Expedition to Tierra del Fuego – February 3, 2002
While the team has been capturing birds, Patricia, Gladys, and at times Steve have been doing their best to conduct scans of red knots for color bands. Scanning is not just looking for banded birds but also keeping count of the number of birds scanned so you know the percentage of banded birds in the total count. As with most things in Bahia Lomas, scanning requires a bit more effort than elsewhere. Scanning is best done when birds are feeding because they are moving and legs are exposed. The counter has to keep a still scope and count birds going past. But here, birds feed far out on the mud flat (a few miles from the shore) so the scanning must be done on roosting birds in winds often exceeding 30 knots (35mph). Despite this, Patricia and her team has scanned nearly a thousand birds and this is her report:
On Bahia Lomas we must approach birds just before the water starts covering the mudflats on the incoming tide. This makes the birds walk fast. We walk with them, watch bands always taking care to avoid the deep and dangerous channels that can cut us off from the land when they flood. During the high tide, knots concentrate in roosting flocks, usually standing on one leg, making it more difficult to scan. The weather is also a constraint because the strong winds move the telescopes when watching. For all these reasons it is hard every day to get the chance to run scans and get data.
That is why we are happy to get 955 birds checked for color bands from 26 to 31 January. Fifty-nine of them had flags and color bands a 6.18 percent recovery rate. Of these, 3.50 percent were banded in Delaware Bay, 2.04 percent in Argentina, and 0.45 percent in Brazil. Our most surprising discovery was the re-sighting of two orange flagged knots, an adult and an immature, banded in Rio Grande last November by a shorebird banding expedition led by Allan Baker. Rio Grande is another wintering location south of Bahia Lomas in Argentina hosting about 7,000 knots.
The rest of the team focused on catching birds. On Friday and Saturday the high tides reached their zenith, rushing into the channels and flooding most of the salicornia marsh very quickly, then just as quickly, running off the marsh. The birds were roosting on the very highest ground only to be pushed into even higher ground, then reversing the process until they once again roosted on the tidal flats. We would locate the areas where they roosted, set a net, then attempt to twinkle birds into the catch area only to have the tide flood our net. It was time consuming and ultimately unsuccessful.
On Friday night we had greater success mist netting. We set nets out on a salicornia point between two flooded bays. Within minutes after dark we started catching two-banded plovers and white-rumped sandpipers and then knots. By the end of the night we had capture 37 knots, 12 double-banded plovers, 5 South American oystercatchers . Five of the knots had color bands, two from New Jersey, two from Argentina and one from Delaware. The catch was welcome, and we now knew we could catch knots with mist nets when the weather is right. Our catch provided Anna Maria and Olivia with a suitable sample of knots for Anna Maria’s thesis analyses and an introduction to Professor Hector Hidalgo, Anna Marie Ph.D advisor who came from Santiago to observe our work.
Guy and Ken returned from their survey flight along the Argentine coast with discouraging news. The knot population appears to have disappeared in many of the areas where they once occurred in 1986. This year’s survey was an expansion of our surveys of the last two years, covering more of the Argentine coast up to to San Antonio Oeste. Our hope was to cover all possible wintering locations including Bahia Lomas, Bahia San Sebastian, and Rio Grande because last year we found a 30 percent decline in the knot population in Bahia Lomas and weren’t sure if the birds had actually declined or just moved elsewhere. In their expanded flight, Guy and Ken saw many birds but few knots. They counted 5,000 at Rio Grande and surprisingly nothing at Bahia San Sebastian. The survey suggests not only a decline in numbers but a retraction of the population mostly into just two location, Bahia Lomas and Rio Grande. But before we can draw conclusions they must fly Bahia Lomas, which will be done on Monday. The ground team suspects the worst however. Over the last week we have been conducting ground counts on the western shore, finding no more than 8,000 birds in an area that last year supported 15,000.
Lawrence J. Niles, PhD
Chief, NJ Endangered Species Program