Tag Archives: migration

Birds wearing backpacks trace a path to conservation

Birds wearing backpacks trace a path to conservation (Samantha Knight And Ryan Norris, The Conversation; 9 May 2018; Photo: Julia Baak)

With the arrival of spring, we look forward to the return of hundreds of species of migratory songbirds from their wintering grounds.

Sparrows, swallows, warblers and thrushes, among other songbirds, will be returning from their wintering sites anywhere between the southern United States and distant South America.

Some of these birds will return with a small “backpack” that has recorded their entire migration from their North American breeding grounds to their wintering grounds and back.

Birds provide important ecosystem services, such as preying on insects, dispersing seeds, scavenging carcasses and pollinating plants. Unfortunately, there have been dramatic declines in many migratory songbirds over the past few decades, with some of these populations dropping by more than 80 per cent.

If we are to find ways to slow or reverse these declines, we must first figure out what’s causing them. Climate change, habitat loss and predation by cats are among the leading causes of bird declines.

But with the vast distances these birds move over the course of the year, it can be difficult to pinpoint the main cause for a given species —and where it’s occurring.

Migratory connections

To answer this question, we need to know where individual birds spend their time throughout the year.

We have a good idea of the range —or the total area —the birds occupy during the breeding and wintering periods. But ranges are composed of many populations, and we still have a very poor understanding of how individuals within each of these populations are connected between seasons.

Individuals from different breeding populations may remain segregated during the winter. For example, some ovenbirds winter in the Caribbean whereas others spend their winters in Mexico and Central America.

Or a bird may mix with individuals that originate from other breeding populations, such as bobolinks that mix in South America during the winter.

These patterns of migratory connectivity have critical implications for predicting how migratory songbirds will respond to environmental change.

Habitat loss —deforestation, for example —in one place can have different effects. If habitat loss occurs in a wintering area where breeding populations mix, it may have wide-ranging, yet diffuse, effects on the breeding populations. But if the habitat loss occurs in a wintering area that is occupied by a single breeding population, the effect may be more focused.

For example, habitat loss in South America will likely have range-wide effects on bobolinks, while habitat loss in the Caribbean may only influence a portion of the breeding populations of ovenbirds.

Backpacks for birds

We know that the breeding and wintering populations of most species mix to some extent, but…

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Should I stay or go? Birds migrate to save energy: study

(Mariëtte Le Roux; Nature Ecology & Evolution; 7 May 2018)

 

Why have some birds opted for a taxing life of constant migration—seeking out temperate climes to feed as winter arrives, only to return months later to breed?

Seemingly paradoxically, the behaviour is driven by a quest for energy efficiency, a study said Monday.

Migrating birds, researchers found, gain more energy from whatever is on the destination menu than they expend getting there and back, or could find without making the trek.

Why don’t they just stay in the warm place? Because there is too much competition for food with other species, said the study published in the journal Nature Ecology & Evolution.

Instead, they return to their cold, northern hemisphere home where they don’t have to fight others for the food there is.

The work “provides strong support for the hypothesis that birds distribute themselves in an optimal way in terms of energy,” study co-author Marius Somveille of the University of Oxford’s zoology department told AFP.

While it was known that birds migrate in search of food, it has remained a puzzle why they have adopted this exacting lifestyle.

The new study explains the behaviour of not only migratory birds, but also that of sedentary or “resident” ones, its authors said.

These too weighed the available food against greener pastures, and came to a different conclusion.

Most resident birds are found in the tropics, where food is easier to get by.

Fly or die

The study used a theoretical model to examine why birds migrate—about 15 percent of the total—while others do not.

It started with a model world with similar climatic differences between regions than our real one.

The researchers then added virtual birds, and the estimated amount of “energy”, or food, available in different regions.

Given these inputs, the model birds dispersed very similarly to what happened in real life.

The birds started off in the food-rich tropics, but growing competition forced some to start moving further afield.

“In our increasingly crowded virtual world, species progressively started exploiting more extreme pockets of seasonally available energy supply, often migrating longer distances,” the team wrote.

The model adds to our understanding of how Earth’s plants and animals came to be distributed as they are, the researchers added.

It could also be useful in predicting the future movements of other animals—to determine how they might migrate in response to global warming, for example.

Penguin forensics: Tracking the winter whereabouts of penguins by analyzing tail feathers

Penguin forensics
( Louisiana State University, Physorg 8 >August 2017; Photo M. Polito)

While a postdoctoral researcher at Woods Hole Oceanographic Institution, Polito and his colleagues conducted high-resolution forensic analyses of the chemical composition of the feathers using a technique called compound-specific stable isotope analysis of amino acids.

The scientists were able to identify the unique chemical signatures of penguin’s wintering areas in the ocean based on the coordinates from the tags and the data from the feather analyses. From this understanding, they were able to deduce where the other penguins that had not been tagged went over the winter based solely on the analyses of their tail feathers.

“This novel approach could be applied to different tissues from a wide variety of marine animals that migrate over long distances including seabirds, sea turtles, seals and whales,” Polito said. “Using stable isotope forensics to increase the size and scope of animal tracking studies will help us to better understand these charismatic species and ultimately aid in their conservation.”

Knowing where and how Antarctic penguins, and other seabirds and marine predators, migrate is critical for conservation efforts. Although electronic tracking devices have helped scientists track marine animals’ migration patterns, the devices can be expensive, invasive for the animal and challenging to retrieve. Scientists have discovered a new and potentially better way to track where penguins go over the winter using forensics.

“You can say, penguins ‘are where they eat,’ because a geochemical signature of their wintering area is imprinted into their feathers,” said LSU Department of Oceanography & Coastal Sciences Assistant Professor Michael Polito, the lead author of this study that will be published Aug. 9 in Biology Letters.

Chinstrap and Adélie penguins are part of the family of “brush-tailed” penguins named after their approximately 15-inch long, stiff tail feathers. These birds shed all of their feathers after each breeding season and before they migrate to their oceanic wintering grounds. However, their long tail feathers continue to grow well into the winter when penguins are at sea.

Polito and his collaborators from NOAA Southwest Fisheries Science Center, Oxford University and the Instituto Antártico Argentino attached tags to 52 adult Chinstrap and Adélie penguins at their breeding colonies and retrieved the tags the following breeding season to determine where the birds went over the winter. When they retrieved these tags, the researchers also took a tail feather grown over the winter from each tracked penguin and from 60 other penguins that had not been tagged.

How migrating birds ‘run a marathon,’ burning muscles and organs in long flights

How migrating birds 'run a marathon,' burning muscles and organs in long flights

(Physorg, University of Massachusetts Amherst 12 July 2017)

Migrating birds complete long non-stop flights of many hours for songbirds and days for some shorebirds to reach breeding or wintering grounds. During such flights a bird’s metabolic rate is very high, fueled by stored fat, but also by burning the protein in musc

les and organs in a process that is not well understood, says eco-physiologist Alexander Gerson at the University of Massachusetts Amherst.

Now he has received a three-year, $756,000 National Science Foundation grant to thoroughly investigate the consequences and mechanisms of this phenomenon, which sometimes leads to dramatic reductions in migrating birds’ muscle mass and organs but may not result in significant loss of function.

As he explains, “There is evidence that some birds see a 20 percent reduction in muscle mass and up to 50 percent mass losses in the liver, intestine, kidneys and other organs except the brain and lungs. In one of the longest flights documented in this hemisphere, the blackpoll warbler during migration flies 22 hours over water, where they absolutely cannot stop. When you run a marathon like that, you either run out of fuel or water, but these birds can produce both by metabolizing their muscle and organ tissues.”

He adds, “We’re interested in what happens during flight, where the energy comes from, and how they maintain water balance. Water is produced from metabolism, and breaking down protein yields the most. But what happens when you lose 20 percent of your pectoralis muscles? Do you lose function or just size? These are a few of our questions.”

Gerson says this study will use two ultra-specialized tools not available to most researchers: a field-portable quantitative magnetic resonance imaging (QMRI) machine, and a wind tunnel specifically designed to study long duration flight in birds, one of just three in world, located at the Advanced Facility for Avian Research at Western University in London, Ontario.

The experimental series will look at body fat, lean mass and water content in one larger species, Swainson’s thrush, and one smaller, the yellow-rumped warbler, in the field and in wild birds flying in the climate-controlled wind tunnel. There, researchers can manipulate such factors as humidity and temperature to study the amount of water lost to respiration. This is relevant to climate change, Gerson notes, because flying in warmer air means more protein and water loss.

His research team will also look at water-loss rates in non-flight conditions, at rest, and look for differences among migrants and non-migrants. Further, Gerson and colleagues will conduct metabolic phenotyping and use transcriptomics to explore molecular mechanisms of protein breakdown and regeneration with UMass Amherst molecular biologists Courtney Babbitt and Larry Schwartz.

Gerson intends to engage many undergraduate and graduate students from diverse backgrounds in the research, training them in a range of cutting-edge techniques applicable to many science, technology, engineering and mathematics (STEM) fields. They will in turn develop and implement science communication and outreach programs for middle school students in a local low-income school district yet to be determined.

At the end of three years, Gerson says, “We hope to better understand the influence of climate on flight metabolism and have a better understanding of functional consequences of protein breakdown, which has the potential to be exciting because they burn a lot of muscles and don’t seem to show any dramatic functional loss. It may shed some really new light on questions that have been around for quite some time.”

Birds’ migration genes are conditioned by geography

(Lund University 6 July 2017; Photo Max Lundberg)

The genetic make-up of a willow warbler determines where it will migrate when winter comes. Studies of willow warblers in Sweden, Finland and the Baltic States show that “migration genes” differ — depending on where the birds breed in the summer. The willow warblers that breed in southern Sweden migrate to West Africa, while those in northern Sweden, Finland and the Baltic States fly to southern or eastern Africa.

According to a new study led by biologists at Lund University, the key to the willow warblers’ differing migration patterns probably lies in their genes.

The researchers studied the entire genetic make-up of willow warblers that breed in southern and northern Sweden, Finland and the Baltic States. The comparison shows that the genomes are almost completely identical, but there are significant differences between the birds that breed in southern Sweden and those that breed in the northern parts of the country and east of the Baltic.

The differences are restricted to two regions in the genome, where the comparison shows extensive differences in over 200 genes.

“Of these 200 or so genes, there are several that can be considered to be important for migration-related physiological adaptations and others that, according to our present knowledge, have a poorly characterized or unknown function,” says Max Lundberg, researcher at Lund University.

According to him and his colleagues, the genetic differences are probably decisive in determining that willow warblers in southern Sweden migrate to West Africa, whereas the more northerly willow warblers head for the south-east of Africa.

Researchers have previously known that the migration behaviour of many birds is strongly determined by genetics. Inherited information in the genes determines the direction of migration and a schedule that contains information about when and how far the birds are to migrate. The migration over thousands of kilometres also requires inherited physiological adaptations, for example to store and use fat and energy as efficiently as possible. Up to now, however, very little has been known about the specific changes in the genetic make-up that underlie where birds, in this case willow warblers, migrate.

“Our results represent an important addition to the understanding of migration-related genetics and will guide future studies in the subject,” says Staffan Bensch, a professor at Lund University.

 

Birds’ feathers reveal their winter diet

(AOS 21 June 2017; Photo RM Jensen)
Influences outside the breeding season can matter a lot for the population health of migratory birds, but it’s tough to track what happens once species scatter across South America for the winter months. A study from The Condor: Ornithological Applications tries a new approach for determining what declining migratory grassland birds called Bobolinks eat after they head south for the winter—analyzing the carbon compounds in their plumage, which are determined by the types of plants the birds consume while growing their feathers during their winter molt.

Thanks to a quirk of photosynthesis, rice contains a different ratio of carbon isotopes than most of the native grasses in South America where Bobolinks winter. Rosalind Renfrew of the Vermont Center for Ecostudies and her colleagues took advantage of this, collecting feather samples from wintering Bobolinks in a rice-producing region and a grassland region and from breeding Bobolinks in North America. When they analyzed the feathers’ isotopes ratios, the results from South America confirmed that isotopes in Bobolinks’ feathers reflected the differences in their diets between regions with and without rice production. The samples taken in North America showed that the winter diet of most individuals was weighted more toward non-rice material, but that rice consumption was highest late in the winter, when rice is nearing harvest and the birds are preparing for their northbound migration.

Rice could be beneficial by providing the birds with needed calories as they prepare for their journey north, but it could also increase Bobolinks’ exposure to pesticides and threats from farmers who see them as pests. According to Renfrew and her colleagues, maintaining native grasslands, encouraging integrated pest management programs to reduce toxic pesticide applications, and compensating farmers for crops lost to feeding birds all would be helpful.

“The time spent coordinating the field work for this study may well have been greater than the time spent collecting the data,” says Renfrew. “It was truly a team effort, and the assistance we received from our partners was absolutely essential, especially in South America. Aves Argentinas and the Museo de Historia Natural de Noel Kempff Mercado provided priceless logistical support, and this study could not have happened without them. Some of the same partners have provided input on a Bobolink Conservation Plan that lays out actions to address threats to grassland birds in North and South America, based on results from this and other studies.”

“As Bobolink populations continue to decline, Renfrew and her colleagues use state-of-the-art isotope analysis techniques to assess the Bobolink’s diet on its South American wintering grounds,” according to John McCracken of Bird Studies Canada, an expert on grassland bird conservation who was not involved with the study. “The authors conclude that rice may have negative effects on Bobolinks, owing to its relatively low nutritional quality and from exposure to insecticides.

Fuel loads acquired at a stopover site influence the pace of intercontinental migration in a boreal songbird

(Camila Gómez, Nicholas J. Bayly, D. Ryan Norris, Stuart A. Mackenzie, Kenneth V. Rosenberg, Philip D. Taylor, Keith A. Hobson & Carlos Daniel Cadena 13 June 2017)

 

Although migration is an adaptive behaviour in a wide range of animals1,2,3, it is also thought to impose significant costs on individuals4. Studies on various migratory birds5,6,7, mammals8 and fish9 provide evidence that mortality can be higher during migration than during stationary periods of the annual cycle. In addition, work on birds10, 11 and insects12 indicates that migrating individuals often undergo significant metabolic and behavioural adjustments to fulfil the high energetic demands of migration. Time spent and energy used during migration can also determine subsequent breeding success10, 12,13,14,15, emphasizing the high costs that individuals pay when migrating. Because migration is costly, migratory organisms are expected to maximize their fitness behaviourally via minimizing either the time spent, energy consumed, or the risks incurred during migratory journeys16, 17.

In terms of time, the highest cost of migration is generally thought to be experienced during stopovers rather than during periods of flight18, 19, and birds rely on the time spent at stopover sites to rest and refuel for the next leg of their journeys20. Optimal migration theory provides a framework to study stopover behaviour and its consequences by testing whether migrants are time- or energy-minimizers using data on fuelling rate, stopover duration, fuel loads and potential flight ranges17. Individuals attempting to minimize the overall time spent on migration are expected to maximize the amount of fuel they can acquire at each stopover in the shortest time possible. A key consequence of this strategy is that it maximizes the distance that can be flown between stopovers18, 21. Consequently, the fuel loads (amount of fat carried) of a time-minimizer should be tightly linked to local conditions at stopover sites as well as to the conditions expected ahead because these conditions influence fuelling rates18, 21. Furthermore, stopover durations in time-minimizers are expected to have been shaped by or to respond directly to experienced fuelling conditions17, 18. Larger departure fuel loads should allow for longer flights and a faster overall pace of migration because individuals acquiring sufficient fuel in the shortest time possible will need to make fewer stopovers and be able to take more direct routes to their destination, including being able to fly over physical barriers or large areas of unsuitable habitat such as deserts or oceans rather than circumventing these areas22.

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