Estimating the migratory stopover abundance of phalaropes in the outer Bay of Fundy, Canada

Abstract

We investigated the abundance and turnover rate of phalaropes (Red-necked and Red: Phalaropus lobatus, Phalaropus fulicarius) in the outer Bay of Fundy, Canada during migratory stopover in 2008, 2009, and 2010. We describe estimation procedures designed to calculate size of the total stopover population of phalaropes, adjusting for length of stay. A total of 29 aerial surveys were flown in two nonoverlapping survey regions situated off Brier Island, Nova Scotia and Grand Manan, New Brunswick. Line transect distance sampling methods were used to obtain abundance estimates at discrete time steps from aerial surveys. Estimated number of phalaropes by date ranged between 6000-88,000 in 2009 and 31,000-127,000 in 2010. To quantify the cumulative number of phalaropes in the study area, the temporal dimension of stopover passage was incorporated by an analysis of radiotelemetry data to estimate length of stay. A total of 27 phalaropes were captured and fitted with radio transmitters between 2008 and 2010. Estimated length of stay in days was 15.2 ± 1.91 for a time-integrated stopover population of 103,496 phalaropes in 2009 and 287,558 in 2010. This is particularly relevant to the conservation status of P. lobatus in North America, which has been uncertain since the disappearance of that species from an important stopover site in 1990. Our findings emphasize the need for studies that monitor phalaropes at sea, where they spend the majority of their time, as a means to inform effective management and conservation.

Keywords

• abundance estimates
• aerial line transects
• Bay of Fundy
• distance sampling
• phalarope