Via Eurekalert
Smithsonian scientists find declining rainfall is a major influence for migrating birds
Instinct and the annual increase of daylight hours have long been thought to be the triggers for birds to begin their spring migration. Scientists at the Smithsonian Conservation Biology Institute, however, have found that that may not be the case. Researchers have focused on how warming trends in temperate breeding areas disrupt the sensitive ecology of migratory birds. This new research shows that changes in rainfall on the tropical wintering grounds could be equally disruptive. The team’s findings are published in scientific journal Proceedings of the Royal Society B, March 30.
Many of the bird species that breed in the temperate forests, marshes and backyards of North America spend the winter months in the tropics of the Caribbean, and Central and South America. Insects are the primary food for many birds during the winter, and rainfall largely determines the amount of insects available. Climactic warming, however, is causing declining and more variable rainfall cycles in many areas, affecting the availability of insects and delaying when birds leave for their northern breeding grounds. To examine this, the Smithsonian scientists focused on American redstarts (Setophaga ruticilla), a member of the warbler family, at a non-breeding site in Jamaica where they conduct long-term studies.
“American redstarts were a perfect species for this study since they defend exclusive territories throughout the non-breeding period until they depart for spring migration and most return back to the same territory the following year,” said Pete Marra, research ecologist at the Smithsonian Conservation Biology Institute’s Migratory Bird Center. “These behaviors made it relatively easy to keep track of individual birds over multiple years and document changing spring departures. Each individual was fitted with a unique combination of colored leg bands.”
Precipitation in Jamaica is highly seasonal, with consistent rainfall from September to November and a pronounced dry season from January to March. The scientists observed the redstarts in their non-breeding territories for five years during the dry season. They paid special attention to the annual variation in dry season rainfall. The correlation between the amount of insects in a bird’s territory and the timing of its departure suggested to the team that annual variation in food availability was an important determining factor in the timing of spring migration. Had the redstarts relied on internal cues alone to schedule their spring departure, they would have all left their winter territories at the same time each year.
“Our results support the idea that environmental conditions on tropical non-breeding areas can influence the departure time for spring migration,” said Colin Studds, a postdoctoral fellow at the Smithsonian Conservation Biology Institute’s Migratory Bird Center and lead author of the study. “We found that the same birds changed their spring departure from one year to the next in relation to the amount of rainfall and food in March.”
During the past 16 years, the dry season in Jamaica has become both increasingly severe and unpredictable, leading to an 11 percent drop in total rainfall during the three-month annual drought. Making the future even more dire, climate models predict not only increased warming on temperate breeding areas but also continued drying in the Caribbean.
A critical question for the scientists is whether this variation in the onset of spring migration carries consequences for the birds. Delaying departure could be beneficial if food resources are low and the individual has not yet stored enough energy to migrate. However, delaying departure could affect arrival time to its breeding territory and result in less time to successfully reproduce. “Because American redstarts return to the same site to breed each year, arriving later may make it harder for them remain to remain in synch with their breeding cycle,” Studds said.
Bird specialists should deign to ask amateurs who are a well known resource to ornithology about the adaptability of birds. I grew up in Winnipeg, Manitoba and after an absence of 25 yrs returned one summer to see cardinals and blue jays that never were found in these parts when I was a boy. For some reason the range had shifted westward. Also, here in Ottawa, Ontario, a small flock of ducks winter over in a melted stretch of th Rideau R. where some warm outflow (from a hospital nearby?) Keeps it from freezing. These birds are more cunning, adaptable and individualistic than than your average biologist.
1. PhD’s are only available if the student can do ‘original research’
2. Student’s adviser needs more research funding
3. Original research is getting difficult to find
4. Politically based funding for ‘climate’ studies is the only relatively easy research funding
5. Student adviser and doctoral student try to think up a ‘catastrophic climate change’ angle in their specialist area of real-time underwater basket weaving
6. “Drought caused by catastrophic climate change !!” (doesn’t matter if there is or is not drought there’ll be a model somewhere that says there is)
This is the generation cycle of modern PhD research and as the AGW hypothesis is unfalsifiable and no PhD adjudicators dare appear to disagree with it – thesis defense is so much simpler.
1. Spring conditions do not effect insect emergence. That would be the first null hypothesis. They needed a model for that? Ah. Less expensive. And no one cares about the field studies done decades ago that essentially mapped out this insect behavior tied to spring conditions.
2. Insect emergence does not effect bird population. That would be the second null hypothesis. They needed a model for that? Ah. Less expensive. And no one cares about the field studies done years ago that essentially figured this relationship out.
Field research is so yesterday. And models are cheaper. Problem is, no one is running models under cold conditions. Does this mean that if we get colder, the birds will do just fine because the insects will emerge right on schedule? Everybody in Wallowa County understands: warm = insects, cold = insects gone.
Over here in the Old World, many European breeding warblers (and other birds)spend winter in the semi-arid Sahel zone of Africa located between the Sahara Desert and the rain forests to the south. The climate is dry All winter. The birds arrive in autumn after the end of the summer rains which, in good years, provide ample insects and other food for the next 6 months. Their over-winter survival and spring departure dates are thought to be linked closely with the highly variable rainfall amounts in the preceding summer. In severe and prolonged droughts in the 1970-80s some species populations were much reduced but others were little or not affected. Numbers of all gradually recovered with a return to more ‘normal’ rainfall patterns. In the sahel, there have been cycles of drought for the last 200 years.
Declines in many of our summer migrants that come north from West Africa to breed here are now considered to be caused by breeding habitats deterioration across Europe (a consequence of EU agricultural policies) combined with a rapid expansion in habitats degradation and destruction in West Africa. In that region, rapidly increasing human pressures and expansion are destroying large areas of Sahel vegetation cover ( by livestock overgrazing and for fuel) . This leads to a spread of ‘desertification’ at the northern edge of the Sahel, and further south (it is increasingly suspected) to reduced precipitation in summer. Rain forests are being felled on a large scale further south again.
In both continents the increasing environmental degradation would seem likely to have greater adverse ffects on our migrants than any caused by putative climate warming/changes. It would be interesting to have, for comparison, corresponding data for Jamaica and throughout the breeding and winter ranges of North American migrants.
The robust global hydrological response to global warming means that some areas will get heavier downpours and some areas of the planet will actually get drier. This is a complex response with many interacting pieces but the net effect globally however, of increased CO2, is for greater rock weathering as a result of changes in the global hydrological cycle, as fundamentally, that is the natural negative feedback response which removes CO2 from the troposphere and keeps CO2 within A RANGE. Obviously, with such a robust hydrological response, some species disruption can be expected. An excellent starting paper on this can be downloaded at:
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.140.7788&rep=rep1&type=pdf
Eduardo Ferreyra says:
April 1, 2011 at 7:21 pm
The problem is that swallows have been departing from Goya one two and three days earlier than before.
The problem is also that most of the SJC swallows no longer return to the mission. Some say development has reduced the available insects near the mission, and this change in available prey has caused the birds to nest elsewhere in the area.
I couldn’t find a reference now, but I think I read that the nests at the mission were relocated. I know that Barn and Cliff swallow nests were destroyed at Mission San Luis Obispo de Tolosa, further north, when a few people complained about bird poop on their fabulous garments. Where once there were clouds of swallows over the missions, now there are none.
As others have said, the dangers to songbirds are primarily man-made obstructions, habitat destruction, and especially, the free-roaming house cat, but probably not the weather.
R. Gates says:
April 2, 2011 at 10:40 am
The robust global hydrological response to global warming means that some areas will get heavier downpours and some areas of the planet will actually get drier. This is a complex response with many interacting pieces but the net effect globally however, of increased CO2, is for greater rock weathering as a result of changes in the global hydrological cycle, as fundamentally, that is the natural negative feedback response which removes CO2 from the troposphere and keeps CO2 within A RANGE. Obviously, with such a robust hydrological response, some species disruption can be expected. An excellent starting paper on this can be downloaded at:
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.140.7788&rep=rep1&type=pdf
========================
Read it.
Hated it.
The thing that is “robust”(and the only real hot air to speak of) is the circular reasoning that continues to propagate in this “research”, as well as the robustness of your own use of the word “robust.”
As Pamela Gray mentioned earlier with the only assumptions that only warming will occur….what happens if they are wrong and it turns colder?
And if it does, that adversely affect the little redstart fella more?
Until they stop with the assumptions based on “climate models predict” and “a warming world”…they, as researchers funded by the taxpayer….are just as guilty of circular reasoning as non-researchers like yourself, any old day.
Chris
Norfolk, VA, USA
R. Gates says:
April 2, 2011 at 10:40 am
The robust global hydrological response to global warming means that some areas will get heavier downpours and some areas of the planet will actually get drier.
============================
He [the lil’ redstart in the picture….lets call him Ricky the Redstart] can adapt to a changing climate….whatever nature brings him.
Unfortunately, it seems, homo sapiens can’t.
Too stupid.
They are too busy barking up the wrong tree chasing after the CO2 molecule while rest of the biosphere passes them them by, evolving as they go [including generations of adaptable redstarts].
Chris
Norfolk, VA, USA
Interesting study. It is only when the author attempts the splice with “Global Warming” that the rot sets in.
I think such splices should be written in a different color of ink, and that there should be a computer program that automatically deletes that section of papers and articals. What we would be left with is the interesting dicoveries.
Some birds seem to arrive in a manner you can just about set your watch to. The swallows returning to Capistrano (spelling?) and the buzzards returning to Hinkley(spelling?)
However warblers are more variable. There is a neat thing that sometimes happens that birders call a “warbler wave.”
A “warbler wave” occurs when the warblers are held up by persistant northwest winds and a late season cold snap. If some sort of blocking pattern keeps the cold weather in place, a sort of traffic jam of warblers develops down in the buggy marshes of Virginia and North Carolina, as the bird await a change in the wind.
Then, when the cold spell breaks and the wind shifts to the southwest, and at long last balmy breezes flow over New England, unbelivable amounts of warblers ride that wind. It is not only the species that live in New England, but also species that live further north. And the birders have a blast, stumbling through thickets with binoculars pressed to their noses, looking left and looking right and seeing a multitude of species whichever way they look. And I myself have to admit it pretty cool to be working outside, and to have such a singing flitting by all day.
savethesharks says:
April 2, 2011 at 12:40 pm
R. Gates says:
April 2, 2011 at 10:40 am
The robust global hydrological response to global warming means that some areas will get heavier downpours and some areas of the planet will actually get drier. This is a complex response with many interacting pieces but the net effect globally however, of increased CO2, is for greater rock weathering as a result of changes in the global hydrological cycle, as fundamentally, that is the natural negative feedback response which removes CO2 from the troposphere and keeps CO2 within A RANGE. Obviously, with such a robust hydrological response, some species disruption can be expected. An excellent starting paper on this can be downloaded at:
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.140.7788&rep=rep1&type=pdf
========================
Read it.
Hated it.
_____
It is pretty technical. I suppose the science could be a bit beyond your technical background. Sorry…
Doesn’t seem to be a global thing then:
http://www.rspb.org.uk/news/276299-small-birds-bounce-back
R. Gates says:
April 2, 2011 at 2:42 pm
It’s pretty technical. I suppose the science could be a bit beyond your technical background. Sorry…
=====================
And beyond yours, too….that is most for sure.
Your appeal to authority fallacy aside, regardless, one does not need a “technical background”…to spot circular reasoning.
Such is obvious even to a 7th grader.
Chris
Norfolk, VA, USA