Tag Archives: Migratory birds

Shape-shifting birds in US skies surprise science

The seasons are changing: American avian migrants are now increasingly shape-shifting birds. Their corpses tell an odd story.

LONDON, 25 June, 2021 − America’s migratory birds are setting off for the breeding grounds ever earlier. That’s not the only change. As global temperatures creep ever higher, the birds’ bodies are getting smaller − but their wings are getting longer. And, a little unexpectedly, the changes producing these shape-shifting birds may not be connected, according to new research.

“We know that bird morphology has a major effect on the efficiency and speed of flight, so we became curious whether the environmental pressure to advance spring migration would lead to natural selection for longer wings,” said Marketa Zimova, of the University of Michigan.

“We found that birds are changing in size and shape independently of changes in their migration timing, which was surprising.”

The study, in the Journal of Animal Ecology, is however a lesson for non-scientists and natural historians in the extraordinary value of museum collections, and a bleak reminder that humankind is casually but relentlessly reducing the numbers and variety of the living things that keep planetary ecosystems − and humans − in good health.

Migrants’ problems

The researchers arrived at their conclusion simply by examining the bodies of birds that had flown into the windows of tall buildings and died on the spot. The scale of this is alarming: between 1978 and 2016 the Field Museum in Chicago assembled 70,716 carcasses of migratory birds, all preserved and recorded with the date of death. Chicago, the researchers write, “is one of the most dangerous cities in the United States for building collisions driven by artificial light at night.”

Within this vast haul of accident victims they counted 11 families, 30 genera and 52 species. All but two of the species − a rail and a woodpecker − were passerines, perching songbirds. To make sure their specimens reliably told a tale of migration timing, the scientists selected only those species of which they had 100 or more individuals and, of those, there had to be at least 10 from each decade in the last 40 years.

Global heating has begun to impose change on the natural world: vulnerable species are at risk, and the sheer numbers of insects, reptiles, amphibians, birds and mammals have fallen dramatically as human numbers and human economies have grown.

Climate change creates special problems for migratory birds because food supplies may not be in step with earlier seasonal shifts, and there has been repeated evidence of change either in bird numbers or bird behaviour as thermometer levels rise. And this is as true for North American birds as for those on any other continent.

“Birds are changing in size and shape independently of changes in their migration timing, which was surprising”

So the mere existence of a huge and growing reservoir of accidentally-killed specimens gave the researchers a chance to examine the links between physical change, higher temperatures and earlier springs in more detail.

On the evidence preserved in the Field Museum the earliest spring migrants are arriving five days earlier than 40 years ago, with the earliest fall migrants heading south 10 days earlier than once they did.

In a warming world, creatures tend to become smaller − because with a bigger surface-to-volume ratio it’s easier to keep cool − but the shift to longer wings is less easy to explain. It’s just possible that with earlier springs, birds flying north don’t need to stop so often.

“And there might be other adjustments that allow birds to migrate faster that we haven’t thought about − maybe some physiological adaptation that might allow faster flight without causing the birds to overheat and lose too much water,” Dr Zimova said. − Climate News Network

The seasons are changing: American avian migrants are now increasingly shape-shifting birds. Their corpses tell an odd story.

LONDON, 25 June, 2021 − America’s migratory birds are setting off for the breeding grounds ever earlier. That’s not the only change. As global temperatures creep ever higher, the birds’ bodies are getting smaller − but their wings are getting longer. And, a little unexpectedly, the changes producing these shape-shifting birds may not be connected, according to new research.

“We know that bird morphology has a major effect on the efficiency and speed of flight, so we became curious whether the environmental pressure to advance spring migration would lead to natural selection for longer wings,” said Marketa Zimova, of the University of Michigan.

“We found that birds are changing in size and shape independently of changes in their migration timing, which was surprising.”

The study, in the Journal of Animal Ecology, is however a lesson for non-scientists and natural historians in the extraordinary value of museum collections, and a bleak reminder that humankind is casually but relentlessly reducing the numbers and variety of the living things that keep planetary ecosystems − and humans − in good health.

Migrants’ problems

The researchers arrived at their conclusion simply by examining the bodies of birds that had flown into the windows of tall buildings and died on the spot. The scale of this is alarming: between 1978 and 2016 the Field Museum in Chicago assembled 70,716 carcasses of migratory birds, all preserved and recorded with the date of death. Chicago, the researchers write, “is one of the most dangerous cities in the United States for building collisions driven by artificial light at night.”

Within this vast haul of accident victims they counted 11 families, 30 genera and 52 species. All but two of the species − a rail and a woodpecker − were passerines, perching songbirds. To make sure their specimens reliably told a tale of migration timing, the scientists selected only those species of which they had 100 or more individuals and, of those, there had to be at least 10 from each decade in the last 40 years.

Global heating has begun to impose change on the natural world: vulnerable species are at risk, and the sheer numbers of insects, reptiles, amphibians, birds and mammals have fallen dramatically as human numbers and human economies have grown.

Climate change creates special problems for migratory birds because food supplies may not be in step with earlier seasonal shifts, and there has been repeated evidence of change either in bird numbers or bird behaviour as thermometer levels rise. And this is as true for North American birds as for those on any other continent.

“Birds are changing in size and shape independently of changes in their migration timing, which was surprising”

So the mere existence of a huge and growing reservoir of accidentally-killed specimens gave the researchers a chance to examine the links between physical change, higher temperatures and earlier springs in more detail.

On the evidence preserved in the Field Museum the earliest spring migrants are arriving five days earlier than 40 years ago, with the earliest fall migrants heading south 10 days earlier than once they did.

In a warming world, creatures tend to become smaller − because with a bigger surface-to-volume ratio it’s easier to keep cool − but the shift to longer wings is less easy to explain. It’s just possible that with earlier springs, birds flying north don’t need to stop so often.

“And there might be other adjustments that allow birds to migrate faster that we haven’t thought about − maybe some physiological adaptation that might allow faster flight without causing the birds to overheat and lose too much water,” Dr Zimova said. − Climate News Network

Rising temperatures ground ducks

EMBARGOED until 2301 GMT on Monday 13 May As temperatures climb in parts of northern Europe, some bird species, unable to find other ways of adapting to the warmer conditions, are simply not migrating as they once did. LONDON, 14 May – Most birds are acutely sensitive to changes in temperature. Scientists now say that changes in climate and warmer temperatures in parts of Europe have resulted in the migration patterns of certain birds being radically altered. A study looking at the migration patterns of three species of duck – the goldeneye, goosander and tufted duck – has found there has been a sharp decrease in the number of birds migrating south. The study, published in Global Change Biology, examined the migration patterns of the three duck species over the 1980 to 2010 period. It found that mid-winter numbers of individual ducks at the southern edge of the species’ normal distribution range – in France, Ireland and Switzerland – had dropped by nearly 120,000. Meanwhile mid-winter numbers of the species in Finland and Sweden – in areas where the ducks breed in summer  – had increased by a similar amount. Chas Holt of the British Trust for Ornithology, a co-author of the study, says ornithologists in Finland were the first to notice that numbers of ducks were no longer flying south in winter. “It’s essentially a fairly gradual shift in behaviour, but it’s clear that a rise in temperatures in regions of Finland and Sweden means the ducks no longer fly south but stay closer to their summer breeding grounds all year round”, Holt told Climate News Network. Early winter temperatures in the ducks’ breeding grounds in Finland were found to have increased by 3.8°C over the 1980 to 2010 period.

Food under pressure

  “There is a sharp correlation between these shifts in the range of migration and the rise in temperatures”, says Holt. “Three decades ago there would have been no open water for the ducks in winter in these north-eastern areas of their normal range.  Now there is – and the ducks don’t have to move so much from their breeding grounds.” Scientists say that if increasing numbers of birds do not migrate, there’s a risk that habitats will come under increasing pressure as food supplies dwindle. They also say that while many bird species have shown an ability to adapt to changes in temperature, many may not be able to alter their behaviour fast enough if temperatures fluctuate rapidly. “What happens if there is an exceptionally cold winter in the midst of a period of relatively mild ones?” asks Holt.  “Can birds such as these ducks adapt fast enough and resume their old migration patterns? “The whole issue has to be placed in context.  We are seeing declines everywhere in various bird species. These changes in migration patterns also mean we have to adapt our conservation strategies as new bird wintering areas are established.” – Climate News Network

EMBARGOED until 2301 GMT on Monday 13 May As temperatures climb in parts of northern Europe, some bird species, unable to find other ways of adapting to the warmer conditions, are simply not migrating as they once did. LONDON, 14 May – Most birds are acutely sensitive to changes in temperature. Scientists now say that changes in climate and warmer temperatures in parts of Europe have resulted in the migration patterns of certain birds being radically altered. A study looking at the migration patterns of three species of duck – the goldeneye, goosander and tufted duck – has found there has been a sharp decrease in the number of birds migrating south. The study, published in Global Change Biology, examined the migration patterns of the three duck species over the 1980 to 2010 period. It found that mid-winter numbers of individual ducks at the southern edge of the species’ normal distribution range – in France, Ireland and Switzerland – had dropped by nearly 120,000. Meanwhile mid-winter numbers of the species in Finland and Sweden – in areas where the ducks breed in summer  – had increased by a similar amount. Chas Holt of the British Trust for Ornithology, a co-author of the study, says ornithologists in Finland were the first to notice that numbers of ducks were no longer flying south in winter. “It’s essentially a fairly gradual shift in behaviour, but it’s clear that a rise in temperatures in regions of Finland and Sweden means the ducks no longer fly south but stay closer to their summer breeding grounds all year round”, Holt told Climate News Network. Early winter temperatures in the ducks’ breeding grounds in Finland were found to have increased by 3.8°C over the 1980 to 2010 period.

Food under pressure

  “There is a sharp correlation between these shifts in the range of migration and the rise in temperatures”, says Holt. “Three decades ago there would have been no open water for the ducks in winter in these north-eastern areas of their normal range.  Now there is – and the ducks don’t have to move so much from their breeding grounds.” Scientists say that if increasing numbers of birds do not migrate, there’s a risk that habitats will come under increasing pressure as food supplies dwindle. They also say that while many bird species have shown an ability to adapt to changes in temperature, many may not be able to alter their behaviour fast enough if temperatures fluctuate rapidly. “What happens if there is an exceptionally cold winter in the midst of a period of relatively mild ones?” asks Holt.  “Can birds such as these ducks adapt fast enough and resume their old migration patterns? “The whole issue has to be placed in context.  We are seeing declines everywhere in various bird species. These changes in migration patterns also mean we have to adapt our conservation strategies as new bird wintering areas are established.” – Climate News Network