Copyright 2007 by Richie Swanson
A luminous-yellow warbler-head pokes out a hole in a stump. Tiny black eyes glisten brilliantly in dark forest-shadow. The prothonotary warbler sings Cheet!-weet!-cheet!-cheet!-cheet!-wee! He ducks inside the hole, sings invisibly, pops out, flashes white tail patches, cranks up his cheet!-weet!-cheets! He goes in, and a female–a paler yellow–clings by toes to the hole’s rim. She tips her head in, and he pushes his face out between her tarsi, bird-ankles. She can’t squeeze past him, he can’t dart out. He sings beneath her belly, and both finally squirm down into the possible nest-site. The next morning a house wren pushes a four-inch twig across the two-inch hole, the stick bending, not fitting until he pokes it straight and drags it. Now his potential mate follows him in.
The wrens come out, wings quivering, and the male’s song gushes like a slender thread of river racing through a tiny crack. Luminous-yellow bullets streak at the wrens, chasing them through foliage, chipping loudly.
The male wren and prothonotary each attract females to cavities. The wren sings spontaneous song-types, varying syllables uniquely, bubbling out songs up to 600 times in an hour. He usually carries away any material found inside a hole, sometimes destroying other birds’ nests, also removing parasitic mites. He places ten to 400 twigs in a cavity, starting as many as seven nests, and the female will choose and finish one, making as many as 300 twig-trips per day.
A male prothonotary also sings near cavities, chasing other males as wrens and other birds do. He puts moss in cavities before females arrive, and after they’re here, he flutters above trees with head-up and tail open, then flutters down–singing, you know. The female builds the nest, using more moss than any other cavity-nester, perhaps to maintain a stable temperature for eggs and hatchlings.
The prothonotary nests only in a hole in a mature floodplain forest above or near water. The species has been losing habitat ever since steamboats started to churn up the Mississippi, and early visitors cleared trees for wood-hungry boilers. Only ten percent of prothonotary-habitat remains.
The house wren’s breeding opportunities have probably increased ever since fields and houses started replacing forests. The species nests many places, including farmyards, city parks, suburbs, forest-edges, open woods, coastal swamps, coniferous clear-cuts, even in cattle skulls, boots and fishing keels hung from walls. People provide the house wren nesting boxes from shopping malls, websites, craft fairs–literally thousands of convenient locations.
The wren pecks or removes eggs and offspring of other species from cavities. The wren may also kill adult cavity-nesters. Its impact on other species remains inadequately studied, but scientists have implicated the wren’s cavity-takeovers and destructions of eggs and nestlings as a primary source of nesting failure for tree swallows, chickadees, bluebirds and the prothonotary warbler.
David Flaspohler found house wrens the most abundant species at prothonotary study-sites on the Mississippi River and Black River, Wisconsin, 1993-1994. Wrens were observed destroying only one of 42 prothonotary-nests; however missing eggs and disturbed nest-linings caused Flaspohler to suspect wrens played a larger role in nest failure, as found in previous studies.
Prothonotary-nests fail other ways. June flooding in 1993 destroyed eight of 22 nests during Flaspohler’s study. Raccoons appeared to destroy 825 of 2,726 prothonotary-nests studied in the Cache River Watershed, 1993-2000. Red and gray squirrels, mink and blue jays are also likely predators at Aghaming.
Shortly after the two prothonotaries squirmed inside their short-lived hole, a female popped out a second hole and then looked into a third. Another female dive-bombed her, and the two zoomed down to dead maple roots. They glared at each other, pecking moss-hairs, then burst through the under-story in a golden flurry with a singing male. A female cowbird flew immediately into a low buttonbush beside the roots, turning her head toward all three holes, perhaps eyeing potential sites to deposit her eggs.
Cowbirds parasitized cavities at Flaspohler’s nest-sites at the highest rates reported in any prothonotary study, 26.9%. Cowbirds rarely lay eggs in house wrens’ nests or cause them to neglect young by feeding cowbird chicks. Just four of 2,861 house-wrens nests were parasitized in a Canadian study.
I took down my wren boxes years ago, as some wildlife managers suggest, since the wrens as well as cowbirds, raccoons and other competitors of prothonotaries have increased dut to landscape changes since Euro-American settlement.
The prothonotary and other warblers may be declining faster than scientific resources can detect. Ten years ago, 22 warbler-species used Aghaming on May 18, 20 in a single hour after a rainstorm. This May 18, I spent six hours finding eight species. Though 20 warbler-species have used Aghaming since mid-April, and my comparison is anecdotal, not mathematical, warblers have seemed sparse this spring. I have not yet encountered the rapidly declining cerulean warbler at historic breeding sites here this year.
The Mississippi Alluvial Valley, the river valley south of the Ohio River, once had immense old-growth bottomland forests that supported abundant cerulean warblers. The forests also supported the Bachman’s warbler, now probably extinct. Today, the remnants of those woods help support 20% of the world’s prothonotary warblers, which breed in the Mississippi Alluvial Valley. They exemplify crucial habitats nearly gone from the river and Earth.
SOURCES
Flaspohler, D.J. 1996. Nesting Success of the Prothonotary Warbler in the Upper Mississippi River Bottomlands. Wilson Bulletin 108: 457-466.
Hamel, P.B. 1995. Bachman’s Warbler (Vermivora bachmani). In The Birds of North America, No. 150 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences,
Hamel, P.B. 2000. Cerulean Warbler (Dendroica cerulean). In The Birds of North America, No. 511 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Hoover, Jeffrey P. 2005. Water depth influences nest predation for a wetland-dependent bird in fragmented bottomland forests. Biological Conservation.
Johnson, L.S. 1998. House Wren (Troglodytes aedon). In The Birds of North America, No. 380 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Petit, Lisa J. 1999. Prothonotary Warbler (Protonoria citrea). In The Birds of North America, No. 408 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Stokes, Donald W. 1979. A Guide to Bird Behavior, Volume 1. Little, Brown and Company,
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