- Email: [email protected]
Bird feeders delay the dawn chorus
For new stories every day, visit www.NewScientist.com/news
David Kjaer/naturepl.com
PUT up a bird feeder in spring and great tits could end up choosing a secure food supply over sex. People put up bird feeders to help wild birds survive the winter, but little is known about how they affect behaviour. To find out, Valentin Amrhein of the University of Basel in Switzerland set up feeders in a forested area outside Oslo, Norway, home to territorial great tits (Parus major). Two weeks later they taped the dawn singing of each bird with a feeder in its territory and compared it with birds with no feeder. The dawn chorus is thought to be important for attracting and defending females, yet well-fed birds delayed their singing by an average of 20 minutes, often waiting until after sunrise. They were still delaying the chorus two weeks after the food had been removed (Animal Behaviour, DOI: 10.1016/j.anbehav.2010.11.008). Amrhein thinks the birds might be chasing other males away from their valuable larder instead of singing. Stuart Bearhop of the University of Exeter, UK, agrees but cautions that this remains a theory. Whatever the cause, Amrhein advocates taking bird feeders down in the spring. Any change in singing behaviour could be costly for the birds: females listen to male songs to assess their performance and choose a mate.
How to sort the dwarfs from the planets WHAT’s the difference between a planet and a brown dwarf? That can be a tricky question, because some objects straddle the conventional boundary between the two categories. Now the discovery that there is a dearth of cosmic bodies whose mass lies within a particular range could provide a clean dividing line between planets and brown dwarfs, which are heavier than planets but lighter than stars. Objects are traditionally classed as planets if they have less than about 13 times the mass of Jupiter,
and as brown dwarfs if they are heavier. Uncertainties in the measurement of mass make it hard to classify borderline objects this way. But when Johannes Sahlmann of the Geneva Observatory in Switzerland and colleagues surveyed brown dwarfs and planets orbiting stars, they found a dearth of objects between 25 and 45 times Jupiter’s mass, but plenty of objects outside this range (arxiv.org/abs/1012.1319). This dividing line could have arisen because the heavier and lighter objects form in different
ways. Planets, on the light side of the divide, may form from leftover gas and dust in discs swirling around newborn stars, while stars and brown dwarfs form from the collapse of clumps of gas. Other surveys found hints of a poorly populated “trough” at around this mass range, says Stanimir Metchev of the State University of New York in Stony Brook, who was not involved in the study. He predicts, however, that a few borderline objects will fall within this range. Steve Mason/getty
Great tits choose food over sex
Magma rain and a moon mystery IF MOLTEN rock once rained onto Earth’s surface, it might explain puzzling differences between the chemical compositions of our planet and the moon. After a Mars-sized body struck the infant Earth, a common atmosphere of rock vapour enveloped the resulting magmacovered Earth and its disc of orbiting magma. This atmosphere should have thoroughly mixed material from Earth and the disc, which later formed the moon. But while the Earth and the moon have the same relative abundance of different oxygen isotopes, some measurements suggest that moon rocks are iron rich and magnesium poor compared with those on Earth. Magma rain could explain the discrepancy. A team led by Kaveh Pahlevan at Yale University calculate that as rock vapour rose from Earth’s hot, roiling surface, the magnesium oxide it contained would have condensed into droplets and rained back to the surface more readily than the more volatile iron oxide, which could then have mixed into the moon-forming disc (Earth and Planetary Science Letters, DOI: 10.1016/j.epsl.2010.10.036).
Exercise link to lower cognitive skill WOMEN who habitually take strenuous exercise might be at risk of damaging their cognitive function later in life. Strenuous exercise is known to reduce oestrogen levels in women and girls. This can delay the start of menstruation, and can lead to irregular periods in adult women. Low levels of oestrogen in premenopausal women have been linked to impaired mental function in later life. Mary Tierney at the University of Toronto, Canada, reasoned that strenuous exercise might therefore lead to impaired cognition in later life. She asked 90 healthy post-
menopausal women to report their life-long exercise habits, and then tested their cognitive ability. The results, which will be reported in the Journal of Alzheimer’s Disease, showed a statistically significant decrease in performance in various cognitive tasks in women who said that they exercised strenuously compared with those that had exercised moderately. The overall benefits of regular exercise are well established, but Tierney says the possible impact of strenuous exercise on cognition should be investigated further to see if it is significant.
8 January 2011 | NewScientist | 15
David Kjaer/naturepl.com
PUT up a bird feeder in spring and great tits could end up choosing a secure food supply over sex. People put up bird feeders to help wild birds survive the winter, but little is known about how they affect behaviour. To find out, Valentin Amrhein of the University of Basel in Switzerland set up feeders in a forested area outside Oslo, Norway, home to territorial great tits (Parus major). Two weeks later they taped the dawn singing of each bird with a feeder in its territory and compared it with birds with no feeder. The dawn chorus is thought to be important for attracting and defending females, yet well-fed birds delayed their singing by an average of 20 minutes, often waiting until after sunrise. They were still delaying the chorus two weeks after the food had been removed (Animal Behaviour, DOI: 10.1016/j.anbehav.2010.11.008). Amrhein thinks the birds might be chasing other males away from their valuable larder instead of singing. Stuart Bearhop of the University of Exeter, UK, agrees but cautions that this remains a theory. Whatever the cause, Amrhein advocates taking bird feeders down in the spring. Any change in singing behaviour could be costly for the birds: females listen to male songs to assess their performance and choose a mate.
How to sort the dwarfs from the planets WHAT’s the difference between a planet and a brown dwarf? That can be a tricky question, because some objects straddle the conventional boundary between the two categories. Now the discovery that there is a dearth of cosmic bodies whose mass lies within a particular range could provide a clean dividing line between planets and brown dwarfs, which are heavier than planets but lighter than stars. Objects are traditionally classed as planets if they have less than about 13 times the mass of Jupiter,
and as brown dwarfs if they are heavier. Uncertainties in the measurement of mass make it hard to classify borderline objects this way. But when Johannes Sahlmann of the Geneva Observatory in Switzerland and colleagues surveyed brown dwarfs and planets orbiting stars, they found a dearth of objects between 25 and 45 times Jupiter’s mass, but plenty of objects outside this range (arxiv.org/abs/1012.1319). This dividing line could have arisen because the heavier and lighter objects form in different
ways. Planets, on the light side of the divide, may form from leftover gas and dust in discs swirling around newborn stars, while stars and brown dwarfs form from the collapse of clumps of gas. Other surveys found hints of a poorly populated “trough” at around this mass range, says Stanimir Metchev of the State University of New York in Stony Brook, who was not involved in the study. He predicts, however, that a few borderline objects will fall within this range. Steve Mason/getty
Great tits choose food over sex
Magma rain and a moon mystery IF MOLTEN rock once rained onto Earth’s surface, it might explain puzzling differences between the chemical compositions of our planet and the moon. After a Mars-sized body struck the infant Earth, a common atmosphere of rock vapour enveloped the resulting magmacovered Earth and its disc of orbiting magma. This atmosphere should have thoroughly mixed material from Earth and the disc, which later formed the moon. But while the Earth and the moon have the same relative abundance of different oxygen isotopes, some measurements suggest that moon rocks are iron rich and magnesium poor compared with those on Earth. Magma rain could explain the discrepancy. A team led by Kaveh Pahlevan at Yale University calculate that as rock vapour rose from Earth’s hot, roiling surface, the magnesium oxide it contained would have condensed into droplets and rained back to the surface more readily than the more volatile iron oxide, which could then have mixed into the moon-forming disc (Earth and Planetary Science Letters, DOI: 10.1016/j.epsl.2010.10.036).
Exercise link to lower cognitive skill WOMEN who habitually take strenuous exercise might be at risk of damaging their cognitive function later in life. Strenuous exercise is known to reduce oestrogen levels in women and girls. This can delay the start of menstruation, and can lead to irregular periods in adult women. Low levels of oestrogen in premenopausal women have been linked to impaired mental function in later life. Mary Tierney at the University of Toronto, Canada, reasoned that strenuous exercise might therefore lead to impaired cognition in later life. She asked 90 healthy post-
menopausal women to report their life-long exercise habits, and then tested their cognitive ability. The results, which will be reported in the Journal of Alzheimer’s Disease, showed a statistically significant decrease in performance in various cognitive tasks in women who said that they exercised strenuously compared with those that had exercised moderately. The overall benefits of regular exercise are well established, but Tierney says the possible impact of strenuous exercise on cognition should be investigated further to see if it is significant.
8 January 2011 | NewScientist | 15