John G. Blake

BIRD ASSEMBLAGES IN SECOND-GROWTH AND OLD-GROWTH FORESTS, COSTA RICA: PERSPECTIVES FROM MIST NETS AND POINT COUNTS

Abstract Second growth has replaced lowland forest in many parts of the Neotropics, providing valuable habitat for many resident and migrant bird species. Given the prevalence of such habitats and the potential benefit for conservation of biodiversity, it is important to understand patterns of diversity in second growth and old growth. Descriptions of species-distribution patterns may depend, however, on method(s) used to sample birds. We used data from mist nets and point counts to (1) describe species diversity and community composition in second-growth (young and old) and old-growth forests at La Selva Biological Station, Costa Rica; and (2) to evaluate perspectives on community composition provided by the two methods. We recorded 249 species from 39 families, including 196 species captured in mist nets (10,019 captures) and 215 recorded during point counts (15,577 observations), which represents ∼78% of the terrestrial avifauna known from La Selva (excluding accidentals and birds characteristic of aquatic or aerial habitats). There were 32 threatened species, 22 elevational migrants, and 40 latitudinal migrants. Species richness (based on rarefaction analyses of capture and count data) was greatest in the youngest site. Latitudinal migrants were particularly common in second growth; elevational migrants were present in both young and old forest, but were more important in old-growth forest. Several threatened species common in second growth were not found in old-growth forests. Trophic composition varied less among sites than did species composition. Mist nets and point counts differed in numbers and types of species detected. Counts detected more species than nets in old-growth forest, but not in young second growth. Mist nets detected 62% of the terrestrial avifauna, and point counts detected 68%. Fifty-three species were observed but not captured, and 34 species were captured but not observed. Six families were not represented by mist-net captures. Data from mist nets and point counts both support the conclusion that second-growth vegetation provides habitat for many species.

INFLUENCE OF PATCH‐ AND LANDSCAPE‐LEVEL FACTORS ON BIRD ASSEMBLAGES IN A FRAGMENTED TROPICAL LANDSCAPE

A major challenge in studies of habitat fragmentation is to determine the influence of patch quality and landscape context on patch use by animals. Few studies have simultaneously examined effects of patch (area, shape, and vegetation structure) and landscape (e.g., amount of arboreal vegetation in close proximity) on abundance patterns of animals. In this study, we examined how these characteristics influence bird species distribution and abundance in a pasture-dominated landscape in the Los Tuxtlas region of Veracruz, Mexico. We focused on three types of landscape elements: forest edge sites (n = 8), forest remnants (n = 8), and riparian forest remnants (n = 9). We quantified habitat use and community composition of birds by conducting seven counts of birds in each site between October 1996 and April 1997. Species typically restricted to forest were influenced by two patch-level factors, whereas species not so restricted were influenced by both patch- and landscape-level factors. At a community level, b...

DIVERSITY OF BIRDS ALONG AN ELEVATIONAL GRADIENT IN THE CORDILLERA CENTRAL, COSTA RICA

Abstract Species diversity and community composition of birds change rapidly along elevational gradients in Costa Rica. Such changes are of interest ecologically and illustrate the value of protecting continuous gradients of forest. We used mist nets and point counts to sample birds along an elevational gradient on the northeastern Caribbean slope of the Cordillera Central in Costa Rica. Sites included mature tropical wet forest (50 m); tropical wet, cool transition forest (500 m); tropical premontane rain forest (1,000 m); and tropical lower montane rain forest (1,500 and 2,000 m). We recorded 261 species from 40 families, including 168 species captured in mist nets (7,312 captures) and 226 detected during point counts (17,071 observations). The sample included 40 threatened species, 56 elevational migrants, and 22 latitudinal migrants. Species richness (based on rarefaction analyses) changed little from 50 to 1,000 m but was lower at 1,500 and 2,000 m. Mist nets and point counts often provided similar views of community structure among sites based on relative importance of difference categories of species (e.g. migrant status, trophic status). Nonetheless, important differences existed in numbers and types of species represented by the two methods. Ninety-three species were detected on point counts only and 35 were captured only. Ten families, including ecologically important ones such as Psittacidae and Cotingidae, were not represented by captures. Elevational migrants and threatened species occurred throughout the gradient, illustrating the need to protect forest at all elevations. A comparable study from the Cordillera de Tilarán (Young et al. 1998) demonstrated similar patterns of species change along an elevational gradient. Comparisons with that study illustrated that point counts are a valuable complement to mist-net studies. Both studies indicated the diverse nature of the avifauna along elevational gradients in Costa Rica.

Population Variation in a Tropical Bird Community

B ird communities in tropical forest are tremendously diverse relative to those in temperate forests; more species have been reported from Costa Rica than from all of North America (Stiles et al. 1989). Similarly, approximately the same number of species (400-410) have been recorded from La Selva Biological Station, a 15-square-kilometer wet forest site in Costa Rica, as from the entire state of Missouri (Blake et al. 1990, Robbins and Easterla 1992). Species diversity is even greater in parts of South America: territories of more than 160 species overlap at a single point in forest in Peru (Terborgh et al. 1990). Many factors contribute to the greater diversity of tropical forest bird communities (Terborgh 1980), including the year-round availability of certain resources (e.g., flowers and fruits) that are rare in temperate habitats (Karr 1971, Orians 1969). Whereas the number of species is much greater in tropical rather than in temperate habitats, the total density of birds does not differ, Terborgh and his colleagues (1990) concluded from one of the most detailed comparisons between temperate and tropical bird communities (see also Thiollay 1990). The relationship occurs primarily because many tropical species are relatively rare (Karr 1990a). Total biomass of birds, however, can be

Social networks in the lek-mating wire-tailed manakin (Pipra filicauda)

How social structure interacts with individual behaviour and fitness remains understudied despite its potential importance to the evolution of cooperation. Recent applications of network theory to social behaviour advance our understanding of the role of social interactions in various contexts. Here we applied network theory to the social system of lek-mating wire-tailed manakins (Pipra filicauda, Pipridae, Aves). We analysed the network of interactions among males in order to begin building a comparative framework to understand where coordinated display behaviour lies along the continuum from solitary to obligately cooperative dual-male displays in the family Pipridae. Network degree (the number of links from a male to others) ranged from 1 to 10, with low mean and high variance, consistent with the theory for the evolution of cooperation within social networks. We also assessed factors that could predict social and reproductive success of males. Four network metrics, degree, eigenvector centrality, information centrality and reach, some of which assess circuitous as well as the shortest (geodesic) paths of male connectivity, predicted male social rise. The duration of a males territorial tenure during the 4 years of the study predicted his probability of siring offspring.

NEOTROPICAL FOREST BIRD COMMUNITIES: A COMPARISON OF SPECIES RICHNESS AND COMPOSITION AT LOCAL AND REGIONAL SCALES

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

OBTAINING OFFSPRING GENETIC MATERIAL: A NEW METHOD FOR SPECIES WITH HIGH NEST PREDATION RATES

Abstract ABSTRACT Over the past decade, the field of moleculargenetics has revolutionized our understanding ofavian mating systems, by demonstrating that socialbonds might not accurately reflect parentagebecause of unknown levels of cryptic mating(e.g., extra-pair copulations). Use ofmolecular genetics tools for paternity analysisrequires genetic material from putative parents andnestlings. Unfortunately, high nest predation ratesoften preclude detailed genetic studies of tropicaltaxa. Here, we describe a nondestructive methodthat increases the efficiency of obtaining geneticmaterial from offspring for a group of tropicalpasserines (Pipridae). The method entailsreplacing eggs with plaster replicas, incubatingeggs artificially, and returning hatchlings totheir original nests for further development. Thismethod greatly improved our ability to sampleoffspring, as we collected genetic material from100% of manipulated nests, compared to52% of unmanipulated nests.

Diversity Patterns of Bird Assemblages in Arid Zones of Northern Venezuela

Abstract In northern Venezuela, arid zones are represented by isolated areas, which are important from an ornithological perspective because of the occurrence of restricted-range birds, which depend exclusively on arid scrub for their survival. From September 2004 to August 2005, bird surveys were conducted bimonthly using distance sampling at point counts in six areas of northern Venezuela, which differ in size and geological origin. A total of 21 228 individuals representing 96 species and 26 families were recorded throughout the study areas. Bird species richness, community composition, and species abundance varied among areas. Number of species recorded per area ranged from 37 to 82. An analysis of similarity showed that areas differed in overall community composition based on species presence or absence (Global R = 0.68). The Vermilion Cardinal (Cardinalis phoeniceus) was the only restricted-range species with a high indicator value (52%) identified through an indicator species analysis. The most abundant birds in all six areas were widespread generalist species, such as the Tropical Mockingbird (Mimus gilvus) and Tropical Gnatcatcher (Polioptila plumbea), and only one of the restricted-range birds, the Buffy Hummingbird (Leucippus fallax), had high densities (range: 2.67–9.00 individuals ha−1) throughout all the study areas. Densities of two restricted-range birds, the Yellow-shouldered Parrot (Amazona barbadensis) and Vermilion Cardinal varied among areas as a consequence of poaching in some areas. Species richness was not a reliable indicator of an areas conservation value because the protection of the area with highest species richness does not guarantee the effective conservation of all the restricted-range birds.