bluuebunny/crossref_metadata_2025 huggingface dataset:
Nest Site Selection and Nesting Success in Saltmarsh Breeding Sparrows: The Importance of Nest Habitat, Timing, and Study Site Differences
Authors: Gjerdrum Carina , Elphick Chris S. , Rubega Margaret
Published: September 2019

We examined nest-site selection and nesting success in Saltmarsh Sharp-tailed (Ammodramus caudacutus) and Seaside Sparrows (A. maritimus), at seven sites in Connecticut. We found 160 Saltmarsh Sharp-tailed Sparrow nests and 23 Seaside Sparrow nests, and compared characteristics of their locations to each other and to random locations. We tracked success of all nests, quantified nest productivity and causes of nest losses, and tested for habitat differences between successful and unsuccessful nests. Saltmarsh Sharp-tailed Sparrows nested in higher than average locations, where the vegetation was taller and more dense than at random locations, where there was a deep layer of thatch, and where saltmeadow cordgrass (Spartina patens) dominated the vegetation. There was little evidence that habitat characteristics influenced the success of nesting birds, but the timing of nest initiation relative to spring tides was important. Seaside Sparrow nests occurred in even taller vegetation, that was more sparse than average and dominated by the tall form of smooth cordgrass (S. alterniflora). Habitat influenced the success of Seaside Sparrow nests, but timing did not; on average, successful nests occurred in taller vegetation. Model comparisons suggest that vegetation structure influences site selection more than species composition or inherent differences among marshes. Overall, our results indicate that nest flooding is a major threat to successful reproduction in both species, but they have different strategies to avoid flooding. Saltmarsh Sharp-tailed Sparrows time their reproduction to avoid especially high tides, while Seaside Sparrows avoid flooding spatially by nesting in tall vegetation.
Simultaneous Multiple Clutches and Female Breeding Success in Mountain Quail
Authors: Beck Jeffrey L. , Reese Kerry P. , Zager Peter , Heekin Patricia E.
Published: September 2019

To evaluate the contribution of simultaneous clutches to breeding success in female Mountain Quail (Oreortyx pictus), we located nests of radio-marked male and female Mountain Quail in west-central Idaho from 1992 to 1995 and estimated rates and parameters of nesting success. In our sample, 29 females, 19 males, and 4 quail of unknown sex, including 12 apparently monogamous pairs, incubated nests. Using logistic regression, we found that constant survival and sex were the best-supported models to explain nest success for 45 nests of known age. Odds of success for male-incubated nests were 1.7-times (95% CI: 0.4–7.9) greater than for female-incubated nests. Mean clutch size for first nests was 11.8 (range: 6–16) and clutches incubated by males (12.6 ± 0.3 eggs) were significantly larger than female-incubated clutches (11.4 ± 0.4 eggs). Mean hatching date for all nests was 2 July (range: 10 June–23 July). Two of six females whose nests were depredated renested. Paired females produced an average of 24 eggs (range: 20–28). Mean hatching date for nine paired males was 30 June ± 3 days and 3 July ± 3 days for females. The estimated average number of days spent on nesting activities for nine successfully hatched pairs was 59 (range: 54–64). All 12 paired females hatched at least eight chicks from both clutches. Our findings indicate that simultaneous clutches in Mountain Quail ensures breeding success in females under conditions that may not be amenable to other forms of multiple brooding.
Incubation Length of Dabbling Ducks
Authors: Wells-Berlin Alicia M. , Prince Harold H. , Arnold Todd W.
Published: September 2019

We collected unincubated eggs from wild Mallard (Anas platyrhynchos), Gadwall (A. strepera), Blue-winged Teal (A. discors), and Northern Shoveler (A. clypeata) nests and artificially incubated them at 37.5°C. Average incubation lengths of Mallard, Gadwall, and Northern Shoveler eggs did not differ from their wild-nesting counterparts, but artificially incubated Blue-winged Teal eggs required an additional 1.7 days to hatch, suggesting that wild-nesting teal incubated more effectively. A small sample of Mallard, Gadwall, and Northern Shoveler eggs artificially incubated at 38.3°C hatched 1 day sooner, indicating that incubation temperature affected incubation length. Mean incubation length of Blue-winged Teal declined by 1 day for each 11-day delay in nesting, but we found no such seasonal decline among Mallards, Gadwalls, or Northern Shovelers. There is no obvious explanation for the seasonal reduction in incubation length for Blue-winged Teal eggs incubated in a constant environment, and the phenomenon deserves further study.
Correction of Erroneous Records of Cormorants From Archeological Sites in Alaska
Authors: Olson Storrs L.
Published: September 2019

In previous studies, bones from archeological midden deposits on Kodiak and Amchitka Islands, Aleutians, were erroneously identified as belonging to Great Cormorant (Phalacrocorax carbo), Pallas's Cormorant (P. perspicillatus), and Japanese Cormorant (P. capillatus), none of which is otherwise known from Alaska. These specimens are all re-identified as having come from the Double-crested Cormorant (P. auritus), which is much larger in Alaska than in middle and southern latitudes in North America.
Environmental Correlates of Song Structure in Forest Grosbeaks and Saltators
Authors: Tubaro Pablo L. , Lijtmaer Dario A.
Published: September 2019

We compared the song structure of 19 species of forest grosbeaks and saltators based on the songs of 271 individuals recorded from Argentina to Canada, and analyzed their ecological correlates. On each spectrogram we measured eight temporal, frequency, and structural features of the song. Both a principal components analysis and a univariate analysis showed consistent differences in song structure between open and closed habitats. These differences were also found in an independent contrasts analysis, in which phylogenetic relationships between the species of the group were taken into account. In particular, the songs of species living in open habitats had wider bandwidths and higher maximum frequencies than those of species living in more closed habitats. In addition, the songs of open-habitat species had more notes, which were of shorter duration. These findings are compatible with predictions derived from the Acoustic Adaptation Hypothesis, according to which bird song structure is adapted to the habitat in which the signal is used.
Apparent Effects of Light Pollution on Singing Behavior of American Robins
Authors: Miller Mark W.
Published: September 2019

Astronomers consider light pollution to be a growing problem, however few studies have addressed potential effects of light pollution on wildlife. Sunlight is believed to initiate song in many bird species. If light initiates song, then light pollution may be influencing avian song behavior at a population level. This hypothesis predicts that birds breeding in areas with large amounts of artificial light will begin singing earlier in the day than birds in areas with little artificial light. Birds in highly illuminated areas might begin singing earlier than did birds in those same areas in previous years when artificial light levels were known to be, or were presumably, lower. Also, birds should begin singing earlier within a site on brightly lit nights. In 2002 and 2003 I documented initiation of morning song by breeding American Robins (Turdus migratorius) in areas with differing intensity of artificial nocturnal light. I compared my observations among sites and against historical studies. Robin populations in areas with large amounts of artificial light frequently began their morning chorus during true night. Chorus initiation time, relative to civil twilight, was positively correlated with amount of artificial light present during true night. Robin choruses in areas with little, or presumably little, artificial light have almost never begun during true night, instead appearing to track the onset of civil twilight. Proliferation of artificial nocturnal light may be strongly affecting singing behavior of American Robins at a population level.
Species Richness and Nesting Success of Migrant Forest Birds in Natural River Corridors and Anthropogenic Woodlands in Southeastern South Dakota
Authors: Gentry Dale J. , Swanson David L. , Carlisle Jay D.
Published: September 2019

Forest fragmentation is thought to be partially responsible for declines in many Neotropical migrant birds due to the combined effects of higher rates of brood parasitism and increased predation near forest edges. A majority of the forested habitat in the northern prairie region is found in riparian corridors, but this native habitat has been much reduced from its historical extent. However, additional woodland nesting habitat has been established within the last century in the form of isolated woodlots on farms. We compared abundance, species richness, and nesting success of migrant forest birds breeding in native riparian corridors and anthropogenic woodlots. The two habitats had similar bird abundances but native riparian woodlands were more species-rich than woodlots. We located a total of 650 nests, with 320 nests of 15 species in woodlots and 331 nests of 25 species in riparian corridors. Nesting success was not significantly different between the two habitats for all species combined or for individual species with ≥15 nests in each habitat. Nests above 5 m were more successful than lower nests, but distance to woodland edge did not influence nesting success. Nests initiated in the middle and late portions of the nesting season were more successful than early season nests, significantly so in woodlots. Thus, anthropogenic woodlots were as suitable as natural habitats for successful nesting. However, many of the Neotropical migrants occurring in riparian habitats were absent from woodlots, which suggests that riparian corridors are especially important habitats for breeding birds in the northern prairie region.
Cerulean Warbler Abundance and Occurrence Relative to Large-Scale Edge and Habitat Characteristics
Authors: Bohall Wood Petra , Bosworth Scott B. , Dettmers Randy
Published: September 2019

We examined Cerulean Warbler (Dendroica cerulea) abundance and occurrence in southwestern West Virginia, where the coal-mining technique of mountaintop removal mining–valley fill converts large contiguous tracts of deciduous forest to forest patches surrounded by early successional habitats. Our study objectives were to quantify abundance and occurrence of Cerulean Warblers relative to (1) distance from the edge of extensive reclaimed grasslands and (2) habitat structure and landscape characteristics. Cerulean Warbler abundance increased with distance from the edge and edge effects extended 340 m into the forest. Percent occurrence did not vary with distance from mine edge, suggesting a degree of tolerance to the extensive edge occurring at the interface of forest and reclaimed lands. Abundance and occurrence were greater on ridges and midslopes than in bottomlands; consequently, disturbances such as mountaintop mining in which ridges are removed may have a greater impact on populations compared to other sources of fragmentation where ridges are not disturbed. Models based on the information-theoretic approach indicated that Cerulean Warblers were more likely to be present in productive sites on northwest to southeast facing slopes, upper slope positions (midslope to ridgetop), and forests with low sapling density. Cerulean Warbler abundance was positively associated with more productive sites, higher snag density, large blocks of mature deciduous forest, and low amounts of edge in the landscape. In addition to outright loss of forested habitat, mountaintop mining-valley fill alters the spatial configuration of forested habitats, creating edge and area effects that negatively affect Cerulean Warbler abundance and occurrence in the reclaimed mine landscape.
The Allometric Relationship between Resting Metabolic Rate and Body Mass in Wild Waterfowl (Anatidae) and an Application to Estimation of Winter Habitat Requirements
Authors: Miller Michael R. , McA. Eadie John
Published: September 2019

We examined the allometric relationship between resting metabolic rate (RMR; kJ day−1) and body mass (kg) in wild waterfowl (Anatidae) by regressing RMR on body mass using species means from data obtained from published literature (18 sources, 54 measurements, 24 species; all data from captive birds). There was no significant difference among measurements from the rest (night; n = 37), active (day; n = 14), and unspecified (n = 3) phases of the daily cycle (P > 0.10), and we pooled these measurements for analysis. The resulting power function (aMassb) for all waterfowl (swans, geese, and ducks) had an exponent (b; slope of the regression) of 0.74, indistinguishable from that determined with commonly used general equations for nonpasserine birds (0.72–0.73). In contrast, the mass proportionality coefficient (b; y-intercept at mass = 1 kg) of 422 exceeded that obtained from the nonpasserine equations by 29%–37%. Analyses using independent contrasts correcting for phylogeny did not substantially alter the equation. Our results suggest the waterfowl equation provides a more appropriate estimate of RMR for bioenergetics analyses of waterfowl than do the general nonpasserine equations. When adjusted with a multiple to account for energy costs of free living, the waterfowl equation better estimates daily energy expenditure. Using this equation, we estimated that the extent of wetland habitat required to support wintering waterfowl populations could be 37%–50% higher than previously predicted using general nonpasserine equations.
Reproductive Parameters and Productivity of the Yellow-Shouldered Parrot on Margarita Island, Venezuela: a Long-Term Study
Authors: Sanz Virginia , Rodriguez-Ferraro Adriana
Published: September 2019

We studied the breeding biology of the Yellow-shouldered Parrot (Amazona barbadensis) on Margarita Island from March-August, 1990 to 1999. The timing of the different phases (egg-laying, hatching, fledging) was consistent over the years, except during 1998 when all phases were delayed. The average clutch size was 3.38 ± 0.78 eggs per nest, with a range of one to five eggs per clutch, and most eggs survived until hatching (3.36 ± 0.80 eggs per nest). Total clutch size and hatching success of this species on Margarita Island are among the highest in the genus Amazona, suggesting the Yellow-shouldered Parrot has a higher reproductive potential than other species of the genus. We detected interannual differences for some of the reproductive parameters, all in 1998, a year with an extreme drought. Egg losses totaled 20% and were caused by hatching failure, predation, and human disturbance. Forty-nine percent of nestlings were lost, mainly due to poaching. The number of fledglings per nesting pair averaged 1.27 ± 1.61, but varied greatly among years. Thus, in relation to the average total clutch laid, each pair lost an average of 62% of its initial reproductive investment.
Effects of Sex and Age on Survival of Northern Flickers: a Six-Year Field Study
Authors: Fisher Ryan J. , Wiebe Karen L.
Published: September 2019

Although many forestry management strategies rely on population estimates of indicator species such as woodpeckers (Picidae), empirical estimates of demographic parameters within this taxon are few. We used program MARK to assess influences of age and sex on apparent survival of adult Northern Flickers (Colaptes auratus) from a six-year mark-recapture study. The top model suggested no differences in apparent survival between the sexes with an overall survival estimate of 0.43 (95% CI: 0.38–0.48). Other models suggested that recapture efficiency differed between the sexes (males: 0.87; females: 0.78), perhaps because males were more philopatric to nest sites. We suggest that high parental investment by male flickers relative to other taxa such as passerines may lead to relatively equal mortality rates between the sexes, rather than the common pattern of female-biased mortality. Survival rates relative to age were constant at least up to the age of three years. Overall, flickers appear to have lower survival than some other woodpecker species and may invest relatively heavily in current reproduction.
Sources of Variation in Survival of Breeding Female Wood Ducks
Authors: Hartke Kevin M. , Grand James B. , Hepp Gary R. , Folk Travis H.
Published: September 2019

In waterfowl, reproduction is physiologically demanding and females are exposed to varying risks of mortality at different periods of the breeding cycle. Moreover, differences among females may influence survival within breeding periods. We captured and fitted female Wood Ducks (Aix sponsa) with radio-transmitters before nest initiation during two breeding seasons to estimate survival and investigate sources of variation in survival. We partitioned the breeding season into three periods (preincubation, incubation, postnesting) according to breeding status of individual females, and used information-theoretic methods to compare models in which daily survival varied among periods, between successful and failed nesting females, and with parameters describing individual heterogeneity. Our analysis suggested that daily survival was best modeled as a function of breeding period, differences between successful and failed nesting females during postnesting, and early incubation body condition of successful females during postnesting. Model-averaged daily survival was 0.9988 (95% CL: 0.9963–0.9996) during preincubation and 1.0 during incubation. Postnesting daily survival was 1.0 for failed nesting females and 0.9948 (0.9773–0.9988) for successful females, suggesting a trade-off between current reproduction and survival. Female age, body condition at capture, nest initiation date, and brood size generally were not useful for explaining variation in survival. Only early incubation body condition was important for modeling survival of successful females during postnesting; however, weight of evidence was limited and the effect on survival was weak. Mortality was greatest for females during preincubation and for females that nested successfully. Results support the hypothesis that brood care is costly for females.
Nest Attributes, Aggression, and Breeding Success of Gulls in Single and Mixed Species Subcolonies
Authors: Ellis Julie C. , Good Thomas P.
Published: September 2019

We investigated attributes of nests, aggressive interactions, and reproductive success in mixed and single species subcolonies of Great Black-backed Gulls (Larus marinus) and Herring Gulls (L. argentatus) on Appledore Island, Maine. Distances to the nearest neighboring nest were smaller for L. argentatus than L. marinus, with greatest distances between nests at edges of subcolonies in both species. More L. argentatus nests had natural screens (vegetation or rock >30 cm tall) adjacent to them than did L. marinus nests, but screen presence did not differ among nest positions within the colony. Clutch size did not differ between species; however, hatching success (number of chicks hatched per nest) was higher in L. argentatus than L. marinus. Fledging success (number of chicks fledged per nest) of L. marinus was greater at nests with heterospecific neighbors, whereas the opposite was true for L. argentatus. For both species, the frequency of aggressive interactions was lower at nests with L. argentatus neighbors. Overall, L. marinus nesting near L. argentatus experienced less aggression and greater reproductive success than those nesting among conspecifics, where intraspecific aggression was relatively high. L. argentatus nesting near L. marinus experienced more aggression and lower reproductive success than those nesting among conspecifics, where intraspecific aggression was relatively low. The costs and benefits of nesting in mixed species colonies may depend on the relative size and aggressiveness of the heterospecifics. Interactions with L. marinus in mixed species colonies may be contributing to the current declines of L. argentatus throughout New England.
Postbreeding Movements of Frigatebirds Tracked with Satellite Telemetry
Authors: Weimerskirch Henri , Le Corre Matthieu , Marsac Francis , Barbraud Christophe , Tostain Olivier , Chastel Olivier
Published: September 2019

Using satellite telemetry, we studied the postbreeding movements of Great (Fregata minor) and Magnificent Frigatebirds (F. magnificens) at two breeding colonies in the Indian and Atlantic Oceans. After breeding failure, 67% of the birds with satellite transmitters remained on the breeding colonies and continued to perform foraging trips similar to those undertaken while breeding. Two Magnificent Frigatebirds that bred at a colony off the coast of French Guiana moved west along the coast of South America, and one of the two reached Trinidad 1400 km away. One Great Frigatebird moved 4400 km from Europa Island in the Mozambique Channel to the Maldive Islands. It roosted there for at least four months, making foraging trips of up to 240 km, mainly to an area known for its high concentration of tuna. These results show that frigatebirds are able to make rapid and directed long-distance dispersal movements to other colonies or roosting sites, although the majority of birds remain based on breeding colonies.
Conflicting Temporal Changes in the Frequency and Intensity of Cowbird Parasitism on Four Common Hosts in Ontario over 130 Years
Authors: McLaren Celia M. , Underwood Todd J. , Sealy Spencer G.
Published: September 2019

We tested the hypothesis proposed by Friedmann (1963) that multiple parasitism (nests with more than one parasitic egg) by Brown-headed Cowbirds (Molothrus ater) is a recent phenomenon associated with increased densities of cowbirds. We used Ontario Nest Records Scheme data to quantify frequencies of parasitism and multiple parasitism on four common host species over the last 130 years. Frequency of multiple parasitism significantly increased over all decades only in Chipping Sparrows (Spizella passerina). We also analyzed data separately before and after 1970 because at about this time cowbird abundance began to stabilize and then decline. Pre-1970, multiple parasitism significantly increased on Chipping Sparrows and Song Sparrows (Melospiza melodia), but neither had significant trends post-1970. There were no significant trends in multiple parasitism on Red-eyed Vireos (Vireo olivaceus) or Northern Cardinals (Cardinalis cardinalis). For all time periods analyzed, there were no significant trends in overall frequency of parasitism on any species. Our results provide limited support for the hypothesis that temporal variation in parasitism patterns has followed changes in cowbird density over the past century.
A Variance-decomposition Approach to Investigating Multiscale Habitat Associations
Authors: Lawler Joshua J. , Edwards Thomas C.
Published: September 2019

The recognition of the importance of spatial scale in ecology has led many researchers to take multiscale approaches to studying habitat associations. However, few of the studies that investigate habitat associations at multiple spatial scales have considered the potential effects of cross-scale correlations in measured habitat variables. When cross-scale correlations in such studies are strong, conclusions drawn about the relative strength of habitat associations at different spatial scales may be inaccurate. Here we adapt and demonstrate an analytical technique based on variance decomposition for quantifying the influence of cross-scale correlations on multiscale habitat associations. We used the technique to quantify the variation in nest-site locations of Red-naped Sapsuckers (Sphyrapicus nuchalis) and Northern Flickers (Colaptes auratus) associated with habitat descriptors at three spatial scales. We demonstrate how the method can be used to identify components of variation that are associated only with factors at a single spatial scale as well as shared components of variation that represent cross-scale correlations. Despite the fact that no explanatory variables in our models were highly correlated (r < 0.60), we found that shared components of variation reflecting cross-scale correlations accounted for roughly half of the deviance explained by the models. These results highlight the importance of both conducting habitat analyses at multiple spatial scales and of quantifying the effects of cross-scale correlations in such analyses. Given the limits of conventional analytical techniques, we recommend alternative methods, such as the variance-decomposition technique demonstrated here, for analyzing habitat associations at multiple spatial scales.
Sources and Expectations for Hierarchical Structure in Bird-habitat Associations
Authors: Kristan William B.
Published: September 2019

Hierarchical structure in bird-habitat associations can arise from hierarchical structure in environmental variables and from the scale-dependent responses of birds to habitat. Hierarchical structure in environmental variables is expected to result from interactions between variables that differ in grain size (spatial resolution) and frequency, and should occur commonly. Birds cannot accurately sample habitat characteristics at all spatial scales simultaneously, and the habitat chosen for a given purpose may differ depending on whether a bird samples from high above the ground (which is best for sampling coarse-grained variables) or from ground level (which is best for sampling fine-grained variables). Additionally, birds may exhibit an absolute response to a habitat variable, if it is unsuitable beyond some threshold level, or a relative response, if all available habitat is suitable but some is preferred. Models that can represent hierarchical structure in habitat, as well as hierarchical, scale-dependent responses by birds, should provide researchers the best chance of understanding avian habitat associations.
Effects of Nestling Health on Postfledging Survival of Wood Storks
Authors: Hylton Rebecca A. , Frederick Peter C. , De La Fuente Teresa E. , Spalding Marilyn G.
Published: September 2019

Little is known about the period between fledging and breeding in long-lived birds, including survival rates and factors affecting survival, yet this period may be critical to population regulation. We conducted health exams on 72 nestling Wood Storks (Mycteria americana) aged 4–6 weeks, and monitored survival of these birds via satellite telemetry for up to two years of age. Eighty-two percent of nestlings fitted with transmitters in 2002 (n = 33) survived to fledging. Of these fledglings (n = 27), 44% survived their first year. Second-year survival for the same cohort (n = 12) was 75%. In contrast, 50% of nestlings fitted with transmitters in 2003 (n = 34) survived to fledging, and 6% of fledglings (n = 17) survived the first year. Of the health parameters we measured in large nestlings, white blood cell count was consistently the most closely related to postfledging survival. Significantly elevated heterophil:lymphocyte ratios in 2003 coincided with the observed high colony abandonment that year. After controlling for health parameters, gender also appeared to play a significant role in predicting survival, with males at greater risk of mortality. Hematological factors and gender were both more closely associated with survival in 2003 than in 2002, suggesting these factors may play a greater role in regulating postfledging survival or, in the case of hematology, serve as indicators of poor health in less favorable years when nestling storks are exposed to multiple stressors.
Juvenile Movement and Natal Dispersal of Northern Goshawks in Arizona
Authors: Wiens J. David , Reynolds Richard T. , Noon Barry R.
Published: September 2019

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.
Survival and Movements of Juvenile Burrowing Owls During the Postfledging Period
Authors: Morgan Davies J. , Restani Marco
Published: September 2019

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.
A Productivity Model for Parasitized, Multibrooded Songbirds
Authors: Powell Larkin A. , Knutson Melinda G.
Published: September 2019

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.
Nut Selection by Captive Blue Jays: Importance of Availability and Implications for Seed Dispersal
Authors: Moore Jeffrey E. , Swihart Robert K.
Published: September 2019

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.
Seasonal Differences in Immunological Condition of Three Species of Thrushes
Authors: Owen Jennifer C. , Moore Frank R.
Published: September 2019

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.
Coevolutionary Interactions Between Common Cuckoos and Corn Buntings
Authors: Antonov Anton , Stokke Bård G. , Moksnes Arne , RØskaft Eivin
Published: September 2019

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.
Do Nearctic Northern Wheatears (Oenanthe Oenanthe Leucorhoa) Migrate Nonstop to Africa?
Authors: Thorup Kasper , Thorup Kasper , Ortvad Troels Eske , RabØl JØrgen
Published: September 2019

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.
Genetic and Demographic Criteria for Defining Population Units for Conservation: The Value of Clear Messages
Authors: Esler Daniel , Iverson Samuel A. , Rizzolo Daniel J.
Published: September 2019

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.
Intraspecific Phylogeography and Adaptive Divergence in the White-Headed Woodpecker
Authors: Alexander Matthew P. , Burns Kevin J.
Published: September 2019

This study uses mitochondrial DNA (mtDNA) to examine the phylogeography of the White-headed Woodpecker (Picoides albolarvatus), one of the least-studied woodpeckers in North America. A mismatch distribution and calculation of Tajima's D indicate that the overall phylogeographic history of the species is characterized by a recent range expansion that probably occurred after the start of the Pleistocene. In addition, a nested clade phylogeographic analysis indicates that additional processes such as allopatric fragmentation and restricted gene flow have influenced the evolutionary history of this species. Traditionally, the White-headed Woodpecker has been split into two subspecies whose distributions meet in the northern part of the Transverse Ranges in California. The two subspecies differ morphologically, with the southern subspecies having a larger bill in proportion to its body size than the northern subspecies. Geographical variation in mtDNA is concordant with a division at the Transverse Ranges that corresponds to the morphological variation seen between the two subspecies. An analysis of molecular variance indicates that 27% of the genetic variation results from differences between the northern and southern subspecies. Furthermore, birds in the northern part of the range differ from those in the southern part of the range by at least one base substitution. These results agree with the hypothesis that the larger bill of the southern subspecies is the result of recent local adaptation to feeding on the large cones of Coulter pines (Pinus coulteri).
Song Learning by Chipping Sparrows: When, Where, and From Whom
Authors: Liu Wan-Chun , Kroodsma Donald E.
Published: September 2019

Given the difficulty of following free-living, dispersing juvenile songbirds, relatively little is known about when, where, how, and from whom these young birds learn their songs. To explore these issues, we studied the Chipping Sparrow (Spizella passerina), males of which have a single, simple song, but populations of which may contain 20–30 different songs. In our western Massachusetts study sites, we color-banded 324 nestling and 32 fledgling sparrows. Twelve of these banded males returned to our study areas, dispersing a few hundred meters to 1.8 km away from their natal territories. The song of each yearling closely matched only one of his immediate neighbors on the breeding territory, revealing that a yearling sparrow precisely imitates one of his close neighbors after dispersal. Evidence from this field study and a previous laboratory study show that a young male is able to learn songs either during his hatching year or the following spring, perhaps depending on his chances of song exposure or social interaction with territorial neighbors.
Territoriality, Site Fidelity, and Survivorship of Willow Flycatchers Wintering in Costa Rica
Authors: Koronkiewicz Thomas J. , Sogge Mark K. , Van Riper Charles , Paxton Eben H.
Published: September 2019

We studied wintering Willow Flycatchers (Empidonax traillii) in two seasonal freshwater wetland habitats in northwestern Costa Rica during five boreal winters, to determine habitat occupancy, overwinter and between-year site and territory fidelity, and the degree to which the sexes maintain and defend winter territories. Both males and females used agonistic displays, song, and other vocalizations to maintain and defend mutually exclusive winter territories. Males were generally more abundant than females, but this varied by site and year. There was no significant difference in male and female territory size, nor any indication of sexual habitat segregation. Similarity in morphology and aggressiveness between the sexes may account for the lack of habitat segregation and the ability of females to maintain territories at wintering sites. Each year, 80%–92% of banded flycatchers that were present in midwinter remained at the site until late winter; of these, 86%–100% of individuals maintained the same territories throughout the entire period. We also observed nonterritorial floaters that subsequently established and held winter territories. Between-year site fidelity averaged 68%, and almost all returning birds established territories with boundaries similar to the previous year. Between-year apparent survivorship estimates ranged annually from 54%–72%, with no difference between sites but weak support for higher survivorship of males compared to females. Values for winter site and territory fidelity were generally higher than those reported for other species and for Willow Flycatchers on the breeding grounds; between-year survivorship estimates were similar to those reported for breeding flycatchers.
Geographic Variation in the Trade-Off Between Nestling Growth Rate and Body Condition in the Tree Swallow
Authors: Ardia Daniel R.
Published: September 2019

Nestlings can exhibit considerable variation in developmental patterns both within and among locations due to differences in environmental conditions and parental investment. I investigated trade-offs between nestling growth rate and residual body mass (body condition) at three locations across the range of the Tree Swallow (Tachycineta bicolor). Nestlings at the northern extreme of the range in Alaska had slower growth rates, lower body mass, and higher residual body mass than nestlings in New York and Tennessee. High insect availability was correlated with increased growth rates of nestlings in New York and Tennessee, but not in Alaska. Conversely, nestlings in Alaska showed increased residual body mass with high insect availability, but nestlings in New York and Tennessee did not. The trade-off between growth rate and residual body mass varied among sites, with fast-growing nestlings in Tennessee maintaining a higher residual body mass than those in Alaska. These results suggest that factors affecting offspring growth and condition vary among sites, leading to geographical differences in offspring development trajectories.
Green-Tailed Towhee Response to Prescribed Fire in Montane Shrubland
Authors: Jehle Gretchen , Savidge Julie A. , Kotliar Natasha B.
Published: September 2019

Fire alters the structure and composition of shrublands and affects habitat quality for the associated avifauna. Because shrubland ecosystems have been greatly reduced from their original extent in western North America and fire is increasingly being used to manage these landscapes, a better understanding of how fire affects the associated vegetation and wildlife is imperative. We evaluated the response of Green-tailed Towhees (Pipilo chlorurus) to prescribed fire in the montane shrublands of Rocky Mountain National Park, Colorado during 2002 and 2003. Three to five years following prescribed burning, Green-tailed Towhee density and shrub cover were generally higher in unburned areas. Nests (n  =  179) were located in unburned vegetation; within burned sites, all nests were in remnant patches. Green-tailed Towhee nest survival was 57% (95% CI  =  49%–65%) across the two years of the study. More than half of the nests were in common juniper (Juniperus communis) shrubs, and nest survival was higher for nests in junipers than those in other shrub species. Daily nest survival rates were lower at the site with the highest density of towhees and declined over the breeding season. With regard to shrub cover, opposite trends were observed for nest-site selection and nest survival: nest plots had greater shrub cover than non-nest plots, but nest survival decreased with increasing shrub cover. Because shrub cover affects towhee density and nest survival in conflicting ways, fire management at Rocky Mountain National Park alters both habitat availability and suitability for Green-tailed Towhees.