Scientific Findings
Hummingbirds Migrating Earlier in Spring

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Contributing to Scientific Research

For over a decade, volunteers have contributed spring migration sightings of ruby-throated hummingbirds to Journey North. These data were recently analyzed by Jason Courter and his colleagues, and the findings were published in a scientific journal.

Thank you Citizen Scientists!

"A project of this magnitude would have been impossible without the contributions of thousands of Citizen Scientists throughout North America -- we particularly thank observers from Journey North for their faithful reporting of hummingbird arrivals for more than a decade," says Courter.

Photo: Vicky Floyd
Summary of Findings
  1. Ruby-throated hummingbirds are arriving in North America 12 to 18 days earlier than in the past.

  2. Broad networks of citizen volunteers can contribute to meaningful ecological research.

  3. Climate influences hummingbird migratory patterns.
arrival dates map
Photo: Clemson University
Mean first arrival dates of RTH
Read the Published Paper
The Auk
Full text

The original research paper was published by The Auk, Volume 130. A detailed migration study description is posted on the Clemson University Blog entitled, "Warming trends bring earlier migrating Ruby-throats; will flowers and small insects stay in sync?"

Phenological patterns in birds appear to be temperature-dependent in part, and global temperatures are undergoing change. Many studies of bird phenology are conducted at broad temporal but local spatial scales, making it difficult to assess how temperature affects bird migration across landscapes. Recently, networks of "citizen science" volunteers have emerged whose collective efforts may improve phenology studies as biases associated with such efforts are recognized and addressed. We compared mean Ruby-throated Hummingbird (Archilochus colubris) first arrival dates from Journey North (2001–2010) with data from the North American Bird Phenology Program (1880–1969). Ruby-throated Hummingbirds arrived earlier in the more recent period throughout the eastern United States; these advances, however, varied by latitude from 11.4 to 18.2 days, with less pronounced changes above 41°N. Warmer winter and spring temperatures in North American breeding grounds were correlated with earlier arrivals at lower latitudes in our recent period. Surprisingly, Ruby-throated Hummingbirds arrived later at high latitudes (42–43°N) during warmer winters and later at both mid-and high latitudes (38–39, 41–44°N) during warmer springs, which perhaps indicates extended migratory stopovers below 40°N during these years. Overall, weather variables predicted arrival dates better in the recent than in the historical period. Our results document spatial variability in how warming temperatures affect hummingbird arrivals and add credence to the hypothesis that spatial differences in arrival patterns at high versus low latitudes could exacerbate asynchrony between some birds and their food resources and modify associated ecosystem services such as pollination and insect pest suppression.

Further reading:

  • Clemson University blog: article
  • The Associated Press: "Study: Hummingbirds migrating earlier in spring" (PDF)