Does available foraging area, location or colony character control the size of multispecies egret colonies?

Abstract

Food supply is commonly regarded as ultimately controlling the size of bird colonies. Most studies examining this problem have been on seabirds, and all in the Northern Hemisphere. To search more widely for evidence of the importance of food as a factor controlling the size of bird colonies, we investigated egret colonies in a Southern Hemisphere region. We examined the relationship between colony size and the area of potential feeding habitat around each colony, compared with variables associated with the location and the physical characteristics of each colony. All colonies (13 in total) along 800 km of coastline in New South Wales, Australia, were studied. Colony size ranged from 7 to more than 2000 nests. There were very few correlations between the number of nests and the areas of different types of feeding habitat within 20 km of colonies. However, the available area of saltmarshes proved to be a significant predictor of colony size for great (Ardea alba), intermediate (A. intermedia) and little egrets (Egretta garzetta). Saltmarshes may be stable, long-term feeding habitats for these three native ‘aquatic feeders’, but not for the terrestrially feeding cattle egret (Ardea ibis). Nest numbers of this latter species were related positively to the area of saltmarshes, and negatively to latitude, suggesting that nest numbers of this exotic species may be influenced by climate, with proximate factors such as colonial nesting with the three native species also being important. Because of the numerical dominance of cattle egrets, the numbers of nests of all species followed the same pattern as that for cattle egrets.

Assessing the Ecological Risk of a Municipal Solid Waste Landfill to Surrounding Wildlife: a Case Study in Florida

“…This was consistent with a previous analysis by Ogden, Kushlan and Tilmant (1978) that found White Ibis move nesting locations rapidly, with large colonies disbanding and new ones forming in the space of 1 or 2 years. Numerous factors drive colony dynamics; however, food supply and predation pressure are commonly regarded as the principle factors (Drent and Daan 1980;Burger 1982;Gibbs and others 1987;Frederick and Collopy 1989b;Baxter and Fairweather 1998;Bokach 2005). In the Everglades, prey availability to wading birds is directly related to hydrologic variables including depth and the drying process or recession rate (Frederick and Collopy 1989a; for review, see Gawlik and others 2004 and references therein).…”

Ecology, disturbance and restoration of coastal saltmarsh in Australia: a review

“…The size of breeding colonies of egrets has been positively correlated to the area of saltmarsh within 20 km radius of the breeding colony (Baxter 1998).…”

Nesting tree characteristics of heronry birds of urban ecosystems in peninsular India: implications for habitat management

“…Even though heronry birds vary in their habitat preference, diet, and behavior, their fundamental requirements for nesting remain more or less the same ( Hafner 2000 ). Multiple factors affect habitat selection and colony site dynamics of waterbirds ( Kharitonov and Siegel-Causey 1988 ; Fasola and Alieri 1992 ; Boulinier and Lemel 1996 ; Erwin et al 1998 ); habitat quality, including the nesting tree quality, has been demonstrated as one of the most important habitat selection criteria ( Fasola and Alieri 1992 ; Baxter and Fairweather 1998 ). Therefore, studying nesting ecology of the birds in urban ecosystems can suggest methods to improve their urban habitats.…”