'Snowbirds' versus real birds

December 12, 2003

The destruction of tropical forests to create vacation resorts for human "snowbirds" who fly south from Canada and the northern U.S. every winter is creating serious breeding problems for real migratory birds, say Queen's University biologists.

A new study, headed by Ph.D. student Ryan Norris and his advisor, Professor Laurene Ratcliffe, shows for the first time that declining winter habitats of migratory songbirds significantly affect their ability to reproduce when they return north in the spring - and the evidence is found in tiny drops of their blood.

The study, highlighted recently in the journal Science, and co-authored by Dr. Peter Marra of the Smithsonian Institute, appears on-line in the current Proceedings of the Royal Society: Biological Sciences, and will be published in an upcoming print edition of Proceedings.

"Our findings help explain why many species of long-distance migratory songbirds have declined over the last few decades," says Mr. Norris, noting that a relatively small geographic band - across the Caribbean, Greater Antilles, and central America - is the annual destination of an estimated five billion migratory birds flying south each year from Canada. The species in this study is a small, migratory warbler called the American redstart.

Until now, understanding how and why these migratory populations are declining has been a problem, since it is difficult to track individuals throughout their yearly travels. A new technique for detecting "biological signatures" provides the solution.

Using equipment and expertise of the Queen's Facility for Isotope Research (QFIR) headed by geology professor Kurt Kyser, the team measures stable carbon isotopes found in the warblers' blood. These samples are taken immediately after the birds arrive at the university's biological field station north of Kingston, Ontario in the spring.

Since the turnover time of the blood cells is from six to eight weeks, they provide a good indicator of the quality of the birds' previous habitat on the wintering ground. The carbon signature of each redstart has been deposited by insects the bird ate, and the insects in turn fed on vegetation growing in the winter habitat. "It's basically a 'food chain signature'," says Mr. Norris.

The researchers first determined what were high and low quality habitats for redstarts, which winter in the Caribbean and central America, and breed in deciduous forest throughout Canada and the U.S. They found that what makes a better winter habitat is primarily the degree of wetness, particularly at the end of the season (late winter/early spring) when low quality habitats tend to dry out.

The second step was to develop isotope "markers" that identify the quality of each type of habitat. Next, blood samples were taken from warblers in their breeding grounds, and finally the birds' reproductive success was measured by counting the number of "fledged" offspring to leave their nests.

The study, funded by the Natural Sciences and Engineering Research Council (NSERC), Canada Foundation for Innovation (CFI), and National Science Foundation (NSF), shows that redstarts wintering in high quality habitats, such as mangroves and lowland tropical forests, arrive earlier on the breeding grounds, nest earlier, and are more successful in producing young.

"Our work shows that destroying these high quality habitats has a disproportionate effect on the redstart populations: they lose the areas most capable of supporting them," says Dr. Ratcliffe.

"As biologists, to see such a significant effect on the birds' reproductive success is absolutely fascinating," the biology professor continues. "Now we'll need to go much deeper to discover all the complexities, and to determine if there are applications to other organisms as well."
-end-
Contacts:

Nancy Dorrance, Queen's News & Media Services, 613.533.2869
Nancy Marrello, Queen's News & Media Services, 613.533.3227

NOTE: High-resolution digital images are available of American redstarts feeding their young, and of the three key research team members at the Queen's isotope laboratory.

Queen's University

Related Tropical Forests Articles from Brightsurf:

Restoring degraded tropical forests generates big carbon gains
An international team of scientists from 13 institutions has provided the first long-term comparison of aboveground carbon recovery rates between naturally regenerating and actively restored forests in Malaysian Borneo.

Warming threat to tropical forests risks release of carbon from soil
Billions of tonnes of carbon dioxide risk being lost into the atmosphere due to tropical forest soils being significantly more sensitive to climate change than previously thought.

New global study shows 'best of the last' tropical forests urgently need protection
The world's 'best of the last' tropical forests are at significant risk of being lost, according to a paper released today in Nature Ecology and Evolution.

Scientists identify a temperature tipping point for tropical forests
Carbon dioxide is an important greenhouse gas, released as fossil fuels are burned.

Tropical forests can handle the heat, up to a point
Tropical forests face an uncertain future under climate change, but new research published in Science suggests they can continue to store large amounts of carbon in a warmer world, if countries limit greenhouse gas emissions.

Long-term resilience of Earth's tropical forests in warmer world
A long-term assessment of the sensitivity of hundreds of tropical forest plots to increasing temperatures brings encouraging news: in the long run, Earth's tropical forests may be more resilient to a moderately warming world than short-term predictions have suggested.

Online tool helps to protect tropical forests
A new tool maps the threats to the tropical dry forests in Peru and Ecuador.

A glimpse into the future of tropical forests
Tropical forests are a hotspot of biodiversity. Against the backdrop of climate change, their protection plays a special role and it is important to predict how such diverse forests may change over decades and even centuries.

Shedding light on how much carbon tropical forests can absorb
Tropical forest ecosystems are an important part of the global carbon cycle as they take up and store large amounts of CO2.

Tropical forests' carbon sink is already rapidly weakening
The ability of the world's tropical forests to remove carbon from the atmosphere is decreasing, according to a study tracking 300,000 trees over 30 years, published today in Nature.

Read More: Tropical Forests News and Tropical Forests 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.