River Bird Blog

Copyright 2007 by Richie Swanson

I took a last look into Aghaming Park and Preserve after birding it dawn-to-noon four mornings per week since February. A prothonotary warbler flashed luminously yellow, biting a mayfly’s head, feeding fledglings.  A great crested flycatcher rasped, dive-bombing a yellow-bellied sapsucker from a tree-hole. An American redstart slapped a caterpillar against a branch until gut-juices squirted. A yellow-billed cuckoo pumped its tail and wings in time to its knocker-call. An Eastern wood peewee slurred pee-ah-wee sleepily, then abruptly chased another bird from a hunting perch. All these birds winter in mature forests disappearing from Central and South America.  They’re breeding in woods on the Upper Miss and need them on the Lower Miss too.

Aghaming stands amid the Upper Miss Refuge, the largest reserves of bottomland forest in the Upper Midwest, woods about 90% gone from the region. However, woods once grew nearly everywhere on the Lower Miss too, covering 95% of the river valley south of the Ohio. During the early 1900s Bachman’s warblers bred abundantly on the Lower Miss in interminable shrubs, palmetto and cane that escaped all but the highest floods, as far as scientists know. Loggers, railroads and farmers cleared the driest ground first, and virtually no habitat remains for the Bachman’s warbler on the Mississippi. The species has not seen since 1961.

Cerulean warblers, which bred at Aghaming reliably 1993-1998, were among the most numerous warblers during the 1800s in Lower Miss woods, especially in old-growth. Now the old-growth is gone, and trees comprise less than one-fifth of the lower valley, and the cerulean declines so precipitously Wisconsin lists it as state-threatened. I found no cerulean breeding at Aghaming this year.

Maybe 100 pairs of prothonotary warblers bred here, perhaps more. The species arrived as silver maples leafed out, and river birch catkins emerged in late April. It carried mouthfuls of nest-moss and battled house wrens for nest-holes in stumps beside every slough. It sometimes fed brown-headed cowbirds fledglings instead of its own. The prothonotary nests only in floodplain forests. Only ten percent of its habitat remains. The Lower Miss may support 20% of the species’ entire population.

As sloughs thawed during late March, yet another species dependent upon Lower and Upper Miss stepped as nimbly as a tightrope artist along a wiry branch above water. The rusty blackbird tossed pieces of bark from floating logs and ate caddis fly larvae and other aquatic insects at Aghaming. It swarmed by the hundreds around flood pools and the forest floor. Audubon Society has called the species North America’s most sharply declining bird. It has declined 95% since 1966. It winters primarily in Lower Miss woods and breeds mostly north of the contiguous 48, where global warming and acid rain may be compromising aquatic insects and other nutritional resources in boreal wetlands.

Hooded mergansers and wood ducks also appeared late March, looking for nest-holes in older-larger trees, ultimately feeding young amid marshes crowded with bulrush, water lilies and arrowhead. The Lower Miss supports 61% of North America’s “hoodeds” during winter.

The lesser scaup fed and rested here throughout April.  Its population has been declining since the 1980s, losing perhaps 150,000 ducks per year. Female scaups may die during spring migration, lay fewer eggs, or fail to breed due to low fat reserves. They may lack food resources, especially freshwater shrimp, at migratory stopover-sites in the Upper Midwest. Pool 19 of the Upper Miss, Keokuk to Burlington, Iowa, provides the “bluebills” a reliable feeding place, but scientists wonder if too many use only one site.

Tundra swans hooting overhead in April, heading to arctic breeding grounds, raised a similar issue. Twenty percent of their eastern population now migrate on the Upper Miss. Forty thousand swans used pools seven and eight, Trempealeau to Genoa, Wisconsin, on a single day last fall, replenishing fat stores on only a small part of the river. Forty percent of North America’s waterfowl migrate on the Upper Miss, also concentrating in just a few pools.

During a waxing moon April 28 a whip-poor-will called, a species suffering local disappearances in many states. The next week Blackburnian, Cape May and blue-winged warblers fed around swamp white oak leaves the size of squirrels’ ears. Northern waterthrushes, veerys, ovenbirds, Swainson’s and Gray-cheeked thrushes picked around leaf-litter and slough-edges. Yellow warblers, yellowthroats, marsh wrens, even prothonotaries fed around cattails emerging.

Many of these birds flew across the Gulf of Mexico or through Central America and up the Lower Miss to the Upper. Now they utilized Aghaming habitats top-to-bottom. No Aghaming migrant rivals the blackpoll. The half-ounce bird may leave Bolivia or Brazil, fly to Hudson Bay, turn left and fly to Alaskan shores on the Bering Sea or Arctic Ocean. Blackpolls return across Canada to the Atlantic, turn south and fly up to 88 hours nonstop behind northwesterly winds to Bermuda, then behind southwesterlies to Venezuela or Guyana. They depend upon forests there to refuel before completing fall journeys of nearly 5,000 miles.

The state-threatened red-shouldered hawk at Aghaming lambasted owls and other raptors, screaming ear-splitting shrieks, evidently defending nestlings, chasing any would-be predator. I encountered the species only inside gates installed to block traffic, away from cars and boats with booming engines.

In late June, federal officials announced the removal of the bald eagle from the Endangered Species Act’s list of threatened species.  The same week, two eagle fledglings perched beside a nest established last year, the first I had seen at Aghaming in 30 years. A state-threatened osprey fanned her wings, shading hatchlings chirping in a nest box atop a power pole. State-endangered peregrine falcons nested just a glance upriver at the river-bluff called Castle Rock. All three raptors recovered reproductive abilities after the 1972 ban on DDT.

Peregrines have now bred at Castle Rock five years consecutively.  At least two young falcons fledged at the site this year.  Peregrines nested in Wisconsin at ten known cliff-sites along the Upper Miss this year.  DDT and other causes had prevented peregrines from breeding in Wisconsin as recently as 1965-1985.

More than 100 state-threatened great egrets hunted green frogs and other prey around sloughs and marshes, finding food for fledglings only a mile or two from nests, a crucial ingredient for a species that failed to breed in Minnesota as recently as 1980. Least bitterns and black terns used Aghaming’s marshes to breed, but I saw none of the declining American bittern or black-crowned heron or the state-threatened yellow-crowned night heron.

Two woodpeckers that have declined by more than 50% since 1966 used the granddaddy oaks and cottonwoods where I took my last look. Northern flickers mated as cottonwood buds emerged early April and called by nest-holes throughout Aghaming through June. Two red-headed woodpeckers pivoted sharply together and mated on a courtship limb near a nest-hole June 2. They vanished in the middle of reproductive efforts, along with at least two other calling red-headeds. Why? Did insect prey draw them to a bank on a nearby highway, where their low take-offs frequently lead to death? Did they get into creosote in abandoned railroad ties nearby? Did a nearby owl or Cooper’s hawk eat them? Did European starlings evict them from their hole?

Humankind must answer many such questions and create and facilitate remedies to help red-headed woodpeckers rebound like the river’s raptors. We must overcome problems as enormous as global climate change and navigational channels that supplant islands and trees to help prevent other species from joining the ranks of the Bachman’s warbler, and the passenger pigeon which once used the Upper and Lower Miss by the millions.

SOURCES

Anderson, Bob.  Peregrine falcon information (update by e-mail).

Anteau, M.J., Ph.D.  Research Wildlife Biologist.  Northern Prairie Wildlife Research Center.  Jamestone N.D.  (update by e-mail.)

Anteau, M.J., Afton A.D.  July 2004.  Nutrient Reserves of Lesser Scaup (Aytha Affinis) During Spring Migration in the Mississippi Flyway: A Test of the Spring Condition Hypothesis.  The Auk.

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, Philadelphia PA.  The American Ornithologists’ Union, Washington D.C.

Hamel, P.B. 2000.  Cerulean Warbler (Dendroica cerulean).  In the Birds of North America Online, No. 511.  (A. Poole and F. Gill, eds.).  Philadelphia PA.

http://audubon2.org/webapp/watchlist?viewSpecies.jsp?id=165.

http://nationalzoo.si.edu/ConservationandScience/MigratoryBirds/Research/Rusty_Blackbird/decline.cfm.

McCrimmon, D.A., Jr., J.C. Ogden, and G.T. Bancroft.  2001.  Great Egret (Ardea alba).  In the Birds of North America, No. 570 (A. Poole and F. Gill, eds.).  Philadelpia PA.

Sauer, J.R., J.E. Hines, and J. Fallon. 2005.  The North American Breeding Bird Survey, Results and Analysis, 1996-2005.  Version 6.2.2006.  USGS.  Patuxent Wildlife Research Center.  Laurel MD.

Upper Mississippi National Wildlife & Fish Refuge.  2006.  Comprehensive Conservation Plan.

Weidensaul, Scott.  2000.  Living on the Wind: across the hemisphere with migratory birds.  North Point Press.  New York.