Monday, January 14, 2008

Tierra del Fuego: 1/14/08

Our Seventh Expedition to Tierra del Fuego: 1/14/08

Humphrey and I left Punta Arenas early to survey the area along the Strait of Magellan at high tide. We left our comfortable digs at the Hotel Noriega at 7.00 am, leaving the rest of the team to pull together all we would need for the first leg of our three week field trip. Fortunately Jorge Jordan and his staff lent us a hand, gathering equipment left since last year, helping to arrange hard-to-get supplies as well as organizing rooms at the hotel.

Tierra del Fuego

(Jorge Jordan and Mandy at Jorge’s Hotel Noriega)

On arriving on the Strait, we found far fewer red knots than we had seen last year. This may not mean much; after 7 years of fieldwork, we have grown used to frequent shifts in their roosting sites and feeding habitats. Last year we documented a significant new roost along the narrows, which was particularly suitable for cannon netting because of the steeply sloping beach. The knots feed on mussels, and move up to the roost site at high tide. The gentle gradient of the wide flats of Bahia Lomas, 6 km from high tide to low tide in some places, makes it very difficult to predict where the 30 ft high tide will ebb. The bay’s 60 mile waterfront creates a second dimension allowing birds to roost anywhere they want making cannon netting virtually impossible.

Tierra del Fuego

(Looking out over the flats of Bahia Lomas)

With no birds at the Strait we had little choice but to forego cannon netting and use our mist nets; we did this reluctantly because just as the tide is extraordinarily unpredictable so is the weather. Mist netting works best on dark nights with the nets set over the high tide line. We try to set the nets so that the innermost net is just below high tide and the outmost net lies over water about 3 feet deep. True to their name, when their low tide feeding areas are covered, shorebirds tend to fly over the water parallel to the shoreline as they move to their nighttime roost sites. Mist nets set properly should cross their paths so that the birds are caught in the fine mesh. If the tide floods too far, there is a danger that birds caught on the outer nets will hang low into the water and possibly drown; if the tide stops short of the nets, few birds will be caught because they do not usually fly over dry mud.

Tierra del Fuego
(Walking in 70 mph winds on the shore of Bahia Azul)

Fortunately the SAG/USDA team assisted ours and the 12 nets were set in quick time. Unfortunately we caught few birds: 6 two-banded plovers and 5 white-rumped sandpipers. The tide fell short, leaving all but the outer four nets out of the water. But strangely we heard few birds, only the plaintiff whistles of the Magellanic oystercatchers. The raucous nighttime sounds of roosting godwits and knots were altogether missing.

Tierra del Fuego

(A Knot feeding on a mussels on the Bahia Azul site)

The next morning, Sunday, Guy Morrison gave us preliminary results of the first aerial survey, a disappointing 8000-10,000 knots which pointed to a possible 30% decline over last year’s count for the same area. With such a low figure, Guy and his counting partner, Ken Ross, decided to confirm the result by carrying out a second count the next day. Guy also told us of a new roost on a beach beside a fenced area with land mines in Bahia Lomas just south of the Strait. We decided to discontinue mist netting and attempt a cannon net catch at the new site.

Tierra del Fuego

(Survey plane with Guy and Ken rounding Punta Espora)

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