bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal Migration and Genetic Population Structure in House Wrens
Authors: Arguedas Nidia , Parker Patricia G.
Published: September 2019

Neotropical migrant birds have undergone significant changes in population size, due in part to alterations in the landscape in their breeding range. Some alterations have resulted in the isolation of areas containing optimal habitat for breeding. Isolation between habitat fragments could reduce gene flow between populations, which might result in loss of genetic variation due to genetic drift. To test whether isolation due to distance between populations may affect migratory birds as much as sedentary birds, we used four microsatellite loci as genetic markers to compare gene flow and population structure in migratory and sedentary House Wrens (Troglodytes aedon and T. musculus, respectively). If migratory behavior enhanced gene flow, we expected to find that populations of migratory birds were genetically more similar than populations of sedentary birds, and that gene flow declined more rapidly with distance in sedentary than in migratory populations. Blood samples were collected from 18–25 migratory House Wrens at each of six sites in Ohio separated by distances from 25 to over 300 km, and from 16–20 sedentary House Wrens at each of six sites in Costa Rica, also at distances up to 350 km. We used heterologous microsatellite primers to obtain estimates for RST (population subdivision) and Nm (number of immigrants per generation) in relation to distance between pairs of populations. In the migratory populations, Mantel permutational tests showed no effect of distance on RST or Nm at distances between 25 and 300 km. In the sedentary birds, RST increased and Nm decreased significantly as distance between populations increased from 25 to 300 km. FST values were not different from those obtained using Slatkin's (1995) RST statistics. These results are consistent with our hypothesis that migratory behavior enhances gene flow.
Use of Arboreal Termitaria by Nesting Birds in the Peruvian Amazon
Authors: Brightsmith Donald J.
Published: September 2019

I documented the use by nesting birds and availability of arboreal termite nests (termitaria) in the Peruvian Amazon. Birds occupy about 1% of the termitaria annually, suggesting that termitarium availability does not limit reproductive output. Birds choose termitaria that are larger and higher than average, and the three most common termitarium-nesting species differ in their use of termitaria. Two species of Brotogeris parakeets use termitaria with similar characteristics, but Tui Parakeets (B. sanctithomae) nest in young forests and edge habitats whereas Cobalt-winged Parakeets (B. cyanoptera) use mature forests. Termitaria used by Black-tailed Trogons (Trogon melanurus) are larger and lower than those used by the two Brotogeris species. The contention that birds usually nest in termitaria still occupied by termites was upheld, but the presence or absence of termites did not explain a significant proportion of the difference between used and available termitaria after removing the effects of height, volume, and substrate type. Birds choose to nest in termitaria inhabited by both termites and aggressive biting ants (Dolichoderus sp.). These ants may be protecting the birds' nests by attacking predators or by providing a sort of “olfactory camouflage.”
Use of Two Song Categories by Golden-Cheeked Warblers
Authors: Bolsinger Jeffrey S.
Published: September 2019

I tape-recorded and counted the songs of color-banded Golden-cheeked Warblers (Dendroica chrysoparia) on Fort Hood, Texas in 1993 and 1994 to determine whether males use a two-category song system common to many wood-warbler species. More than 97% of all songs I documented belonged to two categories: A and B. A songs were higher in frequency, shorter, less complex, and were delivered at lower rates than B songs. Males used A songs primarily early in the nesting season, when near females, and from the interior of territories. In contrast, B songs were more common later in the nesting season, at dawn, and when males sang near territory boundaries. Songs delivered near territory edges were usually sung from one or two preferred perches on each male's territory that often coincided with the edge of a cliff or a break in the forest canopy. Based on these data, and in contrast to the implications of an early account of Golden-cheeked Warbler song use, this species shares the song system used by many wood-warbler species. Furthermore, the patterns of song use that I observed suggest that males do not sing randomly with respect to time or location on territory, and monitoring efforts that assume random singing across time and space may result in inaccurate or biased estimates of population sizes and habitat preferences.
The Diet of the Magnificent Frigatebird During Chick Rearing
Authors: Calixto-Albarrán Itzia , Osorno José-Luis
Published: September 2019

We describe the diet of the Magnificent Frigatebird Fregata magnificens at Isla Isabel off the Pacific coast of Mexico based on 158 regurgitates (555 prey items) from males, females, chicks, and juveniles. The diet included 50 species of fishes (21 identified to genus only), 1 species of squid, and 2 species of crustaceans. Diplectum pacificum and Anchoa lucida were the most frequent species of fish in the frigatebird's diet. No differences in prey composition or prey size were found between males and females, but females disgorged 62% more food. This difference mirrors the bigger size (15% larger than males) and larger contribution of females to chick feeding. Flying juveniles consumed prey in different proportions than the adults and disgorged marginally more food. Juveniles may obtain food in different patches than adults and complement this source with maternal feedings, or they may be more likely to regurgitate. Diet composition of males, females, and flying juveniles changed during the 4-month period of this study, but the mass of regurgitates did not change as the breeding season progressed, suggesting that availability of prey species changes over time. Most of the diet of this population probably comes from opportunistic feeding on fisheries, because the variety of fishes disgorged is remarkably similar to the published list of fishes discarded by prawn-fishing boats in the area. If our assumption is true, kleptoparasitism and direct fishing are only marginally represented in the diet of this population.
Nocturnal and Diurnal Foraging Activity of Hawaiian Albatrosses Detected With a New Immersion Monitor
Authors: Fernández Patricia , Anderson David J.
Published: September 2019

We used a new immersion monitor to study the foraging movements of two species of albatrosses that nest in the Hawaiian Islands. The monitors showed that breeding male Black-footed Albatrosses (Phoebastria nigripes) land on the water more frequently during the day than at night. Breeding male Laysan Albatross (Phoebastria immutabilis) behavior was more variable and also showed a diurnal bias. We found no evidence of a nocturnal foraging bias in either species; in particular, these species do not seem to be limited to live capture of nocturnally available squid. Such squid may, nonetheless, contribute to the diet as a result of scavenging.
Effects of Forest Fragment Size and Successional Stage on Mixed-Species Bird Flocks in Southeastern Brazil
Authors: Maldonado-Coelho Marcos , Marini Miguel Â
Published: September 2019

We analyzed patterns of species richness, size, structure, and composition of mixed-species flocks in relation to forest fragment size and forest successional stage during dry and rainy seasons, at the state of Minas Gerais, southeastern Brazil. Three forest fragments (1.7, 50, and 200 ha) were used for fragment size analysis, and two fragments (200 and 300 ha) were used for successional stage analysis. Fragment size and season affected flock richness, size, stability, and composition. In the 1.7-ha fragment, flock species richness, size, and stability were significantly different only during the rainy season. Fragment successional stage also influenced flock richness and size, although season did not. Flock composition also had changes related to fragment successional stage. Fragment geometry seems to be an important factor influencing flock structure and composition.
The Spatial Response of Male Hooded Warblers to Edges in Isolated Fragments
Authors: Norris D. Ryan , Stutchbury Bridget J. M. , Pitcher Trevor E.
Published: September 2019

We tested whether Hooded Warblers (Wilsonia citrina) avoided abrupt forest edges by radiotracking males breeding in small, isolated forest patches (0.5–2.0 ha) in northwest Pennsylvania. Because territory edges were synonymous with abrupt forest edges in all cases, we compared space use patterns with males radiotracked in a nearby continuous forest (150 ha), where we defined edge from territorial boundaries. Based on the proportion of edge to core area, males in both habitats avoided the area within 20 m of the edge, implying that males responded to the presence of territory edge rather than forest edge. Surprisingly, however, males in isolated fragments used the edge area significantly more than males in continuous forest, even when measured against the relative amount of edge area within each territory. Elevated levels of edge use were not related to distance of nests to edges, nest stage, or time of day. We conclude that the presence of physical edges is not the sole determinant of territorial space use in this species and there are likely additional social factors influencing occupancy rates in small, isolated woodlots. Therefore, definitions of forest-interior species based on edge use need to be reconsidered.
Demography of a Declining Population of Warbling Vireos in Coastal California
Authors: Gardali Thomas , Ballard Grant , Nur Nadav , Geupel Geoffrey R.
Published: September 2019

We investigated population trends, adult survival, and productivity indices of a breeding population of Warbling Vireos (Vireo gilvus) in north coastal California using capture-recapture data from 19 years of standardized mist-netting conducted at Point Reyes National Seashore. We found significant long-term declines in abundance of both breeding and migratory Warbling Vireos. In addition, we found a significant long-term decline of hatching-year birds captured during the breeding season. The number of new adults in a given year, defined as those birds not previously banded and assumed to be an index of adult recruitment, was significantly correlated with the capture rate of hatching-year birds in the previous year, suggesting a link between reproductive success and adult abundance and recruitment. Our analysis of capture-recapture data provided an estimate of 50.4% for adult annual survival, similar to estimates for other species in stable populations. We could detect no temporal trend in survival. Nest survivorship from areas near our netting site was relatively low. We suggest that the decline of breeding and migratory populations of Warbling Vireos observed in coastal California may be the result of low productivity on the breeding grounds.
Molt of the Gray Vireo
Authors: Voelker Gary
Published: September 2019

Using museum specimens, I document the molt cycles and molting grounds of the Gray Vireo (Vireo vicinior). During prebasic molts, adult female Gray Vireos replace their primaries in 57 days, whereas adult males take 70 days; all body plumage is replaced during this molt. Prebasic molts occur almost exclusively on the breeding grounds; just 3 of 41 specimens replacing primaries were collected away from breeding grounds. No molting specimens were collected from wintering areas. Prealternate molt occurs on the wintering grounds, and appears limited to the replacement of innermost secondaries and a limited molt of body plumage. By performing prebasic molt on breeding grounds, the Gray Vireo differs from several other western breeding passerine species that use desert regions of the southwestern United States and northwestern Mexico to exploit late summer food resources. The areas of these southwestern desert regions used by other species form a small portion of the breeding grounds, and encompass the entire wintering grounds, of Gray Vireos. I hypothesize that this contrast in molting regions is not due to differences in the general timing of prebasic molts among these species; rather, the contrast may be due to constraints imposed on Gray Vireos by a dietary shift to fruit during winter and the need to defend winter territories.
Nesting Effort of Northern Pintails in Alberta
Authors: Guyn Karla L. , Clark Robert G.
Published: September 2019

We studied nesting effort and success of Northern Pintails (Anas acuta) in southern Alberta. Annual nesting success estimates ranged from 6–18%. Clutch size averaged 7.2, and declined in a simple curvilinear fashion with nest initiation date. We found no relationship between egg size and clutch size or evidence from one year to the next of a trade-off between current and future investment in eggs. Within-year renesting rate ranged from 55%, based on a sample of 20 decoy-trapped females that lost their first nests to predators, to 85% based on a sample of 13 nest-trapped females forced to renest when we removed their clutches. Greater investment in initial clutches led to longer delays in laying replacement clutches. Because delays in renesting are costly (late-nesting females produce fewer offspring), females must contend with a trade-off between maximizing reproductive output in initial clutches versus the risk of delayed renesting if the first clutch should fail. We suggest that pintail reproductive traits have evolved primarily in response to short nesting seasons and variable environments.
Interactive Effects of Vegetation and Predators on the Success of Natural and Simulated Nests of Grassland Songbirds
Authors: Dion Nancy , Hobson Keith A. , Larivière Serge
Published: September 2019

We examined the influence of vegetation and predator community on nesting success of songbirds in the grasslands of eastern North Dakota, USA. Each year, eight sites were chosen: four were subject to predator removal, and four were non-removal sites. On each site, nests of grassland songbirds were monitored, and simulated nests were used to examine how vegetation characteristics at nests affect nest success. Vegetative characteristics at simulated nests did not differ from those at natural nests, but successful natural nests had greater forb and lesser grass cover than unsuccessful nests, whereas no differences in vegetation were detected between successful and depredated simulated nests. On non-removal sites, small mammals and ground squirrels (Spermophilus sp.) depredated nests in taller and denser cover when compared to nests destroyed by medium-sized mammals and birds. On removal sites, we found no difference in vegetation characteristics of nests depredated by different predator types. However, each group of mammalian predators depredated simulated nests with different vegetation characteristics on removal versus non-removal sites. On sites where predators were removed, small mammals and ground squirrels preyed on simulated nests in shorter vegetation containing fewer forbs, ground squirrels preyed on nests with higher grass cover and lower vertical density, and medium-sized carnivores preyed on nests in taller vegetation. These results support the hypothesis that high predator diversity may reduce the chance of “safe” nest sites, and suggest that the behavior of low-level predators may change when top-level predators are removed.
Seasonal Energetics of Mountain Chickadees and Juniper Titmice
Authors: Cooper Sheldon J.
Published: September 2019

I used behavioral, meteorological, and laboratory metabolism data to calculate daily energy expenditure (DEE) in seasonally acclimatized Mountain Chickadees (Poecile gambeli) and Juniper Titmice (Baeolophus griseus). Analyses of laboratory metabolic data revealed that foraging energy requirements were not significantly higher than alert perching energy requirements. Respective DEE of chickadees and titmice were 48.8 kJ day−1 and 48.3 kJ day−1 in summer and 66.3 kJ day−1 and 98.7 kJ day−1 in winter. DEE as a multiple of basal metabolic rate (BMR) was 2.31 in summer chickadees and 1.91 in summer titmice. DEE was 2.70 times BMR in winter chickadees and 3.43 times BMR in winter titmice. The marked increase in calculated DEE in winter birds compared to summer is in contrast to a pattern of increased DEE in the breeding season for several avian species. These data suggest that winter may be a period of even greater stringency for small birds than previously believed.
Responses of Birds to Broken Eggs in Their Nests
Authors: Mallory Mark L. , Rendell Wallace B. , Robertson Raleigh J.
Published: September 2019

We tested the responses of two bird species which nest on unmovable substrates (e.g., cavities and walls) to simulated and actual egg damage in their nest. Tree Swallows (Tachycineta bicolor) and Barn Swallows (Hirundo rustica) removed broken eggs and continued to incubate the rest of their clutch, but response times took up to 8 days, and observed rejection rates were lower than reported for some other passerines. Collectively, these data and other studies suggest that broken eggs represent a continuing selection pressure to which all birds respond, although there appears to be some variability among species in the strength and speed of the response to damaged eggs.
Brain, Eye, and Skull Growth in Embryonic Geese
Authors: Gille Uwe , Zachen Frank , Salomon Franz-Viktor
Published: September 2019

We tested the hypothesis that bill proportions at hatching are a byproduct of overall skull proportions which are a result of constraints of brain growth. We measured brain and eye weights, eye diameter, and some skull dimensions in domestic geese (Anser anser f. domestica) varying in age between embryonic day 7.5 and 29.5 (hatching), and in five adult geese. With respect to age, weights show divergent growth patterns resulting in complex allometry for eye but simple allometry for brain weight. This differs from the situation in Galliforms and probably reflects the high cerebralization of Anseriforms. Length measurements show similar growth patterns. Cranial length realizes a larger part of overall growth during incubation when compared to facial length. Cranial width is similar to eye diameter and brain weight. Bill width exhibits a unique growth pattern. Bill proportions are similar to the whole head but differ from those of the bony brain capsule. Therefore, although all craniometric measurements strongly correlate to brain size, brain growth probably influences growth of the cranial but not of the facial part of the skull.
Cloacal Microbes in House Sparrows
Authors: Stewart Reuven , Rambo T. Birch
Published: September 2019

We examined the communities of bacteria and fungi associated with the cloaca of adult House Sparrows (Passer domesticus) to investigate whether microbes could be transferred during copulation and thus represent a cost to mating. The levels of microbes in the cloacae of the male and female of eight breeding pairs were significantly correlated. The levels of microbes on the rim of the cloacal protuberance, which comes into direct contact with another bird during copulation, were similar to those inside the cloaca. These findings are consistent with microbes being transferred during copulation. Females could also receive non-cloacal pathogens during copulation, given that two of five males sacrificed had microbes within their testes, which could be incorporated into the ejaculate. Undeveloped eggs were screened for the presence of microbes, although only a low proportion (18%) was contaminated. It seems unlikely that microbial contamination is a general cause of egg failure in this species.
Infectious Bursal Disease Virus Antibodies in Eider Ducks and Herring Gulls
Authors: Hollmén Tuula , Franson J. Christian , Docherty Douglas E. , Kilpi Mikael , Hario Martti , Creekmore Lynn H. , Petersen Margaret R.
Published: September 2019

We measured antibodies to infectious bursal disease virus (IBDV) in blood of nesting Common Eider (Somateria mollissima) females and immature Herring Gulls (Larus argentatus) in the Baltic Sea, and in blood of Spectacled Eider (Somateria fischeri) females nesting in a remote area of western Alaska. Positive (≥ 1:16) IBDV titers occurred in 75% of the eiders and 45% of the Herring Gull chicks. In eiders, the prevalence of positive titers differed among locations. We found no evidence that IBDV exposure impaired the immune function of Herring Gull chicks, based on their response to inoculation of sheep red blood cells. We suggest that eider ducks and Herring Gulls have been exposed to IBDV, even in locations where contact with poultry is unlikely. The presence of this virus in wild bird populations is of concern because it causes mortality of up to 30% in susceptible poultry.
Satellite Tracking of Cory's Shearwater Migration
Authors: Ristow Dietrich , Berthold Peter , Hashmi Dean , Querner Ulrich
Published: September 2019

Transmitters were attached to four adult male Cory's Shearwaters (Calonectris diomedea) caught at their breeding sites off Crete, Greece, in autumn 1998. The birds had left the Mediterranean by the beginning of December. Two were last recorded in the eastern tropical Atlantic in January/February. The other two wintered east of the Mid-Atlantic Ridge, one at about 10°N, the other one in equatorial waters, and could be tracked until return migration in March/April. The seasonal variation in travel speed is in accordance with a conventional pattern of migration with phases of migration and wintering, rather than continuous movement throughout the nonbreeding cycle. The birds left the Mediterranean later and wintered farther north than expected. We suggest that the known longitudinal cline in body size, morphology, and vocalizations of Cory's Shearwater may also be found in migration behavior.
Effects of Sampling Design on Age Ratios of Migrants Captured at Stopover Sites
Authors: Kelly Jeffrey F. , Finch Deborah M.
Published: September 2019

Age classes of migrant songbirds often differ in migration timing. This difference creates the potential for age-ratios recorded at stopover sites to vary with the amount and distribution of sampling effort used. To test for these biases, we sub-sampled migrant capture data from the Middle Rio Grande Valley of New Mexico. We created data sets that reflected the age ratios of migrants that would have been captured with stratified and concentrated designs at four levels of mist-netting effort. Analysis of these data indicate that age-ratios of Neotropical migrants varied significantly with sampling design, but not with sampling effort. More after-hatch-year Neotropical migrants were captured with stratified than with concentrated sampling designs. Age-ratio of temperate migrants did not vary with either amount of sampling effort or sampling design. Sampling design is an important consideration in the interpretation of age ratios among stopover sites, and standardization of sampling among sites could improve our understanding of differential migration of age classes.
Time-Activity Budgets of Harlequin Ducks Molting in the Gannet Islands, Labrador
Authors: Adams Peter A. , Robertson Gregory J. , Jones Ian L.
Published: September 2019

We studied the time-activity budgets of Harlequin Ducks (Histrionicus histrionicus) molting at the Gannet Islands, Labrador in the summer of 1998. For the entire population, a large proportion of time was spent hauled out of the water (61.4%), and resting (53.5%). Only a small proportion of time was spent foraging (11.6%). Male Harlequin Ducks undergoing the pre-basic molt were hauled out of the water significantly more (92.2%) than males in basic plumage (8.1%). Males undergoing the pre-basic body feather molt foraged significantly less (1.7%) than males in basic plumage (17.7%). Harlequin Ducks do not appear to increase their food intake to meet the nutritional requirements of molt. Instead they may try to reduce thermoregulatory and maintenance costs by engaging in activities that do not consume much energy, and by staying out of cold water while their plumage is not intact. Furthermore, they may deliberately lose body mass while molting to regain the ability to fly at an earlier stage of wing molt.
A New Hybrid Warbler (Dendroica Nigrescens × D. Occidentalis) and Diagnosis of Similar D. Townsendi × D. Occidentalis Recombinants
Authors: Rohwer Sievert , Wood Christopher , Bermingham Eldredge
Published: September 2019

We use 13 color characters to describe the first known Dendroica nigrescens × D. occidentalis hybrid. Because this specimen was collected in the southeastern Cascade Mountains of Washington during the breeding season, D. townsendi, D. occidentalis, and D. nigrescens are the only plausible parents for a hybrid male falling within the black-throated clade of Dendroica warblers. Multiple character states in the hybrid refute the alternative parental combinations, townsendi × occidentalis and townsendi × nigrescens. Two characteristics of this hybrid suggested further tests of the parentage of 38 problematic hybrids that were treated previously as townsendi × occidentalis recombinants by assumption only. These hybrids lack yellow on their breast, the only character that refutes a nigrescens × occidentalis parentage. The new hybrid is intermediate between nigrescens and occidentalis in the color of its posterior face and its anterior crown; thus, we scored these new characters in the 38 problematic hybrids. None of these 38 specimens was intermediate or white in either of these regions, and there was no correlation between having tinges of white in these regions and the extent of flank streaking. These results fail to support nigrescens in the parentage of these 38 specimens; furthermore, none of the problematic hybrids carried a nigrescens mitochondrial DNA haplotype. Thus, we conclude that all are unusual recombinants of townsendi × occidentalis hybridization, rather than nigrescens × occidentalis hybrids.
Breeding and Post-Breeding Habitat Use by Forest Migrant Songbirds in the Missouri Ozarks
Authors: Pagen Rich W. , Thompson III Frank R. , Burhans Dirk E.
Published: September 2019

We compared habitat use by forest migrant songbirds during the breeding and post-breeding periods in four Missouri Ozark habitats: mature upland forest, mature riparian forest, 9- to 10-year-old upland forest, and 3- to 4-year-old upland forest created by clearcutting. Adult forest-ground species showed a decrease in abundance in all habitats during the post-breeding period, but hatching-year birds of one of the two forest-ground species were most abundant in early-successional forest during this time. Adults of the two forest-canopy species tended to increase in abundance in 3- to 4-year-old forest from breeding season to post-breeding season. During the breeding season, some forest species were detected with mist-nets in the two early-successional habitats, but infrequently or not at all with point counts in those habitats. Forest birds captured in early-successional habitats during the breeding season may have been nonbreeding floaters, or may have been foraging there from nearby territories in mature forest. Dense shrubs or young trees in early-successional forest may provide habitat for nonbreeding and post-breeding forest migrant songbirds in the Missouri Ozarks.
Breeding Bird Abundance in Bottomland Hardwood Forests: Habitat, Edge, and Patch Size Effects
Authors: Sallabanks Rex , Walters Jeffrey R. , Collazo Jaime A.
Published: September 2019

We studied breeding bird communities in extensive bottomland hardwood forests along the lower Roanoke River in North Carolina during 1992 and 1993. We documented a rich avian community and recorded exceptionally high densities of two species (Prothonotary Warbler Protonotaria citrea, Acadian Flycatcher Empidonax virescens), as well as modest densities of three species rarely encountered elsewhere in the region (Cerulean Warbler Dendroica cerulea, Swainson's Warbler Limnothlypis swainsonii, American Redstart Setophaga ruticilla). The effects of patch size and edge on bird abundance were small in this forested landscape, but forest type had a large effect. We found half of the species analyzed to differ in abundance between the two primary habitat types, swamp forest and levee forest. In contrast, no species was consistently more abundant at patch interiors than near edges, and only two forest birds were more common in large compared with small patches. Species analyzed included permanent residents, short-distance migrants, Neotropical migrants, and those identified as forest-interior and area-sensitive species in other studies. Our results suggest that the Roanoke River bottomland forests may be functioning effectively as a reserve for a number of bird species.
Pair Formation and Copulation Behavior in Least Flycatcher Clusters
Authors: Tarof Scott A. , Ratcliffe Laurene M.
Published: September 2019

Least Flycatcher Empidonax minimus pairs form dense clusters of territories on the breeding grounds. We describe pair formation and copulation behavior (both within- and extra-pair) in Least Flycatcher clusters. Pair formation involved a complex behavioral sequence of trill vocalizations and visual display. Within-pair copulations were five times more likely to achieve cloacal contact than were extra-pair copulations. Least Flycatchers exhibited an overall within-pair mating effort of 2.0 ± 0.5 events pair−1 hr−1 compared to an extra-pair mating effort of 1.8 ± 0.3 events pair−1 hr−1. Within- and extra-pair mating behavior by focal birds were distinctly different with respect to rate, conspicuousness, duration, aggression intensity, and pre-copulatory display. The rate of territory incursions for extra-pair copulations was high. We discuss copulation behavior in the context of male and female mating tactics, and highlight the disparity in our knowledge of mating behavior in other members of this genus.
Artificial Nest Predation and Abundance of Birds Along an Urban Gradient
Authors: Jokimäki Jukka , Huhta Esa
Published: September 2019

We studied nest predation pressure on birds along an urban gradient in urban parks in three Finnish towns. Artificial ground nests with Japanese Quail (Coturnix coturnix japonicus) eggs were depredated more in the urban area than in the adjacent forest area. Within each town, the nest predation rate was higher in the town center than in the less urbanized area of detached houses. Predation rates did not vary from year to year or between study towns. Abundances of generalist avian predators were higher in the town center than in the area of detached houses and in the surrounding forest area. Most of the nests in the town center were destroyed by avian predators. Predation rate of artificial nests in each of the town areas was higher in managed parks than in unmanaged parks, presumably due to the less dense vegetation in the managed than the unmanaged parks. A test involving covering nests revealed that artificial nests covered by adjacent vegetation survived better than nests with less cover. In our study, artificial nest loss reflected the distribution of avian nest predators. Ground nesters were present at lower abundances in areas where concealing vegetation was missing and avian nest predation was high. Apparently, nest predation is one of the several possible mechanism affecting urban bird assemblages.
Do Band-Tailed Pigeons Seek a Calcium Supplement at Mineral Sites?
Authors: Sanders Todd A. , Jarvis Robert L.
Published: September 2019

We tested the hypotheses that mineral sites in western Oregon are used by Band-tailed Pigeons (Columba fasciata) to supplement dietary calcium and sodium. We compared mineral composition of sites used by Band-tailed Pigeons, adjacent unused sites, and three major food items during the nesting season. Sixty-five percent of used mineral sites were low in calcium (<200 ppm), whereas mean concentrations in food items were high (1,960–2,290 ppm). All but one used mineral site were high in sodium (≥678 ppm), whereas mean concentrations in food items were low (20–254 ppm). Food items were high in mean concentrations of potassium (12,470–26,980 ppm) and potassium:sodium ratios (138–656). Used and adjacent, unused, estuary mineral sites were similar in calcium and sodium concentrations. We hypothesize that because of insufficient sodium intake and inefficient sodium retention, Band-tailed Pigeons seek a sodium source to supplement their diet during the nesting season. Use of mineral sites probably depends upon sodium concentration, but also vegetation structure, development, human activity, and congregation use by Band-tailed Pigeons. Used mineral sites appear to be scarce in western Oregon, and are seemingly essential resources for this species. Eighty-six percent of known currently-used mineral sites are privately owned and subject to possible alteration from land-use practices. Mineral sites used by Band-tailed Pigeons should be included in the overall management scheme for maintaining stable breeding populations of this species.
A Molecular Phylogeny of the Dove Genus Zenaida: Mitochondrial and Nuclear DNA Sequences
Authors: Johnson Kevin P. , Clayton Dale H.
Published: September 2019

We reconstructed a phylogeny for the seven species of doves in the genus Zenaida on the basis of a combined analysis of mitochondrial (ND2 and cytochrome b) and nuclear (fibrinogen intron 7) DNA sequences. This phylogeny, which is completely resolved, is well supported with all nodes showing greater than 50% bootstrap support. There was no significant conflict between trees based on each gene independently, although trees produced from fibrinogen intron 7 did not resolve relationships among five of the Zenaida species. The species status of Z. graysoni, as well as that of Z. meloda, is suggested based on their divergence from sister taxa (about 1% and 4%, respectively) and other differences. Zenaida can be divided into two major groups: Zenaida asiatica and Z. meloda versus Z. aurita, Z. galapagoensis, Z. auriculata, Z. graysoni, and Z. macroura.
Species Limits and Recent Population History in the Curve-Billed Thrasher
Authors: Zink Robert M. , Blackwell-Rago Rachelle C.
Published: September 2019

We surveyed 1,115 base pairs of mitochondrial DNA sequence from three gene regions in 66 Curve-billed Thrashers (Toxostoma curvirostre) taken from throughout their range. We found that populations sorted unambiguously into three groups. Two of these groups, the Curvirostre and Palmeri groups, have been known for many years because of their distinctive phenotypic characteristics, and their status was recently confirmed with an intensive morphometric analysis. The third (southern) group consists of populations in Puebla and Oaxaca, Mexico. The strong morphological and mtDNA distinctiveness of the Curvirostre and Palmeri groups suggests that they warrant species status. We recommend that more specimens of the southern group be obtained prior to formal taxonomic recognition of this form. Coalescence analyses suggest that the Curvirostre group has undergone a recent population increase, whereas the Palmeri group seems to have been more stable in its Sonoran Desert range.
Pacific Coast and Southwest Interior Populations of the Hutton's Vireo Differ in Basic Song Parameters
Authors: Baril Colette T. , Barlow Jon C.
Published: September 2019

Comparisons of song parameters, including syllable length and maximum and minimum frequency, from six populations of the Hutton's Vireo (Vireo huttoni) show differences in syllable length and minimum frequency measurements. Specifically, syllables produced by Pacific coastal birds tend to be shorter than those from southwest interior populations, although these differences are not statistically significant at the pairwise-comparison level. Syllables produced by most coastal populations have significantly higher mean minimum frequencies when compared with those from interior populations. Differences between songs of coastal and interior populations are consistent with genetic differences that separate the two groups. Differences in song may be attributed to the acoustical properties of coastal versus interior habitats.
Roost Site Selection of Great Horned Owls in Relation to Black Fly Activity: An Anti-Parasite Behavior?
Authors: Rohner Christoph , Krebs Charles J. , Hunter D. Bruce , Currie Douglas C.
Published: September 2019

We document a shift in roosting behavior of Great Horned Owls (Bubo virginianus) from winter and late spring to summer. During summer, Great Horned Owls roosted near the ground or exposed on open ground, whereas they chose concealed perches at mid-canopy level for the rest of the year as typical for forest owls. This shift of roosting behavior coincided with the emergence of ornithophilic black flies, which transmit avian malaria (Leucocytozoon spp.). The shift in roosting behavior was consistent with measurements of parasite exposure at different habitat positions. Black fly activity was highest at mid-canopy level, and almost no black flies were active on open ground. Ground-roosting was not caused by poorly developed flying capability of juveniles, because solitarily-roosting adult owls showed the same behavioral shift in a second year of study. Black flies and avian malaria are widely distributed, and the effect of the vertical distribution of these parasites in forests on roosting, nesting, and foraging of sylvatic birds deserves further study.
Observations of the Pale-Eyed Blackbird in Southeastern Peru
Authors: Orians Gordon H. , Orians Elizabeth N.
Published: September 2019

We report the first known nest of the Pale-eyed Blackbird (Agelaius xanthophthalmus) and describe the behavior of breeding and nonbreeding pairs at Cocha Cashu, Manu National Park, Peru. Birds traveled as pairs within limited areas, whether or not they were breeding. During incubation, which is performed only by the female, the male typically remains near the nest and the birds are in regular vocal contact by means of frequent duets. Its monogamous social system is similar to that of other marsh-nesting species in its clade.
Contrasting Brood Sizes in Common and Arctic Terns: The Roles of Food Provisioning Rates and Parental Brooding
Authors: Robinson James A. , Hamer Keith C. , Chivers Lorraine S.
Published: September 2019

Arctic Terns (Sterna paradisaea) and Common Terns (S. hirundo) are similar in many aspects of their breeding ecology, but Common Terns generally lay three eggs per clutch whereas Arctic Terns lay two. In our study, Common Terns had a higher rate of food delivery and energy supply to the nest and higher nest attendance, indicating that they made trips of shorter average duration. This suggests that the number of chicks raised by these two species was primarily limited by the rate at which parents could supply food. However, estimated daily metabolizable energy intake of chicks was about 30% higher in Common Terns than in Arctic Terns. Common Tern chicks apparently spent a higher proportion of daily energy intake on maintenance of body temperature. It remains unknown whether this difference was because Common Tern parents could not brood three chicks as effectively as Arctic Terns brooded two or because the energy requirements for heat production in the third-hatched Common Tern chick were particularly high. If brooding did play a less important role in the energy budgets of Common Terns, the number of chicks that Arctic Terns could raise may have been limited not only by the rate at which parents could supply food to the nest but also by the requirements of chicks for brooding. We suggest that more detailed studies on the role of brooding constraints in limiting brood size in these species are required to clarify this matter.
Post-Fledging Dispersal of Burrowing Owls in Southwestern Idaho: Characterization of Movements and use of Satellite Burrows
Authors: Andrew King R. , Belthoff James R.
Published: September 2019

Using radiotelemetry, we monitored dispersing juvenile Western Burrowing Owls (Athene cunicularia hypugaea) within a migratory population in southwestern Idaho during 1994 and 1995. Owls remained within natal areas for an average (± SE) of 58 ± 3.4 days post-hatching before moving permanently beyond 300 m, which was our operational cutoff for dispersal from the natal area. On average, owls dispersed on 27 July (range: 15 July to 22 August), which was approximately 4 weeks after fledging. After initiating dispersal, juveniles continued moving farther away from their natal burrows and, by 61–65 days post-hatching, they had moved 0.6 ± 0.2 km. Each juvenile used 5.1 ± 1.2 satellite burrows, and individual satellite burrows were used for up to 14 days. The average date on which we last sighted radio-tagged juveniles was 13 August, and all but one juvenile departed the study area by early September. Our study illustrates the importance of satellite burrows to dispersing Burrowing Owls.
Effects of Brown-Headed Cowbirds on the Nesting Success of Chipping Sparrows in Southwest Colorado
Authors: Ortega Catherine P. , Ortega Joseph C.
Published: September 2019

We documented effects of Brown-headed Cowbird (Molothrus ater) parasitism on Chipping Sparrows (Spizella passerina) in southwest Colorado. Overall, 17 of 77 nests (22%) were parasitized. Abandonment was significantly higher among parasitized nests (29%) than unparasitized nests (5%). More Chipping Sparrows hatched and fledged per unparasitized nest than per parasitized nest. Reduction of host hatching and fledging rates in parasitized nests was attributable to smaller clutch size and higher abandonment. The major source of nest failure was predation, not parasitism; overall, 53% failed from predation, and only 6% failed from parasitism. There were no differences in weight, ulna length, tarsometatarsus length, or length of outermost primary between sparrow nestlings in parasitized and unparasitized nests. Only 18% of cowbird eggs laid resulted in a fledged cowbird. We observed no differences in nest placement or nest concealment between unparasitized and parasitized nests.
Daily Energy Expenditure of Nestling Bald Eagles in Northern Wisconsin
Authors: Dykstra Cheryl R. , Karasov William H. , Meyer Michael W. , Warnke D. Keith
Published: September 2019

We measured field metabolic rate of nestling Bald Eagles (Haliaeetus leucocephalus) in northern Wisconsin, using doubly-labeled water. In inland northern Wisconsin and along the Wisconsin Lake Superior shore, eaglets aged 39–60 days, weighing 3.08–4.85 kg, expended an average of 2,427 ± 100 kJ day−1. Nestling field metabolic rate was weakly correlated with nestling age, but not with mass. Field metabolic rate of eaglets can be used to estimate the biomass of food that adult eagles must provide from their environment, a datum that is important for determination of habitat suitability.
Accipiter Predation of American Redstart Nestlings
Authors: McCallum Cynthia A. , Hannon Susan J.
Published: September 2019

We used small video cameras to film predators at nests of American Redstarts (Setophaga ruticilla). We filmed three predation events, all by accipitrine hawks, in which no signs of predation were left at nests. Hence, as suggested by other workers, predator identification based on signs left at nests is unreliable. In addition, predation rates may be underestimated if accipiters or other predators take nestlings just prior to fledging without leaving signs. These incidents may be interpreted by field workers as nests where young fledged successfully.
Importance of the Supratidal Habitats for Maintaining Overwintering Shorebird Populations: How Redshanks Use Tidal Mudflats and Adjacent Saltworks in Southern Europe
Authors: Masero José A. , Pérez-Hurtado Alejandro
Published: September 2019

The prey-size selection, foraging behavior, and intake rate of overwintering Redshanks (Tringa totanus) were studied in a supratidal-intertidal system with high intertidal densities of shorebirds (100 birds ha−1). For assessing the importance of the energy obtained in the supratidal habitat (saltworks), daily consumption in this habitat was compared with the total daily energy requirement. Redshanks passively select prey within a certain size range from those accessible on the intertidal area. Despite the high prey biomass on the mudflats, Redshanks exhibited a low intake rate during winter (0.321 kJ min−1). This low intake seems to be related to the influence of the high densities of foraging shorebirds on the behavior of prey. Although intake rate was higher in the saltworks, the majority of Redshanks did not choose to feed there in winter. This foraging pattern seems to be related to density-dependent effects in habitat occupancy, as social interactions could have kept Redshanks out of the saltworks in winter according to the predictions of the ideal-despotic model. Energy intake in the supratidal habitat contributed 23% and 82% of the total daily energy requirement in winter and the pre-migration period, respectively. Redshanks were able to meet the total daily energy requirement during the pre-migration period by increasing foraging time in the saltworks. The availability of supratidal foraging habitats seems to contribute significantly to the maintenance of the population of overwintering Redshanks.
Nonbreeding Habitat Selection and Foraging Behavior of the Black-Throated Green Warbler Complex in Southeastern Mexico
Authors: Greenberg Russell , Gonzales Claudia Elia , Bichier Peter , Reitsma Robert
Published: September 2019

We studied the ecological distribution and foraging behavior of three species in the Black-throated Green Warbler (Dendroica virens) species group in the Eastern Highlands of Chiapas, Mexico. The three species, Black-throated Green, Hermit (D. occidentalis) and Townsend's (D. townsendi) Warblers are largely allopatric on the breeding grounds and variably sympatric during the winter. We surveyed the composition of 166 mixed-species flocks and recorded habitat variables associated with the flock location along an elevational transect. We found that Black-throated Green and Townsend's Warblers segregated by altitude, whereas Hermit Warbler overlapped extensively with both other species. Even though Townsend's and Hermit Warblers co-occurred commonly in the same flocks, the latter showed strong selective use of pine trees and the former showed weaker selectivity of oak trees. Black-throated Green Warbler showed no tree-type selection. The combined differences in elevational distribution and tree-type use resulted in very low ecological overlap for the three species. The Black-throated Green Warbler was the most distinct in its foraging behavior, occurring more often in the outer and upper branches of trees, and using hanging, aerial, and hovering maneuvers more than its congeners. In addition, it showed a higher movement frequency and a lower rate of between-branch flights. The Black-throated Green Warbler also is the most morphologically distinct as a result of its overall smaller body size, which is consistent for the trend towards larger body size in more conifer-specialized species in this genus. We propose that as new breeding populations were founded, and speciation occurred, individuals of the more derived species occupied decreasingly productive winter habitats.