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Clutch size and egg volume in great tits (Parus major) increase under low intensity electromagnetic fields: a long-term field study.

Environmental research · 2012 · Mixed · Low evidence

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MixedLow evidencePaper 4508

In a wild great tit population studied over nine breeding seasons, EMF exposure from an electric power line was associated with increased clutch size (7%) and egg volume (3%), implying a 10% increase in clutch volume compared with an adjacent reference area. …

Study snapshot

PublicationEnvironmental research · 2012
Study typecohort
Reported directionMixed
Evidence ratingLow

Abstract

Exposure to electromagnetic fields (EMFs) can affect a wide range of biological processes, including reproduction, growth and development. Experiments aimed at investigating the biological effects of EMFs, focused on potential harmful effects on humans, have been mostly carried out in vitro or with animal models in laboratory conditions. By contrast, studies performed on wild animals are scarce. The effects of EMFs created by an electric power line on reproductive traits of a wild great tit (Parus major) population were explored by analysing data gathered during nine breeding seasons. EMF exposure significantly increased clutch size (7%) and egg volume (3%), implying a 10% increase in clutch volume. This indicates an increase in reproductive investment from parent birds exposed to EMFs as compared to the adjacent reference area. These results cannot be attributed to habitat or adult quality differences between the exposed and reference group. Nevertheless, no differences in hatching success or final productivity (fledging and reproductive success or nestling body mass) could be detected. Our study clearly shows that EMFs created by power lines can have biological consequences in wild organisms that live intimately with them. To our knowledge, this is the first study showing an increase in clutch size, and one of the few reporting an increase in egg size, associated with EMF exposure. The possible mechanisms by which great tits invest more under EMF exposure are discussed, and future research directions to evaluate the effect of EMFs on avian reproduction in the wild are suggested.

Machine Enhanced Logic

AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typecohort
Effect directionmixed
PopulationWild great tits (Parus major) population
Sample sizeNot supplied
Exposurenine breeding seasons
Evidence strengthLowConfidence: 78% · Peer reviewed: yes

Main findings

In a wild great tit population studied over nine breeding seasons, EMF exposure from an electric power line was associated with increased clutch size (7%) and egg volume (3%), implying a 10% increase in clutch volume compared with an adjacent reference area. No differences were detected in hatching success or final productivity (fledging/reproductive success) or nestling body mass.

Outcomes measured

  • clutch size
  • egg volume
  • clutch volume
  • hatching success
  • final productivity (fledging and reproductive success)
  • nestling body mass

Limitations

  • Frequency/intensity of EMF exposure not specified in the abstract
  • Sample size not reported in the abstract
  • Observational field comparison (exposed vs adjacent reference area) may be subject to residual confounding despite authors stating results cannot be attributed to habitat or adult quality differences
View raw extracted JSON
{
  "study_type": "cohort",
  "exposure": {
    "band": null,
    "source": "electric power line",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": "nine breeding seasons"
  },
  "population": "Wild great tits (Parus major) population",
  "sample_size": null,
  "outcomes": [
    "clutch size",
    "egg volume",
    "clutch volume",
    "hatching success",
    "final productivity (fledging and reproductive success)",
    "nestling body mass"
  ],
  "main_findings": "In a wild great tit population studied over nine breeding seasons, EMF exposure from an electric power line was associated with increased clutch size (7%) and egg volume (3%), implying a 10% increase in clutch volume compared with an adjacent reference area. No differences were detected in hatching success or final productivity (fledging/reproductive success) or nestling body mass.",
  "effect_direction": "mixed",
  "limitations": [
    "Frequency/intensity of EMF exposure not specified in the abstract",
    "Sample size not reported in the abstract",
    "Observational field comparison (exposed vs adjacent reference area) may be subject to residual confounding despite authors stating results cannot be attributed to habitat or adult quality differences"
  ],
  "evidence_strength": "low",
  "confidence": 0.78,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "electromagnetic fields",
    "power lines",
    "avian reproduction",
    "great tit",
    "clutch size",
    "egg volume",
    "field study",
    "long-term"
  ],
  "suggested_hubs": [
    {
      "slug": "occupational-exposure",
      "weight": 0.15,
      "reason": "Exposure source is an electric power line; while not occupational, it relates to power-line EMF exposure contexts."
    }
  ]
}
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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1016/j.envres.2012.07.007
PubMed: 22863551

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