Status and ecology of deer mice (Peromyscus maniculatus subsp.) on Anacapa, Santa Barbara, and San Miguel Islands, California : summary of monitoring 1992-2000

Schwemm, Catherin; Coonan, Timothy

Monitoring of island deer mice (Peromsycus maniculatus subsp.) populations was conducted as part of the long-term ecological monitoring program at Channel Islands National Park from 1992 to 2000. Three subspecies of deer mice were monitored on nine grids on Anacapa, San Miguel, and Santa Barbara islands. Density and population numbers were estimated from mark/recapture data. Weight and sex information was also collected, and information on animal movement was obtained by analyzing trapping results. Density estimates among all islands ranged from less than 10 mice per hectare to over 900 per hectare. Fall densities were correlated with previous winter rainfall but not with any measure of vegetation. Spring densities were positively correlated with precipitation occurring during the winter two years previous, with spring vegetation measurements from the previous year, and negatively correlated with current-year winter rainfall. Average adult weights were consistently higher on Santa Barbara during all periods studied. Weights on Santa Barbara and San Miguel islands were significantly different among habitats, being higher in shrub habitat than in grasslands. There were few relationships between density and measurements of dispersal, although on San Miguel Island there was a significant positive relationship between the number of single captures and density. Spring densities of mice on Santa Barbara Island were compared with the amount of predation on Xantu’s murrelets (Synthliboramphus hypoleucus) during the spring nesting season and no relationship was found. Mouse predation was found to negatively affect annual productivity of murrelets. Mice were found to have a significant negative relationship on short-term Coreopsis productivity on Santa Barbara Island. On San Miguel Island mouse densities rose sharply after a population crash of island foxes (Urocyon littoralis littoralis) resulted in the elimination of the fox as the primary predator from the system. Population numbers apparently cycled with a three to four year periodicity on Santa Barbara Island, however no cyclic patterns were apparent on Anacapa or San Miguel islands. Density tolerance appears to be extreme on Santa Barbara Island and a result of adaptation, while on San Miguel Island indications are that predation functioned to limit population numbers and tolerance for high densities is reduced. Finally, suggestions are provided for application of mouse monitoring data in selecting alternatives for two current management issues.

Status and ecology of deer mice (Peromyscus maniculatus subsp.) on Anacapa, Santa Barbara, and San Miguel Islands, California : summary of monitoring 1992-2000

Series

Collections