Chile 2007 – Trapping Birds Night and Day
We began the day preparing for a cannon net catch of red knots on the salicornia marsh close to our camp. Over the last few days, Knots have gathered in the area during the highest tides looking for a good place to roost. At normal tides the birds spend all their time feeding or roosting along the tide line. But twice in each lunar period, at the new and full moon the high tides rise much higher forcing them to roost ever closer to vegetation bringing them within hunting grounds of predators like the Patagonia fox. These spring tides nearly double the width of the intertidal muds and create a marsh dominated by salicornia which actually stays dry most of the month. This marsh provides our best chance to catch the birds.
Only a short drive from the camp we quicky made our set. We intended to fire a net measuring 22 m by 10 m powered by 3 cannons. We furled it into a 22 m trench to keep its profile even with the marsh surface; we then carefully cover it with bits of salicornia as camouflage. We had observed the knots for several hours on the previous day’s high tide to determine the best place to set the net and decided on an island of salicornia on which the birds took refuge from the advancing tide. We had to make sure they would not be caught over mud because they cannot preen it off and leaves them vulnerable to the damp and cold. After an hour of hard work we moved off.
We established a fire position that allowed us a good view of the catch area but far enough away that it did not disturb the birds. Within the hour, the tide rose high enough to bring in a flock of about 2,000 knots and 7,000 godwits. But it came in much faster and higher than predicted. This tide was to be only 0.1 m higher than the previous high tide so we thought our set would remain dry at high water.
We were wrong. At first, the tide flooded the area and the birds gathered in much the same way as the previous day. But then they started moving out, at first in small groups and finally the entire flock. For a brief period we had about 20 birds in our catching area, but they too left joined the others. Meanwhile the tide rushed in and flooded the net. We were done, but our day was not over, not nearly.
After a quick lunch, we gathered our mist-netting equipment. A mist net is a fine small mesh net that can be stretched between poles and catches flying birds at night when the nets can’t be seen. Normally we would set 20 nets, each about 12 m long. Tonight we decided to set ten at the edge of the salicornia marsh perpendicular to the shoreline. By dinner all was ready.
Nightfall in this section of Chile is very late because of its high latitude. At 1030 while some light persisted in a cold grey sky, Humphrey, Mandy and I inspected the net while Mark and Steve set up the base station where all caught birds would be processed. The wind blew hard from the east promising to increase the height of the tide, but by this time the peak of the spring tide was past and the high tides would start to get lower. We caught a few birds in the first hour, both white-rumped sandpipers. By then the night sky was black and we could only see a hint of our path through the marsh. Then the tide charged over the mudflats.
Within only a few minutes the water rose several feet and the wind blew whitecaps on waves rolling through the catching area. We heard birds hitting the net and, as we found later, over a 100 knots were in the net at once evenly spread out over all ten nets. By the time we got out to the outer net the water was chest-high and filling our waders as we started removing birds from the nets.
Instead of falling as predicted the tide rose another foot with waves even higher. We soon found our selves in a difficult situation. Each bird had to be extracted while keeping balance against pounding waves that would occasionally splash over our chest waders. Each extracted bird had to be moved 200 m back to the base camp for processing though chest deep water, breaking waves, wailing wind and pitch dark. Anyone else would have panicked but the team rose to the occasion and within a few hours all was under control and we had 110 red knots and 6 Hudsonian godwits in the keeping cages. It took us close to three hours to process every bird including measuring, weighing, taking feather samples for sexing and isotope analysis, and of course banding with red flags with unique ids.
We recaptured 10 knots from four countries; four from the Delaware Bay, two from Argentina, two from Chile and one from Brazil:
Fl(PPO) Money Island June 6 2004
Fl(JEV) Mispillion Harbor, May 21 2005
A knot banded at Ted Harvey, Delaware, May 19 2001 recaptured May 29 2002
A knot metal-banded at Reed Beach May 24, 2001
Fo(NW) (Argentina no capture data) recaptured at Mispillion Harbor, May 21, 2003
Fr(CU) Bahia Lomas, Feb 8 2004
Fr Bahia Lomas Feb 2 2003
Fr Bahia Lomas Feb 1 2002
One bird from Brazil and another from Argentina both with no capture records
Mark, Steve and Humphrey have resighted about 40 flagged birds including one white flagged bird banded in the Arctic by our team.