River Bird Blog

Copyright 2007 by Richie Swanson

The south wind blows all day, gusting almost 40 mph, and the lazy-brown river suddenly rolls like surf, heaving backward, hurling spray up-channel. Leaves slap noisily on treetops, and birds from South and Central America dart around low in dense cover of exotic honeysuckles and buckthorn, foraging on leeward banks and dikes. Seventeen species that winter in mature forests in the tropics use Aghaming this weekend. Sixteen warblers use it, four considered conservation priorities by U.S. Fish & Wildlife Service, rare or declining. A Canada warbler spins on a branch, revealing a black necklace, and a prothonotary pokes its bill into a knothole, a possible nest site. A blue-winged forces his softly-sung beee-buzzzz into the wind-rattle, and a Cape May gleans bugs from river-birch catkins, flashing electric-chestnut ear-patches on yellow cheeks.

The prothonotary, Canada and Cape May symbolize challenges faced by many tropical migrants breeding in North America. They nest more successfully in large, unbroken forests than in smaller fragments, freer of predators and brown-headed cowbirds that penetrate edge-habitats. They require specific niches to reproduce. They shun disturbance, but their tropical woods are turning rapidly into pastures, cane fields and other peopled environs.

The prothonotary, of course, breeds only in mature floodplain forests. The Mississippi River Valley south of the Ohio River supports 20% of the species’ entire breeding population. The prothonotary breeds abundantly at Aghaming and suffers high rates of cowbird parasitism on the Upper Miss. Raccoons appeared to destroy 825 of 2726 nests studied in the Cache River Watershed, 1993-2000.

The Canada migrates from as far as northern Brazil and nests in dense-wet cover in boreal and northern hardwood forests in root wads, tree stumps, sphagnum-moss hummocks and rhododendron thickets. It has declined 40% since 1966. Rapid human growth and deforestation diminish its strongholds in the northern Andes.

The Cape May also breeds in boreal woods. Its populations swell during outbreaks of spruce budworms, an insect that defoliates fir and spruce in eastern U.S. and Canada. The Cape May nests high in thick crowns of conifers, probably needing trees older than most logging practices allow. It winters almost exclusively in the West Indies, thankfully using shade-coffee plantations, landing almost always in Florida as it migrates.

See the blue-winged warbler, see a little bird made of sunshine wearing wings spun from the noon-sky. The species’ nests in saplings and young trees at edges between forests and fields. Its breeding range expanded northward more than 100 years as North American forests were cleared, and abandoned farms turned into shrub habitat, and the climate warmed. Now older forests and urban sprawl usurp its habitat. The blue-winged hybridizes with—and replaces—the gold-winged warbler, another USFWS conservation priority, due at Aghaming any day.

Some tropical-forest species find food and refuge here temporarily, ultimately nesting farther north. A northern waterthrush tosses dead-drenched weeds from a floating log, bobbing so intensely the slough ripples beneath the “honeysuckle” dike. A gray-cheeked thrush skulks in leaf-litter—it breeds in dense shrubs in taiga and adjacent tundra from Newfoundland to eastern Siberia. A blue-headed vireo perches knee-level, a blackpoll gleans river-birch bark at eye-level, and Tennessee warblers trill fast-dry chips from tree crowns.

When the blackpoll returns from northeastern America, it may fly over the sea 88 consecutive hours, traveling 1500 to nearly 2200 miles to mainland South America. The species declined dramatically and inexplicably in some parts of its boreal breeding range 1980—2002: 54% in Alaska, 91% in British Columbia and Quebec, 78% in Newfoundland.

Other tropical-forest species will breed in the floodplain or nearby. A veery twirls on buttonbush above a slough, showing a smooth-tawny back, then the waxy-tawny wash on its speckled throat. An ovenbird kicks tiny-pink legs through dead foliage on the dike, jutting its russet-crown forward, pecking beneath new nettle-leaves, gulping. A black-and-white warbler zigzags eye-level on hackberry, then ash, oak and sassafras bark. It goes upside-down like the resident nuthatch and gleans insects with a decurved bill like the resident creeper. It’s only one of three of 241 neo-tropical migrants found in western Mexico that the ornithologist Richard Hutto classified as a habitat generalist.

An American redstart perches in sun head-high in honeysuckle, and a blue-gray gnatcatcher buzzes sharply, flicking a tail 45% of its body length, chasing a Cape May warbler from high in a walnut. The dearie-come-here of the yellow-throated vireo descends harshly and hoarsely from a granddaddy cottonwood.

Approach these woods from the Wagon Bridge, they may seem like the same local place. But birds from another continent’s forests have transformed them from ground-to-treetop since last week, filling them with darting-dashing-fluffing colors, with zee-zee-zoos, tseet-tseet-tseets, buzzes, carols, chips, with insect sorties, dive-bomb chases, leaf-litter hunts, tail-feather flashes, catkin-pecks, population problems.

Warbling vireos, chimney swifts, gray catbirds, green herons, eastern kingbirds, indigo buntings, Least flycatchers, common yellowthroats and Wilson’s warblers also showed up at Aghaming this week.  Baltimore orioles piped tones even richer than the robin’s, slurring and drawing out notes ever-so slowly from the forest’s canopy.

SOURCES

Baltz, M.E., and S.C. Latta. 1998. Cape May Warbler (Dendroica tigrina). In The Birds of North America, No. 332 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.

Conway, C.J. 1999. Canada Warbler (Wilsonia canadensis). In The Birds of North America, No. 421 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.

Dobkin, David S., Ehrlich, Paul R., and Wheye, Darryl.  1988.  The Decline of Eastern Songbirds.  http://www.stanford.edu/group/stanfordbirds/text/essays-/Eastern_Songbirds.html.

Gill, F.B., R.A. Canterbury, and J.L. Confer. 2001. Blue-winged Warbler (Vermivora pinus). In The Birds of North America, No. 584 (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.

Kricher, John C. 1995. Black-and-white Warbler (Miniotilta varia)). In The Birds of North America, No. 158 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, and The American Ornitholgists’ Union, Washington D.C.

http://audubon2.org/webap/watchlist/viewSpecies.jsp?id+165.

http://www.borealbirds.org/birdguide/bd0365_species.shtml

Swanson, R. 1998. The Breeding Birds of Aghaming Park. Aghaming Park: A Community Resource Plan. City of Winona, Minnesota. The bird report can be accessed at www.WarblingRichie.com.

U.S. Fish & Wildlife Service. January 2002. Fish and Wildlife Resource Conservation Priorities. Region 3. Version 2.0.