Tropical birds sensitive to environmental cues that can be impacted by global warming

November 12, 2004

Blacksburg, Va. - A bird's song is music to our ears -- and to the ears of his potential mates -- and a warning to other males to stay out of his territory. To Ignacio Moore, assistant professor of biology at Virginia Tech, bird songs were a curiosity that made him want to find out why birds sang at some times and not at others, at some places and not elsewhere.

Moore and University of Washington, Seattle, researchers John C. Wingfield in biology and Eliot A. Brenowitz in psychology, looked at seasonal changes in the brains of birds that account for their singing, which is a part of the male mating behavior. In the Nov. 10 issue of The Journal of Neuroscience (www.jneurosci.org/), the official journal of the Society for Neuroscience, they report that birds in high latitudes are driven to sing by seasonal changes in the length of the day, which causes changes in the song-control nuclei of the brain. However, in the tropics, where the day length does not vary much by season, the propensity for birds to sing still changes, but is driven by environmental cues that vary by locale -- a fact that could mean those birds are more susceptible to global warming than birds in higher latitudes.

Correct timing of breeding is necessary for reproductive success, Moore said. Research by others has shown that testosterone is the main physiological cue regulating seasonal changes in the neural song-control system. Seasonal changes in the song-control system have been demonstrated by other scientists in all northern latitude species that have been investigated. But no one had researched whether seasonal changes occurred in the brains of birds in tropical areas where day-length changes are minimal. "We think it's probably still testosterone that causes tropical birds to sing, but that the environmental cue is different," Moore said. The scientists wanted to determine whether "seasonal changes in brain structure can be mediated by local environmental cues."

Moore and his colleagues looked at two populations of the rufous-collared sparrow only 25 km apart. The two populations are at the same latitude but are on the east and west slopes of the Andes, which have very different climate patterns. "At the time of year when birds in the Papallacta population were breeding (August to September), birds in Pintag were in nonbreeding state," the researchers wrote in The Journal of Neuroscience ("Plasticity of the Avian Song Control System in Response to Localized Environmental Cues in an Equatorial Songbird"). "Correspondingly, the song control nuclei were fully grown in the breeding Papallacta population when they were regressed in the nonbreeding Pintag population. Singing behavior also changed seasonally in both populations.

"Our observations of seasonal brain plasticity in these tropical birds demonstrate that the vertebrate brain is extremely flexible and sensitive to diverse environmental cues that can time seasonal reproductive physiology and behavior," they wrote. While it is not yet known what environmental cues signal breeding time, Moore hypothesizes that it could be rainfall, temperature, or food availability -- or all these cues.

Human beings are contributing to global warming, which affects factors such as temperature and rainfall, and thus food availability, but does not affect the seasonal day-length changes of higher latitudes. Therefore, Moore said, global warming could change the brain functions of tropical birds and cause problems with the timing of their mating seasons. "We're not going to change day length," he said. "We can change weather patterns. Studies show changes in the timing of breeding and migration in birds." Global warming could be the reason, he said, and, if the brain is truly sensitive to environmental cues, the changes due to global warming could have "effects we haven't thought of before."

While Moore's research was driven primarily by curiosity and not by conservation concerns, "you can't save things if you don't understand them," he said. "Every little bit of knowledge about how things works is useful." They will next try to determine which specific environmental cues are affecting tropical-bird mating processes. Moore's research is funded through fellowships and grants from the Society for Neuroscience and the National Science Foundation.
-end-


Virginia Tech

Related Global Warming Articles from Brightsurf:

The ocean has become more stratified with global warming
A new study found that the global ocean has become more layered and resistant to vertical mixing as warming from the surface creates increasing stratification.

Containing methane and its contribution to global warming
Methane is a gas that deserves more attention in the climate debate as it contributes to almost half of human-made global warming in the short-term.

Global warming and extinction risk
How can fossils predict the consequences of climate change? A German research team from Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), the Museum of Natural History Berlin and the Alfred Wegener Institute compared data from fossil and marine organisms living today to predict which groups of animals are most at risk from climate change.

Intensified global monsoon extreme rainfall signals global warming -- A study
A new study reveals significant associations between global warming and the observed intensification of extreme rainfall over the global monsoon region and its several subregions, including the southern part of South Africa, India, North America and the eastern part of the South America.

Global warming's impact on undernourishment
Global warming may increase undernutrition through the effects of heat exposure on people, according to a new study published this week in PLOS Medicine by Yuming Guo of Monash University, Australia, and colleagues.

Global warming will accelerate water cycle over global land monsoon regions
A new study provides a broader understanding on the redistribution of freshwater resources across the globe induced by future changes in the monsoon system.

Comparison of global climatologies confirms warming of the global ocean
A report describes the main features of the recently published World Ocean Experiment-Argo Global Hydrographic Climatology.

Six feet under, a new approach to global warming
A Washington State University researcher has found that one-fourth of the carbon held by soil is bound to minerals as far as six feet below the surface.

Can we limit global warming to 1.5 °C?
Efforts to combat climate change tend to focus on supply-side changes, such as shifting to renewable or cleaner energy.

Global warming: Worrying lessons from the past
56 million years ago, the Earth experienced an exceptional episode of global warming.

Read More: Global Warming News and Global Warming Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.