"Spring migration" refers to the movement of animals, particularly birds, from their wintering grounds to their breeding grounds during the spring season. Full definition
When to drink this coffee (field oriented): All day long, doing spring migration counts or breeding bird census work, even on warm days. (coffeehabitat.com)
The author accuses Stantec of choosing to do a survey only of spring migration for the birds while birds are actually at greater risk in the fall because they are moving more slowly (there is not the push to build a nest and raise this year's offspring), and because there are young birds making the trip for the first time. (windconcernsontario.ca)
The Bowhead can live deep into a second century if unmolested, it has a gorgeous seven - octave song, and is a keen listener (Cornell's Chris Clark recorded 35,000 vocalizations during spring migration in 1985, with only 19 overlaps!). (dotearth.blogs.nytimes.com)