Gender identification is important in demographic studies of bird populations but is difficult with monomorphic bird species. Flow cytometry, a method which estimates differences in DNA content in erythrocyte nuclei, is one potential sexing method. In another sexing method, differences between the autosomal and sex-linked (W) copies of the chromo-helicase-DNA binding (CHD) gene can be determined using the polymerase chain reaction (PCR). Frozen blood samples collected during the breeding season from known-sex adults and juvenile birds were used to test the applicability of flow cytometry and PCR as sexing methods for the Wood Thrush (Hylocichla mustelina). With flow cytometry, 86% of 14 known adults were definitively and correctly sexed. PCR correctly sexed 100% of 11 known adults. Of the 18 juveniles, 15 were sorted definitively by flow cytometry: 14 as male and one as female. PCR sexed the same 18 juveniles as 11 males and seven females, including the three juveniles that were unclassified by flow cytometry. In addition, three juveniles identified as males using flow cytometry were identified as females by PCR, among which were two individuals that consistently fell into the high end of the male genome size range. We conclude that PCR is a reliable sexing method for the Wood Thrush, but flow cytometry has limited reliability due to the lack of disparity in intergender genome size.

We describe observational evidence of niche shifts of smaller species in response to the presence of larger species in flocks of tits in Korea. Overall, in this guild of tits there was more aggression directed from larger toward smaller species than vice versa. At the guild level, there was a significant effect of the presence of larger species on vertical rather than horizontal distribution of smaller species. For example, in the presence of the dominant P. varius, the subordinate P. major foraged at lower heights than in the absence of P. varius. This is the first observation of foraging niche shifts in P. major, a typical dominant in European flocks, in response to the presence of larger P. varius, absent in European flocks of tits.

This paper evaluates the effectiveness of the area search method to measure breeding landbird populations at the plot level. During June 1999, 10 plots in grassland and shelterbelt habitats of north-central South Dakota were surveyed three times using the area search method. The results were then compared with those simultaneously obtained by the spot mapping census method, which served as the standard for comparison. Area searches detected an average of 96.0% of the landbird species present on the grassland plots, and 84.2% of the species on the shelterbelt plots. Species accumulation curves were identical between techniques, suggesting that an increase in number of visits to each plot would likely increase the number of species detected during area search surveys. Estimates of territory density from spot mapping were available for five passerine species. Across all species, area searches underestimated territory densities by an average of 50% when visit data were summarized by taking the average. When data were summarized using the maximum value among visits to each plot, area searches underestimated territory density by an average of 26%. Precision of density estimates using area search was similar between summarization methods, and was generally lower in comparison to spot mapping. Across all species, area search and spot mapping density estimates were strongly associated, suggesting that area search has potential as an index to abundance. However, correlation coefficients in abundance varied considerably within individual species. Since area search surveys typically underestimated both species richness and density of territories, further experimentation with increased survey duration is warranted.

Austral migrant birds were banded during austral fall (March–April) and spring (October–November) in the Chaco of Santa Cruz, Bolivia. The Tyrannidae was the most common family captured in terms of number of species and total individuals. The difference in capture numbers between the austral spring and fall seasons was the greatest for the Fuscous Flycatcher (Cnemotriccus fuscatus), although most species exhibited little change among seasons. In terms of numbers of captures across each season, no apparent trends in migratory timing were evident. The Creamy-bellied Thrush (Turdus amaurochalinus) exhibited similar fat class distributions among seasons. Within-season trends showed that in fall Creamy-bellied Thrushes with lower fat levels arrived at the study site earlier than fatter birds. Most migrant species captured were not sexually dimorphic or in breeding condition, so sexing was generally not possible. Our lack of knowledge on habitat use and migratory routes of austral migrants in the Chaco, combined with the current high rate of habitat destruction in the region, makes an understanding of the migratory patterns of these birds important.

We studied the breeding bird communities of 19 reclaimed surface coal-mine grasslands in southwestern Indiana in 1997–1998, using roadside point counts and off-road transects. The mine grasslands in this study were large, ranging from 110 to 3180 ha in area (median, 590 ha). Although dominated by a few Eurasian grass species, they supported diverse bird communities in which grassland-dependent species were prominent along with grassland-associated and successional scrub species. The mean abundances of species (relative to one another) on roadside and off-road counts were positively correlated. Red-winged Blackbirds (Agelaius phoeniceus), Eastern Meadowlarks (Sturnella magna), and Grasshopper Sparrows (Ammodramus savannarum) were present at >90% of point count locations. Other common species, in descending order, included Dickcissels (Spiza americana), Common Yellowthroats (Geothlypis trichas), Killdeers (Charadrius vociferus), Indigo Buntings (Passerina cyanea), Henslow's Sparrows (Ammodramus henslowii), Field Sparrows (Spizella pusilla), and Song Sparrows (Melospiza melodia). Brown-headed Cowbirds (Molothrus ater) were rare, as were seven grassland-dependent species that were near the edges of their geographic distributions.

We conducted a pen study to evaluate two methods of attaching radio transmitters to Wild Turkey (Meleagris gallopavo) poults. Transmitters (1.8 g) were attached interscapularly to 2-d-old turkeys, either with glue or as implants. Attachment method had no detectable effect on the growth or survival of poults. Transmitter retention differed between the methods. Mean retention times were 27.6 d for glued backpacks and 30.5 d for interscapular implants. Ease of implementation and behavioral differences of birds immediately after application suggest that glued backpacks are preferred in situations where a retention time of 29 d is adequate.

We studied the behavior of the Dusky Bush-Tanager (Chlorospingus semifuscus; Thraupinae) in southwestern Colombia, where it seems to exhibit singing assemblages resembling leks. A lek mating system would be paradoxical in a genus noted for its active participation in mixed-species flocks, largely insectivorous diet, and stable pair bond. We used the bird's behavior and the relations between fruit availability, its diet, and its participation in mixed flocks to try to explain the social system. We found males singing in dense linear assemblages, regularly spaced along ridgetops, during early morning and late afternoon hours during much of the year, with a peak from May through August. Singing males occupied small circular territories, which usually were reoccupied the next year by the same males. The critical resource is likely the males themselves, although fruit availability may permit them to remain on territories for long periods; nesting areas are apparently far from the ridgetops. Participation in flocks occured year-round but was somewhat reduced during the singing season and in the singing hours. The evidence of pair bonds in this species, in which males participate at least in nest-site selection and feeding of young, excludes the possibility of a lek mating system in the strict sense. Nevertheless, the system of singing linear assemblies appears to have been superimposed upon the typical social system of the genus. This social system is unique in the entire nine-primaried oscine assemblage.

Energetic costs of nest construction are difficult to estimate for birds, and currently estimates are available for only a handful of species. In this paper, I estimate the minimum cost of nest construction by a pair of Black-billed Magpies (Pica hudsonia). Data on the number of sticks and mud pellets comprising a nest were used to determine the minimum number of trips required to construct the nest, and were combined with information on distances to the nearest sources of nesting materials, data on flight speeds, and bird morphometric measures to estimate costs of transporting nesting materials. For the Black-billed Magpie pair I observed, nest construction required a minimum of 2564 trips for nesting materials, 276.2 km of commuting, 8.4 h of flight, and cost 209.1 kJ. Spreading this cost over the 40 d required to build the nest yields an estimate of 2.61 kJ/adult/day. I compared this value to published estimates of daily metabolizable energy intake for Black-billed Magpies, and calculated that breeding adults would need to increase their daily intake between 0.7% and 1.0% to cover the energetic costs of nest construction. In contrast, egg laying is estimated to require a full 23% of the daily energy expenditure of female magpies. These values suggest the energetic cost of nest building in Black-billed Magpies is relatively insignificant.

We examined nest-site selection by Spanish Imperial Eagles (Aquila adalberti) in Doñana National Park (southwestern Spain) from 1984–1994. Spanish Imperial Eagles are large birds of prey that defend and occupy a territory year-round. Identifying a territory's nest-site characteristics represents a critical step in safeguarding this endangered species' habitat. We measured seven habitat variables describing microhabitat, vegetative composition, land use, and degree of human influence for 73 nest sites averaged for 14 occupied territories and 73 randomly selected sites for 14 unoccupied territories. Our best logistic regression model included two habitat variables representing microhabitat (height of nest tree) and human influence (distance to the nearest urban centre). The logistic regression model correctly classified 78.6% of the occupied and 85.7% of unoccupied territories. This analysis suggests that the presently occupied Spanish Imperial Eagle territories represent the majority of the remaining suitable habitat for this endangered species in and around Doñana National Park. There is an urgent need to create suitable nest sites for Spanish Imperial Eagles that would include tall trees in small tree stands away from intense human activity.

Considerable attention has been devoted to the technical aspects of terrestrial bird surveys during the breeding season. However, there is relatively little information specifically addressing the methodology of bird surveys at other times of the year when birds are less vocal and are mobile over areas larger than territories. We tested a method for surveying forest birds in winter, based on the use of playbacks of mobbing calls of Black-capped Chickadees (Poecile atricapilla). When compared to pre-playback 5-min standard point counts, playbacks of mobbing calls of the same duration allowed the detection of more individuals and more species. Time of day, with or without playbacks, had no effect on the number of individuals detected or on species richness. We recommend the use of playbacks of mobbing calls of Black-capped Chickadees for surveying forest birds during the non-breeding season because of their efficiency.

The use of an injectable combination of tiletamine-zolazepam to immobilize King Penguins (Aptenodytes patagonicus) in the field was tested in non-incubating and incubating adults and in chicks. We also compared the behavioral and physiological response to this anesthetic agent according to the position used for immobilization (dorsal: lying on the back; ventral: lying on the belly) and following repeated administrations at one or several day intervals throughout a prolonged natural fast. A 5-mg/kg dosage administered intra-muscularly allowed an efficient immobilization of 97% of the adults for about one hour and after an induction time averaging 5 min. Birds kept in the dorsal position and without thermal insulation remained immobilized longer than those kept in the ventral position. Chicks were immobilized for 80 min after receiving a 4-mg/kg dosage. The anesthetized birds lost the pain, noise, touch and podal reflex but not the palpebral one and showed no major side effects. Penguins responded similarly to repeated injections and recovered without complications or adverse reactions. Five of eight incubating adults resumed incubation after having been anesthetized. We conclude that immobilization of King Penguins with tiletamine-zolazepam is safe and efficient, allowing routine health examination and interventions such as, for example, vein catheterization and adipose tissue biopsies.

The Venezuelan Wood-Quail (Odontophorus columbianus) is an endemic species of Venezuela that dwells in the humid forests of the northern coastal mountain range and southeastern Andes. Its biology, ecology and conservation status are poorly known. The aim of this study was to establish quantitative relationships between the presence and absence of the species and habitat features in the humid forest of Henri Pittier National Park, Aragua State, Venezuela. Twenty-six habitat variables were recorded in 20 plots located at places where quails were observed while foraging and compared with those of 22 plots located at random in areas where quails were not observed. Principal component analysis and logistic regression were used to identify the relevant set of variables determining the presence or absence of the species. The best predictive variables were high frequency of non-palm monocots, high vertical foliage density, and low frequency of palms (Bactris spp). The logistic model allows one to predict the presence or absence of quails in similar areas to those of our study with probabilities of 0.80 and 0.86, respectively. This type of habitat analysis may help in the designing of future research and management plans for this and other elusive, poorly known species.