Tag Archives: foraging

Dramatisk försämring för stenskvättor – verkar inte hitta tillräckligt med insekter

Stenskvätta.JPG

(Erik Hansson, Natursidan 2017-11-10)

I jordbrukslandskapet utanför Uppsala har forskare följt stenskvättor i 25 år och de ser en dramatisk försämring. Troligen orsakad av att fåglarna inte hittar lika mycket insekter och andra småkryp som föda, enligt en ny studie från SLU som publicerats i tidskriften Ecology and Evolution.

De senaste 25 åren har exempelvis stenskvättans ungars vikt minskat med i snitt 2 gram från 19,5 gram till 17,5 gram. Dessutom överlever färre ungar (från i snitt en unge per bo till en unge i var femte bo) och antalet häckande par har minskat. Anledningen verkar inte vara att stenskvättan har problem med att anpassa sig till de allt tidigare vårarna (i snitt elva dagar tidigare nu jämfört med i början av 90-talet). Troligtvis är orsaken matbrist, menar SLU-forskarna som gjort en av få långsiktiga internationella studier av fåglar i jordbrukslandskapet.

– Det är en dramatisk förändring. Ungens vikt har stor betydelse för dess chans att överleva. När den hoppar ut ur boet behöver den reserver. Om ungen är hungrig och sitter och skriker blir den uppäten på en gång, säger Tomas Pärt, professor på institutionen för ekologi.

Forskarna fann inget samband mellan hur stenskvättornas förmåga att häcka i takt med när våren anländer och hur väl de lyckades med häckningen. De är glädjande nog ganska bra på att anpassa sig efter ett nytt, varmare klimat.

– Vår misstanke om att de negativa trenderna berodde på att stenskvättorna inte längre lyckades pricka in bästa tiden för att häcka blev alltså inte bekräftad. Våra resultat visar hur viktigt det är att inte dra slutsatsen att två trender som följer varandra hör ihop – alltså tidigare vår och försämrad fortplantning och överlevnad i det här fallet, säger Debora Arlt, forskare på institutionen för ekologi.

De låga vikterna på ungarna och andra tecken tyder på att de sämre häckningsframgångarna hänger ihop med tillgången på mat, som till stor del består av insekter och andra kryp. Kan det finnas ett samband med det som kallats en ”ekologisk katastrof” – studierna i Tyskland om att mängden insekter har minskat med över 75% på 27 år? Det finns ingen långsiktig data för liknande fenomen i Sverige.

– Miljön kan ha försämrats för både insekter och stenskvättor. Om vi visste vad det berodde på kanske vi också skulle kunna förklara varför många andra jordbruksfåglar minskar. Det ligger ju i allas intresse att hitta sätt att långsiktigt bruka landskapet så att det gynnar både biologisk mångfald och produktion, säger Debora Arlt.

Samtidigt vill forskarna inte skylla på jordbruket.

– Det är lätt att skälla på lantbrukarna men jordbruket påverkar den biologiska mångfalden positivt också. Utan dem skulle det överhuvudtaget inte finnas förutsättningar för stenskvättorna och andra arter som är knutna till det öppna jordbrukslandskapet, säger Tomas Pärt.

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Cover crops provide bed and breakfast layover for migrating birds

(University of Illinois, 30 Oct 2017;Photo Cassandra Wilcoxen)

After harvesting a corn or soybean crop, farmers may plant a cover crop for a variety of reasons — to reduce soil erosion and nutrient runoff, increase organic matter in the soil, and improve water quality. Now there’s another reason. University of Illinois research shows that migratory birds prefer to rest and refuel in fields with cover crops.

“Here in the Midwest, we’re in one of the major flyway zones for migratory birds, where there once was plenty of habitat for grassland birds to safely forage and rest during their migration. Now that agriculture is the dominant landscape, they’re finding it harder to get the resources they need on the way to their breeding grounds,” says Cassandra Wilcoxen, a graduate research assistant in the Department of Natural Resources and Environmental Sciences in the College of Agricultural, Consumer and Environmental Sciences at U of I.

“We think cover crops, such as cereal rye, likely provide migrating birds with more vegetation and a safe area to escape from the elements and from predators,” Wilcoxen says. “Cover crops also increase insect abundance, another food source for birds. The increased number of insects allows migrants to fuel up faster and move on to their breeding grounds.

“Grassland birds prefer large, open areas: the bigger, the better. Agricultural fields are huge, so the cover crops provide a large habitat where birds can rest, forage, and potentially even nest.”

Fields with cover crops are not going to replace natural habitats, but in early spring there can be miles of fields with little vegetation. The advent of cover crops provides a potentially important habitat for birds returning to the Midwest from areas as far south as Argentina. The large green fields are likely a beacon for migratory birds.

Over two planting seasons, Wilcoxen monitored birds in corn and soybean fields with and without cover crops. She observed 6,133 individual birds of 52 species, with 13 species accounting for 90 percent of all birds detected. The most common species were the red-winged blackbird, common grackle, and American robin.

“Fields with cover crops always had more birds, and corn fields with a cover crop were the overall winners,” Wilcoxen says. She thinks corn plus a cover crop, especially cereal rye, was the favorite because there is more residue on the fields; the remaining corn stalks along with rye provide more cover for the birds.

What’s the downside? Wilcoxen says it’s all in the timing.

“The window of time to plant a cover crop in the fall is fairly short. Cover crops can be aerial seeded, drilled, or broadcast. But depending on how wet the fall is, there is only a short time when it can be planted. Drilling is the best method because you know you’re getting good seed-to-soil contact,” she says.

Another timing issue emerges in the spring: when to kill the cover crop.

Wilcoxen says it’s tricky. “Some grassland birds nest in the spring, so in order to give birds the time they need, farmers may need to hold off terminating their cover crop. Those are the sorts of recommendations that will require more research,” she says. “It’s true of any new farming practice. You have to play around with it to get it right.”

“In our experience, most farmers using cover crops have learned about the practice from their neighbors, and we are hoping this continues and cover crop use continues to grow,” Wilcoxen says.

Will what’s best for migratory birds motivate farmers to plant cover crops and terminate them a bit later to allow birds to use them for habitat? Wilcoxen is hopeful. She says one of the aspects of her work that she enjoys most is bringing together the agricultural community and the wildlife community to work together for long-term environmental health.

“Production agriculture has taken a lot of habitat from wildlife, but we need it to provide food for us and the world. But how do we mesh the two? Where are the opportunities? No-till is a great example. It helps slow soil erosion and it helps birds. Now cover crops are another overlapping win-win opportunity to benefit both agriculture and wildlife.”

New paper explores why Peru’s parrots eat clay

New paper explores why Peru’s parrots eat clay
(Jenna Marshall 4 August 2017; Photo Donald Brightsmith)

For more than 16 years, researchers and volunteers have been observing wildlife along the clay cliffs of Southeastern Peru’s Tambopata River. They’ve gathered data every day, logging more than 20,000 hours and building one of the most extensive datasets on tropical parrots in the world.

In a new paper published in Ibis, Elizabeth Hobson, a postdoctoral fellow with the Arizona State University-Santa Fe Institute Center for Biosocial Complex Systems, and Donald J. Brightsmith, a professor in the Texas A&M University College of Veterinary Medicine & Biomedical Sciences (CVM) and director of the Tambopata Macaw Project, begin to analyze the data from this long-term study.

In particular, the team explores the potential drivers behind geophagy—or intentional soil consumption—they’ve regularly observed in 14 different parrot species there.

This region of the Tambopata River in Southeast Peru is an ideal spot to study the nearly two-dozen parrot species that live nearby in the Amazon rainforest. In the thick foliage of the jungle, the birds are difficult to see, but when they emerge to gather up beakfuls of the sodium-rich clay soil, “it’s a crazy, screaming kaleidoscope of color,” Hobson said.

“They’re all quiet when they take flight, but in a few seconds, they all begin to scream, and some drop bits of the clay from their mouths,” said Brightsmith, who has led the Tambopata Macaw Project since 1999. “It’s an incredible experience.”

But geophagy is a somewhat confounding behavior—clay soil is basically inert.

“It doesn’t have proteins, carbohydrates, or really anything that you’d need,” Brightsmith said. “If we can understand why it’s so important to these parrots, we can learn more about the ecosystem and how it affects the other insects, birds, and mammals who also eat this soil.”

Geophagy occurs around the world and in many types of animals, and scientists have proposed many explanations for the behavior. In their paper, Hobson and Brightsmith explore the two leading theories for these Amazonian parrots—that clay soils help protect the birds from food toxins when ideal food sources are scarce and that clay soils provide necessary minerals not available in the parrots’ regular diet.

Like previous studies, their analysis suggests that toxin-protection is not a driver. But parrot geophagy there is highly correlated with breeding season, suggesting the increased nutritional demands are likely behind the soil consumption. This study also joins a large body of research suggesting that hunger for sodium, specifically, is that driver.

“There’s lots of evidence that’s pointing in that direction,” Hobson said. “Sodium in the rainforest is really rare, and the place on these clay licks most preferred by the birds also has the highest sodium content.”

Understanding how nutritional needs are—and are not—being met during breeding season becomes even more important in light of climate change, according to Brightsmith. Some of the larger macaws are already breeding right before a seasonal crash in the food supply, requiring parents take their fledgling young on long flights to find food.

“If climate change starts messing with the macaw’s food supply, it could disrupt their ability to breed,” he said.

Grown-up gannets find favorite fishing grounds

(University of Exeter, Science Daily  27 July 2017)

Like humans, some birds can spend years learning and exploring before developing more settled habits.

A study of northern gannets has shown adults return to the same patch of sea over and over again to find food.

But younger gannets search far and wide and tend not to return to the same places — even if they find good hunting grounds, University of Exeter researchers found.

The study also compared successful breeding adults with those which failed to breed, and found successful breeders stuck to their feeding grounds more reliably.

“It’s common for birds like gannets to return to the same foraging grounds year after year,” said Dr Stephen Votier, of the Environment and Sustainability Institute on Exeter’s Penryn Campus in Cornwall.

“They disperse widely at sea, and the fact that they return to specific areas is presumably linked to finding good foraging conditions.

“However, gannets don’t breed until they’re four or five years old, and our research shows that this tendency to return to favoured foraging grounds is lacking in birds younger than this.

“This finding suggests that such behaviours are probably learned, and that gannets use their long period of immaturity finding good sites and remembering where they are.

“However, foraging sites in adults are not absolute — when experienced birds had more time on their hands after a failed breeding attempt, some became more exploratory. This suggests that refinement occurs throughout an animal’s lifetime.”

The research team studied gannets on the Welsh island of Grassholm, supported by the RSPB, and used precision global positioning system (GPS) loggers to find out whether individual birds returned to the same foraging grounds time after time.

Successful breeders showed strong attachment to certain areas and took similar routes when travelling to and from them.

Immature birds (aged two or three years) were much more varied both in foraging sites and routes taken.

The results support the “exploration-refinement foraging hypothesis” — that birds explore and slowly improve their foraging with age and experience.

Mystery of birds’ movements at sea solved

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RSPB 7 July 2017; Photo Chris Gomersall)

  • New research reveals where British and Irish seabirds go when they’re not on land.
  • The five year project GPS-tracked over 1,300 breeding seabirds and used computer models to predict where they go to find food.
  • Results reveal the majority of ‘hotspots’, where seabirds gather to feed, are concentrated in the coastal waters of Scotland, highlighting the need for robust conservation measures in this area.
  • The new maps will be used to protect threatened species by assessing potential impacts from offshore wind farms, pollution and other human activities on seabirds.  

New research has identified the most important areas for Britain and Ireland’s seabirds at sea, with the majority of ‘hotspots’ revealed in the coastal waters of Scotland.

Experts used GPS-tracking (1) and computer models on an unprecedented scale to map where breeding seabirds go when they leave land to feed, providing a unique insight into the lives of these enigmatic birds.

The study (2), headed by the RSPB in partnership with over a dozen scientists from leading research institutes (3), used five years of tracking data to estimate the areas used by four species: kittiwakes, shags, razorbills and guillemots.

This comes as the Scottish Government considers the creation of Special Protection Areas at sea to safeguard key seabird feeding areas, as well as planning future management of marine activities in Scottish waters outside of the EU and the Common Fisheries Policy.

During the project, lightweight GPS tags were fitted to over 1,300 adult birds from 29 different colonies. The tracking data was then used to create a computer model for each species, so that all of the important areas at sea could be predicted.

The results (see study maps attached) show the extent to which birds travel to find food. The majority of seabird ‘hotspots’, where different species gather to feed, are concentrated in the coastal waters of Scotland, highlighting the need for robust conservation measures to protect these areas. Overall, the four species use at least 1.5 million square km of sea around Britain and Ireland – an area three times the size of Spain.

This is a major step forward in our understanding of seabirds and is a powerful tool to help protect birds from potentially harmful activities at sea, including helping to make better decisions about where those activities can be undertaken to limit their impacts on seabirds.

Understanding more about our seabirds is vital because they are one of the most endangered groups of birds in the world. Over the last 30 years, kittiwake and shag numbers have declined by 72% and 68% respectively in Scotland. This is partly due to the impacts of climate change and fishing, and a new OSPAR report (4) underlines this trend, highlighting widespread seabird breeding failures in the North and Celtic Seas. Scotland is also home to internationally important populations of breeding seabirds so we have a global responsibility to safeguard them.

Dr Mark Bolton, RSPB Principle Conservation Scientist, said: “Our rich and diverse marine environment makes Britain and Ireland one of the greatest areas in the world for seabirds and this new research is further evidence of just how important our seas are for seabirds and their chicks during the breeding season. In order to strengthen this research and our predictions, there is an urgent need for a complete seabird census which will provide an accurate and up-to-date estimate of the size of our seabirds breeding colonies.”

Dr Ellie Owen, who led on the tracking work, said: “The sight and sound of hundreds of thousands of seabirds flocking to our shores is an amazing natural spectacle and something that we must help protect for future generations to enjoy. The methods used in this study could be applied to other seabird species, to show where they go at sea. This will be an invaluable tool in helping to protect seabirds, as it will greatly improve our ability to assess the likely impacts on breeding seabirds of offshore wind farms, oil spills and other potentially harmful activities in our increasingly industrialised seas.”

Dr Ewan Wakefield, lead author of the research, said: “Many seabirds are at the top of the marine food web. They feed on sandeels and other small fish but that prey is declining because of human pressures, including climate change. The result is that thousands of seabird chicks are dying each year because their parents can’t feed them. For the first time, this study provides us with a full map for each breeding colony of the feeding areas for some of our most important seabird species. That means we can now protect the places these birds catch the fish they need to feed their hungry chicks, securing the fate of future generations of these amazing creatures.”

Study reveals albatross interactions with fishing vessels in the southern ocean

Study reveals albatross interactions with fishing vessels in the southern ocean

An international research team involving the University has tracked the foraging patterns of albatrosses in the southern ocean and found that nearly 80 percent of them follow fishing boats, giving scientists new insight into the risk fishing vessels present to seabirds.

The extent to which albatrosses and fishing vessels overlap was revealed by newly developed XGPS radar loggers which were fitted to fifty-three incubating wandering albatrosses. The loggers are able to detect vessel radar by an omnidirectional micro strip antenna integrated with the bird’s geo-positional GPS device.

The data showed that during breeding, tagged Crozet wandering albatrosses patrolled over an area of more than 10 million square kilometres and as much as 79.5 percent of the birds equipped with the loggers detected vessels, at distances up to 2500 kilometres from the colony.

About 300,000 seabirds are killed annually in longline fishing, including albatrosses which are an endangered species and one of the most threatened families of birds internationally, with 15 of the 22 species in the group threatened with extinction.

The study took place in Possession Island in the Crozet Islands, in the southern Indian Ocean, from January to March in 2015 and 2016 and the research team included the University, the Centre d’Etudes Biologiques de Chize, France, Sextant Technology Ltd and the Museum of New Zealand Te Papa Tongarewa.

Henri Weimerskirch, from the Centre d’Etudes Biologiques de Chize who was the lead author, said: “This study is incredibly important, as albatrosses are well-known ship followers and their populations have been severely impacted through accidental mortality due to their encounters with fishing vessels.”

Liverpool Ecologist, Dr Samantha Patrick, said: “We know very little about fisheries in international waters due to both logistical and political constraints. However, wide ranging seabirds spend a large proportion of their time in these areas and so understanding their behaviour throughout their range is paramount.”

Susan Waugh, from Museum of New Zealand Te Papa Tongarewa, added: “This high rate of encounter shows that a far higher proportion of the population are exposed to fisheries mortality risk than previously supposed. The tagged birds showed varying patterns of encounter and attendance at vessels that challenge our perception of foraging behaviour of seabirds.”

“Being able to detect the presence of vessels throughout a species’ range is essential to derive comprehensive encounter, attendance and mortality rates and detect changes in foraging behaviour triggered by the presence of vessels.”

The paper `Use of radar detectors to track attendance of albatrosses at fishing vessels’  is published in the Conservation Biology online journal.

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.