Expedition to Tierra del Fuego – February 7, 2004
The moon, tides and sun restrict our trapping effort significantly. The moon rises just as the sun sets, leaving us with too much light to catch birds with our mist nets. Bahia Lomas has two zones important to the birds. The normal daily tide floods about half of the sand and mud flats along the bay and in that littoral zone exists most of the red knot and Hudsonian godwit prey. The upper flat only floods at tides influenced by the full and new moon, rising more than 3 m. In that zone, prey densities are very low and once the littoral zone is flooded the birds must roost in the upper zone. Last night we ran the nets for a short period of dark before the moon rose and caught 35 birds, 6 of which were knots
The six captured birds included two over 150 grams. These are the heaviest birds of the last four years of work suggesting they are preparing for their journey back to the Arctic. In addition, several birds were about 25% into their breeding plumage. We banded each bird with a Chilean red flag with a unique combination of two letters which can be seen with a spotting scope. These flags will allow all observers along the east coasts of South and North America to identify each individual we catch.
Cannon netting must wait until the tide reaches the vegetation at the end of the flats forcing the birds to roost in places where we can set a net. Two days ago we set a net for Magellanic and American Oystercatchers where they were roosting on a stone and shell beach. We captured only 38 but took the opportunity to attach unique bands to the Magellanic Oystercatchers, providing Chilean observers the opportunity to identify individuals as they move around the region. Kees went to observe the birds the next day and relocated six birds and identified the main prey as a 3 inch bivalve.
While we try to capture birds, Dan Hernandez is expanding his Ph.D study on foraging strategies of red knots on Delaware Bay to foraging on Bahia Lomas. He observes birds with a video camera and then scrutinizes the tape back in the lab to measure how birds find prey and how much effort they put into the search. It is the first time we have observed birds at all stages of the tide. Combined with our study of marine sediments and invertebrate populations conducted by Carmen Espoz and her student Alejandra, we will have a much better idea of the foraging ecology of both red knots and Hudsonian godwits on the bay.
A second night at the mist nets set to the north of camp proved unsuccessful but we are finally getting water under the mist nets set to the south. We have been furthered hampered by the tide being lower than predicted and the birds concentrating south of camp. The higher tides are finally moving birds into the area of our nets and are now high enough to allow limited mist netting and hopefully more cannon netting.
Kim Korth 2/7/04