Hornsby Bend Bird Observatory
The Birds of Hornsby Bend
by John Kelly, Travis Audubon Society
Austin has an international airport, but it's not at Austin-Bergstrom Airport, though it's not too far from there. It's at the old wastewater treatment facility at Hornsby Bend, a few miles from the airport on the north side of the Colorado River (see map).
Over the course of the year, thousands of birds visit the lagoons at Hornsby Bend, en route to and from their wintering grounds. Some of these birds nest as far away as Siberia, almost 6000 miles from Central Texas. Others winter in the southernmost South America, about 5000 miles away. And still other rarely venture more than a mile or so from Hornsby. But regardless of the distances these birds travel, Hornsby is essential to their lives.
Probably the best way to get an appreciation of Hornsby's importance is to start off with its quietest month, June. By the first of June, the northward spring migration is largely over: only a few laggard birds, such as some small flycatchers, are still on the move. The lagoons are almost empty of wintering waterfowl, hosting just a few ducks and coots which-for whatever reason-failed to return to the north. Most of the permanently resident birds, species such as Carolina Wrens, are finishing the years nesting activities; but they're not as conspicuous as they were earlier in the year, singing less as they strive to raise their young before the Texas summer arrives. Also in the race to fledge their young are such summer residents as Red-eyed Vireos and Dickcissels. But the overall impression is one of quiet. A visitor to Hornsby during June might well be forgiven for wondering why local birders consider this place so important.
A hint of the answer begins during the heat of July, as shorebirds begin returning from their Arctic and subarctic nesting grounds. The first of these shorebirds are mostly birds which failed in their breeding attempts. But by the last week of the month, hundreds of successfully breeding adults are also present, abandoning their young on the nesting grounds to insure that the fledglings won't face adult competition for the far north's rapidly decreasing food resources.
By August young shorebirds begin appearing, as do the earliest southbound landbirds such as warblers and vireos. Swallows begin massing near the lagoons, taking advantage of the summer's insect hatch. A few of the earlier-migrating ducks, such as Blue-winged Teal, begin returning. From their nesting colonies along the Gulf of Mexico, ibises, herons, and egrets arrive at Hornsby, part of the late summer dispersal which may take them as far north as southern Canada. Most if the locally-nesting birds fall silent, as the molt their old feathers in preparation for either migration or the coming winter.
September sees the peak movement of southbound landbirds. Migrant hawks begin appearing in numbers. More ducks arrive, and most of the shorebirds depart for wintering grounds far to the south. Some of the permanently resident birds, having completed their molt, begin a fall song period.
By October, most of the southbound shorebirds and landbirds have left. Wintering landbirds such as sparrows begin arriving in numbers. Ducks continue to arrive, the males in their drab, female-like "eclipse" plumage. Coots arrive in numbers. Geese and cranes pass overhead: relatively few stop at Hornsby, though a Whooping Crane has been recorded at the lagoons this month. Hawk migration reaches its peak.
Duck and coot populations reach their peak during November: daily counts may exceed 3000 birds. Male ducks begin emerging from their eclipse into brilliant breeding plumage. Almost all the shorebirds and landbirds have departed by the end of the month. The Great-Horned Owl-the local species with the most prolonged breeding cycle-begins its breeding activities.
Some ducks and coots continue to arrive during early December, while others continue south. By mid-month, though, the fall migration is essentially over. The only new arrivals are birds force to move south by exceptionally severe weather in the north.
January is almost as quiet as June: the birds have now settled in for the winter. Only local movements take place, as ducks wintering on the lagoons seek food in nearby lakes, ponds, and fields. But, of course, the lagoons are much more crowded than in June, usually hosting 1000 to 2000 birds. And the nearby woods are full of wintering landbirds.
By early February, things are beginning to stir. A number of waterfowl begin leaving Hornsby for the north, and a few wintering landbirds start pulling out. Some local nesters (such as Eastern Screech-Owl and Carolina Wrens) begin their annual breeding cycles.
By March, the migration is in full swing. Blue-winged Teal begin returning from the south, while other waterfowl begin to depart for their northern breeding grounds. The earliest migrant landbirds, such as White-eyed Vireos, begin returning from the tropics. The first migrant shorebirds appear, including Pectoral Sandpipers on their annual round-trip between the pampas of South America and the tundra of Siberia. Many wintering hawks and falcons depart. Local nesting activities start to intensify.
April is the high month for Spring migration. The numbers of both the landbirds and shorebirds migrants peak. By the end of the month, essentially all waterfowl (other than the few which will oversummer) have left. The first fledglings appear-the young of such species such as Tufted Titmice and Carolina Chickadees. Many local breeders begin their second nesting attempts.
The landbird and shorebird migration rapidly dwindles during May: by mid-month almost all the migrants have moved on, except for a few stragglers and late migrating species such as Yellow-bellied Flycatchers. The lagoons now seem quite empty. They'd appear emptier if it weren't for the Wood Ducks, our only locally-nesting waterfowl: from miles around, female Woodies bring their broods to Hornsby for the safety and food the lagoons provide. More landbird fledglings appear, and more second nesting attempts begin.
And so the annual cycle of bird activities at Hornsby comes full circle, a cycle which can fully be appreciated only by considering each month of the year. Over the course of that year many tens of thousands of birds will stop at Hornsby Bend-some to rest and refuel for the next leg of their migration, others to overwinter, still others to raise their young.
Hornsby Bend is critical to all their lives: there's nothing like it in the Austin area. That's why Hornsby's preservation is so important-not only to the birds, but also to the humans whose lives are enriched by the birds which come from three continents and thousands of miles to stop at our Hornsby airport.
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www.hornsbybend.org/seasonalguide.html (Last modified Jun-16-03)