bluuebunny/crossref_metadata_2025 huggingface dataset:
Productivity of Black Oystercatchers: Effects of Recreational Disturbance in a National Park
Authors: Morse Julie A. , Powell Abby N. , Tetreau Michael D.
Published: September 2019

National parks in Alaska are generally assumed to be high-quality, undisturbed wildlife habitats. However, these parks attract recreational users, whose presence may reduce the suitability of key habitats for nesting shorebirds. In Kenai Fjords National Park, Black Oystercatchers (Haematopus bachmani) often breed on gravel beaches that are also popular campsites. In this study, we examined the effects of recreational activities in coastal Alaska on reproductive performance of Black Oystercatchers. We monitored survival of nests and chicks on 35 to 39 breeding territories annually during four breeding seasons (2001–2004). Most recreational disturbance on these territories occurred after the peak hatching date of first clutches. Annual productivity was low (average of 0.35 chicks per pair), but was not strongly affected by recreational disturbance. Daily survival of nests varied annually and declined over the season. Our results suggest that nest survival was lower during periods of extreme high tides. Daily survival rate of broods increased over the season and was higher on island than mainland territories, likely due to differences in predator communities. Territory occupancy rate and site fidelity were high; 95% of color-banded oystercatchers returned to the same breeding territory in the subsequent year. We conclude that Black Oystercatchers are resilient to low levels of recreational disturbance. However, in light of projected increases in recreation, we suggest managers move campsites away from the traditional nest sites identified in this study to minimize future disturbances.
Prebasic Molt and Molt-Related Movements in Ash-Throated Flycatchers
Authors: Butler Luke K. , Rohwer Sievert , Rogers Michelle
Published: September 2019

We describe the timing and location of the prebasic molt in the Ash-throated Flycatcher (Myiarchus cinerascens), a hawking insectivore with resident populations in Mexico and migrant populations that breed in the western United States. The timing of fall molt with respect to migration is of particular interest for Ash-throated Flycatchers from the United States because they breed in arid lowland habitats that are probably unproductive in late summer, and because time constraints on molt might force northern populations to leave their breeding grounds before molting. Adults and juveniles depart their breeding grounds to arrive and molt in the region of the Mexican monsoon shortly after the monsoon rains begin. Diminishing food on the breeding grounds and increasing food in the monsoon region seem more important than time constraints for explaining molt-related movements by northern populations, because more southerly breeding birds east and west of the monsoon region also move to the monsoon region to molt. We found age class differences in the timing and duration of molt. In adults the primary molt starts approximately 14 July and requires 76 days to complete, whereas in juveniles, primary molt starts approximately 1 August (18 days after adults) but requires only 50 days to complete. We found no evidence that juveniles molt more primaries simultaneously than adults, so we conclude that the daily growth rate of individual feathers must be higher in juveniles than adults.
Slave to the Tides: Spatiotemporal Foraging Dynamics of Spring Staging Black Brant
Authors: Moore Jeffrey E. , Black Jeffrey M.
Published: September 2019

Arctic-nesting geese depend on nutrients acquired during spring migration for reproduction, and thus should attempt to maximize nutrient intake while on staging areas. We investigated site use of Black Brant (Branta bernicla nigricans) at an important staging location—Humboldt Bay, California—to determine whether birds selected the most profitable feeding areas available. Migrating Brant feed almost exclusively on eelgrass (Zostera marina), which is restricted in availability due to daily and seasonal tidal cycles. We mapped foraging Brant locations during low tides and collected eelgrass samples to describe food resources in 31 areas in the bay. We used negative binomial regression to evaluate goose densities during different tidal levels and times of season as a function of food biomass and nutrient content, distance from grit sites, and substrate elevation. Results varied by time of season and tidal depth, but Brant densities were positively correlated with eelgrass protein, calcium, and biomass in most analyses. Brant usually fed in the deepest possible areas permitted by tides, and closer to tidal channels, where biomass and nutrient content of eelgrass were greater and where depletion from grazing was probably less. During higher low tides, Brant fed closer to previously visited grit sites. Tide cycles change over the course of the Brant's staging period on the bay, enabling longer and more frequent access to deeper eelgrass meadows as spring progresses. These seasonal changes in tidal pattern coincide with seasonal changes in Brant use of the bay. Thus, migration patterns for estuarine bird species might be shaped by latitudinal gradients in both food phenology and seasonal tidal patterns.
Nutritional Condition of Pacific Black Brant Wintering at the Extremes of Their Range
Authors: Mason Danielle D. , Barboza Perry S. , Ward David H.
Published: September 2019

Endogenous stores of energy allow birds to survive periods of severe weather and food shortage during winter. We documented changes in lipid, protein, moisture, and ash in body tissues of adult female Pacific Black Brant (Branta bernicla nigricans) and modeled the energetic costs of wintering. Birds were collected at the extremes of their winter range, in Alaska and Baja California, Mexico. Body lipids decreased over winter for birds in Alaska but increased for those in Baja California. Conversely, body protein increased over winter for Brant in Alaska and remained stable for birds in Baja California. Lipid stores likely fuel migration for Brant wintering in Baja California and ensure winter survival for those in Alaska. Increases in body protein may support earlier reproduction for Brant in Alaska. Predicted energy demands were similar between sites during late winter but avenues of expenditure were different. Birds in Baja California spent more energy on lipid synthesis while those in Alaska incurred higher thermoregulatory costs. Estimated daily intake rates of eelgrass were similar between sites in early winter; however, feeding time was more constrained in Alaska because of high tides and short photoperiods. Despite differences in energetic costs and foraging time, Brant wintering at both sites appeared to be in good condition. We suggest that wintering in Alaska may be more advantageous than long-distance migration if winter survival is similar between sites and constraints on foraging time do not impair body condition.
Combining Breeding Bird Survey and Distance Sampling to Estimate Density of Migrant and Breeding Birds
Authors: Somershoe Scott G. , Twedt Daniel J. , Reid Bruce
Published: September 2019

We combined Breeding Bird Survey point count protocol and distance sampling to survey spring migrant and breeding birds in Vicksburg National Military Park on 33 days between March and June of 2003 and 2004. For 26 of 106 detected species, we used program DISTANCE to estimate detection probabilities and densities from 660 3-min point counts in which detections were recorded within four distance annuli. For most species, estimates of detection probability, and thereby density estimates, were improved through incorporation of the proportion of forest cover at point count locations as a covariate. Our results suggest Breeding Bird Surveys would benefit from the use of distance sampling and a quantitative characterization of habitat at point count locations. During spring migration, we estimated that the most common migrant species accounted for a population of 5000–9000 birds in Vicksburg National Military Park (636 ha). Species with average populations of >300 individuals during migration were: Blue-gray Gnatcatcher (Polioptila caerulea), Cedar Waxwing (Bombycilla cedrorum), White-eyed Vireo (Vireo griseus), Indigo Bunting (Passerina cyanea), and Ruby-crowned Kinglet (Regulus calendula). Of 56 species that bred in Vicksburg National Military Park, we estimated that the most common 18 species accounted for >8150 individuals. The six most abundant breeding species, Blue-gray Gnatcatcher, White-eyed Vireo, Summer Tanager (Piranga rubra), Northern Cardinal (Cardinalis cardinalis), Carolina Wren (Thryothorus ludovicianus), and Brown-headed Cowbird (Molothrus ater), accounted for >5800 individuals.
Monitoring Low Density Avian Populations: An Example Using Mountain Plovers
Authors: Dreitz Victoria J. , Lukacs Paul M. , Knopf Fritz L.
Published: September 2019

Declines in avian populations highlight a need for rigorous, broad-scale monitoring programs to document trends in avian populations that occur in low densities across expansive landscapes. Accounting for the spatial variation and variation in detection probability inherent to monitoring programs is thought to be effort-intensive and time-consuming. We determined the feasibility of the analytical method developed by Royle and Nichols (2003), which uses presence-absence (detection-nondetection) field data, to estimate abundance of Mountain Plovers (Charadrius montanus) per sampling unit in agricultural fields, grassland, and prairie dog habitat in eastern Colorado. Field methods were easy to implement and results suggest that the analytical method provides valuable insight into population patterning among habitats. Mountain Plover abundance was highest in prairie dog habitat, slightly lower in agricultural fields, and substantially lower in grassland. These results provided valuable insight to focus future research into Mountain Plover ecology and conservation.
Pattern of Damage to Albino Great Frigatebird Flight Feathers Supports Hypothesis of Abrasion by Airborne Particles
Authors: Schreiber Ralph W. , Schreiber Elizabeth A. , Peele Ashley M. , Burtt Edward H.
Published: September 2019

On 11 July 1985, an albino juvenile Great Frigatebird (Fregata minor) was collected by RWS and EAS on Christmas Island (2°N, 157°W) in the tropical Pacific. First observed on 13 July 1984 as a 55–60-day-old chick, the albino was seen flying about the colony on 4 November 1984 and again in February 1985. In July 1985 the juvenile was at its nest with such badly abraded plumage that it could not fly. Burtt (1986) proposed an aerodynamic model that predicts the distribution of melanic feathers in response to abrasion from airborne particles in a flying bird. The albino frigatebird provides a test of this model, since frigatebirds spend most of their time flying and rarely contact water, ground, or objects. Abrasion of the primaries and tail of this albino Great Frigatebird follows the pattern predicted by Burtt (1986). Furthermore, the pattern of damage to secondaries and tertiaries suggests that friction of feathers against each other is another important source of wear.
Distribution and Prevalence of Mosquito-Borne Diseases in O’ahu ’Elepaio
Authors: Vanderwerf Eric A. , Burt Matthew D. , Rohrer Joby L. , Mosher Stephen M.
Published: September 2019

The endemic Hawaiian avifauna is one of the most imperiled on earth, and diseases have been one of the most serious causes of species declines. From 1995–2005, we mist-netted and banded 266 endangered O’ahu ’Elepaio (Chasiempis sandwichensis ibidis) from 27 sites, examined them for visible symptoms of avian pox virus (Poxvirus avium), and screened blood samples for avian malaria (Plasmodium relictum). Pox-like lesions and malaria were found in all ’Elepaio populations on O’ahu; no parts of the island were free of these mosquito-borne diseases. Each year, 20% ± 4% of ’Elepaio had active lesions likely caused by pox and an additional 16% ± 4% had deformities and missing toes indicative of healed pox lesions. Prevalence of malaria was 87% over all years combined. Pox prevalence varied among years and was associated with annual rainfall, presumably due to greater abundance of mosquito breeding sites in wet years. Rainfall amounts at least as high as those associated with pox epizootics in 1996 and 2004 have occurred in 13 years since 1947, or once every 4.5 years. Severity of infection varied considerably among birds, and infections involving three or more toes, the feet, or the head were less common in birds with healed lesions than those with active lesions, suggesting such infections resulted in mortality more often. Disease resistance may be evolving in some areas, but ’Elepaio populations on O’ahu are likely to further decline.
Does Body Size Affect a Bird's Sensitivity to Patch Size and Landscape Structure?
Authors: Winter Maiken , Johnson Douglas H. , Shaffer Jill A.
Published: September 2019

Larger birds are generally more strongly affected by habitat loss and fragmentation than are smaller ones because they require more resources and thus larger habitat patches. Consequently, conservation actions often favor the creation or protection of larger over smaller patches. However, in grassland systems the boundaries between a patch and the surrounding landscape, and thus the perceived size of a patch, can be indistinct. We investigated whether eight grassland bird species with different body sizes perceived variation in patch size and landscape structure in a consistent manner. Data were collected from surveys conducted in 44 patches of northern tallgrass prairie during 1998–2001. The response to patch size was very similar among species regardless of body size (density was little affected by patch size), except in the Greater Prairie-Chicken (Tympanuchus cupido), which showed a threshold effect and was not found in patches smaller than 140 ha. In landscapes containing 0%–30% woody vegetation, smaller species responded more negatively to increases in the percentage of woody vegetation than larger species, but above an apparent threshold of 30%, larger species were not detected. Further analyses revealed that the observed variation in responses to patch size and landscape structure among species was not solely due to body size per se, but to other differences among species. These results indicate that a stringent application of concepts requiring larger habitat patches for larger species appears to limit the number of grassland habitats that can be protected and may not always be the most effective conservation strategy.
The Effects of Postfire Salvage Logging on Cavity-Nesting Birds
Authors: Hutto Richard L. , Gallo Susan M.
Published: September 2019

We investigated the effects of postfire salvage logging on cavity-nesting birds by comparing nest densities and patterns of nest reuse over a three-year period in seven logged and eight unlogged patches of mixed-conifer forest in the Blackfoot-Clearwater Wildlife Management Area, Montana. We found 563 active nests of 18 cavity-nesting birds; all species were found nesting in the uncut burned forest plots, but only eight nested in the salvage-logged plots. All except one species nested at a higher density in the unlogged areas, and half of the species were significantly more abundant in the unlogged plots. Every timber-drilling and timber-gleaning species was less abundant in the salvage-logged plots, including two of the most fire-dependent species in the northern Rocky Mountains—American Three-toed (Picoides dorsalis) and Black-backed (P. arcticus) Woodpeckers. Lower abundances in salvage-logged plots occurred despite the fact that there were still more potential nest snags per hectare than the recommended minimum number needed to support maximum densities of primary cavity-nesters, which suggests that reduced woodpecker densities are more related to a reduction in food (wood-boring beetle larvae) than to nest-site availability. Because cavities were present in only four of 244 randomly selected trees, and because frequency of cavity reuse by secondary cavity-nesters was higher in salvage-logged than in unlogged plots, nest-site limitation may be a more important constraint for secondary cavity-nesters in salvage-logged areas. These results suggest that typical salvage logging operations are incompatible with the maintenance of endemic levels of most cavity-nesting bird populations, especially populations of primary cavity-nesting species.
Factors Influencing Nest Success of Songbirds in Aspen and Willow Riparian Areas in the Great Basin
Authors: Heltzel Jeannie M. , Earnst Susan L.
Published: September 2019

Recent studies have examined the effects oflivestock grazing, agriculture, and humanhabitation on nest predation and brood parasitismin riparian areas in the western United States.However, we know little about factors influencingnest success in riparian areas lacking suchanthropogenic influences, in part because theinfluences are so pervasive. We studied riparianbird communities in a 115 000 hawildlife refuge where livestock grazing wasdiscontinued >10 years ago, and which haslittle nearby agriculture or human habitation. Wemonitored nests on 24 aspen (Populustremuloides) and 10 willow(Salixspp.) plots. Brood parasitism rates weresubstantially lower than at other western sites anddid not differ between aspen and willow habitats.Nest success in aspen was relatively high comparedto that reported for other western sites and higherthan in willow. Predators may have been able tofind nests more efficiently in willow than in aspenbecause territory densities were higher in willow(40 versus 30 pairs per ha,respectively), because willow had lessstructural heterogeneity, or both. We did not findstrong evidence that nest success was influenced byaspen patch size or distance to riparian edge,indicating that even small aspen patches providevaluable nesting habitat. Weather was an importantcause of nest failure, particularly at higherelevations during late-spring snowstorms. Ourresults indicate that riparian areas without majoranthropogenic impacts, especially aspen stands,constitute high-quality breeding habitat andwarrant conservation focus.
Ecological and Physiological Variance in T-Cell Mediated Immune Response in Cory's Shearwaters
Authors: Forero Manuela G. , González-Solis Jacob , Igual José M. , Hobson Keith A. , Ruíz Xavier , Viscor Ginés
Published: September 2019

T-cell mediated immune response (CMI) hasbeen widely studied in relation to individual andfitness components in birds. However, few studieshave simultaneously examined individual and socialfactors and habitat-mediated variance in theimmunity of chicks and adults from the samepopulation and in the same breeding season. Weinvestigated ecological and physiological variancein CMI of male and female nestlings and adults in abreeding population of Cory's Shearwaters(Calonectrisdiomedea) in theMediterranean Sea. Explanatory variables includedindividual traits (body condition, carbon andnitrogen stable isotope ratios, plasma totalproteins, triglycerides, uric acid, osmolarity,β-hydroxy-butyrate, erythrocyte meancorpuscular diameter, hematocrit, andhemoglobin) and burrow traits(temperature, isolation, and physicalstructure). During incubation, immune responseof adult males was significantly greater than thatof females. Nestlings exhibited a lower immuneresponse than adults. Ecological and physiologicalfactors affecting immune response differed betweenadults and nestlings. General linear models showedthat immune response in adult males was positivelyassociated with burrow isolation, suggesting thatmales breeding at higher densities suffer immunesystem suppression. In contrast, immune response inchicks was positively associated with bodycondition and plasma triglyceride levels.Therefore, adult immune response appears to beassociated with social stress, whereas a trade-offbetween immune function and fasting capability mayexist for nestlings. Our results, and those fromprevious studies, provide support for anasymmetrical influence of ecological andphysiological factors on the health of differentage and sex groups within a population, and for theimportance of simultaneously considering individualand population characteristics in intraspecificstudies of immune response.
Large-Scale Movements and Habitat Characteristics of King Eiders Throughout the Nonbreeding Period
Authors: Phillips Laura M. , Powell Abby N. , Rexstad Eric A.
Published: September 2019

King Eiders (Somateriaspectabilis) breeding inwestern Canada and Alaska molt wing feathers andspend the winter in remote areas of the Bering Sea,precluding direct observation. To characterizetiming of migration and habitat used by King Eidersduring the nonbreeding period, we collectedlocation data for 60 individuals (27 femalesand 33 males) over three years from satellitetelemetry and utilized oceanographic informationobtained by remote sensing. Male King Eidersdispersed from breeding areas, arrived at wing moltsites, and dispersed from wing molt sites earlierthan females in all years. Males arriving earlierat wing molt sites molted flight feathers at higherlatitudes. Distributions of molt and winterlocations did not differ by sex or among years. Ofthe variables considered for analysis, distance toshore, water depth, and salinity appeared to bestdescribe King Eider habitat throughout thenonbreeding period. King Eiders were located closerto shore, in shallower water with lower salinitythan random locations. During the winter, lower iceconcentrations were also associated with King Eiderlocations. This study provides some of the firstlarge-scale descriptions of King Eider migrationand habitat outside the breeding season.
Correlated Growth and Survival of Juvenile Spectacled Eiders: Evidence of Habitat Limitation?
Authors: Flint Paul L. , Morse Julie A. , Grand J. Barry , Moran Christine L.
Published: September 2019

We studied the growth andsurvival of Spectacled Eider (Somateriafischeri) ducklings to30 days of age along the lower KashunukRiver on the Yukon-Kuskokwim Delta from 1995 to2000. We replicated this study at a second site,Kigigak Island, in 1999 and 2000. Age-adjustedestimates of duckling mass and survival at30 days posthatching were highly variable.Duckling survival was consistently higher onKigigak Island in 1999 and 2000, averaging67%, while survival on the Kashunuk Riveraveraged 45% during the same time period.Duckling survival was negatively related tohatching date. At the Kashunuk River site our datasupported models that indicated age-adjusted massvaried with habitat type and declined with hatchingdate. Ducklings from Kashunuk River were heavier in1999, while ducklings from Kigigak Island wereheavier in 2000. However, we found a positivecorrelation between 30-day duckling survival andage-adjusted mass, suggesting a localizedenvironmental effect on both parameters. Weconclude that predation may be the proximatemechanism of mortality, but habitat conditions arelikely the ultimate factors influencing ducklingsurvival. Geographic variation in rates of ducklingsurvival and apparent growth suggest that spatialheterogeneity in population vital rates isoccurring at multiple levels.
Trends in Radar-Based Counts of Marbled Murrelets on the Olympic Peninsula, Washington, 1996–2004
Authors: Cooper Brian A. , Raphael Martin G. , Peery M. Zachariah
Published: September 2019

The Marbled Murrelet (Brachyramphusmarmoratus) is a highprofile, federally threatened seabird, but noreliable estimates of population trends at inlandbreeding areas exist for this species. We conductedland-based radar studies of Marbled Murrelets at3–7 sites on the Olympic Peninsula,Washington, in 1996–2002 and 2004 to estimatepopulation changes and to examine relationshipsbetween our counts and oceanographic conditions,murrelet productivity, and regional at-sea countsof murrelets. Morning radar counts of murreletsvaried significantly among and within sites but didnot decline from 1996–2004, suggesting thatthe inland breeding population of murrelets isstable in this area. A retrospective power analysisindicated that we had a 25% and 56%chance of detecting 2% and 4% annualdeclines, respectively. Thus, if relatively smallannual declines did occur during our study period,there is a high probability that they would havegone undetected, even though they could add up to abiologically important decline over time. It isunlikely that murrelets on the Olympic Peninsuladeclined by ≥6% annually, however,because retrospective analyses indicated that powerto detect such declines was >88%. Therewas no significant relationship between radarcounts and at-sea counts or productivity ofmurrelets in the nearby San Juan Islands during thestudy period. We also did not detect a relationshipbetween radar counts and mean sea-surfacetemperatures or the Northern Oscillation Index,suggesting that variation in oceanographicconditions (e.g., the strong 1998 ElNiño event) was not associated withvariation in morning radar counts of MarbledMurrelets. A prospective power analysis indicatedthat small (2%–4%)annual declines could be detected with reasonablyhigh power (≥80%) with thecurrent radar sampling design by extending thestudy to 11–15 years.
Numerical Discrimination by Wild Northern Mockingbirds
Authors: Farnsworth George L. , Smolinski Jennifer L.
Published: September 2019

Optimal foraging theory predicts that birds, when faced with alternative foraging options, will choose the one that provides the greatest rate of return. We tested if wild, free-living Northern Mockingbirds (Mimus polyglottos) could solve a novel foraging problem to attain food rewards with the least amount of effort. We introduced five subjects to experimental feeders in their winter territories in an urban habitat. Feeders contained different numbers of bamboo sticks at each of two ends. Birds could access a food reward (Tenebrio larvae) by removing all sticks from either end; therefore, the optimal choice was to remove sticks from the end with fewer sticks. Each subject was tested in repeated trials to determine if it preferentially chose the end with fewer sticks. All five birds successfully discriminated between one stick and six sticks as well as between two sticks and five sticks. However, all five birds failed to discriminate between three sticks and four sticks. Wild Northern Mockingbirds thus appear to have a limited capacity to solve novel foraging problems by minimizing the number of obstacles to be removed.
Laboratory Metabolism of Incubating Semipalmated Plovers
Authors: Williamson Mark , Williams Joseph B. , Nol Erica
Published: September 2019

The Semipalmated Plover (Charadriussemipalmatus), anarctic-nesting migratory shorebird, regularlyencounters low temperatures during the breedingseason. We measured the basal metabolism of adultsduring incubation at Churchill, Manitoba, Canada todetermine basal metabolic rate (BMR),lower critical temperature(Tlc), total evaporative waterloss (TEWL), and dry thermal conductance(Cm). BMR and Tlcwere 47.4 kJ day−1and 23.3°C, respectively, TEWL was2.5 mL H2O−d,and Cm was1.13 mW g−1 °C−1.Measured BMR and Tlc were consistentwith high values found for other shorebird speciesbreeding in the Arctic, while Cm was18% higher than predicted from allometricequations. These metabolic data suggest thatSemipalmated Plovers are adapted to balance therequirements of incubation against energetic andthermoregulatory demands in the Arctic, especiallyin harsh early breeding season conditions.
Egg Composition in Northern Flickers
Authors: Wiebe Karen L.
Published: September 2019

There have been several studies on egg compositionin birds, but none on woodpeckers. Woodpeckers(Picidae) have among the smallest eggsrelative to their body size of any bird. Idissected Northern Flicker (Colaptesauratus) eggs into shell,yolk, and albumen components, and determined thelipid content of the yolk. The proportional size ofthe yolk in flicker eggs (16%) wasamong the smallest described for any bird. However,the yolk contained a similar amount of lipid(58%) as the yolks of otheraltricial species. The overall energy density inflicker eggs, 3.8 kJ g−1,was also among the lowest reported in birds. Therelative size of the yolk tended toward negativeallometry with increasing total egg mass while theamount of albumen showed positive allometry, butthe confidence intervals for the regression slopesshowed that isometry of these components could notbe excluded. These results demonstrate that flickereggs contain relatively little energy and, comparedto other species, eggs may be relatively cheap forflicker females to produce.
Growth and Plumage Development of Nestling Long-Eared Owls
Authors: Seidensticker Mathew T. , Flockhart D. T Tyler , Holt Denver W. , Gray Kathy
Published: September 2019

We report the growth rates and plumage development of Long-eared Owls (Asio otus) in two developmental stages from hatching to fledging, the nestling period (1–22 days) and prefledging period (23–37 days). We used the logistic growth equation to model nestling mass gain. Mass gain was most rapid during the nestling period. Average mass gain per day was highest between seven and 13 days of age. At 16 days of age nestlings displayed defined facial disks and complete second down. Nestlings left the nest at 22 days of age. Mass gain slowed considerably after nest departure and continued to slow up to fledging. Appearance of defensive and concealment behaviors occurred nearly simultaneously with departure from the nest. To our knowledge this is the first detailed report of nestling growth rates and plumage development for Long-eared Owls in North America.
Old Burns as Source Habitats for Lewis's Woodpeckers Breeding in the Black Hills of South Dakota
Authors: Gentry Dale J. , Vierling Kerri T.
Published: September 2019

Crown-burned pine forests are an important breeding habitat for many cavity-nesting birds, and can serve as a source habitat for some woodpecker species. However, it is unclear if this function continues with postburn succession as predators recolonize burned habitats and snag density declines. Lewis's Woodpeckers (Melanerpes lewis) are considered “burn specialists” and are a species of conservation concern. We monitored Lewis's Woodpeckers nesting in ponderosa pine (Pinus ponderosa) forests to determine the source or sink function of old-burn habitats in the Black Hills of South Dakota (study units burned in 1988 and 1991); concurrently, we examined avian and mammalian predator communities within burned and unburned areas. Between 2002 and 2005 we found 55 Lewis's Woodpecker nests, 51 of which were successful. Using adult and juvenile mortality rates for other melanerpine species taken from the literature, we determined that the old-burn habitats we sampled were acting as sources for Lewis's Woodpeckers. Point counts and tracking tube surveys suggested that both avian and mammalian predators had successfully recolonized these old-burn habitats, as both groups were common in old burns and in unburned forests. The unusually high nesting success of Lewis's Woodpeckers in the Black Hills is likely due to the absence of some common nest predators. While the high success rates might continue, we suggest that the overall contribution of young to the region from these burned sites will decline as suitable habitat components (such as snags) decline with the continuation of postfire succession.
The Effects of Permanent Local Emigration and Encounter Technique on Stopover Duration Estimates as Revealed by Telemetry and Mark-Recapture
Authors: BÄCHLER Erich , Schaub Michael
Published: September 2019

Studies of stopover durations of migrating birds using mark-recapture and resighting techniques are usually restricted to only a part of a stopover site. Therefore, estimates of stopover duration may be negatively biased if birds leave the trapping area permanently, but remain within the stopover site (permanent local emigration). We tested this possible effect by comparing stopover durations of Orphean Warblers (Sylvia hortensis) estimated from recapture and resighting data obtained from a trapping area covering only a part of a stopover site with durations estimated from relocation data of radio-marked individuals sampled over the entire stopover site. To test a possible effect of the different reencounter techniques on stopover duration estimates we compared estimates of stopover duration derived from the recapture and resighting data with those derived from the relocation data restricted to the same trapping area. Stopover duration estimated from relocation data obtained from the entire stopover site was twice as long as stopover duration estimated from recapture and resighting data. While similar estimates of stopover duration were obtained from relocation data when data from only the restricted trapping area were used, the proportion of transients was different between the two data sets. The different estimates of stopover duration were most likely not due to permanent local emigration, but rather to violations of essential model assumptions, such as equal catchability or that the probability of staying for another day is independent of the time a bird has already spent at the stopover site.
Display Behavior and Spatial Distribution of the White-Crowned Manakin in the Atlantic Forest of Brazil
Authors: Castro-Astor Ivandy N. , Alves Maria Alice S. , Cavalcanti Roberto B.
Published: September 2019

We studied the display behavior and spatial distribution of the White-crowned Manakin (Dixiphia pipra, formerly in the genus Pipra) in the Atlantic Forest of the state of Rio de Janeiro, Brazil. The study area included three leks, two apparently solitary display sites, and two “collective display sites,” where definitive-plumaged males, predefinitive-plumaged males, and birds of undetermined sex displayed. The average distance between display sites was 68.0 ± 24.4 m (n  =  8, range  =  41–113 m). Males occupied the same display sites among years. The dispersion pattern of males was typical of exploded or dispersed leks. Males did not display in auditory or visual contact, except at the two display sites that were closest to each other. Lekking White-crowned Manakins used 11 display behaviors and two vocalizations. Four of the 11 display behaviors were recorded only at the collective display sites. We only observed males displaying in the presence of other individuals, regardless of whether it was a collective or solitary display site. Definitive- and predefinitive-plumaged males and birds of indeterminate sex all displayed together. The White-crowned Manakin repertoire of 11 display behaviors indicates a more complex display behavior than previously described.
Free-Living Male Mountain White-Crowned Sparrows Exhibit Territorial Aggression Without Modulating Total or Free Plasma Testosterone
Authors: Lynn Sharon E. , Hahn Thomas P. , Breuner Creagh W.
Published: September 2019

In some species, expression of territorial aggression is accompanied by a rise in testosterone secretion, but in others aggressive behavior is expressed while testosterone levels remain unchanged. Corticosteroid binding globulin (CBG) binds both corticosterone and testosterone in avian plasma. Thus, increasing corticosterone may result in fluctuations in unbound (“free”) testosterone; this could result in greater biological activity of testosterone without an increase in testosterone secretion. We investigated whether such plasma interactions of testosterone, corticosterone, and CBG might result in alterations of free testosterone in male Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha). We conducted simulated territorial intrusions during incubation and compared total and free testosterone of males captured immediately following a simulated territorial intrusion with that of males captured passively. All experimental males showed aggressive behavior, but apparently did not modulate total or free testosterone relative to controls.
Using a Commercially Available Enzyme Immunoassay to Quantify Testosterone in Avian Plasma
Authors: Washburn Brian E. , Millspaugh Joshua J. , Morris Dana L. , Schulz John H. , Faaborg John
Published: September 2019

Using a commercially available testosterone enzyme immunoassay (EIA), we developed and validated an assay procedure for determining testosterone levels in small-volume (20 µL) avian plasma samples. We evaluated this EIA's utility by measuring plasma testosterone levels in Mourning Doves (Zenaida macroura), White-eyed Vireos (Vireo griseus), Red-eyed Vireos (Vireo olivaceus), and Indigo Buntings (Passerina cyanea). Standard biochemical validations (e.g., parallelism, recovery of exogenous testosterone) demonstrated that the assay accurately and precisely measured testosterone in avian plasma. We compared plasma testosterone levels in males and females of all four species and Indigo Buntings in various reproductive stages to physiologically validate the assay's ability to determine biologically important changes in testosterone levels. Plasma testosterone levels were higher in males compared to females in three of four species. Prebreeding and breeding male Indigo Buntings had higher circulating testosterone levels than postbreeding males. Testosterone levels in our study were similar to reported values for other passerine species using radioimmunoassay procedures. Our results suggest that this EIA procedure is very effective for determining testosterone levels in small-volume avian plasma samples and is sensitive enough to detect biologically important changes in the gonadal activity of birds. Thus, this assay has considerable utility for measuring testosterone in small birds (<15 g), from which only small volumes of plasma (20 µL) can be collected.
Subspecific and Temporal Variation in the Structurally Based Coloration of the Ultramarine Grosbeak
Authors: Barreira Ana S. , Lijtmaer Dario A. , Lougheed Stephen C. , Tubaro Pablo L.
Published: September 2019

Ultramarine Grosbeaks (Cyanocompsa brissonii) possess a striking sexual dichromatism, with males dark blue and females brown. There are two subspecies in Argentina: the larger-bodied C. b. argentina, which is common in shrubs and semiopen areas, and the smaller C. b. sterea that inhabits forests. We measured reflectance spectra of six plumage patches from study skins to evaluate the possibility of color differences between males of each subspecies and temporal variation in plumage coloration. We found differences between subspecies in color brightness, hue, saturation, and UV chroma in the plumage patches of more conspicuous coloration, which could be related to ambient light differences between the environments that each subspecies inhabits. We also documented temporal color variation in some plumage patches, in particular a gradual decrease of UV reflectance and a gradual increase in hue after molting, possibly attributable to feather wear.
Potential Ecotoxicological Significance of Elevated Concentrations of Strontium in Eggshells of Passerine Birds
Authors: Mora Miguel A. , Taylor Robert J. , Brattin Bryan L.
Published: September 2019

We investigated the occurrence and potential ecotoxicological significance of elevated concentrations of strontium (Sr) in eggshells of nine passerine birds from four regions in Arizona. Concentrations of Sr in eggshells ranged from 70 to 1360 µg g−1 dry weight (overall mean  =  684 ± 345 SD µg g−1 dw) for the four regions. 23% of the eggshells had Sr concentrations greater than 1000 µg g−1 dw. To our knowledge, these are among the highest levels of Sr that have been reported in bird eggshells in North America. Of the nine species, Brown-headed Cowbirds (Molothrus ater) had the greatest concentrations of Sr. There was a significant positive correlation between Sr and calcium (Ca), and between barium (Ba) and Ca. Ca, Sr, and Ba interact with each other and can exert similar chemical and pharmacological effects. Mean (n ≥ 3) eggshell:egg ratios for Sr varied with species and ranged from 6.1:1 to 40.2:1; ratios for individual eggs reached 92.7:1. Mean Sr/Ca values ranged from 1.3 × 10−3 to 3.0 × 10−3 and mean eggshell thickness ranged from 83 ± 6 to 120 ± 9 µm for all species. Eggshell thickness was not significantly correlated with Sr for any species but tended to increase with Sr concentrations. We postulate that high concentrations of Sr in the shell could affect later-stage embryos by possible interference with Ca metabolism and bone growth, resulting in reduced hatching success and potential minor beak deformities.
Foraging Behaviors of Surf Scoters and White-Winged Scoters During Spawning of Pacific Herring
Authors: Lewis Tyler L. , Esler Daniel , Sean Boyd W.
Published: September 2019

Winter diets of Surf (Melanitta perspicillata) and White-winged Scoters (M. fusca) are composed primarily of bivalves. During spawning of Pacific herring (Clupea pallasi) in early spring, scoters shift their diets to herring eggs. Using radio-telemetry, we contrasted scoter foraging behaviors between winter and herring spawning periods. Scoters increased their dive durations during herring spawning, likely to maximize the amount of roe consumed per dive; in winter, dives were typically terminated upon clam capture. Scoters spent approximately 50% less time foraging (min underwater hr−1) and decreased their dive rate (dives hr−1) by 70% when feeding on roe. The observed reduction in time spent foraging was presumably caused by the abundance of herring eggs, and thus a reduction in prey search-time. Scoters were able to meet energetic requirements with reduced effort, despite potentially increased demands related to spring fattening. Less time spent foraging may also allow more time for premigratory courtship behaviors.
Sound Transmission and Song Divergence: A Comparison of Urban and Forest Acoustics
Authors: Slabbekoorn Hans , Yeh Pamela , Hunt Kimberly
Published: September 2019

Degradation of acoustic signals during transmission presents a challenging selection pressure for animals dependent on vocal communication. Sound transmission properties differ among habitats and may drive the evolution of vocal signals in different directions. Urban habitat is expanding worldwide and an increasing number of species, including many birds, must now communicate around buildings and over concrete. Urban habitats are evolutionarily new, although to some extent they may acoustically resemble rocky habitat such as cliffs and canyons. Neither urban nor these natural habitats have been studied in any detail for the selection pressure they may exert on animal communication. Dark-eyed Juncos (Junco hyemalis) commonly inhabit montane pine forests across North America, but for about 25 years an isolated population has been successfully breeding in an urban environment in southern California. We investigated potentially divergent selection pressures on junco songs, using sound transmission experiments with artificial sound stimuli, in natural forest habitat and in this urban habitat. Transmission properties differed significantly, resulting in tails of reflected sound with gradually declining amplitude in the forest and in multiple discrete echoes in the urban environment. We expected environmental selection in urban habitat to favor shorter songs with higher frequencies and slower trill rates. Despite the presence of relatively short urban songs, there was no significant shortening overall. There were also no differences in trill rates, but we did find a significantly higher minimum frequency in the urban junco population compared to three of four forest populations. Although the pattern of song divergence was not consistent and it is difficult to draw firm conclusions from this single urban population, our transmission results suggest that echoes could be important in shaping urban birdsong.
Habitat, Dominance, and the Phenotypic Quality of Male Black-Capped Chickadees
Authors: van OORT Harry , Otter Kenneth A , Fort Kevin T , McDONELL Zoe
Published: September 2019

The provisioning of offspring is limited by resource abundance and is therefore likely to vary with habitat quality and the ability of parents to obtain food. Provisioning effort may also vary because males choose different life-history strategies depending on their rank and environment. Socially dominant males have higher costs of self-maintenance compared with subordinates, yet this is likely compensated for by their priority access to resources. It is unclear, however, whether this translates into benefits for females through male provisioning effort, and how this might vary with habitat suitability. We assessed patterns of body condition, blood hematocrit levels, and provisioning effort of dominant and subordinate male Black-capped Chickadees (Poecile atricapillus) breeding in two habitats known to differ in quality. Within ranks, males were similar in size and condition across habitats. Dominant males were not structurally larger than subordinates, but they were in better condition than subordinates in both habitats. There was an additive effect of habitat and dominance rank on hematocrit level; dominant males had higher hematocrit levels than subordinates regardless of habitat, and all males breeding in poor habitat had elevated hematocrits. A habitat-rank interaction revealed a greater disparity in provisioning rates among dominant and subordinate males in poor habitats. These results suggest that dominant males may be particularly good mates when resources are scarce.
Neotropical Forest Bird Communities: A Comparison of Species Richness and Composition at Local and Regional Scales
Authors: Blake John G.
Published: September 2019

Species richness and composition of Neotropical forest bird communities vary spatially at both large and small scales, but previous comparisons based on 100 ha plots have not replicated plots within a region. I sampled birds in two 100 ha plots in lowland forest of eastern Ecuador to better understand how species richness and composition vary over smaller spatial scales. Birds were sampled in February and April of 2002–2005 (only in February in 2005). Plots were approximately 1.5 km apart in predominantly terra firme forest. A total of 319 species (285 and 281 per plot) from 43 families were represented in ~16 000 detections per plot; number of species and detections per sample averaged approximately 185 and 2300, respectively. Numbers of species and detections per family were strikingly similar in the two plots, but numbers of detections of individual species often differed, likely in response to differences in habitat between the two plots. Species richness and composition were similar in many respects to comparable data from Ecuador, Peru, and French Guiana, but differed from those of Panama. Differences were most pronounced at the species level, less at the genus level, and least when comparisons were based on families. Differences among sites in South America were correlated with geographic distance at the species and genus levels, but not at the family level. Results illustrate the value of replicated plots within a region for understanding how species richness and composition can vary at small spatial scales, and highlight the importance of beta diversity for determining overall patterns of regional diversity.