Hello from Ian ---An Incredible Journey!
In the upper spruce-fir forests and alpine of the Green and Adirondack Mountains from spring to fall the
Blackpoll Warbler is a hiker’s common companion. These black-capped, black and white striped
chickadee-sized birds flit among the branches saying their hellos all in one high pitched call that starts
softly, gets louder, then tails away.
They are migrating now (September), and their migration is absolutely mind boggling (see below).
Consider the size of the ecosystem in which these birds live – these are birds who weigh LESS THAN ½
OUNCE. [A 150 pound person weighs 5000 times as much as one Blackpoll.
Bryan Pfeiffer, a Vermont Naturalist makes this observation about the Blackpoll’s food needs to migrate
[you can read his whole article at his website: http://www.vermontbirdtours.com/breaking.html#essay.]
"The fat contained in a single serving of Ben & Jerry's Cherry Garcia ice
cream contains enough energy to get a Blackpoll Warbler from New
England to South America. If it were burning gasoline instead of its
reserves of body fat on the flight, the Blackpoll would get about 720,000
miles to the gallon."
==============================
Pam Hunt of New Hampshire Audubon gives us this amazing accounting that happens every year.
OK bird fans, time to try to think like a Blackpoll Warbler.
Part A: The Starting Point
Blackpolls breed all the way from western Alaska to Newfoundland, with a southward extension
into the mountains of NY, northeastern Pennsylvania, and New England (south to Mt. Graylock
in Massachusetts).
Part B: The Destination
Blackpolls winter in South America between the north coast, Andes, and Amazon River.
The rest of the story is about how they get from A to B (with a bit about B to A at the end).
Based on all the available data, the vast majority of Blackpolls funnel through the northeastern
US and eastern Canada during the fall migration (August through early November). For our
purposes, the northeastern US extends as far south as the Outer Banks of North Carolina,
although the bulk of migration passes between Nova Scotia and New Jersey. There are almost
no fall records of Blackpolls in the US west of the Great Plains and they are pretty rare
anywhere south of Ohio, West Virginia, and eastern North Carolina. All of this is all based on
banding and sighting data.
In other words, birds from as far away as Alaska have already traveled across the entire
continent to reach the Northeast, a distance of roughly 3000 miles. When they pile up along
the northeast coast, they may spend a couple of weeks eating, gaining weight, and waiting for
the appropriate weather conditions. And they put on quite a bit of weight, going from a lean
mass of 11-12 grams to as high as 20-23 grams (or from roughly half-an-ounce to an ounce).
The prevailing winds in the Northeast are from the northwest, and birds may wait for a
particularly strong NW flow to start them on their journey. However, given the distance they
are about to travel, a short-lived cold front is not as critical as it might appear.
The birds take off in the evening heading southeast, and essentially fly straight out over the
North Atlantic Ocean. Mass take-offs to the southeast detected by radar cannot be identified
to species, but one assumes that many of these birds are Blackpolls (and for the record, there
is some discussion of whether Connecticut Warblers follow a similar strategy). The birds
maintain a SW bearing until they approach the Tropic of Cancer, at which point the prevailing
winds shift to northeast (the Trade Winds). At this point the birds are deflected south and
southwest toward the South American mainland. Depending on where they left North America,
this distance is between 1500 and 2000+ miles. It can take up to 88 hours (yes, that's threeand-a-half days).
How do we know they take this overwater route? For one thing, Blackpolls are rare in
Southeast in the fall, as already stated. For another, they are a regular fall migrant on
Bermuda (triangle not withstanding), which lies smack dab in the middle of the over water
route. Finally, they have been recorded in sometimes impressive numbers on boats far out to
sea (sometimes even accompanying shorebirds, although the latter are obviously moving
faster).
Blackpolls are also quite rare in the Caribbean west of Hispaniola. They are pretty common on
Puerto Rico, the Virgin Islands, and the Lesser Antilles, which again lie right in the proposed
migration route. When I was doing waterthrush research in Puerto Rico in October, we'd catch
a few Blackpolls. Many were actually below the normal lean weight, suggesting they had
started to metabolize muscle toward the end of the overwater trip. Once they've hit landfall in
the eastern Caribbean or northern South America, they can feed and fatten up enough to
complete whatever legs of the migration remain. Some may still travel 1000 miles or more
southward into Amazonia or beyond.
While most people buy into this scenario, there is one very vocal critic of the overwater
hypothesis, who instead proposes a land route via Florida and the Greater Antilles. A lot of the
debate (such as it is) revolves around the merits of relative abundance data and weight data.
Obviously, I come down on the side of the plan I've outlined, largely because of the species' a)
rarity in Florida (except after storms), b) abundance in Bermuda, and c) low weights in the
Caribbean.
To summarize, the farthest a Blackpoll might travel IN THE FALL (we'll get to spring in a
second) is some 6000-6500 miles between western Alaska and northern Bolivia. The shortest
would be perhaps 1500-2000 from New England to northern Venezuela. Recapture and colorbanding data (some from right here in NH on Mt. Cardigan by yours truly) suggest an average
lifespan of 3-5 years. That's a lot of miles, not even counting the return trip.
In spring (April to May), Blackpolls appear to cross the western Caribbean directly from
Columbia and Venezuela to Cuba, and thence to Florida and the Gulf Coast as far west as
Louisiana. There are a few records from Jamaica, but essentially none from Central America,
so it appears an overland route is out this time as well. From the southern US, they fan out to
the north, spreading as far west as the front range of the Rocky Mountains, and obviously
northeast to the Canadian Maritimes and New England. In general, this spring route is more
direct for western populations, but perhaps a little longer for the northeastern ones. You can't
blame them though - who'd want to travel 2000 miles over water into a headwind!
Add it all together and the average Blackpoll Warbler (let's say it lives to be 4 years old = four
round trips) travels between 14,000 (New England/Venezuela) and 50,000 (Alaska/Bolivia)
miles in its lifetime. For any population, roughly 8000 of these miles are overwater. For a bird
this size, the whole thing is pretty mind-boggling. Shorebirds and seabirds are the only groups
that make long journeys with such an extensive overwater leg. But shorebirds are significantly
larger and fly much faster, while seabirds can stop and eat whenever they want. Remember,
this is a half-ounce insectivorous bird flying NON-STOP for over three days. Maybe it's lucky,
and can take a break in Bermuda, but most don't have that option unless they intend to
become fish food.
People often try to visualize this feat in human terms. On the radio Monday, Mark made the
comment about how many pizzas we'd have to consume to gain weight at the rate a sandpiper
does. But such comparisons will always be flawed, since humans are physiologically so
radically different from migratory birds. Rather than trying for the caloric equivalents, simply
visualize the monumental task of doubling your weight in two weeks, and THEN exerting
yourself (a fast walk, perhaps) for three days without eating. I suspect that we'd be barely
able to move after the initial episode of gluttony, much less carry out sustained activity of any
sort.
So keep that in mind when you next see a Blackpoll Warbler. By the end of the month it will
have launched itself over the North Atlantic, perhaps for the first time in its life, and there's a
50/50 chance it'll be back to do the exact same thing next fall.
Humbling.
Pam
===============
And for the poets among you, another version of this story:
The Journey
by Pamela Denise Hunt (Fall 1999 - February 2001)
It is autumn in the northlands
Nights get longer, leaves turn yellow
Their breeding season over
Restless songbirds start to move
From Alaska, Canada, New England they come
Half-ounce feathered mites of green and yellow
Leaving vast forests of spruce and fir
On a journey most have never made
To the south and east an ocean awaits them
Long as a planet and a fifth as wide
A place without forests, and even food
Where wind and wave shape a watery world
They stop to feed, these tiny travelers
Flitting through coastal thickets and woodlots
Converting insects, even berries
Into a body's worth of fuel
A northwest wind provides the signal
Darkness falls, the flocks take wing
Guided by stars and hidden senses
They set off across the open sea
Three days they fly, maybe more
And some are lost to the waves below
No land in sight, no place to rest
Driven by the call of an ancestral home
The tradewinds shift, and south they turn
And land exhausted on a distant shore
A new continent, vast and green
Where a great river winds through a dwindling forest
Here they spend the winter months
As visitors in a foreign land
Feeding, roaming through the forest
And waiting for the season's turn
In lengthening days they prepare to return
Changing winter colors to those of spring
Gone are the greens and yellows of autumn
Black, white, and gray replace them
Far to the north the greening begins
Newly feathered birds are waiting
For that ancient unknown signal
To commence the arduous journey home
A different, smaller sea awaits them
Necklaced with a string of tropical islands
Over all of this they fly
Returning to the continent of their birth
From this southeastern point of landfall
They spread west and north toward the spruces
Following the birth of insects
Preparing to settle for the summer
And thus the journey comes full circle
Nests are built and young are raised
But soon enough the days will shorten
And tiny birds fly south again