University of Missouri - Saint Louis

The Graduate School

Announcement

An oral examination in defense of the dissertation for the degree

Doctor of Philosophy

Adrián B. Azpiroz
M.S. in Biology, December, 2004, University of Missouri-St. Louis.
B.S. in Biology, June, 1996, Universidad de la República, Montevideo, Uruguay.

Abstract

Grassland bird populations are declining widely as a consequence of habitat loss. The general objective of this study was to examine the effects of habitat modification on the distribution, abundance, and reproductive success of Pampas’ grassland birds. The study focused on bird assemblages that inhabit four grassland habitats which differed in their degree of habitat alteration in Uruguay. Following the characterization of avian diversity patterns, the response of birds to vegetation structure variables was assessed. This information was coupled with data on nest success for a selected group of species, including both common and globally threatened taxa. Cultivated and natural grasslands were dominated by grassland generalist and specialist species, respectively, and some threatened species were largely confined to natural grasslands. In terms of vegetation structure, grass cover and vegetation height were the two variables to which birds responded most strongly, but substantial differences among species were identified. Nest survival analyses indicated strong seasonal and habitat effects. Contrary to expectation, nest survival of threatened taxa did not differ from that of common and widespread congenerics. This study resulted in the first characterization of grassland bird communities inhabiting an agricultural gradient in Uruguay. Management of natural grasslands to conserve obligate grassland birds should consider the different habitat needs of each species. Although natural grasslands are key habitats for several taxa, they remain largely unrepresented in the regional protected area network.

Defense of Dissertation Committee