Biology of Black Oystercatchers Breeding on Triangle Island , British Columbia , 2003 – 2011

The breeding biology of the Black Oystercatcher (Haemotopus bachmani) was studied on Triangle Island, British Columbia, Canada in 2003–2011. Breeding density at this remote site was relatively high, ranging from 2.23 to 3.72 pairs/km of shoreline in the 9 y. Most clutches were initiated in the last 2 wk of May, and the annual mean 1st clutch size ranged from 2.1 to 2.8 eggs/ nest, values similar to those recorded at other sites. Egg size differed little in clutches of 1, 2, and 3 eggs. Hatching success at Triangle Island ranged from 55 to 87% in 5 y, which is on the high end of the range compared to other sites. Limited data suggested that adult survival rates exceeded 90% per annum, and 43% of individuals banded just prior to fledging survived through at least their 1st winter. Oystercatchers are reliable indicators of the health of coastal ecosystems, and these data comprise a baseline against which future changes at Triangle Island can be assessed.