The negative impact of heavy rains on the abundance of a Mediterranean population of European rabbits

Abstract

European rabbits, Oryctolagus cuniculus, are the basic prey of several endangered predators and an important hunting bag in the area of its origin in southwestern Europe. Conversely, they are considered an undesirable species in other areas where they were introduced. Therefore, there is great interest in understanding the factors that influence population dynamics and abundance of this species. I studied the effects of relatively common heavy rains on inter-annual variations in rabbit density in four habitats of Donana National Park and surrounding areas (southwestern Spain) during several years when rainfall was either lower or higher than average. I estimated spring and autumn rabbit densities by line transect sampling between autumn 1993 and autumn 1998, and counted rabbit warrens and entrances in two of the habitats (one with and the other without scrubland vegetation) in 1995, 1996 and 1997. Rabbit density significantly decreased in all habitats during the rainy years, densities being on average 5.3 and 4.6 times lower for spring and autumn censuses, respectively. Both number of warrens and entrances significantly decreased after two consecutive years of heavy rain in both habitat types, although in the scrubland habitats some recovery was observed during the second consecutive year of heavy rains. The area where warrens were apparently free of the effects of rains was only between 2.7 and 3.8% in the open habitat and 21.5% in the scrubland. At least for the open habitat, no clear relationship was observed between the height above sea level and whether warrens were affected by rain or not. The results indicate that heavy rains may be an important factor decreasing rabbit density, at least in flat areas, by negatively acting on warrens during the breeding period.