Wood thrushes are sensitive to breeding forest fragmentation but the loss and/or degradation of habitat in the winter range in Central America is the cause of their population decline.
November 29, 2017 Tulane University
A decline in the number of wood thrushes is probably due to deforestation in Central America, a new study has concluded.
….Wood thrushes breed in the forests of the eastern United States and migrate in the winter to the forests of Central America. Although they remain a relatively common bird, the species has been declining rapidly since the early 1970’s and several researchers have suggested that fragmentation of forests in breeding grounds are playing a major role….
Caz M. Taylor. The shape of density dependence in fragmented landscapes explains an inverse buffer effect in a migratory songbird. Scientific Reports, 2017; 7 (1) DOI: 10.1038/s41598-017-15180-4
A major study looking at changes in where UK birds have been found over the past 40 years has validated the latest climate change models being used to forecast impacts on birds and other animals….
“We are now a lot more confident in what models should be used, and when, to provide a more accurate picture of biodiversity loss from climate change. While this study was on UK birds, we expect these results will also hold for many other birds and animals…
Damien A. Fordham, Cleo Bertelsmeier, Barry W. Brook, Regan Early, Dora Neto, Stuart C. Brown, Sébastien Ollier, Miguel B. Araújo. How complex should models be? Comparing correlative and mechanistic range dynamics models. Global Change Biology, 2017; DOI: 10.1111/gcb.13935
Passenger pigeons were so plentiful and so mobile that beneficial genetic mutations spread and detrimental ones disappeared very quickly throughout their population. This caused a loss in overall genetic diversity, which meant less raw material for adapting to human-induced change
North America was once a utopia for passenger pigeons. When European colonizers first arrived, as many as 5 billion of the gray-backed, copper-breasted and iridescent beauties roamed the continent, possibly the most abundant bird to have ever graced the planet. When they migrated, they swept across the entire sky, obscuring daylight for hours or even days at a time, the seeming embodiment of infinity. Then, in just a few decades, the inconceivable happened: Commercialized and excessively hunted, the birds vanished.
A paper published in Science on Thursday sheds new light on why the creatures went extinct so swiftly and thoroughly. Analyzing the DNA of preserved birds, the researchers found evidence that natural selection was extremely efficient in passenger pigeons.
This might have made the pigeons particularly well-suited for living in dense flocks, but unable to cope with living in sparse groups once their numbers started to plummet, the authors suggest.
Biologists generally assume that a large population corresponds to high genetic diversity, which acts as a buffer to extinction, said Susanne Fritz, an evolution expert at the Senckenberg Biodiversity and Climate Research Center in Frankfurt, Germany, who was not involved in the research.
But passenger pigeons were so plentiful and so mobile that beneficial genetic mutations spread and detrimental ones disappeared very quickly throughout their population. This caused a loss in overall genetic diversity, which meant less raw material for adapting to human-induced change.
It’s “totally the opposite of what you would expect,” Dr. Fritz said….
Many birds are adjusting their life styles to breed 5-12 days earlier to avoid warming that has occurred since the early 1900s, an ongoing survey of California birds and comparison with century-old [Grinnell Survey] data shows. This strategy, combined with the trend of other birds to move northward in range or upward in elevation, allows adaptation to climate change, though eventually the cool window for breeding may become too short for some species…
…Early spring arrivals have long been noted by the public and reported by scientists, but the assumption has been that the birds are tracking resources, primarily food: with warming temperatures, plants produce leaves and seeds earlier, and insects emerge earlier.The new study spotlights another major reason: By nesting a week earlier, birds produce eggs and young at a temperature about 1 degree Celsius (1.8 degrees Fahrenheit) lower than if they nested at the normal time in the same place. This exactly counterbalances the approximately 1 degree Celsius increase in global temperatures over the past century.
“By nesting a week or 10 days earlier, birds are avoiding some of the negative effects of climate warming,” Beissinger said…..”…we don’t know yet whether staying in place and shifting schedules earlier is a permanent solution, or only provides temporary relief from the 2 degree Celsius (3.5 degree Fahrenheit) rise in temperatures forecast to occur..”
Jacob B. Socolar, Peter N. Epanchin, Steven R. Beissinger, Morgan W. Tingley. Phenological shifts conserve thermal niches in North American birds and reshape expectations for climate-driven range shifts. Proceedings of the National Academy of Sciences, 2017; 201705897 DOI: 10.1073/pnas.1705897114
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. New research shows that migratory birds prefer to rest and refuel in fields with cover crops.
Cassandra A. Wilcoxen, Jeffery W. Walk, Michael P. Ward. Use of cover crop fields by migratory and resident birds. Agriculture, Ecosystems & Environment, 2018; 252: 42 DOI: 10.1016/j.agee.2017.09.039
Birds in larger mature forest areas, on the other hand, were better able to withstand the dry conditions since these areas offer more shade and resources. Forest cover helps maintain climatic conditions, including moist soil, which is an important factor for wood thrush food availability
According to a new study by biologists at Virginia Tech and the Smithsonian Migratory Bird Center, the offspring of a certain songbird, the wood thrush, are more likely to survive drought in larger forest plots that offer plenty of shade and resources…
Wood thrush are common to the United States, but populations have declined by more than 60 percent since the 1960s. In addition, many species of songbirds, such as blue jays, robins, and cardinals, as well as wood thrush, face the highest risk of dying within the first five days of leaving their nests.
…Birds in larger mature forest areas, on the other hand, were better able to withstand the dry conditions since these areas offer more shade and resources. Forest cover helps maintain climatic conditions, including moist soil, which is an important factor for wood thrush food availability. These conditions ultimately make areas more resilient to drought.
“The research highlights the role that forest cover can play in buffering animals from stressful environmental conditions — in this case, promoting survival of young birds during drought conditions,” said Amanda Rodewald, professor and director of conservation science at the Cornell Lab of Ornithology, who was not involved with the research. “This finding is yet another that underscores the importance of maintaining forested landscape mosaics in strategies to conserve biodiversity.”….
For ideal survival, then, Vernasco says fledglings do well with a “mosaic” of habitats made up of forests that differ in age and thus vegetation structure.
Ben J. Vernasco, T. Scott Sillett, Peter P. Marra, T. Brandt Ryder. Environmental predictors of nestling condition, postfledging movement, and postfledging survival in a migratory songbird, the Wood Thrush (Hylocichla mustelina). The Auk, 2017; 135 (1): 15 DOI: 10.1642/AUK-17-105.1
“Even birds with relatively limited exposure to oil from the Deepwater Horizon spill sustained damage to circulating red blood cells and had evidence of anemia, which can adversely affect reproduction and reduce survival.”
Many birds and other wildlife die following an oil spill, but there are also other potential long-terms effects of oil exposure on animals.… study that examined blood samples from birds present in the Gulf of Mexico in 2010 and 2011 following the Deepwater Horizon oil spill, even birds with small amounts of oil present on their feathers experienced problems related to their red blood cells.
The findings show that even modest oil exposure can cause problems for individual birds and bird populations.
Jesse A. Fallon, Eric P. Smith, Nina Schoch, James D. Paruk, Evan A. Adams, David C. Evers, Patrick G.R. Jodice, Christopher Perkins, Shiloh Schulte, William A. Hopkins. Hematological indices of injury to lightly oiled birds from the deepwater horizon oil spill. Environmental Toxicology and Chemistry, 2017; DOI: 10.1002/etc.3983
House sparrows are well-adapted to living in urban areas, so it is surprising their numbers have fallen significantly over the past decades. An investigation into this worrying trend finds that sparrows living in urban areas are adversely affected by pollution and poor nutrition. The study also finds the birds suffer more during the breeding season, when resources are needed to produce healthy eggs….
…if our cities are unhealthy for birds, which is what our study is suggesting, then as their neighbors we should be concerned because we are exposed to the same environmental stressors as house sparrows.”
…”We took a small blood sample from each bird, according to its weight and physical condition, and released them unharmed,” she explains. The samples were analyzed for signs of oxidative stress, which can be used to measure how much an environmental stressor, such as pollution, is weakening the bird’s natural defenses….
…”We need to work hard to improve the quality of the urban environment, for example, air quality and the design of green areas. Even the leftovers that we throw in the bin at the park should encourage us to reflect on ourselves: more nuts and fruit and fewer chips and cookies would be better for humans as well as for birds,” Herrera-Dueñas advises.
Amparo Herrera-Dueñas, Javier Pineda-Pampliega, María T. Antonio-García, José I. Aguirre. The Influence of Urban Environments on Oxidative Stress Balance: A Case Study on the House Sparrow in the Iberian Peninsula. Frontiers in Ecology and Evolution, 2017; 5 DOI: 10.3389/fevo.2017.00106
…researchers from the universities of Oxford, Barcelona and Pisa have shown in a new experiment that olfaction — or sense of smell — is almost certainly a key factor in long-distance oceanic navigation….The research is published in the journal Scientific Reports.
Study leader Oliver Padget, a doctoral candidate in Oxford University’s Department of Zoology, said: ‘Navigation over the ocean is probably the extreme challenge for birds, given the long distances covered, the changing environment, and the lack of stable landmarks……removing a bird’s sense of smell does not appear to impair either its motivation to return home or its ability to forage effectively.
However, although the anosmic birds made successful trips to the Catalan coast and other distant foraging grounds, they showed significantly different orientation behaviour from the controls during the at-sea stage of their return journeys. Instead of being well-oriented towards home when they were out of sight of land, they embarked on curiously straight but poorly oriented flights across the ocean, as if following a compass bearing away from the foraging grounds without being able to update their position.
Their orientation then improved when approaching land, suggesting that birds must consult an olfactory map when out of sight of land but are subsequently able to find home using familiar landscape features….’To the best of our knowledge, this is the first study that follows free-ranging foraging trips in sensorily manipulated birds. ..
Cory’s Shearwater, Calonectris borealis, in flight.
O. Padget, G. Dell’Ariccia, A. Gagliardo, J. González-Solís, T. Guilford. Anosmia impairs homing orientation but not foraging behaviour in free-ranging shearwaters. Scientific Reports, 2017; 7 (1) DOI: 10.1038/s41598-017-09738-5
Data-Driven Water Management
It takes science and partnership to figure out the best way to manage limited supplies of fresh water in California’s Central Valley for humans and wildlife. A recent paper co-authored by Point Blue scientists shows a worrisome mismatch in flooded habitat and shorebird spring migration. This has important implications for how government agencies and NGO partners manage water on refuges and in agricultural fields.
Coming soon, thanks to further funding from NASA, we’ll be analyzing more satellite data with our newly hired Quantitative Ecologist, Dr. Erin Conlisk. Our goal is to figure out when and where to put water to achieve the greatest benefit for wetland-dependent wildlife while also recharging groundwater and providing recreational opportunities. Stay tuned for results!
Meadows & Climate Change
Our science is helping to determine if restored Sierra meadows can store enough carbon to help slow climate change while also benefitting birds and other wildlife. The outcome could help direct more funds from California’s cap-and-trade program toward meadow restoration, and it looks promising! Read this wonderful Audubon article highlighting Point Blue’s collaborative work.
Climate Science Education: New Tools!
Today’s young people need climate science knowledge to help build a better future for themselves and the next generations. That’s why we’ve created and disseminated a climate-smart riparian restoration curriculum, which you can find here. We’ve also added a number of our science resources to the Bay Area Climate Literacy and Impact Collaborative database for Bay Area educators here. We invite you to use these resources and share them with others. Together we are educating and inspiring the next wave of climate-smart conservation leaders!