INFLUENCE OF GRASSLAND TYPE, NEST TYPE, AND SHRUB ENCROACHMENT ON PREDATION OF ARTIFICIAL NESTS IN CHIHUAHUAN DESERT GRASSLANDS

Nest predation on artificial nests was examined in relation to nest type, grassland type, and shrub encroachment in Chihuahuan Desert grasslands in southern New Mexico. Open-cup ground, open-cup shrub, and spherical shrub nests (n = 210), mimicking Eastern Meadowlarks (Sturnella magna), Black-throated Sparrows (Amphispiza bilineata), and Cactus Wrens (Campylorhynchus brunneicapillus), were placed in 10 grasslands of tobosa (Pleuraphis mutica) and black grama (Bouteloua eripoda) with low and heavy levels of mesquite encroachment. Nest predation varied among nest types, grassland types, and shrub encroachment, with highest levels of prédation occurring on open-cup shrub nests in tobosa grasslands with heavy shrub encroachment. We detected a significant interaction between nest type and shrub encroachment, but not between grassland type and nest type or grassland type and shrub encroachment. Combined predation rates from the 3 nest types were positively associated with shrub density. The encroachment of shrubs into desert grasslands may act as a corridor for a diversity of species historically not associated with desert grasslands to occupy or move through a patch, increasing vulnerability to nest predation.