We investigated the departure, transient movement, and local settlement stages of natal dispersal in a population of Northern Goshawks (Accipiter gentilis) on the Kaibab Plateau of northern Arizona. The study included 614 color-banded juveniles produced at 555 nests during 1991–2003, 89 of which were radio-marked during 1998–2001. Radio-marked juveniles initiated dispersal between 71 and 103 days posthatching, and spent between 33 and 66 days in the natal territory after fledging. Our best-fitting proportional hazards models predicted the timing of dispersal as a function of annual differences in the density of primary bird and mammal prey species, weather conditions, and natal brood size. Once dispersal was initiated, most juveniles moved into the more open habitats that surrounded the study area and few eventually returned to breed; first-year fidelity to the local natal population was 28%, and only 69 (11%) color-banded juveniles had entered the territorial population by 2004. Median natal dispersal distance on the Kaibab Plateau was 15.0 km (range  =  0.1–58.1 km), a distance equivalent to about four times the diameter of an average breeding territory (3.8 km). Local settlement behavior of Northern Goshawks appeared to be driven by a combination of intraspecific competition for a limited number of breeding opportunities and inbreeding avoidance. However, much of the natal dispersal process operated at broad spatial scales beyond our study population, indicating a potentially high level of demographic connectivity among naturally fragmented breeding populations in the American Southwest.

We used occupancy and productivity data collected at 67 cliffs used for nesting from 1972 to 1999 to assess patterns of distribution and nest-site selection in an increasing population of Peregrine Falcons (Falco peregrinus) in central West Greenland. Peregrine Falcons breeding at traditionally occupied cliffs used for nesting had significantly lower variation in productivity and thus these cliffs were better quality sites. This indicates that Peregrine Falcons occupied cliffs according to a pattern of despotic distribution. Falcons breeding at cliffs that were consistently occupied during the breeding season had higher average productivity and lower variation in productivity than falcons at inconsistently occupied cliffs, and thus consistent occupancy also was indicative of cliff quality. Features of high quality habitat included tall cliffs, greater change in elevation from the lowest point within 3 km of the cliff to the cliff top (elevation gain), and protection from weather on the eyrie ledge. Spacing of suitable and occupied cliffs also was an important feature, and the best cliffs generally were more isolated. Increased spacing was likely a mechanism for reducing intraspecific competition. Our results suggest that Peregrine Falcons use a resource defense strategy to compete for better quality habitats and may use spacing and physical features of a nest site to identify good quality breeding habitat.

Burrowing Owl (Athene cunicularia) populations have declined extensively throughout much of North America, and modeling demography may assist conservation. However, few studies have estimated adult survival, and fewer still have determined juvenile survival. In 2003 and 2004 we monitored survival of 40 radio-tagged juveniles during the postfledging period in the Little Missouri National Grassland, North Dakota, where owls nested in black-tailed prairie dog (Cynomys ludovicianus) colonies. Survival averaged 0.57 (95% CI: 0.41–0.73) prior to autumn migration. Mortality was highest during the first two weeks after nest departure when juveniles were flightless, and two to three weeks later when juveniles became independent. Predation or starvation was implicated in most deaths. Distribution and abundance of escape cover (number of prairie dog burrows within 30 m of nests and size of the natal prairie dog colony) did not affect survival. Body condition and brood size at the time of radio-tagging also did not influence survival. Juvenile owls exhibited nest-centered dispersal, and averaged 108 ± 21 (SE) m and 82 ± 17 m from nests at initiation of migration in 2003 and 2004, respectively. Mean dates of departure from the study area were 2 September (± 3 days) 2003 and 24 August (± 2 days) 2004. Mortality during the postfledging period accounted for approximately two-thirds of mortality in the first year of life.

We present an enhancement of a simulation model to predict annual productivity for Wood Thrushes (Hylocichla mustelina) and American Redstarts (Setophaga ruticilla); the model includes effects of Brown-headed Cowbird (Molothrus ater) parasitism. We used species-specific data from the Driftless Area Ecoregion of Wisconsin, Minnesota, and Iowa to parameterize the model as a case study. The simulation model predicted annual productivity of 2.03 ± 1.60 SD for Wood Thrushes and 1.56 ± 1.31 SD for American Redstarts. Our sensitivity analysis showed that high parasitism lowered Wood Thrush annual productivity more than American Redstart productivity, even though parasitism affected individual nests of redstarts more severely. Annual productivity predictions are valuable for habitat managers, but productivity is not easily obtained from field studies. Our model provides a useful means of integrating complex life history parameters to predict productivity for songbirds that experience nest parasitism.

Survival and reproduction directly affect population growth rate (λ), making λ a fundamental parameter for assessing habitat quality. We used field data, literature review, and a computer simulation to predict annual productivity and λ for several species of landbirds breeding in floodplain and upland forests in the Midwestern United States. We monitored 1735 nests of 27 species; 760 nests were in the uplands and 975 were in the floodplain. Each type of forest habitat (upland and floodplain) was a source habitat for some species. Despite a relatively low proportion of regional forest cover, the majority of species had stable or increasing populations in all or some habitats, including six species of conservation concern. In our search for a simple analog for λ, we found that only adult apparent survival, juvenile survival, and annual productivity were correlated with λ; daily nest survival and relative abundance estimated from point counts were not. Survival and annual productivity are among the most costly demographic parameters to measure and there does not seem to be a low-cost alternative. In addition, our literature search revealed that the demographic parameters needed to model annual productivity and λ were unavailable for several species. More collective effort across North America is needed to fill the gaps in our knowledge of demographic parameters necessary to model both annual productivity and λ. Managers can use habitat-specific predictions of annual productivity to compare habitat quality among species and habitats for purposes of evaluating management plans.

Recent studies have shown that Warbling Vireos (Vireo gilvus) are declining in California and that these trends are due to low reproductive success. Brood parasitism by Brown-headed Cowbirds (Molothrus ater) has been implicated in the low productivity. I explored two hypotheses related to population dynamics of Warbling Vireos along an elevational gradient: (1) potential source populations exist at high elevations where cowbirds are rare, and (2) potential source populations occur in the center of the elevational distribution with less productive populations at upper and lower elevations. From 1985 through 2002 I studied the abundance and productivity of Warbling Vireos over an elevational gradient in the southern Sierra Nevada. Warbling Vireos were most abundant in mid elevation mixed conifer sites, less abundant in lower elevation ponderosa pine sites and upper elevation true fir sites, and rare in upper elevation lodgepole pine sites. Likewise, daily survival rates of nests were highest at mid elevations (1800 m) and gradually decreased at both higher and lower elevations. Compared to other populations studied in California, nest success in mixed conifer habitat was high (60%, n  =  58). Although rates of brood parasitism were high enough to be of concern in low-elevation ponderosa pine forests, cowbird parasitism was not observed in mid- to upper-elevation forests. Warbling Vireos were most productive where they were most abundant. The hypothesis that potential source populations exist at upper elevations did not appear to hold at the upper bounds of the elevational distribution. The results of this study provide support for the hypothesis that potential source populations occur in the center of the elevational distribution, with less productive populations at both lower and higher elevations.

In many duet-singing songbirds, paired birds combine their song types nonrandomly to form duet songs. Several different behavioral mechanisms could generate nonrandom song type associations in duets. I tested female Black-bellied Wrens (Thryothorus fasciatoventris) for one such mechanism: adherence to a set of rules linking female response songs to male stimulus songs. I call this set of rules a “duet code.” Duets of free-living Black-bellied Wrens were recorded in 2001 and 2002. In 2003 I returned to the same territories and played the male song types from the recorded duets. Females answered male song stimuli as if duetting with the playback speaker. Although the known repertoires of females averaged 8.4 song types, each female sang only a single song type in response to each male song type. Random answering could not account for this pattern, supporting the hypothesis that females abide by duet codes. Females that were still paired with their mates from 2001–2002 answered 100% of their mate's songs with the same song types they had used previously, demonstrating that codes are stable over time. In contrast, females that were new to a territory answered an average of only 18% of their mate's song types with the same song type as the previous female, indicating that duet codes are individually distinctive. Duet participation by female Black-bellied Wrens represents a special kind of animal communication, in which discrete vocal signals consistently elicit discrete vocal responses according to an individually distinctive set of rules.

Hermit Warblers (Dendroica occidentalis) sing distinct dialects of type I songs, the most common song before pairing. Eight dialects were identified and described in a 22 900 km² area in southwestern Oregon and northern California. The dialects were well defined geographically with contact areas between dialects seldom extending more than 6 km. Gaps in forested habitat of ≥10 km separated several dialects, but within forested areas dialect boundaries did not conform to obvious habitat, elevation, or geographic boundaries. Few songs containing syllables or phrases from more than one dialect were identified, and birds incorporating elements from two different dialects inhabited areas close to the common boundary between the two. Multivariate analysis showed that birds in neighboring areas had dialects most similar in structure, but a more complex history of dialect development or origin is suggested in other areas.

Foraging strategies of nonbreeding seabirds attending colonies remain virtually unknown. Here we report the results of a satellite telemetry study of nonbreeding Buller's Albatrosses (Thalassarche bulleri) from the Snares island group south of New Zealand in 2000–2001. Two 6- to 7-year-old prebreeding birds dispersed to Tasmania, Australia, from late May until at least late July. Six older birds (five prebreeding birds, one former breeding adult) all adopted a dual strategy of short trips (mean duration 1.3 days, mean foraging range 129 km) and long trips to southern New Zealand (9.6 days, 871 km) or Tasmania (22.0 days, 1918 km). Time allocation to short trips increased with age and experience (both sexes) and nest-site attendance (males), and decreased during the guard (when the chick is attended) and late postguard (chick left unattended) stages (females). Up to the guard stage, most birds present at their colony on consecutive days foraged overnight (mean foraging range 101 km). Nonbreeding birds used the same foraging areas as breeding adults, but allocated more foraging time to short trips during the corresponding incubation period and early postguard stage, and to long trips during the guard stage. Results suggest that prebreeding birds explore foraging areas sequentially, and increase their time ashore by progressing from making only long trips, to introducing short overnight trips, to modifying the duration of and allocation between long and short trips. Changes in body mass recorded on Solander Island (160 km north of the Snares) show that experienced nonbreeding birds initiate long foraging trips to regain mass lost during short trips, and suggest that less frequent short trips (and hence fewer returns ashore) among inexperienced birds are related to less efficient foraging during long trips.

We used pellets and prey dropped near nests to study the diet and feeding ecology of Little Tern (Sterna albifrons) adults and chicks in northern and southern Portugal during 2000–2004. We compared diets among study areas, years, and birds breeding in two main habitat types: sandy beaches and salinas (man-made salt-pans). We also sampled prey fish in one study area and used published data from another area to examine whether the diet of Little Tern adults and chicks corresponded with the abundance of prey found in primary foraging habitats. Adult Little Terns fed mainly on sand-smelts (Atherina spp.) and gobies (Pomatoschistus spp.), which were the most abundant fish species in our estuarine and lagoon study areas. Despite some differences among colonies we did not find clear differences in adult diets among study areas and habitat types. Little Tern chicks also ate primarily Atherina spp., but their diet was more diverse than that of the adults, and characterized by a significantly higher proportion of prey with a high energetic value such as sardines (Sardina pilchardus), garfish (Belone belone), and killifish (Fundulus spp.). Chick diets differed significantly between habitat types, which may be a consequence of the limited foraging range of adult breeding birds. Both adult and chick diets matched the abundance of the main prey in our study areas, confirming the opportunistic foraging character of this species. We suggest that annual variation in prey availability may be the most important factor explaining annual variation in adult diets.

We assessed dietary preference of 14 captive Blue Jays (Cyanocitta cristata) for different food types under different conditions of availability. In four separate feeding trials, we provisioned jays with the following: Trial 1, two nuts each of white oak (Quercus alba), pin oak (Q. palustris), black oak (Q. velutina), northern red oak (Q. rubra), and shagbark hickory (Carya ovata); Trial 2, two small and two large red oak acorns; Trial 3, two germinating and two nongerminating white oak acorns; and Trial 4, one large red oak acorn, one large white oak acorn, and one shagbark hickory nut. We used discrete choice models to describe selection under conditions of changing choice sets. Blue Jays displayed a clear preference for pin oak and strong avoidance of red oak acorns when alternative foods were available. White oak and black oak acorns were selected intermediately. Shagbark hickory nuts were never used. Correlation coefficients suggested that preference was inversely related to seed size and the proportion of seed consisting of hard seed coat. In the absence of alternative food items, small red oak acorns were readily taken, whereas large red oak acorns were mostly avoided but still used by some birds. These results highlight the importance of considering food availability when making conclusions about preference, and lend support to the hypothesis that Blue Jays can be important dispersers of even less-preferred oak species. We discuss the potential as well as the limitations for Blue Jays to act as seed dispersers, with respect to postglacial range expansion of fagaceous tree species, and in the context of present-day dispersal in regions where forests are highly fragmented.

Migratory birds are exposed to a diverse pathogen fauna by virtue of their long-distance travels. Although the immune system is an organism's primary defense against pathogenic microorganisms, few studies have investigated avian immune function during migration, much less shown seasonal differences in immune function. We describe the immunological condition of three intercontinental migratory species, Swainson's Thrush (Catharus ustulatus), Veery (C. fuscescens), and Wood Thrush (Hylocichla mustelina) during spring migration. In addition, we compare their immunological condition with conspecifics captured during fall migration and during the breeding season to provide a frame of reference for the spring immunological data. Measures of immunological condition presented include total leukocyte count, heterophil:lymphocyte (H:L) ratio, heterophil and lymphocyte counts, hematocrit, and IgG titers. In addition, we assessed each bird's energetic condition by measuring body mass and calculating a size-corrected condition index. Migrating birds had lower leukocyte and lymphocyte counts, lower hematocrit, reduced fat stores, and higher H:L ratios relative to nonmigrating individuals sampled during the breeding season. We also found that birds sampled during spring migration had lower lymphocyte counts and reduced fat stores, and higher heterophil counts and H:L ratios than fall migrants. Our results suggest that migrating birds are immunocompromised compared with conspecifics during the breeding season. Furthermore, compared with conspecifics sampled after a shorter overland flight, migrants sampled after crossing the Gulf of Mexico exhibited higher H:L ratios, which is indicative of heightened energetic stress.

We performed a two-year study of extra-pair paternity in the House Sparrow (Passer domesticus) to test a suite of hypotheses relating to ecological factors associated with breeding conditions and parental phenotypes and genotypes. Extra-pair fertilizations (EPFs) accounted for 45 of 419 (11%) nestlings and occurred in 33 of 126 (26%) broods. EPFs were not correlated with breeding synchrony or breeding density, although they were significantly more common toward the end of each breeding season. Body size and the size of the bib, a secondary sexual character, were no different between males that were cuckolded and those that achieved full paternity in their nests. Older males were cuckolded as frequently as yearlings, and there was no difference between males that were cuckolded and those that were not with regard to two measures of individual genetic diversity. There was no evidence that females sought EPFs to avoid inbreeding, since EPFs were equally likely to be present among pairs that were closely related and those that were only distantly related, and females were equally related to their extra-pair mates as they were to their within-pair mates. Furthermore, extra-pair sires did not possess alleles that were rare in the population. In sum, despite a substantial sample size, we found few correlates of extra-pair paternity in House Sparrows.

Although Old World buntings (Emberizinae) may be considered suitable Common Cuckoo (Cuculus canorus) hosts, there is at present no evidence that any of the European species are regularly parasitized. Most historical parasitism records refer to the Yellowhammer (Emberiza citrinella) and Reed Bunting (E. schoeniclus). Both of these species reject almost 100% of experimentally added nonmimetic eggs, and also a considerable proportion of experimentally added conspecific eggs, showing exquisite egg discrimination abilities. In this paper, we report Common Cuckoo parasitism and egg rejection behavior in a Bulgarian population of another Old World Emberizinae, the Corn Bunting (Miliaria calandra). We found this species was regularly parasitized (9%, 8 of 90 nests) and that the parasitism rate was consistent among the three years of our study. Naturally laid Common Cuckoo eggs were fairly good mimics of host eggs and most were accepted (5 of 7). The Corn Bunting proved to be a suitable Common Cuckoo host as we recorded a successfully fledged cuckoo chick. Unlike Yellowhammers and Reed Buntings, Corn Buntings rejected only 42% (16 of 38) of experimentally introduced nonmimetic model Common Cuckoo eggs and none of the experimentally introduced conspecific eggs (n  =  13). Parasitized nests had more and higher trees in the vicinity than unparasitized nests and breeding habitat characteristics may explain the difference in egg discrimination abilities between Corn Buntings and other Old World Emberizinae.

Monitoring populations of auklets and other crevice-nesting seabirds remains problematic, although numerous methods have been attempted since the mid-1960s. Anecdotal evidence suggests several large auklet colonies have recently decreased in both abundance and extent, concurrently with vegetation encroachment and succession. Quantifying changes in the geographical extent of auklet colonies may be a useful alternative to monitoring population size directly. We propose a standardized method for colony mapping using a randomized systematic grid survey with two components: a simple presence/absence survey and an auklet evidence density survey. A quantitative auklet evidence density index was derived from the frequency of droppings and feathers. This new method was used to map the colony on St. George Island in the southeastern Bering Sea and results were compared to previous colony mapping efforts. Auklet presence was detected in 62 of 201 grid cells (each grid cell  =  2500 m²) by sampling a randomly placed 16 m² plot in each cell; estimated colony area  =  155 000 m². The auklet evidence density index varied by two orders of magnitude across the colony and was strongly correlated with means of replicated counts of birds socializing on the colony surface. Quantitatively mapping all large auklet colonies is logistically feasible using this method and would provide an important baseline for monitoring colony status. Regularly monitoring select colonies using this method may be the best means of detecting changes in distribution and population size of crevice-nesting seabirds.

To assess the extent of West Nile virus (WNV) exposure of migrating (Marin Headlands) and wintering (Central Valley) hawks in California, plasma from 271 Red-tailed Hawks (Buteo jamaicensis), 19 Red-shouldered Hawks (B. lineatus), and 30 Cooper's Hawks (Accipiter cooperii) was tested for WNV antibodies during the winter of 2004–2005. WNV antibodies were found in 5% of migrating and 15% of wintering Red-tailed Hawks, 20% of migrating and 58% of wintering Red-shouldered Hawks, and 13% of migrating Cooper's Hawks. No individuals demonstrated visible signs of WNV illness. Red-tailed Hawks that tested positive for WNV antibodies displayed no difference from Red-tailed Hawks without WNV antibodies in weight to wing chord ratio or white blood cell counts. In the Central Valley, WNV antibodies were significantly more prevalent in Red-shouldered Hawks than in Red-tailed Hawks. Significantly more Red-tailed Hawks sampled on wintering grounds tested positive for WNV antibodies than Red-tailed Hawks sampled during migration.

We used four variable microsatellite loci to examine the distribution of genetic variation and degree of genetic structuring among three subcolonies of Waved Albatrosses (Phoebastria irrorata). The breeding population of this species is almost entirely limited to the island of Española in the Galápagos Archipelago. Such strong philopatry could lead to population genetic structure among subcolonies on the island. Pairwise values of the F_ST analog, θ, calculated from microsatellite genotypes, were all less than 0.012, indicating little genetic differentiation and the presence of gene flow throughout the population.

We present data suggesting that Northern Wheatears (Oenanthe oenanthe leucorhoa) breeding in West Greenland and Canada may be able to accomplish migration to their wintering grounds in West Africa in one direct, transatlantic crossing of more than 4000 km (great circle distance). This conclusion is based on analyses of wing lengths, body weights, and timing of departure from West Greenland and arrival on an island 350 km off the coast of Morocco. Previously, it has been suggested that Nearctic wheatears migrate to Africa by a two-step journey, the first leg comprising a shorter transatlantic crossing to western Europe. A long, direct flight has previously been considered unfeasible as the predicted flight costs were considered to be too high. However, recent insights in aerodynamic theory make these long ocean crossings appear more feasible, especially when taking the use of tailwinds into account.

Conspecific brood parasitism occurs in many songbird species but has not been reported in Song Sparrows (Melospiza melodia). In three separate study areas where breeding Song Sparrows experience heavy nest predation pressure and Brown-headed Cowbird (Molothrus ater) parasitism, we observed six instances in which newly laid eggs were attributable to female Song Sparrows other than the nest owners. We also recorded the ejection of a sparrow egg from each of two videotaped nests. In a fourth study area without cowbird parasitism, genetic analysis of parentage revealed no conspecific brood parasitism. Given that egg ejection can accompany conspecific parasitism in Song Sparrows, we suggest that daily nest checks are insufficient to document the frequency of this tactic in some species in the absence of egg marking, videotaping, or genetic analyses. Since standard nest monitoring techniques may fail to detect conspecific brood parasitism, this behavior could be more prevalent than currently thought.

Birds have become increasingly prominent in studies focusing on natural populations and their coevolved pathogens or examining populations under environmental stress from novel and emerging infectious diseases. For either type of study, new DNA-based diagnostic tests, using the polymerase chain reaction (PCR), present challenges in detecting the DNA of pathogens, which exist in low copy number compared with DNA of the host. One example comes from studies of avian malaria: conflicting claims are made by different laboratories about the accuracy of tests using various sets of primers and reagents, especially in relation to blood smears and immunological methods. There is little standardization of protocol or performance among laboratories conducting tests, in contrast to studies of human malaria. This review compares the problems of detecting avian malaria with those of detecting human malaria, and shows definitively that the buffer used to store blood samples following collection is associated with the accuracy of the test. Lower accuracy is associated with use of a lysis buffer, which apparently degrades the DNA in the blood sample and contributes to inhibition of PCR reactions. DNA extraction and purification techniques, and optimization of the PCR reaction, do not appear to be alternative explanations for the effect of storage buffer. Nevertheless, the purest DNA in standard concentrations for PCR is required so that different primers, DNA polymerases, and diagnostic tests can be objectively compared.

Iverson et al. (2004) used estimates of the homing rate for molting adult Harlequin Ducks (Histrionicus histrionicus) in Alaska to draw inferences about population structure. Homing rates, defined as one minus the ratio of birds recaptured elsewhere to those recaptured at the original banding site, were high (0.95–1.00) for males and females. Iverson et al. (2004) concluded that these high rates of homing are indicative of demographic independence among molting groups separated by small distances (tens to hundreds of kilometers) and that conservation efforts should recognize this fine-scale population structure. We re-examined their use of the homing rate, because their assumption of equal detection probability across a wide sampling area could have led to an upward bias in their estimates of site fidelity. As a result, we are hesitant to agree with their conclusion of high adult homing to molting areas and that molt-site fidelity is evidence for demographic independence. Our hesitancy stems from the fact that little is known about juvenile and adult movements within and among years, breeding area origins, and the variation of demographic parameters (e.g., survival and productivity) among molting groups. Furthermore, population genetic data of these molting groups suggest gene flow at both nuclear and mitochondrial loci. Such mixed messages between demographic (i.e., banding) and genetic data are increasingly common in ornithological studies and offer unique opportunities to reassess predictions and make more robust inferences about population structure across broad temporal and spatial scales. Thus, we stress that it is this broader scale perspective, which combines both demography and genetics, that biologists should seek to quantify and conservation efforts should seek to recognize.

In a recent paper on Harlequin Duck (Histrionicus histrionicus) interannual site fidelity (Iverson et al. 2004), we concluded that wintering populations were demographically structured at a finer geographic scale than that at which genetic differentiation was observed and that conservation efforts should recognize this degree of demographic independence. In a critique of our study, Pearce and Talbot (2006) contend that our measures of fidelity were not robust and imply that in the face of “mixed messages” we failed to appreciate the role of genetic data in defining population units. We recognize, as we did in our original paper, that our methods for quantifying site fidelity have some limitations; however, the patterns in our data are consistent with a considerable body of literature indicating high winter site fidelity in Harlequin Ducks. Moreover, we do not consider differences in the scales at which genetic and demographic structure are expressed to be “mixed messages,” given the different spatial and temporal scales at which genetic and contemporary demographic processes operate. We emphasize that a lack of genetic differentiation does not necessarily preclude the existence of contemporary demographic structure with relevance for conservation.