Inter-annual variation in feather growth rates of Hudsonian Whimbrel Numenius hudsonicus and Dunlin Calidris alpina hudsonia from western Hudson Bay

Feather growth rates can reflect the energetic state and nutritional condition of birds during moult, for example when there are increased energetic demands or lowered food availability through disturbance, habitat degradation, or adverse weather conditions. We used ptilochronology (the measurement of feather growth rate) to estimate annual variation in feather growth rate of two long-distant migrants: the Hudsonian Whimbrel Numenius hudsonicus and Dunlin Calidris alpina hudsonia. We collected flight feathers from adult Whimbrel (n = 63) and Dunlin (n = 34) on their Canadian breeding grounds in Churchill, Manitoba and Burntpoint Research Camp, Ontario across multiple study years (Whimbrel 2011, 2012, 2023; Dunlin 2011–2014). In both species, feather growth rate was lower in feathers collected in 2012 than in other years. Extreme weather events (e.g., dry conditions on the breeding grounds, storms in U.S. coastal staging areas) were reported during the moulting period in 2011, when the feathers that were collected in 2012 would have grown, but not in the other years. We suggest that feather growth rate in these species may have been affected by adverse environmental conditions. Feather growth rate differed between breeding locations in Whimbrel and also between sexes in Dunlin, perhaps due to differences in departure timing from the breeding grounds and potential differences in the onset of flight feather moult. This study is one of few to apply ptilochronology to shorebirds and provides a basis for future research in this field.