Visitor Counter

hitwebcounter web counter
Visitors Since Blog Created in March 2010

Click Below to:

Add Blog to Favorites

Grizzly bears, black bears, wolves, coyotes, cougars/ mountain lions,bobcats, wolverines, lynx, foxes, fishers and martens are the suite of carnivores that originally inhabited North America after the Pleistocene extinctions. This site invites research, commentary, point/counterpoint on that suite of native animals (predator and prey) that inhabited The Americas circa 1500-at the initial point of European exploration and subsequent colonization. Landscape ecology, journal accounts of explorers and frontiersmen, genetic evaluations of museum animals, peer reviewed 20th and 21st century research on various aspects of our "Wild America" as well as subjective commentary from expert and layman alike. All of the above being revealed and discussed with the underlying goal of one day seeing our Continent rewilded.....Where big enough swaths of open space exist with connective corridors to other large forest, meadow, mountain, valley, prairie, desert and chaparral wildlands.....Thereby enabling all of our historic fauna, including man, to live in a sustainable and healthy environment. - Blogger Rick

Subscribe via email to get updates

Enter your email address:

Receive New Posting Alerts

(A Maximum of One Alert Per Day)

Monday, November 16, 2015

The migration of songbirds every Spring and Fall is an event most of us do not readily think about.............Natural History writer Todd McLeish informs us that the key to both tiny and larger birds ability to fly over a thousand miles to both winter and summer habitat zones has to do with them having a "digestive system that is highly flexible and different conditions and activities".........Just as Bears ingest vast quantities of food calories prior to their hibernation period, so do birds "dramatically increase their food intake" prior to their setting off on their long flights.........Additionally, the guts of birds go through a metamorphosis that allow them to "shut down their digestive systems so the energy that would have been used to process food can be diverted to fuel flight"

Migration Takes Guts
Illustration by Adelaide Tyrol
As an avid birdwatcher for more than 30 years, I’ve long been familiar with the big picture of songbird migration. Tiny blackpoll warblers, for instance, fly 1,500 miles from southern New England to the Caribbean in a single two- or three-day flight across open water with nowhere to land if they get tired. The even tinier ruby-throated hummingbirds cross the Gulf of Mexico in a similar way. But until recently I haven’t spent much time wondering how these little birds do it. Don’t their flight muscles get tired? How do they replenish their energy reserves in the air?
The answers, according to University of Rhode Island ecologist Scott McWilliams, have everything to do with digestive physiology. Or, as McWilliams likes to say, “migration takes guts.” Yes, strong flight muscles and an innate knowledge of what route to take are crucial, but it also takes a digestive system that is highly flexible and adaptable to different conditions and activities.
In preparation for migration, the gut size of many migratory songbirds, including white-throated sparrows, hermit thrushes and red-eyed vireos, expands significantly over several days through the production of new and larger cells. That makes it possible for the birds to dramatically increase their food intake so they can store up extra energy for their long flights.
But the digestive system is made up of the most metabolically demanding organs in the body. It uses large quantities of energy to operate. During migration, birds can shut down their digestive systems so the energy that would have been used to process food can be diverted to fuel flight. The downside is that the birds’ guts can begin to atrophy during migration. When birds stop along their migratory route or reach their ultimate destination – a time when they are surely extremely hungry – they are constrained from feeding for a day or two until their digestive system becomes acclimated and can operate efficiently again.
This digestive on/off switch explains why migrants do not immediately gain weight when they pause or complete their migration, and it also provides insight into their dietary requirements. Rather than exclusively feeding on high energy (fatty) foods to sustain flight, birds must also consume proteins to help rebuild their digestive tract.
The adaptability of a bird’s gut capacity may be a deciding factor in different species’ ability to cope with climate change. In a laboratory experiment, McWilliams found that white-throated sparrows acclimated to a very cold environment were able to eat two to four times as much food as sparrows acclimated to summer temperatures. The birds were able to accommodate the greater quantity of food they needed to eat to meet their energy needs in the cold and still digest it efficiently.
“That tells us something about their ability to flexibly respond to climate change,” said McWilliams. “Plenty of birds migrate south because they have too limited a capacity to respond in this way. But white-throated sparrows have the spare capacity to modify their physiology to deal with substantial environmental change.” He said the birds that live in places where temperatures don’t change a great deal – like the tropics – have not had to evolve this physiological flexibility, so those species might have more difficulty adapting to changing conditions.

A gallery exhibit featuring Outside Story illustrations and articles is open through November 29 at the Montshire Museum in Norwich, VT. Todd McLeish is an author and natural history writer. His most recent book is entitled, ‘Norwhals: Arctic Whales in a Melting World.’
 Download the Article

No comments: