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Thread subject: Update on Martha Vineyard birds from Rob Bierregaard
||08/16/05 08:40 am
||Copy of email recd today:
For those of you interested in the Martha's Vineyard
population, here's the story:
There are still a couple of nests I need data from, but the
story is pretty much wrapped up. Bottom line--worst year since 1998,
almost entirely due to the awful weather in the early spring. 2 bad
nor'easters hit the early nesting birds very hard. We had between
60-65 breeding pairs and between 7-12 housekeepers. (I checked early
this year and there were some birds hanging around nests that could
have been late breeders or just housekeepers. I've got to make some
calls on the undetermined ones still.) This is a total of 72 pairs
hanging around nests with intent, if not the know-how or experience,
to breed. That's the 2nd highest number since I started the censuses
in 1998 (last year was 75). That makes sense, given the large number
of young fledged each year since '98.
So this year, with the terrible weather early on, 58% of the
active nests failed. Most of the nests failed before hatch. Some of
our best producers, like the Oak Bluffs harbor pair and Cedar Tree
Neck, are early birds--they get here early and lay eggs in a hurry.
Normally this is a good strategy. It's true for most migratory
birds--getting back to the breeding grounds is usually a plus because
you get dibs on the best territories, etc. However, there's no such
thing as a free lunch and there's always the risk that you're going
to run into bad weather, which is what happened this year.
The birds that successfully hatched their eggs did as well as
successful nests do each year, averaging about 1.5 young/successful
nest. This really shows that the problem was in hatching. When you
look at all active nests, the average number fledged was about 0.61.
This is below "replacement rate," but every other year we have
fledged between 0.98 and 1.5. These numbers are remarkable. Over on
the Westport River, where there are 75 breeding pairs, they think
it's a good year when they get to 0.97 young/active nest! So,
remembering that an Osprey may breed for 10 years, one or two bad
years means nothing. A pair of Ospreys during their lifetimes only
has to get 2 young to breeding age to replace themselves.
This is an interesting way to get at the juvenile mortality
thing. Let's say we want the population to grow, that means they
should raise 3 young over their lives (assuming they can't raise a
fraction of a young). If they breed for 10 years, and if they're on
the Vineyard average, they'll fledge about 13 young over their
lifetimes. Given that the population is growing slowly, it seems
they're getting about 3 young to breeding. That means 10/13, or 77%
are dying before they get to breeding age. For the most part, of
course, the 23% are the really good hunters--the losers wind up,
using an appropriate expression from the Mafia flicks, "feeding the
fishes"--and natural selection marches on!
This year 3 pairs fledged 3 young: Lobsterville, Long Point,
and Stonewall. In '04 no pairs raised 3, in '02 only 1 did. Stonewall
is a long-standing, very successful pair (parents of Jaws, our boy
down in Colombia). Lobsterville, with the failure at the OB harbor
pole, Mink Meadows, and Wasque, moves into a tie for second in the
most-productive-pair-on-MVY. The Mink Meadows pair was the leader
after last year with 16 fledged since '98, ahead of the OB Harbor
pair (15) and Wasque (14). As all three of these nests failed this
year, Lobsterville now is tied with OB at 15 young fledged in 8
years, still one behind Mink Meadows.
The Long Point female gets the Mom-of-the-Year award. She
fledged 3 young, despite having a nest that is as exposed as a nest
can be, just in from the dunes, and despite having a pretty
unimpressive provider, who, my grad student Jennifer reports, would
bring in tiny little perch while our heroic female lugged in 24"
We put a satellite transmitter on a young bird at Long Point
and one on a bird over in Jamestown, RI, so this year we'll have
three birds to follow south--Bluebeard, Homer (the Long Pt bird), and
"Conanicus," the Jamestown bird. Details are on my website:
9201 University City Blvd.
Charlotte NC 28223
704 333 2405
||08/16/05 09:24 am
||Karen, thank you ...this is so interesting.........science in the making.........
||08/16/05 10:34 am
||No news of Bluebeard?
||08/16/05 11:42 am
||I read email and the site and assume no birds moving south yet OR no maps posted yet if they are receiving signals
||08/16/05 08:03 pm
||This is so interesting to have these statistics, and to track them with satellite transmitters. I think these birds have a rough life and alot of strikes against them - yet they persist. I watched one catch a fish in a stocked lake today. It stayed under quite a while and the seagulls tried to rob it after all that effort and skill. I don't think they succeeded, however.
||08/17/05 04:54 pm
||Thanks Karen. That one statistic is sobering...that 77% die before reaching breeding age. I hate to think about that :-(