Climate change's disruption of annual "green-up" could lead to quieter springs, study predicts

"Phenological interval" means the
period of time between one life-
cycle event and another.

Scientists say the effect of climate change on the start of spring—which is occurring earlier in many areas and later in some—is increasingly putting birds out of sync with their environment and could lead to an end of spring birdsong, says a study published in Scientific Reports. Researchers were from six universities in the U.S. and Canada, The National Ecological Observatory Network and the Illinois Natural History Survey.

“The rate at which birds are falling out of sync with their environment is almost certainly unsustainable,” ecologist Stephen J. Mayor of the University of Florida told Ben Guarino of The Washington Post. “We can end up with these increasingly quiet springs.” Mayor and his colleagues say some migratory songbirds "can't keep pace with the shifting start of spring," Guarino reports.

The study, the first to survey songbirds across the entire North American continent, found that "for 48 songbird species, the mismatch between arrival date and the onset of spring grew by an average of half a day per year between 2001 and 2012," Guarino reports.

Researchers "combined satellite and citizen science data to estimate rates of change in . . . spring green-up and migratory arrival for 48 breeding passerine species across North America" and found that "although birds adjusted their arrival dates, 9 of 48 species did not keep pace with rapidly changing green-up and across all species the interval between arrival and green-up increased by over half a day per year," Guarino writes.

"Of the species studied, nine fared the worst, with a yawning gap between their arrival date and the spring shift: blue-winged warblers, eastern wood-pewees, great crested flycatchers, indigo buntings, northern parulas, rose-breasted grosbeaks, scarlet tanagers, Townsend's warblers and yellow-billed cuckoos. In the case of the cuckoos, for instance, spring greenery started growing 1.2 days earlier per year, although the birds arrived on average 0.2 days early. Put another way, the timing mismatch increased by an average of one day annually."

"Using satellite imagery, the study authors tracked the start of green-up, the sudden burst of photosynthetic activity that begins in early spring in North America," Guarino writes. "As seen from the sky, green-up is an explosion of leaves. This brings out droves of hungry caterpillars and other plant-eating insects. These bugs are a crucial food supply for songbirds, which travel northward to eat and breed after spending the winter in South or Central America. This invertebrate buffet lasts for a limited time."