Birds are Arriving Earlier, but Not as Fast as Spring

Manomet banding lab data and other long-term studies of spring migrant songbirds have shown that the migrants are responding to global warming trends by heading north earlier. This shift makes sense, as vegetation leaf-out (where dormant buds on trees and plants burst open to produce new leaves), flowering times, and invertebrate emergence are also happening earlier. In New England, for example, the timing of invertebrate peak abundance in spring (think caterpillars on fresh green tree leaves) and migrant bird stopovers or breeding have co-evolved over tens of thousands of years.

In a new study published in The Wilson Journal of Ornithology, our group of co-authors (working from Colby College in Waterville, ME, the US National Park Service in Bar Harbor, ME, Manomet Conservation Sciences, the University of Florida, and Boston University), examined a unique 170+ year series of data sets from the town of Concord, Massachusetts. We began with Henry David Thoreau’s diary from Walden Pond (1851-1854). Then, we combined his observations in Concord with those of various subsequent competent ornithologists, covering the period from 2013 to 2024, as documented in eBird (http://www.ebird.org). For 18 species of spring migrant birds, we compared the first arrival dates and found that, since the 1850s, they were on average arriving back seven days earlier.

However, other studies at Concord show that while wildflowers and trees are now shifting their timing 10–14 days earlier in response to warmer springs — significantly faster than the birds — insects seem to be keeping pace with plants. This creates a risk of “ecological mismatch.” If birds arrive too late, they may miss the peak abundance of insects and other resources needed to fuel their migration farther northwards, or to feed their nestlings. This could potentially harm their survival rates.

Thoreau wrote in Walden: “The first sparrow of the spring! The year begins with younger hope than ever!” Today, that sparrow is arriving earlier—but perhaps not early enough.

Article Reference: Gallinat, A.S., et al. 2025. Integrating historical records and citizen science data to understand bird responses to climate change in Concord, Massachusetts: Thoreau to eBird. The Wilson Journal of Ornithology. DOI: https://doi.org/10.1080/15594491.2025.2583566