Polluted prey causes wild birds to change their tune

Considerable attention has been paid to the effects of endocrine disrupting chemicals in aquatic environments, but rather less attention has been given to routes of contamination on land. A new study, published in PLoS ONE on February 27 by researchers at Cardiff University, reveals that wild birds foraging on invertebrates contaminated with environmental pollutants, show marked changes in both brain and behaviour: male birds exposed to this pollution develop more complex songs, which are actually preferred by the females, even though these same males usually show reduced immune function compared to controls.

Katherine Buchanan and her colleagues studied male European starlings (Sturnus vulgaris) foraging at a sewage treatment works in the south-west UK and analysed the earthworms that constitute their prey. The researchers found that those birds exposed to environmentally-relevant levels of synthetic and natural estrogen mimics developed longer and more complex songs compared to males in a control group.

Specifically, birds dosed with the complete spectrum of endocrine disrupting chemicals found in the invertebrates spent longer singing, sang more often and produced more complex songs, a sexually selected trait important in attracting females for reproduction even though birds dosed at these ecologically relevant levels also showed reduced immune function.

The study also addresses the mechanism for this effect, as the researchers found that the high vocal centre (HVC), the area of the brain that controls male song complexity, is significantly enlarged in the contaminated birds. Estrogen causes masculinisation of the songbird brain and the HVC is enriched with estrogen receptors. Neural development is thus susceptible to exposure to chemicals which mimic estrogen, or to enhanced estrogen levels. The results also confirm the plasticity of the adult songbird brain.

Finally, the scientists found that female starlings prefer the song of males exposed to the mixture of endocrine disrupting chemicals, suggesting the potential for population level effects on reproductive success.

“This is the first evidence that environmental pollutants not only affect, but paradoxically enhance a signal of male quality such as song,” said Katherine Buchanan, the corresponding author of the paper. “These results may have consequences of population dynamics of an already declining species.”

Citation: Markman S, Leitner S, Catchpole C, Barnsley S, Müller CT, et al (2008) Pollutants Increase Song Complexity and the Volume of the Brain Area HVC in a Songbird. PLoS ONE 3(2): e1674. doi:10.1371/journal.pone.0001674 (http://www.plosone.org/doi/pone.0001674)

Source: Public Library of Science

Related stories:

Is that song sexy or just so-so?
Why is your mate's rendition of Marvin Gaye's "Let's Get it On" cute and sexy sometimes and so annoying at other times? A songbird study conducted by Emory University sheds new light on this question, showing that a change in hormone levels may alter the way we perceive social cues by altering a system of brain nuclei, common to all vertebrates, called the "social behavior network."
Songbirds may hold key to advances in treatment of brain degeneration
Ongoing research at Lehigh University may one day help make strides toward therapeutic advances in the treatment of diseases that involve the loss of memory and brain degeneration such as Alzheimer's, Parkinson's, and stroke.
Hormones may affect how brain listens
From zebra fish to humans, reproductive hormones govern behavioral responses to courtship signals. A new Emory University study conducted in songbirds suggests that hormones may also modulate the way the auditory system processes courtship signals. In other words, hormones may affect how the birds actually listen to courtship songs at certain times of the year when it's time to reproduce.
Practice as well as sleep may help birds learn new songs
The reorganization of neural activity during sleep helps young songbirds to develop the vocal skills they display while awake, University of Chicago researchers have found.
Mammals can be stimulated to regrow damaged inner retina nerve cells
Researchers at the University of Washington (UW) have reported for the first time that mammals can be stimulated to regrow inner nerve cells in their damaged retinas. Located in the back of the eye, the retina's role in vision is to convert light into nerve impulses to the brain.
Social interactions can alter gene expression in the brain, and vice versa
Our DNA determines a lot about who we are and how we play with others, but recent studies of social animals (birds and bees, among others) show that the interaction between genes and behavior is more of a two-way street than most of us realize.
Genetic study provides new insights into molecular basis of language development
Scientists have identified the first gene that is associated with a common childhood language disorder, known as specific language impairment (SLI). The gene – CNTNAP2 – has also been recently implicated in autism, and could represent a crucial genetic link between the two disorders.
Exercisers face the challenge of dark times
This time of year tries runners' souls as much as their soles, and the same goes for cyclists and walkers. Really, almost anyone who exercises outdoors in the fall and winter has to deal with darkness descending earlier and earlier.

News discussion:

General Science news