Blackbirds Former mating by street lighting

Light pollution in cities irritates the biorhythms of birds

14/02/2013

Light pollution or urban lighting during the night influences the biorhythms and the willingness to mate of birds. „It has long been suspected that the nocturnal artificial light of cities can influence plants, animals and humans“, reports the Max Planck Institute for Ornithology in Radolfzell on Lake Constance. So far, however, are only a few „Studies that test this influence directly“, Have been carried out. Therefore, the ornithologists of the Max Planck Institute have now examined in a comprehensive investigation, „how the nightly city lighting affects Blackbirds ().“

Due to artificial light from street lamps, traffic lights, illuminated advertising and apartment lighting, the nights in Germany have been getting brighter for years. As a result, the rhythm of plants, humans and animals could be disturbed sensitive, so the many expressed concern. The scientists of the Max Planck Institute for Ornithology have now examined these concerns in a study on blackbirds. They found that birds, „which are exposed to low light intensities at night, comparable to light intensities in cities“, Earlier in the year to reach the reproductive readiness to sing earlier and moult earlier. However, the scientists could not say what consequences these significant changes in the daily and seasonal rhythms have for the future blackbird population.

For „many animals is the seasonal change in daylength one of the most important environmental signals for controlling daytime (eg sleep-wake cycles) and seasonal rhythms (for example breeding season)“, report the ornithologists of the Max Planck Institute in Radolfzell. This effect is exploited for example in laying batteries, where „the egg production by changing the length of the day with the help of artificial lighting“ is increased. Even animals in cities experience partly extreme lighting conditions due to the artificial light. Here, consequences for the biorhythm are a logical consequence, but so far these have been insufficiently scientifically studied. The experts of the Max Planck Institute for Ornithology have therefore reviewed in their study, „What influence does the artificial light have on the daily and seasonal organization of these urban animals?“ Has.

Nocturnal lighting causes significant changes in the biorhythm
First, the scientists determined which light intensity the blackbirds are actually exposed to during the night. The research team led by Jesko Partecke from the Max Planck Institute for Ornithology caught several city natives and equipped them with light sensors that could detect, „which levels of illumination the birds were exposed to on average during the night“, reports the institute. According to the study director, this revealed that „the intensities of 0.2 lux were very small - only a thirtieth of what a typical street lamp emits.“ The researchers then sat down „captured city and Waldermelden over a period of ten months at night from a lighting level of 0.3 lux.“ Already these low values ​​were sufficient to bring about drastic changes in the biorhythm of the birds, according to the report of the Max Planck Institute for Ornithology.

Blackbirds ready for reproduction earlier by nocturnal illumination
The relatively small increase in light intensity during the night was sufficient to ripen the gonads of male blackbirds earlier, according to one of the study's findings. „The results were astounding: the birds' testicles grew on average almost a month earlier than in animals sleeping in the dark at night“, Jesko stressed party corner. Measurements of the testosterone levels in the blood of the birds have been shown to increase earlier in the season due to nocturnal illumination. This also means that the blackbirds rather reach their reproductive readiness. Furthermore, the daytime rhythm of the vocal activity was confused by the artificial light. According to the researchers, the birds began singing about an hour earlier each day. In addition to the evidence of premature reproduction behavior, it has also been shown that the nocturnally lit blackbirds started moulting much earlier in the breeding season than birds with dark nights.

Deviations of the daily and seasonal rhythms
„These results clearly show that the artificial light that we find in cities can drastically change the seasonal organization of wildlife“, explained study leader Jesko Partecke. However, the researchers are still not sure why the artificial light in the blackbirds requires early reproductive readiness and whether this is more of an advantage or disadvantage. An explanation for the earlier reproductive readiness, for example, is that the blackbirds are fooled by the nocturnal artificial light a longer day length. The lighting may also facilitate the nocturnal foraging of the birds, so that the animals have additional energy for reproduction. Finally, the light could „also influence the metabolism of the animals and the altered metabolism provide for earlier gonadal growth“, reports the Max Planck Institute for Ornithology. According to the experts, the birds were more active during the day when the birds were exposed to light at night.

Earlier reproductive readiness an advantage or disadvantage?
The long-term effect of artificial lighting on the blackbird population remains according to the information provided by ornithologists of the Max Planck Institute in Radolfzell so far unclear. „Whether the earlier brooding offers an advantage to the city dwellers or is merely an unwanted accompaniment of the lighting“, can not be determined by the current study results. In fact, theoretically, it would be conceivable that the „Blackbirds in the city brooding by the artificial light earlier in the year, thereby producing more youngsters a year“ explained study leader Jesko Partecke. However, this supposed advantage unfolds only effect, „if the nestlings then also have enough suitable food available“ to have. „Otherwise, the early reproductive ability for the blackbirds could turn out to be an evolutionary disadvantage“, this is the conclusion of the Max Planck Institute for Ornithology. (Fp)

Also read:
Acute spread of the Usutu virus in Germany
Dead blackbird with Usutu virus discovered in NRW
Another blackbird death by Usutu viruses
Tropical virus causes blackbird death
Dangerous tropical fever by bush mosquitoes
New parasite lets pigeons die

Picture: Helene Souza