Green Heron

Butorides virescens

Unlike the other heron species that breed in Missouri, Green Herons normally nest solitarily, preferring dense, brushy thickets near water for nest sites (Andrle and Carroll 1988). Meyerriecks (1960) considered them semi-social, intermediate between the totally solitary American Bitterns and the highly social Night-Herons. In Missouri, nesting usually occurs in the forested margins of ponds, rivers, lakes, marshes and swamps (Kaiser 1982). They normally place their nests in dense cover within 5-7 meters of the ground, but when dense thickets are unavailable, they will nest 15-25 meters high in tall trees (Williams 1950). They sometimes re-build and re-use nests from a previous season (Davis and Kushlan 1994).

Code Frequency

Green Herons are reasonably easy to detect and identify as they fly in straight-line fashion across the sky or along streams. They are also easily located by their sharp calls. As a result, Green Herons were likely absent or in low numbers in those blocks where not recorded. Several factors contributed to the lack of confirmed breeding records for this species. Green Herons are secretive around their nests and therefore nest sites are not likely to be detected until young herons fledge (Peterjohn and Rice 1991). Two-thirds of the confirmed breeding records were obtained by observing fledglings. In only 17 blocks were active nests recorded.

Distribution

Average Number of Birds / 100 stops

Abundance

Green Herons were most abundant in the vicinity of the remnant swamplands of Mingo National Wildlife Refuge and Duck Creek Conservation Area. They were next most abundant in the Ozark Border Natural Division. They were least abundant in the heart of the Osage Plains and Glaciated Plains natural divisions. Breeding Bird Survey data in Missouri reveal a significant average annual decline of 2.1 percent in Green Heron numbers through the period 1967 to 1989. The removal of riparian forests appears to be largely responsible for reduced breeding populations.

Phenology

The initial migrants appear in mid-April, but few individuals are encountered until the very end of April or early May (Robbins and Easterla 1992). Nest construction may begin as soon as the adults return to their territories. Evidence for the earliest onset of nesting was the observation of a bird on the nest on May 10 in Scott County in 1989. The earliest dates for nest with young and fledglings correspond with the dates described by Davis and Kushlan (1994). Green Herons are occasionally double-brooded in Missouri (Kaiser 1982) and late dates for nests with young and fledglings likely indicate a second brood.

Breeding Evidence

Reported in 599 (49.6%) of 1,207 blocks

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