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Metabolic rate and fitness showed no simple link in Eurasian Blue Tits

Research: Physiology, Ecology

A study of Eurasian Blue Tits (Cyanistes caeruleus) in southern Sweden examined whether metabolic rate was related to apparent survival and breeding outcomes. Researchers measured three aspects of metabolism and monitored whether the birds were seen again to breed and how successful their breeding was.

Basal metabolic rate (BMR) reflects the energy used to maintain basic body functions at rest. The researchers also measured maximum cold-induced metabolic rate (Msum), a bird’s capacity to produce heat during cold exposure, and maximum exercise-induced metabolic rate (MMR), its capacity for intense activity. Together, these measures capture different aspects of how birds use energy.

Three measures were linked, but not identical

All three metabolic rates were positively related: birds with higher values on one measure tended also to have higher values on the others. The relationship between cold-induced and exercise-induced metabolism remained even after body mass was taken into account. MMR also showed repeatable differences between individuals across seasons, meaning that birds tended to retain their relative position on this measure over time.

The links with breeding outcomes were less straightforward. In the breeding data, birds with higher metabolic rates in spring were marginally more likely to return to breed the following year. At the same time, higher metabolic rates were associated with somewhat lower reproductive success. These were modest patterns, not a clear overall relationship between metabolism and fitness.

The contrast matters: metabolic rate did not show a consistent association with every measure of fitness. The differing links with return and reproductive success offer tentative support for context-dependent selection on metabolic traits, rather than a general advantage to having a higher metabolic rate. The study found associations; it did not show that metabolism caused either outcome.

Sources and image credit

  1. Fitness and flexibility of metabolic phenotypes in a temperate resident birdPublisher Early View record verifies the Version of Record date. The study abstract was verified through the associated Dryad record; the publisher full text was not accessible for this review.
  2. Data and code from: Fitness and flexibility of metabolic phenotypes in a temperate resident birdAssociated study data and code record; its abstract reports the study scope and findings.

Image: A Eurasian Blue Tit (Cyanistes caeruleus) perches on a budding branch against a clear blue sky. Photo: Martin Kunz / Wikimedia Commons, CC BY-SA 4.0. Representative photograph. · CC BY-SA 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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