Sunday, November 11, 2007

Evening Roost

Where do the White Ibis (Eudocimus albus) go once the sun starts to set? Well, if they are any where near the Waterwheel Fishing Lake, they appear to head for the two cypress trees growing in the middle of the pond. They don't have the benefit of our Global Positioning System (GPS) or Google Earth, but they find their way there every evening. If in Google Earth you type 279 Water Wheel Drive, you will zoom right to the pond. The image shows the two trees in the middle of the pond, in which the birds are roosting.

As dutiful Audubon South Carolina employees, we are doing what we can to reduce our carbon footprint by carpooling from our homes in Summerville to work at the Francis Beidler Forest. With the end of daylight savings time, our commute home has placed us at the fishing pond after sunset and after the birds have moved into the trees within the pond. The tree begins to look like a white Christmas tree once the birds fill branches. We decided to leave work a few minutes early on Friday (due to the "dutiful" thing, don't tell the boss) to get our camera set up before the mini-migration from the high, sunlit trees rimming the pond to the two trees in the middle of the pond. The series of images shows how during the hour from 4:45 pm to 5:45 pm EST, the birds relocated themselves. The first image shows a lone ibis doing its best imitation of the Christmas angel atop the tree. As the sun set in the west and the sunlight slowly crept up the trees surrounding the eastern edge of the pond, birds headed to the cypress in the middle of the pond to begin jockeying for prime roosting spots. The birds high in the trees rimming the pond remained until even those perches were beyond the sun's warming reach. Then too, they launched into a glide towards the lower cypress trees in the pond while appearing to "honk" their displeasure at the quality of roosting options remaining. We're not sure, but the returning ibis comments appeared to translate as, "You snooze, you lose."

Why expend the energy to fly to one communal roosting location? In The Birder's Handbook: A Field Guide to the Natural History of North American Birds, the authors (P. R. Ehrlich, D. S. Dobkin, & D. Wheye) note, "One possibility is that older, more experienced birds are better able to find food; hence younger birds roost with them in order to follow their elders to better foraging grounds. The older birds accept this social parasitism because they tend to be dominant, and are able to appropriate more central and therefore safer positions in the roosting crowd. As long as the costs of increased competition are outweighed by the benefits of increased safety from predators for the older birds, and the benefits of locating rich food supplies for the young outweigh reduced nighttime safety for them, roosting should be communal."

If you like the I SPY series of books, "Two Great Egrets with bills of yellow taller standing than the Ibis fellow."

The images were taken from the public road. If you visit, please respect the owner's property rights.

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