Relationship between bird abundances and landscape characteristics: the influence of scale.

Scale is important to consider when investigating effects of the environment on a species. Breeding Bird Survey (BBS) data and landscape metrics derived from aerial photographs were evaluated to determine how relationships of bird abundances with landscape variables changed over a continuous range of 16 spatial scales. We analyzed the average number of birds per stop (1985-1994) for five songbird species (family Cardinalidae) for each of 50 stops on 198 BBS transects throughout six states in the Central Plains, USA. Land along each transect was categorized into six cover types, and landscape metrics of fractal dimension (a measure of shape complexity of habitat patches), edge density, patch density, and percent area were calculated, with principal components used to construct composite environmental variables. Associations of bird abundances and landscape variables changed in accordance with small scale changes. Abundances of three species were correlated with edge density and one with component I, which subsumes initial variables of patch density for urban, closed forest, open forest, and open country. Fractal dimension and component II (summarizing amount of closed forest versus open country) were associated with the most species. Correlation patterns of fractal dimension with northern cardinal (Cardinalis cardinalis) and painted bunting (Passerina ciris) abundances were similar, with highest correlations at intermediate to small scales, suggesting indirectly that these species thrive in areas where local habitat conditions are most important. Multiscale analysis can provide insight into the spatial scale(s) at which species respond, a topic of intrinsic scientific interest with applied implications for researchers establishing protocols to assess and monitor avian populations.

Prevalence of rabies and LPM paramyxovirus antibody in non-hematophagous bats captured in the Central Pacific coast of Mexico.

To investigate if non-hematophagous bats play a role in outbreaks of rabies and blue eye disease (LPMV), we studied the seroprevalence against both agents in several species of non-hematophagous bats on the sub-tropical Pacific coast of the state of Colima, Mexico. The survey covered a predominantly agricultural area (disturbed), and an area dominated by semideciduous dry forest (undisturbed). A total of 151 non-hematophagous bats of 16 species were captured from the two areas. Fifty-six (37%) had antirabic antibodies (Ab) while 87 (58%) did not and 8 samples (5%) had to be discarded because of hemolysis. A much lower (P<0.05) prevalence of antirabic Ab was found in bats caught in disturbed areas (22.7%) compared with those from undisturbed areas (51.9%). The presence of antirabic Ab was not related to sex, genera or feeding habits. The higher prevalence found in bats in the undisturbed area may be the result of more frequent interspecies encounters. Of the 108 sera analyzed for antibodies against LPMV, only one was positive (a male Rhogeessa parvula major, captured in the undisturbed area). This suggests that bats in the surveyed localities do not play a role in the epidemiology of LPMV.

Relationships of human disturbance, bird communities, and plant communities along the land-water interface of a large reservoir.

We examined the relationships of human activity, bird communities, and plant communities along the land-water interface of Lake Texoma, a large human-made reservoir on the Texas-Oklahoma border. Measurements of human activity, plant surveys, and bird surveys were performed at 40 paired transects, one with human disturbance, the other undisturbed. Both principal components and correspondence analyses of bird-survey data separated disturbed sites from paired undisturbed sites, and typical disturbance-tolerant species from those less tolerant of human activity. Compared to undisturbed sites, disturbed sites tended to have more individual birds per survey, pavement, and mowed lawns, and less canopy, vegetation volume, and vegetation vertical diversity. A principal components analysis of quantitative disturbance measurements revealed that most bird and plant measures were highly correlated with the first disturbance component. However, the correlation between birds and human activity was much stronger than that between birds and plants, or between plants and disturbance. Our data suggest that bird-species composition is regulated more by human activity than by plant-community composition. Also, in this system, bird communities are a better choice than plant communities to index the effect of human disturbance. To maintain regional diversity of both birds and plants, undisturbed areas should be maintained around reservoirs.