Modeling movement of West Nile virus in the Western hemisphere.

We modeled West Nile virus (WNV) movement rates and patterns based on a migratory bird agent (the Swainson's Thrush) and a resident bird agent (the House Sparrow), and compared the results of these models with actual movement data to investigate the likelihood that the pattern of WNV outbreaks observed in the New World was consistent with migrant bird-mediated spread, as reported from the Old World. We found that, contrary to Old World patterns, WNV activity in the Western Hemisphere does not seem consistent with movement by infected migrant birds. Instead WNV spread appears best explained by a non-directional movement, perhaps that of dispersing resident birds.

Relationships between behavior, physiology and weather in avian transients at a migration stopover site.

Populations of avian transients were studied at a stopover area in southern Texas during four consecutive migration seasons, fall, 1973-spring, 1975. We captured individuals by mist net for banding and fat level determination. Concurrently we made observations on behavior of free-flying birds.We worked intensively with a single species, the Northern Waterthrush (Seiurus noveboracensis) while gathering weight fat and behavioral data on other species as well. Many of the patterns of weight change and behavior seen in the Northern Waterthrush were observed in other common passerines which occurred as transients on our study site.Results showed that birds in Zugstimmung and Zugdisposition differ, not only physiologically but behaviorally as well. Individuals of normally non-gregarious species that are in Zugstimmung are gregarious and stay in an area for only a short period. Their habitat needs are broad since these birds are not dependent on the food resources of the area in which they stop while in this physiological state. In contrast, normally non-gregarious migrants in Zugdisposition are hyperphagic and aggressively territorial in defense of resources and may stay at the same site for several days. Their habitat needs are quite specific since they must increase food intake by as much as 40% to build up fat reserves. Not all individuals in Zugdisposition are able to find territories at the same time. Those birds unable to claim territories either continue to migrate or stay in an area as floaters, continually attempting to obtain territories. Weather conditions probably act as a third variable that must be balanced by the individual in a complex optimization strategy with physiological state and success in competition.

The use of movement data as an assay of habitat quality.

Based on our observations and those of others from the literature, we construct a graphical model of habitat use in territorial species at high densities relative to optimal habitat availability. This model ignores differences in abundance among habitats, and, together with other models of habitat use, predicts that there should be greater stability (lower turnover rates) among individuals occupying optimal habitat than among those in suboptimal habitat(s). Future studies assessing quality among habitats might take advantage of this by comparing individual turnover rates among habitat types using standard mark-recapture methodology. As an illustrative example, we present a case in wintering wood thrushes (Catharus mustelinus; Muscicapidae: Turdinae) in which relative abundance and habitat quality were inversely related. Many individuals of this nearctic-neotropic migrant species hold nonbreeding territories in the seemingly crowded rainforest of southern Veracruz, Mexico.

Decadal changes and delayed avian species losses due to deforestation in the northern Neotropics.

How avifauna respond to the long-term loss and fragmentation of tropical forests is a critical issue in biodiversity management. We use data from over 30 years to gain insights into such changes in the northernmost Neotropical rainforest in the Sierra de Los Tuxtlas of southern Veracruz, Mexico. This region has been extensively deforested over the past half-century. The Estación de Biología Tropical Los Tuxtlas, of the Universidad Nacional Autónoma de México (UNAM), protects a 640 ha tract of lowland forest. It became relatively isolated from other forested tracts between 1975 and 1985, but it retains a corridor of forest to more extensive forests at higher elevations on Volcán San Martín. Most deforestation in this area occurred during the 1970s and early 1980s. Forest birds were sampled on the station and surrounding areas using mist nets during eight non-breeding seasons from 1973 to 2004 (though in some seasons netting extended into the local breeding season for some species). Our data suggested extirpations or declines in 12 species of birds subject to capture in mist nets. Six of the eight species no longer present were captured in 1992-95, but not in 2003-2004. Presence/absence data from netting and observational data suggested that another four low-density species also disappeared since sampling began. This indicates a substantial time lag between the loss of habitat and the apparent extirpation of these species. Delayed species loss and the heterogeneous nature of the species affected will be important factors in tropical forest management and conservation.

Birds and influenza H5NI virus movement to and within North America.

Highly pathogenic avian influenza (HPAI) H5N1 expanded considerably during 2005 and early 2006 in both avian host species and geographic distribution. Domestic waterfowl and migratory birds are reservoirs, but lethality of this subtype appeared to initially limit migrant effectiveness as introductory hosts. This situation may have changed, as HPAI H5N1 has recently expanded across Eurasia and into Europe and Africa. Birds could introduce HPAI H5N1 to the Western Hemisphere through migration, vagrancy, and importation by people. Vagrants and migratory birds are not likely interhemispheric introductory hosts; import of infected domestic or pet birds is more probable. If reassortment or mutation were to produce a virus adapted for rapid transmission among humans, birds would be unlikely introductory hosts because of differences in viral transmission mechanisms among major host groups (i.e., gastrointestinal for birds, respiratory for humans). Another possible result of reassortment would be a less lethal form of avian influenza, more readily spread by birds.