bluuebunny/crossref_metadata_2025 huggingface dataset:
Foraging Success and Foraging Habitat Use by Cattle Egrets and Little Egrets in the Camargue, France
Authors: Lombardini Katia , Bennetts Robert E. , Tourenq Christophe
Published: September 2019

We examined habitat use by Little Egrets (Egretta garzetta) and Cattle Egrets (Bubulcus ibis) that nest together in mixed-species colonies in the Camargue of southern France. We explored the relative use of seven habitat types in relation to their availability and tested the hypothesis that selection of habitat types was related to foraging success, with the prediction that increased foraging success in a given habitat corresponded with increased use of that habitat type. Ricefields and other agricultural habitats were used more than expected by Cattle Egrets, an invasive species in southern Europe; whereas Little Egrets, which are native to the Camargue, tended to select natural freshwater marshes and lagoons. Results were consistent with the hypothesis that increasing use of habitats corresponded with higher foraging success for both species. However, when this analysis was restricted to habitats with sufficient numbers of birds to enable estimates of biomass intake, the association was no longer apparent for Little Egrets.
Lilac-Crowned Parrot Diet and Food Resource Availability: Resource Tracking by a Parrot Seed Predator
Authors: Renton Katherine
Published: September 2019

The pattern of food resource availability and use by Lilac-crowned Parrots (Amazona finschi) was evaluated in tropical dry forest of the Reserva de la Biosfera Chamela-Cuixmala, western Mexico. Monthly fruiting phenology transects were conducted throughout the year in deciduous and semi-deciduous forest to determine temporal and spatial variability in resource abundance. Resource use by parrots was evaluated through observations of diet and habitat use. There was significant temporal and spatial variability in food resource abundance, with semi-deciduous forest providing greater food resources for parrots during the dry season, whereas food resource abundance increased in deciduous forest during the rainy season. The critical period of food resource scarcity occurred during May–June at the end of the long dry season. Lilac-crowned Parrots were pre-dispersal seed predators, and exhibited high flexibility in diet, incorporating dietary switching, as well as niche-breadth contraction and expansion, which corresponded with temporal variations in food resource availability. There was low overlap in parrot diets between seasons, with parrots exhibiting a narrow food niche-breadth during the late dry season when resource availability declined. Parrots also demonstrated spatial variation in habitat use, corresponding to fluctuations in the availability of food resources in different habitats. This flexibility in foraging enables parrots to closely track and exploit seed resources which exhibit high temporal and spatial variability in abundance.
Diet and Hunting Behavior of the Crane Hawk in Tikal National Park, Guatemala
Authors: Sutter Jason , Martínez A. Walter E. , Oliva T Francisco , Oswaldo J Nery , Whitacre David F.
Published: September 2019

We studied the breeding diet and hunting behavior of Crane Hawks (Geranospiza caerulescens) in Tikal National Park, Petén, Guatemala in 1994 and 1995. We observed 227 prey items while conducting observations at six nesting attempts, and during opportunistic sightings in the breeding season. Among 181 identified prey items, rodents comprised 47.5%, lizards 19.9%, frogs 16.0%, bats 6.6%, birds 6.1%, and snakes 2.8%; a juvenile skunk also was represented. Rodents accounted for 77% of estimated biomass, including at least eight species representing terrestrial, cursorial, and arboreal habits. More than half of all prey items weighed <20 g, but 40% weighed >50 g; many were nocturnal species presumably taken from daytime hiding places. We observed hunting attempts in all strata of the forest and in several forest types. Hunting behavior included still-hunting from a perch and probing with head or feet in holes, bromeliads and other epiphytes, palm leaf axils, crotches of branches, behind bark in living and dead trees, and in puddles. Compared to other raptors studied at Tikal, the Crane Hawk had a moderately broad food niche that overlapped most with other raptors deemed dietary generalists. However, the Crane Hawk's unique anatomical features and hunting behavior enabled it to capture diurnally reclusive prey presumably unavailable to many other raptors, thus facilitating relatively low dietary overlap.
A New Specimen of the Tiny Middle Eocene Bird Gracilitarsus Mirabilis (New Family: Gracilitarsidae)
Authors: Mayr Gerald
Published: September 2019

A new, second specimen of the tiny Middle Eocene bird Gracilitarsus mirabilisMayr 1998 shows several previously unknown osteological features. The species represents a bauplan unknown among recent birds in that it combines swallow-like length proportions of the major wing bones with a long and slender tarsometatarsus. The feet of Gracilitarsus mirabilis are highly unusual in that the three anterior toes are very short and of nearly equal length, and in that the claws are of great dorso-ventral depth. Gracilitarsus mirabilis is classified within a new family in this study. The species shares some derived characters of the tarsometatarsus with the Paleocene South American species Eutreptodactylus itaboraiensisBaird and Vickers-Rich 1997.
Does Risk of Nest Failure or Adult Predation Influence Hatching Patterns of the Green-Rumped Parrotlet?
Authors: Stoleson Scott H. , Beissinger Steven R.
Published: September 2019

Parent birds may adjust the onset of incubation to minimize periods of high risk of nest failure due to predation (the Nest Failure Hypothesis) or of mortality to adult birds (the Adult Predation Hypothesis). We examine temporal patterns of risk of nest failure and predation on adult females in a population of Green-rumped Parrotlets (Forpus passerinus) to determine whether those patterns explain observed patterns of incubation. Over one-third of nests (38.6%) failed completely, and an additional 2.2% failed after fledging one or more young. Most nests failed due to predation and infanticide. Because parrotlets begin incubation on the first egg, we examined a range of hypothetical failure rates for the period prior to the onset of incubation. Daily survival probabilities for nests were higher during the nestling stage than during incubation or fledging. Survival of adult females varied little through the nesting cycle, but was highest while attending nestlings. Model predictions were highly dependent on assumptions made about survival rates during the pre-incubation period. When empirically based values were used for this period, maximum productivity was achieved with first-egg incubation, consistent with observed patterns. Models were most sensitive to those parameters most difficult to estimate. This study represents the first test of the Nest Failure model with a nonpasserine or tropical species, and the first assessment of the Adult Predation model using field data.
Pathogenicity, Serological Responses, and Diagnosis of Experimental and Natural Malarial Infections in Native Hawaiian Thrushes
Authors: Atkinson Carter T. , Lease Julie K. , Drake Beth M. , Shema Nicholas P.
Published: September 2019

Omao (Myadestes obscurus) from the Hawaiian Islands typically have very low prevalences of infection with avian malaria (Plasmodium relictum) and it is not clear whether they share the same high susceptibility to this parasite that has been documented in native Hawaiian honeycreepers. We exposed four captive Omao to single infective mosquito bites and measured parasitemia, serological responses, and mortality over time. All four birds experienced transient infections with low parasitemias and were immune when rechallenged with multiple infective mosquito bites. By contrast, three of four honeycreepers (Maui Alauahio, Paroreomyza montana) that were exposed to the same dose and parasite isolate succumbed to infection. All four Omao developed antibodies to a common suite of malarial antigens that were detectable on immunoblots of a crude red blood cell extract of P. relictum. We used this technique to screen plasma samples from wild Omao and endangered Puaiohi (Myadestes palmeri) that were captured at elevations between 900 and 1300 m on the islands of Hawaii and Kauai. We found that the true prevalence of infection at elevations where active malaria transmission occurs is much higher than estimates based on blood smears alone. Hawaiian thrushes appear to have a high tolerance for malaria, with most individuals developing chronic, low-level infections after exposure that cannot be diagnosed accurately by blood smears.
Radar-Based Monitoring of Marbled Murrelets
Authors: Cooper Brian A. , Raphael Martin G. , Mack Diane Evans
Published: September 2019

We used radar to measure daily, monthly, and annual patterns of Marbled Murrelet (Brachyramphus marmoratus) abundance and movements at 12 major river valleys in the Olympic Peninsula of Washington. Landward movements of murrelets peaked from ∼75 min to ∼20 min before sunrise, followed by a seaward exodus from ∼20 min before sunrise to ∼65 min after sunrise. This general pattern of a landward movement followed by a seaward exodus varied little, but the timing of the seaward exodus gradually became later from May to July. Within a morning, numbers of landward radar targets averaged twice the numbers of seaward targets, and morning counts were approximately five times evening counts. Species identification error rates were lower for landward radar counts than for seaward counts. Radar counts varied through the season, with numbers increasing from May to July, then dropping in August. Seaward counts were more variable than landward counts. There was wide overlap among months in the amount of daily variation in both landward and seaward counts. Radar appears to be a powerful, cost-effective, and non-intrusive tool that can establish an index of abundance for murrelets at specific inland breeding areas.
Movements, Habitat Use, and Survival of Nonbreeding Piping Plovers
Authors: Drake Katherine R. , Thompson Jonathan E. , Drake Kiel L. , Zonick Curt
Published: September 2019

We studied movements, habitat use, and survival rates of 49 radio-marked Piping Plovers (Charadrius melodus) overwintering along the southern Laguna Madre of Texas during 1997–1998. Plovers exhibited strong site fidelity to nonbreeding areas throughout fall, winter, and spring. Mean home-range size of plovers (based on 95% of locations) was 12.6 km2 with a mean core area (50% of locations) of 2.9 km2. Seasonal home-range size and core areas differed only between fall and winter; home-range and core areas were smaller in fall than winter. Mean linear distance moved was 3.3 km; fall movements were smaller than those made in winter and spring. Habitat use varied seasonally: plovers used algal flats more during fall and spring than during winter; plovers used exposed sand flats more often during winter than in fall and spring. We recorded no mortality of radio-marked birds. High rates of survival and strong site fidelity throughout the nonbreeding period suggest that this period of the annual cycle may not contribute to the declining population size for Piping Plovers wintering in this region. However, because Piping Plovers spend most of the annual cycle on nonbreeding areas, they are likely to be negatively affected by loss of those sites, emphasizing the importance of conserving nonbreeding areas for this threatened and endangered species.
Habitat Preferences of Pinyon-Juniper Specialists Near the Limit of Their Geographic Range
Authors: Pavlacky David C. , Anderson Stanley H.
Published: September 2019

We investigated habitat preferences for five pinyon-juniper specialists during the 1998 and 1999 breeding seasons in Utah juniper (Juniperus osteosperma) woodlands of southwestern Wyoming. We compared avian use and availability of vegetation features using univariate and multivariate analysis to detect selection for vegetative features of pinyon-juniper specialists near the northeastern range boundary of pinyon-juniper habitat on the Colorado Plateau. Gray Flycatchers (Empidonax wrightii), Juniper Titmice (Baeolophus griseus), and Bewick's Wrens (Thryomanes bewickii) preferred woodlands with high overstory juniper cover. The Juniper Titmouse was associated with senescent trees, Blue-gray Gnatcatcher (Polioptila caerulea) with rock outcrops and shrubs in the family Rosaceae, and Black-throated Gray Warbler (Dendroica nigrescens) with pinyon pine (Pinus edulis). We suggest the geographic distribution of four of five pinyon-juniper specialists is limited by the occurrence of pinyon pine in semiarid woodlands on the northeastern Colorado Plateau. The geographic limit for Blue-gray Gnatcatchers in this region may correspond to the presence of mountain mahogany in the woodland understory. The conservation of pinyon-juniper specialists in southwestern Wyoming will benefit from the maintenance of successional processes, particularly those that perpetuate mature woodlands with a pinyon pine component.
Transect Surveys of Columbid Nests on Puerto Rico, Vieques, and Culebra Islands
Authors: Rivera-Milán Frank F.
Published: September 2019

I conducted transect surveys of pigeon and dove (Columbidae) nests on Puerto Rico, Vieques, and Culebra islands. Nest detection probability and density differed between study areas in January–August 1991 and 1992. Nest detection probability and density did not differ between years or among species, so I used transect data from a larger study (1986–1999) to assess the relationships between nest density and rainfall, food abundance, food diversity, and predator abundance along transects. Food abundance was the most important predictor of annual changes in nest density on the surveyed transects in mesic and xeric habitats during May–June 1986–1999. Positive correlations of annual nest density estimates suggested parallel responses among columbid species to similar or covarying resources in mesic and xeric habitats.
Movement Patterns of Adult Male Ovenbirds During the Post-Fledging Period in Fragmented and Forested Boreal Landscapes
Authors: Bayne Erin M. , Hobson Keith A.
Published: September 2019

Movement of forest songbirds among isolated forest patches following breeding represents an important but poorly understood component of landscape ecology and metapopulation theory. Using radio-telemetry, we followed 44 male Ovenbirds (Seiurus aurocapillus) during the post-fledging period to determine if movement patterns differed in landscapes dominated by agriculture versus those dominated by forest. No differences in home-range size, mean distance moved per day, or maximum distance moved were observed for males captured in a forested landscape vs. those captured in forest fragments in an agriculturally dominated landscape. Male Ovenbirds observed with young moved less than males without young and rarely crossed open gaps. Individuals that failed to breed moved more extensively than successful breeders, possibly in an effort to find new territories for use in future breeding seasons.
Sex Ratios of Dunlin Wintering at Two Latitudes on the Pacific Coast
Authors: Shepherd Philippa C. F. , Lank David B. , Smith Barry D. , Warnock Nils , Kaiser Gary W. , Williams Tony D.
Published: September 2019

Latitudinal clines in sex ratio during the nonbreeding season occur in some shorebirds of the Scolopacidae. We compared populations of nonbreeding Dunlin (Calidris alpina pacifica) from two latitudes along the Pacific flyway: the Fraser River Delta, British Columbia, and Bolinas Lagoon, California, to determine whether, and to what degree, they exhibited sex ratios consistent with a latitudinal cline. Dunlin are plumage monomorphic, so we used a maximum likelihood model to estimate overall and monthly sex ratios for each population based on culmen length distributions. Sex ratios in the Fraser River Delta were corrected for sex differences in habitat use. Monthly sex ratios were similar at the two sites but varied throughout the winter, likely reflecting differences in seasonal movement patterns between the sexes. Both populations showed an overall bias toward males (Fraser = 61% males, Bolinas = 65% males). Since there is no evidence to support the possibility of a skew toward males in C. a. pacifica as a whole, our data are consistent with some form of latitudinal cline in the sex ratio of C. a. pacifica. However, additional data from the Oregon coast, southern California, and Mexico are required to resolve this question. We also tested the hypothesis that mean body size within each sex is larger at the higher-latitude site (Fraser River Delta), but this did not appear to be the case.
Factors Influencing Pair Territoriality in the Juniper Titmouse
Authors: Christman Beth J.
Published: September 2019

Pair territoriality outside of the breeding season is a relatively uncommon pattern of social organization in the Paridae (tits, titmice, and chickadees). Within the territorial parids, pair territoriality appears to be the derived state. Because of this, it is possible to address the question: What favors the evolution of this social system? I assessed factors that may be responsible for inducing pair territoriality in Juniper Titmice (Baeolophus ridgwayi), focusing largely on foraging behavior and predation risk. I found that the diet of Juniper Titmice is distinctive as compared to other tits, with large seeds (juniper and pinyon pine) and acorns making up most of the winter diet instead of arthropods. Time budgets reflected that a large proportion of time is spent handling food. Space use was strongly skewed toward locations that should be relatively safe from predators, both because food is located in such sites and because titmice transport seeds to sheltered sites for processing. Seeds decreased significantly in abundance through the course of the winter. Comparisons with group-living tit species that forage largely on arthropods show differences in time and space use. I conclude that the suite of behaviors associated with foraging on large seeds has shifted the cost-to-benefit ratio of group living for Juniper Titmice relative to other tits.
Effect of Group Size on Field Metabolic Rate of Arabian Babblers Provisioning Nestlings
Authors: Anava Avner , Kam Michael , Shkolnik Amiram , Degen A. Allan
Published: September 2019

Arabian Babblers (Turdoides squamiceps; adult body mass 65–75 g) are territorial, cooperatively breeding passerines that inhabit hot, dry deserts. Groups include breeding adults and helpers and generally consist of 3 to 5 individuals (range 2 to 22). All group members provision nestlings at similar rates, and individual visitation rates decline with increasing group size. Consequently, we predicted that the field metabolic rate (FMR) of individuals provisioning nestlings would decrease with increasing group size. To test this prediction, we determined FMR of primary female, primary male, female helper and male helper babblers in different sized groups provisioning nestlings. Field metabolic rate of primary females, but not other classes, decreased linearly with group size. This energy savings could allow primary females in larger groups to start a new nest more quickly. FMR for all babblers was 61% to 66% of the value predicted for a passerine of its body mass provisioning nestlings and was 3.11 × BMR, similar to the mean value of 3.13 × BMR reported for a number of terrestrial species.
Effects of Anthropogenic Food Sources on Movements, Survivorship, and Sociality of Common Ravens in the Arctic
Authors: Restani Marco , Marzluff John M. , Yates Richard E.
Published: September 2019

We investigated survivorship, movements, and sociality of Common Ravens (Corvus corax) exploiting concentrated food resources at a landfill in Greenland. From 1992–1995 we banded 383 ravens: 365 were captured at the landfill and 18 were banded in nearby nests. Thirty-nine ravens were recovered, most by shooting (87%). Mean number of days survived post-banding (494 ± 97) did not differ among age groups, but a higher proportion of juveniles was recovered. Ravens migrated west and south to the coast during winter. No difference existed among age groups in mean distance between locations of banding and recovery (151 ± 31 km). Number of ravens congregating at the landfill declined during the study, coinciding with a decrease in the local human population. Harsh winter climate, limited ice-free land, and abundant human refuse influenced raven use of the wilderness landscape by facilitating the formation of large, nomadic foraging groups.
Species and Sex-Biased Predation on Hatchling Green Turtles by Frigatebirds on Europa Island, Western Indian Ocean
Authors: Lagarde Frédéric , Corre Matthieu Le , Lormeé Hervé
Published: September 2019

Europa Island is a major breeding place for green turtles (Chelonia mydas; 0.7 to 2.4 million juvenile turtles hatch there annually), Great Frigatebirds (Fregata minor; 700 to 1100 breeding pairs), and Lesser Frigatebirds (Fregata ariel; 1000 to 1200 pairs). By visual observation, we quantified the proportions of males, females, and juveniles of both frigatebird species prospecting over the hatching sites and preying on hatchling turtles. Of 1828 juveniles observed hatching at daytime (35 separate turtle emergences), 1632 were immediately eaten by male Great Frigatebirds. Only 10 hatchlings were preyed upon by female Great Frigatebirds; the remaining 186 were captured by juvenile Great Frigatebirds. Such feeding behavior was not observed in Lesser Frigatebirds. We suggest that the sexual and species differences in hatchling turtle predation are due to size differences between the two species and between male and female Great Frigatebirds.
Is Spizella Taverneri a Species or a Subspecies?
Authors: Mayr Ernst , Johnson Ned K.
Published: September 2019

Based on distributional, ecologic, morphologic, and vocal data, Klicka et al. (1999) argued in favor of species status for the form taverneri, long regarded as a subspecies of the Brewer's Sparrow (Spizella breweri). For several reasons we disagree with their conclusion: lack of evidence for the reproductive isolation of taverneri from breweri, loss of information on the close relationship and allopatric distribution of the two taxa that would accompany their elevation to species, and violation of the principle of taxonomic balance. Until the demonstration of vocal or display differences relevant to pair formation and maintenance, taverneri and breweri are best regarded as reproductively compatible subspecies.
Morphological Heritability in a Hybrid Bunting Complex: Nesospiza at Inaccessible Island
Authors: Ryan Peter G.
Published: September 2019

Juvenile Nesospiza buntings measured 7–11 weeks after hatching were compared with the sizes of their parents to estimate the heritability (h2) of six external morphological characters. There was no evidence of size selection before juveniles were seven weeks old, but some additional growth in bill size probably occurred after this age. All characters had significant heritabilities among Tristan Buntings (N. acunhae; h2 = 0.66–0.95) and hybrids with Wilkins' Buntings (N. wilkinsi; h2 = 0.62–0.93). Positive heritabilities also were found within color morphs of the Tristan Bunting, although not all regressions were significant. Hybrid offspring generally were intermediate in size between their parents' phenotypes, but one hybrid pair had an unusually small offspring, possibly the result of an extra-pair fertilization. Differences between h2 estimates from sib-sib and parent-offspring regressions suggest that environmental factors contribute to morphological variability, but the large heritable component confirms the potential for rapid morphological evolution among the small Nesospiza populations. Calculation of the relative importance of genetic and environmental effects requires controlled breeding experiments, but cross-fostering between broods in the field should not be performed, to avoid disrupting the natural population structure.

Heredabilidad Morfológica en un Complejo Híbrido: Nesospiza en Isla Inaccessible

Resumen. Las dimensiones de juveniles de Nesospiza medidos 7–11 semanas después de eclosionar fueron comparadas con las de sus padres para estimar la heredabilidad (h2) de seis caracteres morfológicos externos. No hubo evidencia de selección por tamaño antes de que los juveniles tuvieran siete semanas de edad, pero probablemente ocurrió un crecimiento adicional en el tamaño del pico luego de esta edad. Todos los caracteres tuvieron heredabilidades significativas entre N. acunhae (h2 = 0.66–0.95) y entre híbridos con N. wilkinsi (h2 = 0.62–0.93). También se encontraron heredabilidades positivas dentro de morfos de color de N. acunhae, aunque no todas las regresiones fueron significativas. Las crías híbridas generalmente tuvieron un tamaño intermedio entre el fenotipo de los padres, pero una pareja híbrida tuvo crías inusualmente pequeñas, posiblemente como resultado de una fertilización extra-pareja. Diferencias entre los estimativos de h2 calculados mediante regresiones hermano-hermano y padres-crías sugieren que factores ambientales contribuyen a la variabilidad morfológica, pero el fuerte componente heredable confirma el potencial para evolución morfológica rápida entre las pequeñas poblaciones de Nesospiza. Los cálculos de la importancia relativa de factores genéticos y ambientales requieren experimentos con apareamientos controlados. Sin embargo, para evitar perturbar la estructura poblacional natural no deberían realizarse transplantes de crías entre nidadas en el campo.
Spatial and Temporal Variability in Nest Success of Snail Kites in Florida: A Meta-Analysis
Authors: Dreitz Victoria J. , Bennetts Robert E. , Toland Brian , Kitchens Wiley M. , Collopy Michael W.
Published: September 2019

Nesting success of Snail Kites (Rostrhamus sociabilis) in Florida is highly variable among years and locations, and hydrology is the most frequently reported explanatory factor. We conducted a meta-analysis to evaluate the extent of spatial and temporal variability in nesting success, and explicitly tested for the effects of annual minimum water levels. Data were obtained from six independent studies spanning 22 years and 11 wetlands. Our results indicated there was substantial spatial and temporal variability in nest success and that annual minimum water level, either as a categorical or continuous response, was not a significant source of this variation. Our results do not imply that low water levels do not influence nest success. Rather, they indicate that the number of nests affected by low water conditions was quite low (<1%). A wetland area experiences low water once every 5 to 10 years, and seldom does such an event encompass the entire range of Snail Kites in Florida. During a low water event, kites are capable of moving to alternative locations. Thus, relatively few birds may exhibit low nest success as a result of low water events, and management aimed at preclusion of such events may be unnecessary and detrimental to maintenance of the habitat over long time scales.

Variabilidad Espacial y Temporal en el Éxito de Anidación de Rostrhamus sociabilis en Florida: Un Meta-Análisis

Resumen. El éxito de anidación de Rostrhamus sociabilis en Florida varía ampliamente entre años y localidades. La hidrología es el factor que se ha propuesto con mayor frecuencia para explicar dicha variabilidad. Llevamos a cabo un meta-análisis para evaluar la magnitud de la variabilidad espacial y temporal en el éxito de anidación y pusimos a prueba explícitamente el efecto de los niveles mínimos anuales de agua. Los datos fueron obtenidos de seis estudios independientes comprendiendo 22 años y 11 humedales. Nuestros resultados indicaron que hubo gran variación espacial y temporal en el éxito de anidación y que el nivel mínimo anual de agua (ya sea como una respuesta categórica o continua), no fue una fuente significativa de esta variación. Nuestros resultados no implican que niveles bajos de agua no afectan el éxito de anidación. En cambio, indican que el número de nidos afectados por condiciones de aguas bajas fue bastante bajo (<1%). Un área de humedales presenta aguas bajas una vez cada cinco o diez años y es raro que uno de estos sucesos abarque todo el rango de R. sociabilis en Florida. Durante una época de aguas bajas, las aves están en capacidad de moverse hacia otros sitios por lo que relativamente pocas podrían tener bajo éxito reproductivo como consecuencia de la escasez de agua. El manejo dirigido a suprimir estos eventos podría ser innecesario e ir en detrimento del mantenimiento del hábitat a largo plazo.
Number of Close Spatial and Temporal Neighbors Decreases the Probability of Nest Failure and Shiny Cowbird Parasitism in Colonial Yellow-Winged Blackbirds
Authors: Massoni Viviana , Reboreda Juan Carlos
Published: September 2019

We investigated whether the synchrony and proximity of nests of Yellow-winged Blackbirds (Agelaius thilius) provided protection against nest predation or brood parasitism by Shiny Cowbirds (Molothrus bonariensis). We analyzed the effect of the temporal aggregation of nests on the daily probability per nest of predation, desertion, egg punctures, and parasitism throughout the breeding season. The probabilities of nest predation and nest desertion increased through the breeding season. The temporal aggregation of nests was negatively associated with the probability of nest desertion, egg punctures, and parasitism, but there was no association with the probability of nest predation. We also analyzed the effect of the number of close neighbor nests on the daily probability per nest of predation, desertion, egg punctures, and brood parasitism. The spatial aggregation of nests was negatively associated with the probability of nest failure and brood parasitism, but there was no association with the probability of egg punctures. We discuss whether dilution effect or group defense, two mechanisms proposed to explain the antipredatory advantages of colonial nesting, are likely to apply to our system.

El Número de Vecinos Espaciales y Temporales Disminuye la Probabilidad de Pérdida del Nido y de Parasitismo por Molothrus bonariensis en Colonias de Agelaius thilius

Resumen. Se investigó si la sincronía y la proximidad de nidos del Agelaius thilius proveyó protección ante la depredación del nido y el parasitismo de cría por Molothrus bonariensis. Se analizó el efecto de la agregación temporal de nidos sobre la probabilidad diaria por nido de depredación, abandono, picaduras y parasitismo a lo largo de la temporada reproductiva. Las probabilidades de predación y abandono del nido aumentaron a medida que avanzó la temporada reproductiva. La agregación temporal de nidos estuvo negativamente asociada con la probabilidad de abandono, picaduras y parasitismo pero no se observó asociación de ésta con la probabilidad de predación. También se analizó el efecto del número de nidos vecinos cercanos sobre la probabilidad de pérdida del nido y de parasitismo de cría. La agregación espacial de nidos estuvo asociada negativamente con la probabilidad de pérdida del nido y de parasitismo de cría pero no se observó una asociación de ésta con la probabilidad de picadura de huevos. Se discute si el efecto de dilución o la defensa grupal, dos mecanismos propuestos para explicar los beneficios antipredatorios de la nidificación colonial, son probables de ocurrir en este sistema.
Nesting and Reproductive Activities of Greater Sage-Grouse in a Declining Northern Fringe Population
Authors: Aldridge Cameron L. , Brigham R. Mark
Published: September 2019

In Canada, Greater Sage-Grouse (Centrocercus urophasianus) are at the northern edge of their range, occurring only in southeastern Alberta and southwestern Saskatchewan. The population in Canada has declined by 66% to 92% over the last 30 years. We used radio-telemetry to follow 20 female Greater Sage-Grouse and monitor productivity in southeastern Alberta, and to assess habitat use at nesting and brood-rearing locations. All females attempted to nest. Mean clutch size (7.8 eggs per nest) was at the high end of the normal range for sage-grouse (typically 6.6–8.2). Nest success (46%) and breeding success (55%) were within the range found for more southerly populations (15% to 86% and 15% to 70%, respectively). Thirty-six percent of unsuccessful females attempted to renest. Fledging success was slightly lower than reported in other studies. Thus, reproductive effort does not appear to be related to the population decline. However, chick survival to ≥50 days of age (mean = 18%) was only about half of that estimated (35%) for a stable or slightly declining population, suggesting that chick survival may be the most important factor reducing overall reproductive success and contributing to the decline of Greater Sage-Grouse in Canada.

Actividades de Anidación y Reproducción de Centrocercus urophasianus en una Población del Extremo Norte en Declive

Resumen. En Canadá, Centrocercus urophasianus está en el extremo norte de su distribución, encontrándose sólo en el sureste de Alberta y el suroeste de Saskatchewan. La población de Canadá ha disminuido entre el 66% y 92% durante los últimos 30 años. Utilizamos radio-telemetría para seguir a 20 hembras de C. urophasianus y monitorear su productividad en el sureste de Alberta y para evaluar el uso de hábitat en sitios de anidación y de cría de los pichones. Todas las hembras intentaron anidar. El tamaño promedio de la nidada (7.8 huevos por nido) estuvo en el extremo superior del rango normal de C. urophasianus (típicamente 6.6–8.2). El éxito de anidación (46%) y de reproducción (55%) estuvieron dentro de los rangos encontrados en poblaciones de más al sur (15% a 86% y 15% a 70%, respectivamente). El treinta y seis por ciento de las hembras que no tuvieron éxito intentaron volver a anidar. El éxito en la crianza de polluelos hasta la etapa de volantones fue ligeramente menor que el reportado en otros estudios. Por lo tanto, el esfuerzo reproductivo no parece estar relacionado con el declive poblacional. Sin embargo, la supervivencia de los polluelos hasta 50 días de edad o más (promedio = 18%) fue sólo aproximadamente la mitad de lo que se ha estimado para una población estable o en ligero declive (35%), lo que sugiere que la supervivencia de los pichones podría ser el factor más importante reduciendo el éxito reproductivo en general y contribuyendo al declive de C. urophasianus en Canadá.
Female Condition: A Predictor of Hatching Synchrony in the House Wren?
Authors: Ellis Lisa A. , Styrsky John D. , Dobbs Robert C. , Thompson Charles F.
Published: September 2019

The degree of hatching synchrony in clutches of passerine birds frequently varies among species and among individuals of the same species. Many hypotheses have been proposed to explain why some eggs hatch several days after others in a clutch. We tested one of these hypotheses, the energetic-constraints hypothesis, which proposes that females in poor physical condition postpone initiating incubation and hatch their clutches synchronously, whereas females in good condition begin incubation early and hatch their clutches asynchronously. We tested the hypothesis using the House Wren (Troglodytes aedon) because recent studies have found little difference in productivity between synchronously and asynchronously hatching clutches in this species, suggesting that the degree of hatching synchrony varies for reasons unrelated to nestling growth and survival. We used logistic regression to test the dependence of the degree of hatching synchrony on each of two measures of female condition. We found no relationship between female condition and degree of hatching synchrony. These results and two other lines of evidence are inconsistent with the energetic-constraints hypothesis as an explanation for variation in degree of hatching synchrony in this House Wren population.

¿Predice la Condición de las Hembras la Sincronía de Eclosión en Troglodytes aedon?

Resumen. Con frecuencia, el grado de sincronía en la eclosión de nidadas de aves paserinas varía entre especies y entre individuos de la misma especie. Se han propuesto muchas hipótesis para explicar por qué algunos huevos eclosionan varios días después que otros en una misma nidada. Pusimos a prueba una de esas hipótesis, la de las limitaciones energéticas, que propone que hembras en mala condición física postponen el inicio de la incubación y sus nidadas eclosionan sincrónicamente, mientras que aquellas en buena condición inician la incubación temprano y sus nidadas eclosionan asincrónicamente. Pusimos a prueba la hipótesis usando a Troglodytes aedon, pues estudios recientes en esta especie han encontrado pocas diferencias en productividad entre nidadas de eclosión sincrónica y asincrónica, lo que sugiere que el grado de sincronía en la eclosión varía por motivos no relacionados con el crecimiento y supervivencia de los pichones. Utilizamos regresión logística para evaluar el grado de dependencia de la sincronía de eclosión en dos medidas de condición física de las hembras. No encontramos ninguna relación entre la condición de las hembras y el grado de sincronía en la eclosión. Estos resultados y otras dos líneas de evidencia son inconsistentes con la hipótesis de las limitaciones energéticas como una explicación para la variación en el grado de sincronía de eclosión en esta población de T. aedon.
Influence of Military Activities on Raptor Abundance and Behavior
Authors: Schueck Linda S. , Marzluff John M. , Steenhof Karen
Published: September 2019

We investigated the influence of military training on the abundance and behavior of raptors at a military training area in the Snake River Birds of Prey National Conservation Area in Idaho during the breeding seasons of 1991–1994. Raptor counts on military training ranges did not differ when we compared all training days to all non-training days. However, during one period of intensive military training in one breeding season, raptor counts were lower during training than on non-training days. During training, Northern Harriers (Circus cyaneus) did not alter their behavior on training days. In years when prey numbers were low, falcons, hawks, and eagles perched and flew at low levels less often and flew at higher altitudes more often during training than they did when training did not occur. We observed fewer prey capture attempts on ranges on days with training than on days without training. Specific types of military training activity affected counts of raptors on ranges. The lowest raptor counts were associated with firing of artillery, small arms, and main turret guns or machine guns on tanks. Raptor counts associated with tank preparation (i.e., assembling and loading ammunition), driving, laser training, and convoy traffic were similar to non-training periods.

La Influencia de Actividades Militares en la Abundancia y el Comportamiento de Aves de Rapiña

Resumen. Durante las épocas reproductivas de 1991 a 1994, investigamos la influencia del entrenamiento militar en la abundancia y el comportamiento de aves de rapiña en un área de entrenamiento en el área nacional de la conservación de aves de presa del Snake River, Idaho. Los conteos de aves de rapiña en áreas militares no difirieron entre días de entrenamiento y días sin entrenamiento. Sin embargo, en una época reproductiva los conteos de rapaces fueron menores en días de entrenamiento que en días sin entrenamiento. Circus cyaneus no alteró su comportamiento en días de entrenamiento. Durante el entrenamiento en años cuando los números de presas eran bajos, los halcones, gavilanes y águilas se posaron y volaron en los niveles bajos con menor frecuencia y volaron más alto más a menudo que cuando no había entrenamiento. Observamos menos intentos de captura de presas en días que hubo entrenamiento que en días sin entrenamiento. Las actividades específicas de entrenamiento militar afectaron los conteos de aves de rapiña. Los conteos más bajos estuvieron asociados con disparos de artillería, de pequeñas armas y de las armas principales de la torreta o de las ametralladoras en tanques. Las conteos de rapaces asociados con la preparación de los tanques (ensamblaje y carga de munición), conducción, entrenamiento del laser, y tráfico del convoy fueron similares a los de períodos sin entrenamiento.
Bivouac Checking, A Novel Behavior Distinguishing Obligate from Opportunistic Species of Army-Ant-Following Birds
Authors: Swartz Monica Beth
Published: September 2019

As swarms of the army ant Eciton burchelli forage across forest floors of the lowland Neotropics, birds gather to eat arthropods flushed by the advancing ants. Past efforts to distinguish members of the obligate ant-following bird guild from the many species that forage opportunistically with army ants have been inadequate. Obligate ant-followers track the locations of multiple nomadic ant colonies in order to maintain a consistent food supply. Each morning, they visit the bivouac site of each colony they are monitoring to assess the ants' activity. Only species dependent upon foraging with army ants exhibit this specialized bivouac checking behavior. This paper proposes a new method for distinguishing between obligate and opportunistic ant-following birds by observing which species check bivouacs.

Verificación de Vivaques, un Comportamiento Nuevo que Distingue a Especies Obligatorias de Especies Oportunistas Rastreadores de Hormigas-Ejército

Resumen. Cuando enjambres de la hormiga ejército Eciton burchelli forrajean en los suelos de los bosques bajos Neotropicales, algunas aves se aglomeran para ingerir artrópodos espantados por las hormigas que avanzan. Esfuerzos pasados para distinguir entre aquellos miembros del gremio de aves que rastrean las hormigas obligatoriamente de las muchas especies que forrajean de manera oportunista con hormigas ejército han sido inadecuados. Seguidores obligatorios de las hormigas rastrean los sitios de varias colonias nómadas de hormigas a fin de mantener un suministro consistente de alimentos. Cada mañana, estas aves visitan el sitio de vivaque de cada una de las colonias que controlan con fin de evaluar las actividades de las hormigas. Sólo aquellas especies que dependen del forrajeo de las hormigas ejército manifiestan este comportamiento especializado de verificar los vivaques. Este artículo propone un nuevo método para distinguir entre las aves oportunistas y las aves obligatorias rastreadoras de hormigas mediante la observación de aquellas especies que verifican los vivaques.
Foraging Before Spring Migration and Before Breeding in Common Eiders: Does Hyperphagia Occur?
Authors: Guillemette Magella
Published: September 2019

Foraging performance of Common Eider (Somateria mollissima) was studied to find out if hyperphagia occurs before migration and breeding in this species. Diving efficiency and time spent feeding were quantified concomitantly for two subspecies that differ in the timing of their reproduction and migration. The foraging performance of female S. m. dresseri preparing for breeding and female S. m. borealis preparing for migration were compared with their male counterparts, which are known to achieve energy balance during these periods. Female dresseri spent 41% of their time feeding and made 404 dives daily, for a total of 169 min spent underwater each day. Female dresseri spent more time diving than did males by about one hour each day. There were no detectable differences in the foraging performances of male and female borealis, probably because the body mass of migrating females increased only slightly prior to migration. Hyperphagia in breeding female dresseri appears to be the main cause of increased body mass, although other mechanisms may play a role.

Quête Alimentaire Chez l'Eider à Duvet Avant la Migration Printanière et la Nidification: Est-Il Possible de Déceler un Phénomène d'Hyperphagie?

Résumé. Le quête alimentaire de l'Eider à duvet (Somateria mollissima) fut étudiée au printemps avant la migration et avant la nidification dans le but de déceler, s'il y a lieu, un phénomène d'hyperphagie chez cette espèce. Le temps passé à s'alimenter et l'efficacité de la plongée furent quantifiés simultanément pour deux sous-espèces qui diffèrent quant à leur chronologie de nidification et de migration. La quête alimentaire des femelles S. m. dresseri, se préparant pour la nidification, et des femelles S. m. borealis, se préparant pour la migration, fut comparée avec celle des mâles de chacune des sous-espèces respectives. Les mâles furent utilisés comme “témoins” puisqu'il y a des évidences que ces derniers maintiennent l'équilibre énergétique durant cette période. Les femelles dresseri ont passé en moyenne 41% de leur temps à s'alimenter et elles ont réalisé 404 plongeons quotidiennement, pour un total de 169 min. passées en plongée par jour, soit environ une heure de plus que les mâles. Il n'y avait pas de différences dans la performance de la quête alimentaire des femelles et des mâles borealis, probablement parce que les femelles n'emmagasinent que très peu de réserves avant leur départ pour la migration. En conclusion, un phénomène d'hyperphagie se manifeste chez la femelle dresseri bien que d'autres mécanismes d'accumulation de réserves peuvent jouer un rôle.
Nest Desertion and Apparent Nest Protection Behavior by Bell's Vireos in Response to Cowbird Parasitism
Authors: Budnik Joel M. , Burhans Dirk E. , Ryan Mark R. , Thompson III Frank R.
Published: September 2019

Bell's Vireos (Vireo bellii) deserted 51% of nests parasitized by Brown-headed Cowbirds (Molothrus ater) in central Missouri from 1996–1998. Deserting vireo pairs fledged more host young within a season than pairs that accepted cowbird eggs when only successful nests were considered; parasitized acceptor nests never fledged any vireo young. Vireo pairs that deserted did not always desert parasitized nests. We observed five encounters between female cowbirds and Bell's Vireos at four nests. In one observation the female vireo used nest-protection behavior, which resulted in the cowbird egg appearing beneath the nest; this nest was not deserted. We found a total of eight nests where cowbird eggs remained on the ground below nests, five of which were abandoned. Nest desertion appears to benefit Bell's Vireos by allowing for unparasitized renests, but the stimuli eliciting nest desertion by Bell's Vireos remain in need of further study.

Deserción de Nidos y Aparente Comportamiento Protector de Vireo bellii en Respuesta al Parasitismo de Molothrus ater

Resumen. Individuos de Vireo bellii abandonaron el 51% de los nidos que fueron parasitados por Molothrus ater en el centro de Missouri entre 1996–1998. Las parejas desertoras de V. bellii criaron más juveniles propios por estación que parejas que aceptaron huevos de M. ater cuando solamente se consideraron nidos exitosos; los nidos parasitados aceptados nunca produjeron ningún juvenil de V. bellii. Las parejas desertoras de Vireo no siempre abandonaron nidos parasitados. Observamos cinco encuentros entre hembras de M. ater y de V. bellii en cuatro nidos. En una observación, la hembra de Vireo realizó comportamientos de protección del nido que resultaron en la aparición del huevo de M. ater debajo del nido; este nido no fue abandonado. Encontramos un total de ocho nidos con huevos de M. ater tirados en el suelo debajo de los nidos, cinco de los cuales fueron abandonados. La deserción de nidos parece beneficiar a V. bellii al permitirle re-establecer nidos no parasitados, pero el estímulo que impulsa la deserción de nidos en V. bellii necesita aún ser estudiado.