Songbird Population Decline Associated with Early Spring

The declining population of songbirds might be due to their inability to keep up with the changes in spring timings, says a new study. The late arrival at feeding grounds is preventing the birds from getting the food needed to help them become breeders.

For the study, researchers from the York University and their colleagues tracked the migration of purple martins from the Amazon basin to two breeding sites in eastern North America. Researchers collected this data for over five years using tiny geolocator "backpacks".

The study team found that the departure time of the songbird was rather consistent, even though there has been a variation in spring arrival.

"We found that purple martins migrating between the Amazon Basin and North America did not adjust their migration timing even during the hottest spring on record in 2012. This means that they arrived 'late' for the advanced spring, and likely missed out on peak food they need to be productive breeders," said Kevin Fraser, a Postdoctoral Fellow in York's Department of Biology, Faculty of Science and lead author of the study, according to a news release.

Purple martins are extremely vulnerable to weather changes that affect insect populations. These birds start dying of starvation if there is an abrupt change in weather en route.

Many birds, especially the ones that feed on insects (aerial insectivores), are seeing a sharp decline in population, mostly due to their breeding sites shifting further north with each passing year. In Europe, these birds are late to migrate to warmer places, and this study shows that in America, these birds are reaching breeding sites during peak spring.

"Our results suggest that long-distance migrants may receive limited or conflicting environmental cues about conditions at the breeding grounds while still at overwintering sites or along migration routes," said Fraser."Some migratory songbirds may not have the flexibility they need to respond quickly to earlier springs and more variable weather with climate change, which could contribute to the strong population declines we see in many species. Identifying which species or populations may be at greatest risk will be very important for guiding effective conservation action."

The present study suggests that short-time changes in temperatures don't affect the songbirds' migration timings, and so it will take multiple years of early spring to change the birds' timings, Fraser concluded.

The study is published in the journal PLOS One.