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Longer Telomeres in Yearling Barn Swallows Predicted Longer Lives and More Fledglings

Adult barn swallow on the ground carrying a twig, with the long outer tail feathers visible
Research: Molecular biology & biochemistry, Physiology

Barn swallows (Hirundo rustica) with longer telomeres when they entered the breeding population as one-year-olds lived longer and produced more fledglings over their lifetimes. Telomeres are protective nucleoprotein structures at the ends of chromosomes that help maintain genome stability. They generally shorten as cells divide and can reflect aspects of an individual’s somatic condition and investment in body maintenance. The result comes from a longitudinal study of 106 adults at five farm colonies south-east of Milan in northern Italy.

The birds belonged to three cohorts recruited in 2013–2015 and were followed until the last individual in the study had died. Researchers repeatedly measured relative telomere length in blood cells and recorded the birds’ survival and breeding. The 59 males and 47 females lived between one and seven years, and complete lifetime reproductive records were available for 76 individuals.

Longer telomeres were linked to more breeding years

Telomere length declined at a steady rate with age. Birds that had longer telomeres at recruitment lived longer, and they fledged more young over their full lives. The association with the average number of fledglings produced per breeding season was positive but not statistically significant. The authors therefore interpret the lifetime reproductive advantage as being driven mainly by longer-lived birds having more opportunities to breed.

Sexual traits showed different telomere patterns

Telomeres also varied with two sexually selected traits. Females with longer outer tail feathers had shorter telomeres, and females whose tails lengthened more between consecutive years showed faster telomere shortening. In both sexes, birds whose ventral plumage became darker between years showed less telomere shortening over the same period.

The study was correlational. The authors could not determine whether longer telomeres directly contributed to longevity or whether telomere length and lifespan reflected common underlying factors such as early-life conditions. For males, lifetime fledgling counts reflected social rather than strictly genetic paternity because extra-pair fertilization occurs in the population.

Sources and image credit

  1. Novelli et al. (2026), Molecular Ecology — Telomere Length at Recruitment Predicts Lifespan and Lifetime Reproductive Success in the Barn Swallow (Hirundo rustica)Primary peer-reviewed open-access longitudinal study, first published 5 August 2026. The researchers followed 106 barn swallows (59 males and 47 females) recruited as one-year-old breeders in 2013–2015 at five farm colonies south-east of Milan, Italy, until the last study bird died; lifespan ranged from one to seven years. Lifetime reproductive success was available for 76 birds. Relative telomere length declined consistently with age. Longer telomeres at recruitment predicted longer realized lifespan and more fledglings over the lifetime, while the association with average fledglings per breeding season was positive but not statistically significant. The authors state that the study is correlational and cannot distinguish a direct telomere effect from shared underlying determinants such as early-life conditions. Male lifetime reproductive success counts social rather than strictly genetic offspring because extra-pair fertilization occurs in the population.
  2. Novelli et al. (2026), Data@UNIMI — data and R codePrimary dataset and analysis code supporting the study.

Image: Jörg Hempel — barn swallow (Hirundo rustica) collecting nest material in Chemnitz, Germany, 3 May 2009; Wikimedia Commons, CC BY-SA 3.0 DE. Representative species image; not one of the Italian barn swallows in the study. · CC BY-SA 3.0 DE · Source

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Molecular biology & biochemistry

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