Meeting Abstract

S10.1  Tuesday, Jan. 6  Ecological influences on seasonal (and aseasonal) breeding in brush mice MABRY, Karen E; Miami University mabryk@muohio.edu

The timing of breeding may be influenced by both seasonal and aseasonal factors, particularly for animals living in seasonal but relatively temperate environments. The brush mouse (Peromyscus boylii) is a generalist small mammal that lives under a variety of environmental conditions across western North America. The timing of breeding in this species appears to vary across the range, and there is some indication that these mice may breed opportunistically when conditions are favorable. Over three years, I monitored the reproductive status of brush mice in the Northern Coast Ranges of California, an area that experiences predictable seasonal variation in weather, with cool, wet winters and hot, dry summers. However, ecological factors which may influence reproduction, such as population density and the availability of food resources, are less predictable. From June 2004-2007, I live-trapped individually-marked mice monthly, and recorded the reproductive status of each animal on every capture. I used a model-selection approach to determine the relative influence of the following factors on breeding: season (wet/dry), population density, and food (acorn mast) availability. I found that both season and acorn mast had a substantial impact on the probability of breeding. Brush mice reproduced primarily during the summer dry season, but also responded opportunistically to favorable conditions during other parts of the year. Up to 100% of adults were in reproductive condition between May and July each year, with only 0-25% of adults in breeding condition during a typical winter. However, after a relatively large acorn mast crop in fall 2004, brush mice reproduced continuously through the following winter. These results suggest that both seasonal and aseasonal factors affect the timing of breeding in this species.