Chile]2007- An Important New Food for the Shorebirds of Bahia Lomas
After two days of warm sun and a mild wind the weather has turned to wind and cold rain. Good reason to be writing in the warmth of our cook tent. With little communication from the outside world we seem to have lost our sense of the day of the week and date. We just know how much time we have left. These last two days have opened up an entirely new line of investigation that will require all the time we have.
Guy Morrison and Ken Ross completed their yearly flight of the Strait of Magellan and Bahia Lomas to count Red Knots and Hudsonian Godwits. Their survey is yet to be completed as it also includes sections of the Atlantic Coast of Argentina. In our area they found roughly the same number of knots and godwits which is both good and bad news. The good news is that the number of birds has not gone down, the bad news is that they have not gone up. Allan Baker from the Royal Ontario Museum conducted a ground count in Rio Grande and found a significant reduction from his last count in 2006. We hope for the best in Guy and Ken’s count.
Guy also stunned us with the news that most of the birds were not in the area that we would have predicted. In all years past, the knot population divided into two main flocks, about half in the eastern part of the bay and the other near our camp on the western side. But this year a number of events puzzled us. First, we had roughly half of our normal number. Second, after the spring tides they virtually disappeared to the north. On Friday, we found very few knots feeding at low tide near our camp where we had found several thousand in previous years.
From the air, Guy could see two main flocks, one of about 5,000 on the south side of the narrows, not far from the ferry that crosses the Strait of Magellan, and a second of about the same number on the north side about 10 km east of the narrows. This has never occurred in the 7 years of our work here, or the 21 year history of the aerial survey. We were determined to find out why: first to determine whether anything has gone wrong in the normal feeding areas and second to investigate the possibility of a new cannon netting opportunity because the new locations would much more suitable if we could get access to them.
On Saturday, Mark, with Andy the nature photographer in tandem, focused on resightings of marked birds on Bahia Lomas. Humphrey, Mandy, Steve and I searched for the new roost near the ferry. After a nail-biting ride across a mile of beach close to the location where we nearly lost a truck to the tide in 2005, we came to the end of a small sandy/shell pile spit that was literally covered with mussels, many in the size range suitable for red knots. Within a few minutes, we found about 500 knots feeding on mussels. Positively elated, we raced back to camp to get the rest of the crew, especially Allison and Andy to film our discovery. It was their first chance at filming knots feeding close-up. It was the best chance we have ever had of resighting large numbers of marked birds. We spent the rest of the day on intensive resighting. At high tide we counted 2,500 knots on the roost.
This new discovery of knots feeding on mussels in Bahia Azul, as this section of the Straits of Magellan is called, vastly expanded our understanding of the ecology of knots on Bahia Lomas. We now know that the wintering population uses an area much larger than Bahia Lomas itself, including much of the Straits of Magellan on both the north and south sides. We have also discovered that the knots’ diet in this area extends beyond the shellfish (mainly Darina) found in the mudflats of Bahia Lomas.
We look forward to our investigations of the next few days. Our own work of banding and resighitng of marked birds will be made significantly easier now that we have found a large number of knots feeding and roosting in a relatively small area. Dr Carman Espoz of the University of Santo Thomas has arrived with two of her students Gabriela Gonzalez and Sergio Urrejola. They come at an important moment for studies of Red Knots foraging ecology and the invertebrate prey upon which they rely.