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 med./bio.

By: Tomas G, Barba E, Merino S, Martinez J

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

effects on the reproductive system: avian reproduction: clutch size, egg volume, hatching success, productivity (nestling body mass, fledging, reproductive success)

Exposure

Exposure	Parameters
Exposure 1: 50 Hz Exposure duration: continuous for approx. 40 days	power: 30.8 MW maximum magnetic flux density: 0.84 µT maximum (in the nests) magnetic flux density: 0.2 µT mean (± 0.03 µT (in the nests))

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	magnetic field
Exposure duration	continuous for approx. 40 days

Exposure setup

Exposure source	power line (66 kV)
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 system:

eggs
investigation on living organism

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:

medical/biological study
observational study
full/main study

Study funded by

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

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