Data from: Evaluation of breeding distribution and chronology of North American scoters

Aim: North America's scoter species are poorly monitored relative to other waterfowl. Black (Melanitta americana), surf (M. perspicillata), and white-winged (M. deglandi) scoter abundance and trend estimates are thus uncertain in many parts of these species' ranges. The most extensive source of waterfowl abundance and distribution data in North America is the Waterfowl Breeding Population and Habitat Survey (WBPHS). Although the WBPHS effectively monitors most species, both its timing and geographic coverage may not allow for accurate scoter monitoring. Therefore, our goal was to better define when and where scoters breed to help interpret survey results and optimize survey methods for scoters.

Location: Canadian boreal shield, taiga shield, and low-Arctic tundra; Alaska.

Taxon: Scoters (Genus: Melanitta)

Methods: We integrated satellite telemetry tracking data from scoters marked at multiple molting, staging, breeding, and wintering areas along the Atlantic and Pacific coasts to quantify continent-wide breeding chronology and distribution. We also examined possible drivers of variation in timing of arrival, length of stay, and departure at nesting locations.

Results: We documented a northwest-to-southeast distribution of breeding sites across Alaska and Canada. On average, scoters arrived at nest sites on June 1. Surf scoters arrived earliest, stayed for shorter periods, and departed earliest. Pacific-wintering scoters began breeding earlier than Atlantic-wintering birds. Additionally, birds arrived at nesting locations earlier in years with earlier snowmelt, and later snowmelt reduced lengths of stay for males. Breeding chronology also varied by age group, with adults arriving earlier than subadults.

Main conclusions: Our study is the first to comprehensively describe spatial variation in timing of breeding of both Atlantic and Pacific populations of all three scoter species across North America. Our results increase our understanding of how current surveys enumerate scoters and will inform possible supplemental efforts to improve continental monitoring of scoter populations.