 than 1984, and many larger, ground-nesting birds declined in abundance and occurrence along transects in later years. At the smaller spatial scale, passerines and shorebirds were less abundant in altered than intact freshwater sedge meadows. Our results indicate that most abundant breeding birds on the study area did not exhibit lower densities in later years despite increased effects of goose herbivory on vegetation. At the habitat patch scale, the same groups of species had lower abundances in altered versus largely intact habitats. Although goose herbivory can alter tundra vegetation and lead to lower abundance of several bird species, habitat alteration may have to be widespread and severe to elicit population declines over a large area.

We contrast patterns of variation in morphological traits of migratory and sedentary forms of the Yellow-rumped Warbler (Dendroica coronata) to test functional predictions regarding the evolution of traits related to flight. Sedentary individuals are larger than migrants in all traits except bill width and depth. However, when traits are adjusted for body size differences using multivariate approaches, migrants have longer and more concave wings than do individuals from sedentary populations, suggesting selection for high–aspect ratio wings for fast, sustained flight. Subadults have relatively shorter and rounder wings than do adults of all subspecies except for the long-distance migrant D. c. coronata, and age-related differences are most pronounced in short-distance migrants. We propose a graphic model for the evolution of age-related differences in wing shape that is based on the role of antagonistic selective pressures imposed by migratory flight vs. maneuverability. Size-adjusted differences in tail length are not significant. Longer culmens and tarsi in the sedentary D. c. goldmani subspecies of Guatemala suggest differences in diet and foraging behavior compared to migratory groups. Our results strongly suggest that divergent natural selection has caused the morphological differentiation between migratory and sedentary subspecies.

We examined patterns of nest site occupancy in male House Sparrows (Passer domesticus) to determine if the factors influencing nest site ownership are associated with a putative signal of resource-holding potential. No other study of House Sparrows has examined the correlates of nest site occupancy, despite their importance for understanding how the size of the bib (the patch of black feathers on throat and chest) might influence nest defense. We found that older males and males hatched on our study site were more likely than younger and immigrant males to occupy nest sites. Prior residency (the number of years a male had previously occupied a site) and not age had the greatest influence upon nest site retention between seasons. We found no influence of body size or the area of the bib on the probability of obtaining a nest site. Males hatched on the study site did not differ in bib size from males presumed to have immigrated from elsewhere. Bib size of individual males increased with age, but not years of prior residency. Males that consistently defended a nest site increased in bib size between years, whereas males that consistently failed to defend a nest site decreased in bib size. Bib size also tended to decrease in males that lost a nest site between seasons and increase in males that gained a nest site. Bib size thus may signal age and some types of experience in nest defense, although the details of its role in influencing contests over nest sites remain unclear.

Passerine birds are commonly the subjects of studies of sexual size dimorphism. Yet, save for secondary sexual characters, passerine sexual dimorphism is commonly treated as a mere size difference without regard to its shape distribution. Using principal components analysis (PCA) to generate estimates of relative size and reduced major axis (RMA) regression to test for isometry, I analyzed 19 skeletal measurements from 31 socially monogamous passerines of 15 genera. Dimorphism does not scale isometrically within the skeleton. Most sexual size dimorphism resides in the pectoral girdle and wing in the Savannah Sparrow (Passerculus sandwichensis), in the wood-warbler genus Dendroica, in the wood-warbler family (Parulidae), and in a selection of six passerine families. These results suggest that comparisons that include both sexes but that rely on a single measurement in order to "correct for body size" (commonly the tarsus) are unlikely to be reliable.

Song Sparrows (Melospiza melodia) provide one of North America's best examples of geographic variation in phenotype, with approximately 26 described subspecies recognized. However, researchers have found inconsistent signals when making comparisons between subspecies and genetic markers. We examined seven microsatellite loci from 576 Song Sparrows of 23 western North American populations representing 13 recognized subspecies. We assessed the level of concordance between microsatellite genotypes and subspecies. We found that in some, but not all, instances neutral genetic structure corresponded to recognized phenotypic structure. However, some populations not currently recognized as subspecies were found to be genetically differentiated from all other populations that are considered to be the same subspecies. We suggest that a combination of phenotypic characters, behavioral traits, and multiple loci be used when assessing geographic variation in birds, and that sampling should be conducted in more than one location within broadly distributed subspecies.

We investigate the effects of body mass and breeding habitat use on the timing and location of the fall molt of western Neotropical migrant passerines. Most western migrants that molt within their breeding ranges breed in coniferous forests, while most that move south before molting breed in low elevation broadleaf or open habitats. We show that larger passerines take longer to molt than smaller passerines and that larger species are more likely to migrate south before molting, whereas smaller species are more likely to molt in their breeding ranges, presumably because their molts take less time. To test our habitat results, we surveyed Cassin's Vireos (Vireo cassinii) during their breeding and molting season in Washington to assess up-slope movements. Vireos that bred in low elevation coniferous forest (usually ponderosa pine [Pinus ponderosa] or Douglas-fir [Pseudotsuga menziesii]) moved up-slope at least 300 m to molt in wetter, high-elevation Douglas-fir forests.

We estimated the population size of McKay's Buntings (Plectrophenax hyperboreus) from surveys across their restricted breeding range on St. Matthew and Hall Islands, Alaska (326 km²). We used a multimodel approach to (1) estimate population size from counts with distance sampling, and (2) account for the effects of observers, habitat, flock size, and date on detectability. We counted 2400 buntings along 202 km of transects; most birds were in tundra (44%) or rocky uplands (46%). Breeding density was higher on Hall Island (154 ± 20 [SE] birds km⁻²) than St. Matthew Island (93 ± 7 birds km⁻²), possibly due to differences in habitat. Population size was 31 200 ± 2000 birds (CI_95% = 27 500–35 400 birds), 5–11 times greater than previously reported, but still small among North American passerines. Populations of this species should therefore be closely monitored and the focus of conservation.

Once one of the most common species seen at bird feeding stations across much of North America in winter, the Evening Grosbeak (Coccothraustes vespertinus), appears to be experiencing a population decline. Like other finches associated with the boreal forest or high elevations, Evening Grosbeaks form flocks in winter, often irrupting out of their breeding range and frequenting supplemental feeding stations where populations may be monitored. We sought to quantify the extent of changes in the abundance and distribution of Evening Grosbeak populations using data gathered in winter by Project FeederWatch, a continent-wide monitoring program that began in 1987. FeederWatch data gathered between 1988 and 2006 indicated a significant surveywide decline in the mean flock size recorded over time. The proportion of sites reporting Evening Grosbeaks plummeted by 50% in 18 years. At locations where the species continued to be seen, mean flock size declined by 27%. Similarly, analysis of data from 391 sites reporting data for at least 10 consecutive years indicated significant declines in Evening Grosbeak abundance at 76 sites and increases at no sites. Although the Evening Grosbeak has experienced dramatic rangewide population declines in recent years, the mechanisms contributing to these changes remain unclear. Given the geographic extent and rapid rate of observed population changes, urgent investigation of the mechanisms driving these declines is warranted.

Double brooding is the initiation of a second clutch of eggs after successfully raising young from the first clutch. Migratory birds that nest in temperate North America are often single-brooded, but there is widespread intra- and interspecific variation. Tree Swallows (Tachycineta bicolor), which are becoming a model species in biology, are typically classified as a single-brooded species. We documented 18 cases of double brooding in a population of Tree Swallows recently established in the Shenandoah Valley, Virginia. Double brooding may be underreported in this species or may be increasing as a result of climate change or range expansion. If double brooding is as common elsewhere as it was in our study population, it could significantly alter estimates of seasonal or lifetime reproductive success in this widely studied bird.

Birds in which both sexes produce complex song are more common in the tropics than in the temperate north, where typically only males sing. Yet surprisingly little is known about female song characteristics in most tropical species. Here we present a comparison of female and male singing behaviors in the Streak-backed Oriole (Icterus pustulatus), a tropical songbird in which both sexes perform solo songs. Females sing much more frequently than males and produce songs with similar acoustic complexity. Rates of singing by both sexes were higher during breeding than postbreeding while the rates of most other vocalizations did not change, suggesting that song plays an important role in breeding. To our knowledge, this is the first reported species in which females regularly sing at higher rates than males; however, few studies have examined female song in other sexually monomorphic or weakly dimorphic species, so such patterns might not be unique.

We tested how food supplementation affects extraterritorial behavior in the socially monogamous Northern Cardinal (Cardinalis cardinalis). Assuming extraterritorial movements are energetically costly, we predicted that if these movements function for gaining extra-pair matings, females on supplemented territories would spend more time off territory, make more extraterritorial forays, and have larger home ranges in relation to territory size than those on unsupplemented territories. If extraterritorial movements function for foraging purposes, then supplemented females should spend less time off territory, make fewer forays, and have smaller home ranges than unsupplemented females as a result of plentiful food on their home territories. We radio-tracked seven females during their fertile periods and found a trend for supplemented females to make more extraterritorial forays and spend more time off territory than unsupplemented females; however, there was no significant difference in home range sizes between treatment groups. Our findings provide some support for the extra-pair copulation function of extraterritorial movements in female Northern Cardinals.