Patterns of New World partial bird migration at north vs. south temperate latitudes

JAHN, A.E,; BRAVO, S.P.; CUETO, V.R.; LEVEY, D.J.; MORALES, M.V.

EMU

CSIRO PUBLISHING

Año: 2012 vol. 112 p. 17 - 22

0158-4197

Abstract.- Determinants of partial bird migration remain poorly understood at different 1 latitudes.2 We describe partial migration of passerine birds across temperate latitudes in the New World.3 Due to lower seasonality near the coast of North America, the proportion of partial migrants at4 high latitudes in North America should be lower when excluding coastal records. We detected a5 10% decrease in the proportion of partial migrant species at high latitudes when excluding those6 whose only winter records at those latitudes are coastal. We also expected a smaller proportion of7 partial migrants inland in North America vs. South America. However, at high latitudes, (i.e.,8 >39°) we found a similar proportion but a different taxonomic makeup of partial migrants9 between continents. Specifically for the Tyrannidae (New World flycatchers), we evaluated the10 latitude at which species overwinter in North vs. South America. The mean latitude at which11 North American partial migrant flycatchers overwinter when excluding those near the coast is12 30.4° N (2.8 SD), which is lower, but not significantly so, than of wintering flycatchers when13 considering winter records at all distances from the coast (32.3° N, 3.2 SD). Furthermore, the14 mean latitude at which New World partial migrant flycatchers overwinter in temperate South15 America (30.3° S; 5.6 SD) vs. inland North America is not significantly different. These results16 suggest that partial migrant bird species in the New World may be under different constraints,17 depending on factors such as habitat occupancy and distance of a population from the coast.