Interbreeding of a Tricolored Heron and a Snowy Egret in South Dakota

Abstract

Reports of interbreeding among herons are uncommon and include a Little Blue Heron (Egretta caerulea) and a Cattle Egret (Bubulcus ibis) in California (Bailey et al. 1989), a Little Blue Heron and a Snowy Egret (E. thula) in Florida (Sprunt 1954), and a Little Blue Heron and a Tricolored Heron (E. tricolor) in Arizona (Phillips et al. 1964). In addition, a possible hybrid between a Snowy Egret and a Tricolored Heron was photographed in Florida in 1960 (Dickerman and Parkes 1968). In this paper, we report interbreeding between a Tricolored Heron and a Snowy Egret. To our knowledge, this hybrid combination has not been reported previously. Tricolored Herons and Snowy Egrets occur sympatrically along the Atlantic coast from New York to South America, and along the Pacific coast from Mexico to Peru (Hancock and Elliott 1978). Tricolored Herons rarely inland as far north as South Dakota (Schmidt 1979, Skadsen 1986), whereas Snowy Egrets have been locally common breeders in eastern South Dakota since at least the early 1980s (South Dakota Ornithologists' Union 1991). On 23 June 1995, we observed a Tricolored Heron in a mixed-species heronry in Brown County, South Dakota (45?40'N, 98?05'W). This observation was only the fifth record of a Tricolored Heron in South Dakota (South Dakota Ornithologists' Union 1991). The heronry was in a flooded, 5-ha stand of dead Russian olive (Elaeagnus angustifolia) trees. Extensive flooding in 1993 and 1994 had increased the available aquatic habitat and probably contributed to the establishment of the heronry. Nesting species included Cattle Egrets, Great Egrets (Ardea alba), Snowy Egrets, Little Blue Herons, and Black-crowned Night-Herons (Nycticorax nycticorax). About 1,200 pairs of herons (mostly Cattle Egrets) nested in the heronry in 1994 (Peterson 1995), and about 5,950 pairs (95% Cattle Egrets) nested there in 1995 (Naugle unpubl. data). On 30 June 1995, we marked a site after observing the Tricolored Heron perched on the rim of a bowl. This contained four light-bluish eggs and was constructed of Russian olive branches about 30 cm above the water. On 2 July, a Snowy Egret was incubating the remaining two eggs in the marked nest, which also contained two nestlings. While we were observing the incubating Snowy Egret, a Tricolored Heron landed near the nest. Subsequently, we observed a nest relief in which the Tricolored Heron and the Snowy Egret raised their head plumes and began bill-nibbling and vocalizing (see Rodgers 1977). Following the relief ceremony, the Tricolored Heron settled on the and incubated the eggs. All four eggs had hatched by 6 July. During that visit we photographed and recorded a relief ceremony on standard 1.25-cm VHS tape. The Snowy Egret fed the chicks regurgitated food. The Tricolored Heron also fed the chicks in the absence of the Snowy Egret. On 1 August, photographs were taken of the four juveniles (which were in the late branching stage of development) at the site (VIREO accession batch V06/24/001-005; Academy of Natural Sciences, Philadelphia). Their plumage and soft-part colors were unlike those typical of juvenile Snowy Egrets or Tricolored Herons (McVaugh 1972, 1975). Their heads were marked with a gray-brown crown that extended down the nape of the neck and graded to a slate gray on the back and wings (see Fig. 1). The sides of the neck and breast varied among individuals from slate gray to pale rufous. All juveniles were white on the head and undersides of the neck and body. Their irides were yellow, and their bills were black above and dark orange below, grading to black distally. The legs were yellow-green proximally and posteriorly, grading to dark on the distal anterior surface. There was no brownish-red color on the primary or secondary coverts or on the sides of the neck or breast, as would be typical of juvenile Tricolored Herons.