Night-light's affecting bird breeding

19 September 2010
Posted by Chris Smith.

Worsening light pollution is significantly affecting bird's breeding habits, a new study has revealed.

Bart Kempenaers and his colleagues at the Max Planck Institute for Ornithology in Seewiesen, Germany, writing in Current Biology, carried out a 7 year study comparing the behaviours of five different songbird species (robins, blackbirds, great tits, blue tits and chaffinches) inhabiting either dark, central woodland territories, or light-contaminated "edge" territories.

Blue tit - Parus caeruleusMale birds living in the light-polluted areas, they found, were starting to sing significantly sooner - in some cases up to two hours earlier in the morning - than their darker-living counterparts. The effect was also more marked amongst the species that naturally tended to wake up earlier anyway, such as robins and blackbirds. Females exposed to light-pollution were also laying eggs an average of 1.5 days earlier.

The team also found that males living in lighter "edge" territories were twice as likely to father "extra-pair" offspring (the avian equivalent of love children), probably because they won more female attention by starting to sing sooner than darker-living rivals.  However, since females usually select as extra-pair mate choices males they perceive to be highly reproductively "fit", basing their selection on dawn song as a measure of healthy male virility, the early male risers may be thwarting the selection system and fooling females into breeding with the wrong guys with obvious negative consequences for the species.

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