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Journal of Avian BiologyZoologyPeer-reviewed journal article

Warm and cool temperatures decrease early-life telomere length in wild pied flycatchers

Clemence FuriciD, Coline MarciauiD, Bin‐Yan HsuiD, Nina Cossin‐SevriniD, Julie FleitziD, Sophie ReichertiD, Suvi RuuskaneniD, Antoine StieriD

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Abstract

Climate change represents a major challenge for avian species. It is characterized by an increase in average ambient temperatures, but also in occurrence of extreme weather events, such as heat weaves and cold snaps. These abrupt temperature changes can modify the immediate and long-term survival prospects of nestling birds, when their thermoregulatory capacities are still not fully developed. While immediate nestling survival can easily be measured, long-term survival is more challenging to evaluate. Early-life telomere length has been suggested as a potential biomarker of future fitness prospects. To evaluate the potential impact of changes in early-life temperature, we thus experimentally increased (ca. +2.8{degrees}C) and decreased (ca. -1.7{degrees}C) average nestbox temperatures in wild pied flycatchers (Ficedula hypoleuca) during nestling postnatal growth, and measured nestling telomere length before fledging. Shorter telomeres were observed in individuals exposed both to an experimental heating or cooling during growth. Our results suggest that long-term survival prospects or long-term performances of individuals exposed to abrupt changes in early-life temperature may be decreased. O_FIG O_LINKSMALLFIG WIDTH=197 HEIGHT=200 SRC="FIGDIR/small/651824v2_ufig1.gif" ALT="Figure 1"> View larger version (118K): org.highwire.dtl.DTLVardef@2ec526org.highwire.dtl.DTLVardef@915e9borg.highwire.dtl.DTLVardef@1da157borg.highwire.dtl.DTLVardef@b857ce_HPS_FORMAT_FIGEXP M_FIG C_FIG

In-depth summary

Claude Opus 5.5 · xhigh effort · 5 Nov 2026 · from the full text of version 2 (5 Sept 2025) · CC BY-NC 4.0

Both experimental nestbox heating (+2.83°C) and cooling (-1.72°C) during early postnatal development significantly shorten day-13 relative telomere length in wild pied flycatcher nestlings without altering body mass.

Climate change increases the frequency of heatwaves and cold snaps during avian postnatal development when altricial nestlings transition from ectothermy to endothermy. Prior field studies tested postnatal heating or brief cooling, leaving the causal effects of sustained postnatal cold snaps and heatwaves on early-life telomere length unresolved.

Key results

  1. ShownExperimental nestbox heating during early nestling development increased nestbox temperature and reduced nestling relative telomere length at day 13.

    Heated nestboxes were +2.83°C warmer on average than non-heated controls (95% CI: [1.73; 3.53], t = 6.09, p < 0.001), and nestlings from heated nests had significantly shorter telomeres (LMM: t26.39 = 2.85, P = 0.008; n = 97 nestlings across 41 nests). · Heating experiment (2018); Nestbox temperature: experimental effects and…; Effect of experimental manipulations and natural…

  2. ShownExperimental nestbox cooling between postnatal days 7 and 13 lowered nestbox temperature and shortened nestling relative telomere length at day 13 without affecting body mass.

    Cooled nestboxes were -1.72°C cooler on average than non-cooled controls (95% CI: [-1.56; -0.45], t = -3.52, p < 0.01), yielding shorter telomeres in cooled nests (LMM: t35.26 = 2.23, P = 0.032; n = 56 nestlings across 48 nests) and no body mass difference (t = 0.39, P = 0.70). · Cooling experiment (2019); Effect of the experimental manipulations of…; Nestbox temperature: experimental effects and…; Effect of experimental manipulations and natural…

  3. ShownDirectly measured nestbox temperatures correlated with shorter telomeres for mean temperature in the cooling experiment but not significantly in the heating experiment.

    In the 2019 cooling cohort, lower mean nestbox temperature correlated with shorter telomeres (β ± SE = 0.068 ± 0.032, P = 0.043), whereas in the 2018 heating cohort, maximum temperature showed only a non-significant trend (β ± SE = -0.017 ± 0.009, P = 0.073) and mean temperature was not associated (β ± SE = -0.012 ± 0.015, P = 0.43). · Relationships between nestbox temperature and…; Effect of experimental manipulations and natural…

  4. ShownNatural inter-annual temperature differences between 2018 and 2019 did not produce corresponding differences in telomere length or body mass among control nestlings.

    Although 2019 had higher June-July ambient air temperature (+1.54°C, 95% CI: [0.93; 2.15], t = 4.98, p < 0.001) and control nestbox temperature (+2.16°C, 95% CI: [1.08; 3.24], t = 3.92, p < 0.01) than 2018, control nestlings showed no significant year effect on telomere length (LMM: t5.00 = -0.31, P = 0.77) or body mass (LMM: t = 0.30, P = 0.76). · Year effect on telomere length; Nestbox temperature: experimental effects and…; Natural variation in telomere length and body…

Methods, data and reproducibility

Conducted cross-fostered nestbox temperature manipulations in wild pied flycatchers on Ruissalo Island, Finland, applying heating pads for 6 days starting on postnatal day 2 in 2018 and exterior frozen cooling pads from days 7 to 13 in 2019. Quantified relative telomere length from day-13 brachial vein blood DNA via qPCR (Tel1b/Tel2b normalized to RAG1) and analyzed effects with linear mixed-effects models.

  • 2018 nestbox heating experiment blood DNA and nestbox iButton temperature logs · pied flycatcher (Ficedula hypoleuca) · n = 97 nestlings from 41 nests (42 heated, 55 non-heated) · 10.6084/m9.figshare.28844615
  • 2019 nestbox cooling experiment blood DNA and nestbox iButton temperature logs · pied flycatcher (Ficedula hypoleuca) · n = 56 nestlings from 48 nests (25 cooled, 31 non-cooled) · 10.6084/m9.figshare.28844615
  • Hourly ambient air temperature from Artukainen weather station (Finnish Meteorological Institute) · n = June 4th to July 12th in 2018 and 2019
Methods & tools
qPCR, LinRegPCR, R, lme4, DHARMa
Reagents & environment
R software version 4.3.2 with packages lme4 and DHARMa; LinRegPCR
Reproducibility gaps
Statistical analysis scripts are not publicly provided.
Limitations (3)
  • The heating (starting postnatal day 2 in 2018) and cooling (days 7 to 13 in 2019) manipulations differed in developmental timing and study year, precluding direct statistical comparison between the two experiments. · stated by the authors
  • Candidate physiological mechanisms linking temperature shifts to telomere shortening, including glucocorticoid levels, mTOR signaling, nestling body temperature, and telomerase activity, were not measured. · stated by the authors
  • Long-term survival and adult fitness consequences of early-life telomere shortening could not be confirmed because post-fledging recapture rates are very low in this passerine population. · stated by the authors

Read this if you study physiological ecology, thermal developmental plasticity, or telomere dynamics under experimental climate extremes in wild vertebrates.

Citations
6
FWCI
21.14
Field percentile
top 1%

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