Water Dependence of Birds in a Temperate Oak Woodland

Observations from June to September 1977 at a spring in central coastal California showed that 24 of 45 species of birds found within a 1.6-km diameter area used the spring as a source of free water. Color-banded individuals of several species drank more than once a day. A significant seasonal variation in the number of drinking visits per hour was found for all species combined. Only the Brown Towhee showed a conspicuous diurnal drinking pattern, however. Temperature on a particular day was not correlated with number of species visiting the spring, the total number of visits by all birds to the spring, or the number of visits by five of the six species considered to be water dependent. Granivory was significantly, positively correlated with water dependence. Permanent residents were more regular drinkers than summer residents, but this was a secondary effect resulting from the high proportion of granivory among permanent residents. The habitat surrounding the water hole, species abundance, and human disturbance at the spring all showed possible influence on our measures of water dependence. These findings suggest that surface water may be an important determinant of species distribution and community organization in mesic as well as desert environments.