Arthropod Prey Availability in Cactus Wren Territories in San Diego County

The primary purpose of this study was to document the abundance and availability of arthropod species found in the territories of coastal cactus wren, a California Species of Special Concern and Multiple Species Conservation Program-covered species, in San Diego County.

In addition, the study aimed to identify associations between prey and particular plant species found in cactus wren territories, and to provide insect material for the development of a DNA library of potential food taxa for comparison with DNA-barcoded cactus wren fecal sacs.

Led by Curator of Entomology Dr. Michael Wall, the team sampled arthropod fauna at 23 cactus wren nesting territories during the early, mid-, and late nesting season at four locations in southern San Diego County. Within each territory, museum entomologists used pitfall traps and vacuum samplers to collect arthropods from nine potential cactus wren foraging plant species (e.g., California sagebrush, California buckwheat) or groups of plants (invasive mustards, native bunchgrasses); the cactus wren’s preferred nesting plants, cholla and prickly pear; and bare ground.

With in-house entomologists, a large team of volunteers, and the largest entomological reference collection in the region, the Museum has a unique ability to conduct such a study. Scientists examined arthropod abundance and diversity by sampling method, survey timing, host plant, and sampling period; and compared these results against arthropod abundance data generated from cactus wren fecal sac DNA analysis (i.e., previously documented nestling diet).

When added to existing knowledge of coastal cactus wren diet, examining arthropod diversity and its association with host plants within cactus wren habitat provide helps inform management decisions when preserving or restoring cactus wren habitat.