Document: PAU-3-81-6

Arroyo toad terrestrial habitat preferences vary by sex and scale of analysis.

GRIFFIN, P.C.* ¹ and T.J.CASE ²

University of Montana Missoula MT 59812 USA ¹
University of California San Diego La Jolla CA 92093 USA ²

Abstract:
The endangered southwestern arroyo toad, Bufo californicus, is now limited to 22 watersheds in southern California. We set out to identify habitats that are preferred by adult arroyo toads for burrowing and surface activity. We examined the land cover type preferences of arroyo toads at a coarse scale, based on comparisons of minimum convex polygons [MCP] of area used by each animal to available habitats in the study site, using compositional analysis. The land cover types were agricultural, campground, channel, terrace, and upland. We also examined the microhabitat preferences of arroyo toads for different substrate, vegetation, and vegetation structure types relative to the amounts of those habitat types available within their MCP. Substrate types were clay, silt, fine sand, medium sand, coarse sand, gravel, and cobble. Vegetation types were willow and mulefat, sycamore, oak, coastal sage, chapparal, non-native grasses, large exotic plants, low annual plants, agriculture, debris pile, and no vegetation. We designated vegetation structure types according to total canopy coverage and canopy height distribution. We attached radio transmitters to arroyo toads using an external belt attachment system and tracked 83 arroyo toads over an average period of 30.9 days (S.D.= 29.0) in 1998. Female arroyo toads (n=15) significantly preferred terrace and channel habitats over campground, agricultural, or upland habitats. During the breeding season, male arroyo toad preference for channel habitats was greater than all other habitat types, probably because channel habitats were closest to breeding sites. Sands of all size classes were the preferred substrates for arroyo toad burrowing. Dense, canopied vegetation structures were the least preferred sites for arroyo toad burrows during this study.

Keywords: amphibian ecology, habitat preference, compositional analysis, upland habitat use

This abstract is being presented at: 11:00 AM in session:
Oral Session #38: Amphibian Ecology.