Tierra del Fuego – Gale Winds and Shorebirds
Our Seventh Expedition to Tierra del Fuego: 1/20/08
Our Friday morning started by saying goodbye to Sergio and Gabriella, the veterinary students from University of Santo Thomas. Their major professor is Carmen Espoz. Carmen left the night before. We were sorry to see them go; they are hard working intelligent people who are always willing to lend a hand. Now we have a team of 7 people, small but adequate.
(Carmen with her daughter Antonia.)
While working on the catch of Magellanic Oystercatchers, Ricardo found a new roost for red knot, the oddest one we had ever encountered. Shorebird roosting sites are usually straightforward. Night roosts are usually far away from land and isolated by water to provide a defensible perimeter from ground predators. During the day they choose areas with good visibility to provide reasonable forewarning of approaching birds of prey.
In Bahia Lomas knots and godwits often roost just at the waters edge and roll forward with the advancing tide, until it peaks. Afterwards they move back with the ebbing tide. At Bahia Azul on the Strait they roost on a spit of land between a small river and the sea, and move up and down the slope of the spit. It’s only at the spring tides, those high tides that flood all of the inter-tidal flats, that the shorebirds find the need to roost on the highest ground mostly dominated by two species of salicornia. It is dangerous to be on the salicornia, Patagonian fox patrol it regularly hunting roosting birds.
Ricardo found the roost at least a kilometer from the high tide line which is amazing by itself. Even more amazing, nearly the entire population of the west side of Bahia Lomas roosted in one small isolated patch of salicornia. 3,000 red knots sat happily only 100 m from the high ground. The reason was the wind.
(Knots roosting in salicornia along Bahia Lomas far from the waters edge)
The previous three days a strong wind from the west blew towards the sea. On Wednesday it blew hurricane force. On Thursday the wind fell to a slightly more moderate 40 mph. On our first visit to the site we found small clusters of knot droppings on the lee side of the salicornia clumps. Such places afforded a little shelter and the proximity of the high ground cut the wind more. At the level of the birds there was virtually no wind.
Knowing all this still does not assure a catch. The wind had died down overnight and was now a more modest 20-30 mph which is high but not abnormal for Tierra del Fuego. More importantly we had attempted many catches on salicornia in the past, all failures because it was just too difficult to set the net in the right position and the birds were virtually impossible to move in the right direction. Could we set our net in the right place? Could they be moved without flying far away? Would the birds return now that the wind had slowed; they might prefer to roost along the waterline.
(Daytime roost along the straits of Magellan at Bahia Azul in 2007)
The team set the net in good time, but it was slow work because we had to hack out a trench for the net in rock hard ground. In the midst of net-setting a small group of godwits and knots flew over our heads swinging around and landing not 200 m from our net. After a chaotic rush to finish setting the net and move equipment, we were ready. In the meantime the 3,000 knot flock had arrived and we began the process of twinkling them into position.
But they wouldn’t move into the catching area in front of the net. This is an area of about 10 x 23 m in to which birds must be induced to go if they are to be caught. Humphrey, Ricardo and I tried repeatedly but the birds would always move from one side of the net to the other, always avoiding the catching area.
Our problem was obvious. To be safe we used very obvious piles of rock to mark the catch area and the danger zone, a 2 meter strip in front of the net that must be clear to avoid
hitting birds with the net. We also placed two wooden decoys to draw birds into the area. It was clear that the birds were being put off by the markers and decoys so we removed the decoys and reduced the size of the markers.
Within 20 minutes, we made a catch, a wonderful catch, onefor the records. We caught and processed 201 red knots, and probably caught another 20 or so that made their way out of the net before we could secure it. Although we worked until 11:00 pm processing the catch we went back to camp happy and satisfied because we had met our major objective. Anything else would be gravy.
(Larry, Steve, Humphrey, Ricardo, Gerry and David processing catch of knots. processing catch of knots ( Photo by Mandy Dey))