Continuation Migration Case Studies

Onward Migration Case Studies:

Port Blake CA, Huron, Ontario - 7 May 2023

ebird checklist - google maps for location - archived weather conditions - surface map

Key Species: 

• 4000+ Yellow-rumped Warblers

Spring 2023 had a slow start in the southern Great Lakes, with cold conditions leading to migration generally being "behind schedule" in early- to mid-May. This may be the reason for an apparent "onward" migration of Yellow-rumped Warblers, with significant numbers pushed against the Lake Huron shoreline by southeast winds. Two possible factors often seem to be at play with spring "onward" migrations: 

1. Birds are "late" or "behind" in their expected migration timing, perhaps pushed to make up for "lost time" and continue flying during the day. Also: 

2. Suitable nocturnal migratory conditions terminate near the watch-location. Note the surface warm front just south of the watch location. It seems possible that some birds (specifically, some of the "behind schedule" species), have "pent-up" migratory energy after being forced to land part way through their nocturnal migration, and that they then use their underutilized energy to use during the morning hours. 

Yellow-rumped Warblers seem more predisposed to undertake "diurnal migration" than other warblers; however, these largest northbound flights occur during "late" springs rather than every year. This gives some credibility to considering them "onward" migrants. The very low number of southbound individuals of other species (e.g., EAKI) also indicates that general reorientation does not appear to be significantly occurring. 

Other Checklists:

Essex, Ontario - May 1, 2019: "Why is it so slow at Pelee today?" ... an onward migration migration of passerines flying north out of the national park.