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Red Crossbills Rapidly Increase Their Capacity to Produce Heat in the Cold

Red crossbill perched in conifer habitat
Research · Physiology

Cold weather can make it harder for a bird to maintain its body temperature. Researchers tested how quickly Red Crossbills (Loxia curvirostra) can adjust their capacity to produce heat, comparing two ecotypes that differ in how nomadic they are during spring migration.

The captive birds were kept either at 6 °C or at 21 °C, a thermoneutral temperature at which they do not need extra energy to stay warm, and researchers measured them repeatedly over nine days. They used summit metabolic rate, or Msum, as a measure of the birds’ maximum capacity to produce heat. Both ecotypes increased Msum exceptionally quickly. The researchers describe the rate of increase as the fastest documented in songbirds.

The greater heat-producing capacity came with higher basal maintenance costs: the birds needed more energy for their ongoing bodily functions. But baseline levels of corticosterone, a hormone involved in the stress response, did not increase. Even a single 90-minute cold exposure during testing temporarily raised Msum in birds otherwise kept at 21 °C.

Type 5 crossbills showed a slightly steeper increase in Msum than Type 3 birds. The researchers note that Type 5 birds are considered less nomadic and often live at very high elevations, so the difference does not point to nomadism alone as the explanation for how quickly heat-producing capacity increased.

Rapidly increasing heat-producing capacity could help crossbills cope with sharp changes in temperature during migration, although the higher maintenance costs show that this flexibility requires extra energy. The researchers suggest that the duration and severity of cold may matter more than nomadism alone. Because the experiment involved captive birds, it does not establish how quickly free-living crossbills make the same adjustments in nature.

Sources and image credit

  1. Nomadic songbirds achieve rapid increases in thermogenic capacity during cold acclimation while maintaining low corticosterone.Primary journal article. The accessible abstract was used to verify the study and findings; the publisher full text was unavailable for this check.
  2. Nomadic songbirds achieve rapid increases in thermogenic capacity during cold acclimation while maintaining low corticosterone.Bibliographic record and accessible abstract for the primary journal article.

Image: Wild red crossbill in Germany. Photo: TRinaud / Wikimedia Commons, CC BY 4.0. Representative photograph of a wild-form bird. · CC BY 4.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

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