Research Objectives:

1. Determine the minimum patch size thresholds of reproductive success for three Neotropical
   migratory songbirds.
   
   
2. Determine whether thresholds for presence, territory establishment by males, or pairing success were indicative of thresholds of reproduction.
   
   
3. Determine whether the proportion of pairs fledging Brown-headed Cowbird (Molothrus ater) young was related to patch size.
   
   
4. Determine the affects of patch size on a measure of food abundance (i.e., arthropod abundance). 

Management Implications:

1. Managers involved in juniper clearing in north-central Texas particularly, and across the distribution range of
   Golden-cheeked Warblers and Black-and-white Warblers in general, should be cautious not to decrease patches below 20 ha.1.

Project Summary:

Retaining relatively large patches of suitable habitat is recommended for increasing long-term population viability for area-sensitive species.  In practice, the issue of patch size revolves around the question of minimum thresholds, above which additional area of habitat is likely to contribute to species conservation, and below which contribution is unlikely.  Relationships whereby the area-normalized occurrence of brood parasitism and food abundance are related to patch size provide examples of underlying relationships that might explain why some species are area-sensitive.  Our objectives were to determine (1) the minimum patch size thresholds of reproductive success for three insectivorous, migratory songbirds; (2) whether thresholds for presence, territory establishment by males, or pairing success were indicative of thresholds of reproduction; (3) whether the proportion of pairs fledging Brown-headed Cowbird (Molothrus ater) young was related to patch size, and (4) the affects of patch size on a measure of food abundance.  We found minimum patch size thresholds of reproductive success for Golden-cheeked Warblers (Dendroica chrysoparia) and Black-and-white Warblers (Mniotilta varia), but not for White-eyed Vireos (Vireo griseus).  The minimum patch size threshold of reproductive success for the warblers was between 15 and 20.1 ha.  Minimum patch size thresholds for presence, territory establishment by males, and pair formation did not consistently reflect the threshold for reproductive success; therefore, conservation practices for target species based on thresholds of presence, territory establishment, or pair formation may not address issues of reproduction.  We failed to find relationships between patch size and cowbird parasitism or patch size and arthropod biomass.  The ability to identify thresholds of reproductive success for target species could be useful in conservation and management in multiple ways including setting goals for retention and restoration of target species’ habitat patch size.