Artificial light speeds sexual maturity in blackbirds

Blackbird singing with mouth open

Related Stories

A study has found that urban nocturnal light makes European blackbirds develop reproductive systems a month before their woodland counterparts.

Birds exposed to higher light levels developed functional testes on average 26 days earlier than control birds.

Further results suggested that urbanisation may alter the physiological traits of songbirds.

Scientists say the findings highlight the consequences of artificial lighting on the ecology of urban animals.

The findings are published in the journal Proceedings of the Royal Society B.

Common blackbird

Davide Dominoni, from the Max Planck Institute for Ornithology in Germany and part of the research team told BBC Nature: "We knew that birds in urban areas sing earlier in the morning and breed earlier in season than conspecifics living in rural habitats."

"There was evidence that urban blackbirds showed not only advanced egg-laying date, but the whole reproductive physiology was turned on approximately three weeks before than in rural birds."

The scientists, from the Max Planck Institute and Konstanz University in Germany, measured the nocturnal light levels that eight "free-roaming" European blackbirds (Turdus merula) were exposed to in the field using miniature light loggers.

Light loggers are programmable, miniature devices, weighing 3g, which are able to record and store the light intensity over a long period of time.

Mr Dominoni explained: "We released the blackbirds equipped with light loggers and then we recaptured them after approximately 2 weeks.

"We used only the data recorded during the night, excluding the twilight values."

Into the lab

Researchers used data from the light loggers to simulate the nocturnal light environment in a controlled experiment in captivity.

Start Quote

Our data show that light at night can strongly modify one of the most crucial life-history traits, reproduction.”

End Quote Davide Dominoni Max Planck Institute for Ornithology, Germany

The scientists exposed birds captured from urban and woodland areas nearby to two different light treatments.

"Birds were exposed to either dark night conditions or to a night-time light level of 0.3 lux, a value representative of what we measured with the light loggers," said Mr Dominoni.

Birds were monitored for an entire breeding season.

Every month the scientists measured the size of the testes, the testosterone level in the blood and the singing behaviour in the early morning.

The study revealed that not only do birds exposed to light at night develop reproductive system up to one month earlier, but also that they moult earlier and have an earlier onset of the dawn song.

Mr Dominoni commented on the findings: "Although the effect we found was big, it is not fully clear what are the costs and benefits of being ready to breed during the early breeding season.

"Supposedly, birds which start to breed earlier could gain the best territories and eventually also increase the number of clutches per season, therefore increasing reproductive output, too."

Wider implications

"Our results hint at a very strong role played by artificial light in urban habitats to shape the physiological phenotypes of songbirds," said Mr Dominoni.

Baby blackbird in nest Nocturnal light can make blackbirds lay eggs earlier than rural birds

"[They are] much stronger than other cues like temperature and food availability, which are more likely to affect ultimate reproductive decisions such as egg-laying. On the contrary, the reproductive physiology seems to be under complete control of light."

The results have wider implications regarding the impact of human-induced lighting on the ecology for millions of urban animals and the scientists called for an understanding of the fitness consequences of light pollution.

According to Mr Dominoni: "Our data show that light at night can strongly modify one of the most crucial life-history traits, reproduction.

"However, this might come at a physiological cost because reproduction requires a great energetically investment which is traded-off with other physiological processes like immune-defence.

"Birds might particularly suffer from decrease immuno-competence in the winter when conditions are not optimal."

Join BBC Nature on Facebook and Twitter @BBCNature.

More on This Story

Related Stories

The BBC is not responsible for the content of external Internet sites

More from nature

  • Cardinal fish and ostracodFish filmed spitting 'fireworks'

    Film crew captures ostracods' spectacular defensive lightshow that makes predatory fish spit them out.

  • Arapaima'Locally extinct'

    A giant fish which used to dominate the Amazon river is now absent in many areas


  • DragonflyRapid reactions

    Dragonfly's super quick reactions recorded in slow motion by BBC film-makers


  • Wingless adult male of the midge Belgica antarcticaExtreme survivor

    Antarctic midge's small genome may be an adaptation to its extreme environment


  • Myotis midastactus specimen (previously identified as Myotis simus)Golden discovery

    A bat from Bolivia is described as a new species by scientists


  • Dinosaurs 'shrank' to become birds

    Huge meat-eating, land-living dinosaurs evolved into birds by constantly shrinking for over 50 million years, new research shows.

  • Would we starve without bees?

    Honey bees are under threat, and as pollination significantly contributes to the food we eat, what would we do without them?

  • Eggshells may act like 'sunblock'

    Birds' eggs show adaptations in pigment concentration and thickness to allow the right amount of sun for embryos, scientists say.

  • Female shrimps are more aggressive

    Female snapping shrimps are more aggressive than males when defending their territories despite their smaller claw size, a study shows.

BBC iWonder

  • Honey bee close-upInsect intelligence

    Are honey bees as smart as your sat nav?

  • Tyrannosaurus rex skull (c) Mark Williamson / Science Photo LibraryDinosaur dynasty

    One group of dinosaurs survived and their descendants can be seen all around us today


  • Brown rat cluse upRise of the rodent

    Reports of giant, 'super rats' are filling the headlines. But why are we being overrun by rats?


  • Cuckoo portraitHoliday hotspot

    What makes the UK such an attractive destination for visiting wildlife?


There have been 75 solar eclipses and 167 major volcanic eruptions in my lifetime

Nicole Malliotakis on Twitter comments on the events that have happened since she was born by using our personalised Your Life on Earth interactive infographic.

Get Inspired

ACTIVITY FINDER

More Nature Activities >

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.