Behavior of Whistling and Capped Herons in the Seasonal Savannas of Venezuela and Argentina

Abstract

Behavior, habitat use, and foraging of the Whistling Heron (Syrigma sibilatrix) and Capped Heron (Pilherodius pileatus) were studied in Venezuela and Argentina. Both foraged primarily alone or in pairs, but Whistling Herons also fed and roosted socially. Whistling Herons nested solitarily, maintained post-fledging associations with young, and appeared to defend feeding territories. They foraged in patches of short grass in wet savannas, especially where water was a few centimeters deep. Capped Herons also foraged in wet savanna, but the edges of streams or ponds seemed to be their preferred habitat. Whistling Herons fed by standing and slow walking, usually in an upright posture. At times they waved their heads in an exaggerated manner. Capped Herons crouched for long periods and walked slowly. Although the basic foraging tactics of the two species were similar, differences support the suggestion that the Capped Heron is a bird of forested streams and ponds while the Whistling Heron is a bird of open savanna. In many ways, the Whistling Heron resembles paleotropical grassland herons. The Whistling Heron (Syrigma sibilatrix) and the Capped Heron (Philherodius pileatus) are among the least known ardeids in the Western Hemisphere. They are exclusively neotropical with overlapping ranges in south-central and northern South America (Blake 1971). Their systematic relationships have long been uncertain (Bock 1956, Humphrey and Parkes 1963, Payne and Risley 1976), and little is known about their behavior (Hancock and Elliott 1978). The Capped Heron is generally uncommon (e.g., Mitchell 1957, Haverschmidt 1968, Hancock and Elliott 1978, Thomas 1979) whereas the Whistling Heron is locally common but patchily distributed. In this paper we contrast aspects of habitat use, behavior, foraging, and general adaptive habits of these two herons in the seasonal savannas of Venezuela and Argentina.