A Trans-Hemispheric Migratory Songbird Does Not Advance Spring Schedules or Increase Migration Rate in Response to Record-Setting Temperatures at Breeding Sites
Figure 1
Spring migration routes and en route temperatures and rainfall for purple martins.
Birds were tracked from two breeding populations a) Pennsylvania (41.8°N, 79.9°W) and b) Virginia (38.61°N, 77.26°W). Spring routes shown in red (2012) and blue lines (2008-11 PA; 2011 VA). Dashed lines show estimated route based on longitude when latitude was uncertain due to equinox. Black circles show locations of en route temperature and rainfall measurements and correspond to adjacent graphs showing mean ± SD temperature during passage (10 d pre-and post- median passage date) and rainfall sum (30 d pre-median departure/passage date; ± SD where multiple years). Breeding site graphs (Pennsylvania and Virginia) show maximum daily temperature and spring warmth sum at breeding sites March 15– April 15 (circles show mean, bars standard deviation). Last winter roost locations in South America before spring migration are shown by red and blue circles. Error bars, shown for one bird on each map, are typical standard deviation in latitude and longitude for estimated winter locations.