Use of corridor-like landscape structures by bird and small mammal species

Abstract

We investigated the use of corridor-like structures by birds and rodents in coastal San Diego County, California, USA, in areas characterized by dense residential development and small remnant habitat fragments. In 1992 and 1993 we compared the use of remnant strips of coastal sage scrub habitat and revegetated highway rights-of-way (ROW) with that of larger remnant patches of coastal sage scrub habitat to which these strips were connected. Using live trapping we compared rodent species composition, percent of females reproducing, and recapture frequency among the three site types. Rodent species richness did not differ significantly among the three site types. One species, Peromyscus eremicus was significantly more abundant in ROW sites, while several other species, Rheithrodontomys californicus, Chaetodipus californicus and C. fallax showed a similar, though non-significant trend. Peromyscus californicus was most abundant in remnant strips while Neotoma fuscipes used ROW sites less than remnant strips or patches. No significant differences were detected among the three site types in recapture frequency or proportion of females in reproductive condition. Common bird species were a priori divided into two categories based on previous research in this region: fragmentation-sensitive and fragmentation-tolerant. Species richness in remnant strips of habitat was similar to that in remnant patches for both categories of species. Species richness of the fragmentation-sensitive species was significantly lower in ROW sites than in remnant strips or patches by a factor of 4–10. Species richness in fragmentation-tolerant species was significantly lower in ROW sites in 1993 by less than a factor of two. The greater reduction in fragmentation-sensitive species suggests they have more stringent corridor requirements than do fragmentation-tolerant species. The species richness per site for fragmentation-sensitive bird species was significantly correlated with the percent cover of native shrubs in 1993 in patch and remnant strip sites. Fragmentation-tolerant bird species showed no consistent trend with shrub cover. Rodent species richness trended higher with increasing shrub cover in five of six site-type/year combinations, but none of the correlations were significant. Within the range of width and length examined there was no correlation between bird or rodent species richness and length or width of these corridor-like structures. These results indicate that remnant strips of habitat and revegetated highway ROW have potential to serve as habitat linkages for native rodents and fragmentation-tolerant bird species, but only remnant habitat strips appear suitable for fragmentation-sensitive bird species.