Ever notice that not all songbirds migrate north in spring at exactly the same time? Different species move north in waves, from early to late in the migratory season. There’s a reason behind this timing, and it’s interesting to see which birds arrive in each wave.
Migrating birds make the treacherous journey north in spring to reach their nesting grounds at a time when they will be able to find a mate, raise a family, have enough food to feed the chicks and get this all done before they need to start going back south. It’s a stressful time for birds, and there are many factors which influence their journey – from food and adequate stopover availability to temperature and weather.
On the US East coast there are three waves –
1 – Early migrators coming up from the southern US include ubiquitous Yellow-rumped Warblers and kinglets pass through in April
2 – Neotropical Migrators including some warblers like Yellow and Tennessee as well as Ovenbirds arrive in early to mid-May
3 – Insectivores including flycatchers and vireos wait for warmer weather and loads of bugs in mid to late May.
On the US West coast, birds pass through in 2 bursts – the first are insectivores in March including Tree Swallows: the second in April when fruit eaters including Black-headed Grosbeak arrive to take advantage of the berries.
For more information on this wave theory, check out these articles from Black Swamp Bird Observatory and Audubon.