Declining Rainfall Is a Major Influence for Migrating Birds

The team's findings are published in scientific journal Proceedings of the Royal Society B on March 30.

Many of the bird species that breed in the temperate forests, marshes and backyards of North America spend the winter months in the tropics of the Caribbean, and Central and South America. Insects are the primary food for many birds during the winter, and rainfall largely determines the amount of insects available. Climactic warming, however, is causing declining and more variable rainfall cycles in many areas, affecting the availability of insects and delaying when birds leave for their northern breeding grounds. To examine this, the Smithsonian scientists focused on American redstarts (Setophaga ruticilla), a member of the warbler family, at a non-breeding site in Jamaica where they conduct long-term studies.

"American redstarts were a perfect species for this study since they defend exclusive territories throughout the non-breeding period until they depart for spring migration and most return back to the same territory the following year," said Pete Marra, research ecologist at the Smithsonian Conservation Biology Institute's Migratory Bird Center. "These behaviors made it relatively easy to keep track of individual birds over multiple years and document changing spring departures. Each individual was fitted with a unique combination of colored leg bands."

Precipitation in Jamaica is highly seasonal, with consistent rainfall from September to November and a pronounced dry season from January to March. The scientists observed the redstarts in their non-breeding territories for five years during the dry season. They paid special attention to the annual variation in dry season rainfall. The correlation between the amount of insects in a bird's territory and the timing of its departure suggested to the team that annual variation in food availability was an important determining factor in the timing of spring migration. Had the redstarts relied on internal cues alone to schedule their spring departure, they would have all left their winter territories at the same time each year.
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Hottest planet is hotter than some stars

Astronomers have found the hottest planet yet, a gas giant with a temperature of nearly 3200 °C, which is hotter than some stars.

A collaboration called the Super Wide Angle Search for Planets (SuperWASP) announced hints of the planet's existence in 2006. The group had observed periodic dimmings of the parent star possibly caused by a planet about 1.4 times the size of Jupiter passing in front of the star once per orbit.

Follow-up measurements confirmed the planet's presence in 2010, showing distortions of the star's light spectrum that could only be due to a planet's influence. The measurements showed the planet's mass is less than 4.5 times that of Jupiter.

Called WASP-33b, the planet orbits its star at less than 7 per cent of Mercury's distance from the sun, whipping around the star once every 29.5 hours.

Hot star, close planet
That is not the tightest orbit known, but WASP-33b's parent star is one of the hottest known to host a planet. The star is a scorching 7160 °C, far hotter than the sun, whose visible surface is about 5600 °C.

The combination of its close orbit and its parent star's temperature heat WASP-33b to nearly 3200 °C, according to new infrared measurements made with a camera on the William Herschel Telescope in the Canary Islands. Alexis Smith of Keele University in Staffordshire, UK, led the study.

WASP-33b's incredible temperature is higher than some red dwarf stars. It is also about 700 °C hotter than another sizzlingly hot star, WASP-12b, which was measured at around 2300 °C.

Puzzling planets
WASP-33b might help astronomers gain new insight on hot planets, whose properties have proven puzzling, says Drake Deming of NASA's Goddard Space Flight Center in Greenbelt, Maryland, who is not a member of Smith's team.

For example, the outer atmospheric layers of some star-hugging planets appear to be colder than the deeper layers, which is surprising given that they are heated externally by intense radiation from their stars.

This might be due to complex carbon-based chemicals that change the way the planets' atmospheres respond to radiation, Deming says. Such chemicals could be formed by the action of ultraviolet light from the parent stars, which would be especially intense in the case of WASP-33b, given how hot its parent star is, he says.

"This certainly would be a planet that you would want to look at," he says. "It's a really exceptional opportunity to study a planet around a really hot star."
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