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Medical/biological study (observational study)

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

Published in: Environ Res 2012; 118: 40-46

Aim of study (acc. to author)

To study the effects of electromagnetic fields generated by a power line on reproductive characteristics of a wild great tit population by analysing data gathered during nine breeding seasons.
Background/further details: Data was recorded on a wild great tit population breeding near Sagunto (Valencia, eastern Spain). The 110 ha study area was located within a homogeneous orange plantation. Wooden nest-boxes (125 x 117 mm bottom area) were placed each year in February in the same trees at about 50 cm above the ground (the height at which natural holes occur in this habitat). During the breeding seasons, nest-boxes were inspected at least once a week, and nests as frequently as necessary in order to accurately determine the reproductive parameters.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 50 Hz
Exposure duration: continuous for approx. 40 days
General information
Nests were classified as exposed (> 0,01 µT; n=51) or non-exposed (≤ 0,01 µT; n=112)
Exposure 1
Main characteristics
Frequency 50 Hz
Type
Exposure duration continuous for approx. 40 days
Exposure setup
Exposure source
Setup the power line crossed the study area at ca. 11.3 m above the ground; nests and nest-boxes were located 50 cm above the ground
Parameters
Measurand Value Type Method Mass Remarks
power 30.8 MW maximum - - -
magnetic flux density 0.84 µT maximum measured - in the nests
magnetic flux density 0.2 µT mean measured - ± 0.03 µT (in the nests)
Exposed system:
  • animal
  • great tit (Paris major)
  • whole body

Methods Endpoint/measurement parameters/methodology

  • effects on the reproductive system: clutch size (number of eggs), egg volume, hatching success (hatchling/clutch size), nestling body mass, fledging success (fledgings/hatchlings), reproductive success (fledgings/clutch size)
  • body weight, tarsus and wing length of the parents
Investigated material:
Time of investigation:
  • during exposure

Main outcome of study (acc. to author)

The electromagnetic field exposure significantly increased the clutch size (7%) and the egg volume (3%), implying a 10% increase in clutch volume. This indicates an increase in reproductive investment from parent birds exposed to electromagnetic fields as compared to the control group in the adjacent reference area. These results cannot be attributed to habitat or quality differences of the adults in the exposed group and control group. Nevertheless, no differences in hatching success or final productivity (fledging and reproductive success or nestling body mass) could be detected in exposed animals.
The study indicates that electromagnetic fields generated by power lines can have biological consequences in wild organisms living close to them.
Study character:

Study funded by

  • Ministerio Espanol de Educacion, Cultura y Deporte, Spain
  • Ministerio Espanol de Ciencia y Tecnologia (Ministry of Science and Technology), Spain
  • Generalitat Valenciana, Spain
  • Juan de la Cierva programme, Ministerio de Economià y Competitividad (Ministry of Economy and Competitiveness), Spain

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