A Case of Colonial Breeding in the Green-Backed Heron

Long-legged wading birds of the family Ardeidae, which includes the egrets and herons, are well known for their large breeding assemblages. In some parts of their range, these colonies may contain many thousands of pairs of breeding birds, and often include other, more distantly-related species such as storks (Ciconiidae) and ibises (Threskiornithidae) (Maxwell and Kale, 1977; Hancock and Elliot, 1978). However, the degree and type of coloniality exhibited by ardeids vary greatly. For example, Great Blue Herons (Ardea herodias) usually breed in large colonies comprised of this single species (Stephens, 1980). Somewhat more common in temperate areas are the mixedspecies colonies, such as the large one located in Wichita, Sedgwick County, Kansas. In 1992, this breeding colony contained approximately 600 nests, including those of the Black-crowned Night-heron (Nycticorax nycticorax), Cattle Egret (Bubulcus ibis), Great Egret (Casmerodius albus), Little Blue Heron (Egretta caerulea), and Snowy Egret (Egretta thula) (Maccarone, 1993). In contrast, some species of ardeids tend to be solitary or perhaps loosely colonial during the breeding season (Hancock and Elliot, 1978). Into this category would fall the Yellow-crowned Night-heron (Nycticorax violacea) and the Green-backed Heron (Butorides striata). Here we report an unusual case of a small, loosely organized colony of Green-backed Herons. This colony is located within the boundaries of Sedgwick County Park, Wichita, Kansas. The colony may have begun in 1983, when a single nest containing two eggs was observed on 20 May. This nest was located in a 5-m-high pear tree (Pyrus sp.), one of several such trees in a grove dominated by small (ca. 3 m) redbuds (Cercis canadensis) and several larger (> 10 m) elms (Ulmus sp.). We visited the area periodically over the next several breeding seasons, during which time the colony had grown. In 1989, nine nests were found; in 1990, the area contained 12 nests; in 1991, 11 nests were recorded, and in 1992, either seven or eight nests were found. During these last four breeding seasons, some of the nests in the colony appeared to have been inactive, and likely had survived the previous winter more or less intact.