Friday, March 18, 2011

Yellow-crowned Night Heron

Yellow-crowned Night Herons (Nyctanassa violacea) have returned to the swamp around the boardwalk at the Audubon Center at the Francis Beidler Forest.  They winter south to Panama and throughout the Caribbean islands. The heron gets its name from its habit of foraging mainly at night.  In the swamp, these herons can be seen in the dim light slowly wading through the shallow water looking with their large eyes for crayfish moving in the detritus.

In past years, the Yellow-crowned Night Herons have been conspicuous in all wet areas touched by the boardwalk.  However, last year the birds were mainly absent from view.  As the swamp itself appeared not to have changed along the boardwalk, the lack of heron sightings was puzzling.  The mystery was solved during a reconnaissance for cover board sites during planning for the herp-themed summer camp.  As we walked along the edge of the swamp near #112 on the boardwalk, we came upon the beaver dam and the knee-deep water being pooled on the upstream side of the dam.  We already knew about the beaver dam and reported its presence in this blog.  However, we had not realized how the consistent water level behind the dam had changed animal behaviors.

Canada Geese (Branta canadensis) are not denizens of the swamp, but we had begun to hear their familiar honk-like calls coming from the treeless power line right-of-way north of the center where open water pooled like pond.  The chattering call of Belted Kingfishers (Ceryle alcyon) became more frequent within the same power line corridor.  Although Yellow-crowned Night Herons did not seek the open water and sunny environs of the power line corridor, they were actively hunting in the water behind the dam and beneath the tree canopy.  We found a half dozen Yellow-crowned Night Herons in the narrow band of trees between the dam and the power line corridor (see map).  Turtles, snakes, and big fish also found the consistent water depth more to their liking.

If you visit the Francis Beidler Forest and see a Yellow-crowned Night Heron stalking a crayfish, you'll know by the waggle of the bird's tail end that it is prepared to strike with its large bill.  We all tend to waggle in anticipation of good eats!

Image by Mark Musselman

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