Distribution Of Bird Populations Research Articles

BlackcapsSylvia atricapillaon Migration: A Link between Long-Term Population Trends and Migratory Behaviour Revealed by the Changes in Wing Length

Recent climate change has a major impact on the sizes and distribution of bird populations, the phenology of their breeding/migration and migratory behaviour (migration distance, migration strategy). We documented changes in the numbers of juvenile Blackcaps migrating in autumn through the S Baltic that were paralleled by changes in wing length of captured individuals during a 43-year study period (1967–2009). We suggest that the observed trends may indicate changing population composition of migrating birds. In the Blackcap, wing length distinguishes among different populations and increases with increasing migration distance of a given population. Available published data show that long-distance and short-distance Blackcaps pass the study region. Hence, we assumed that shorter-winged birds are short-distance migrants wintering in the southern Europe, and that longer-winged individuals are long-distance migrants wintering in the sub-Saharan region. It seems that in 1967–1980 most Blackcap populations declined, but, as wing length slightly increased, the rate of this decline has been higher in the shorter-winged/short-distance Blackcaps. Over the subsequent 24 years alongside with rapidly growing numbers of birds, we noted a remarkable decrease in wing length. This indicates a pronounced increase in the number of short-distance individuals compared to long-distance migrants. Both groups may benefit from improved conditions at their breeding grounds, but the shorter migration route and favourable conditions at wintering sites north of Sahara could favour short-distance migrants over the longer distance and longer-winged Blackcaps.

Disease and the abundance and distribution of bird populations: a summary

Over the past few years, I have written several reviews about the effects of infectious diseases upon the distribution and abundance of their host populations. One general review and synthesis is in the fmd chapter of a book whose earlier chapters focus mainly on human diseases (Anderson & May 1991). A bird‐specific discussion, with particular reference to conservation issues, is given by Dobson and May (1991). Broadly related questions about the invasion, persistence and spread of infectious diseases within animal communities are explored by Anderson and May (1986) and with emphasis on bird populations by Dobson and May (1986). Also relevant are a set of papers from the Society for Conservation Biology's first‐ever symposium on Conservation and Disease (for an overview, see May 1988, Scott 1988).Rather than burdening the literature with a recapitulation of these existing reviews, this paper gives a sign‐posted guide for those who are not familiar with this particular literature. I first sketch reasons for believing that infectious diseases play an important part in the life history of birds. Next I point towards an analytic framework for understanding the dynamics of host‐pathogen associations. Finally I list some of the implications for the conservation biology of bird populations.

Seasonal Distribution of Bird Populations at the Patuxent Research Refuge

Seasonal Distribution of Bird Populations at the Patuxent Research Refuge