Late-Summer Feeding and Migration Behaviour and Numerical Trends of Common Nighthawks, Chordeiles minor, near Pinawa, Manitoba, 1976-2009

Résumé

Feeding concentrations of Common Nighthawks, Chordeiles minor, during the evening in late summer were observed and counted near the Pinawa, Manitoba, sewage lagoons during 28 of the 34 years from 1976 to 2009. Counts were frequent but non-systematic in 1976-1981, infrequent in 1982-1991, and both frequent and systematic in most years during the period 1992-2009. Results of 226 counts are analysed and interpreted as showing a major decline in the local breeding population during the 1980s but more stable numbers of transient birds, assumed to originate farther north. The timing and other characteristics of feeding and migratory behaviour are discussed. The limitations of interpreting data from a single location are acknowledged and some systematic survey methods are recommended, emphasizing the importance of all-round, long-range visibility to help distinguish between migration and foraging.