Project Osprey Watch – Summer 2002 Update
Contents:
The
2001 Breeding Season
The 2002 Breeding Season
Migration and Satellite Tracking
2002 Fledgling Counts
Future Satellite Tracking
Summary of Breeding Success-1998-2001
The
2001 breeding season was less successful than any since we started careful
monitoring in 1998. While we found 63 active nests (nests with eggs) during our
May inventory–exactly the same number of breeding pairs as in ’99 and
‘00–the number of young produced was down (see Table on p. 3).
Severe weather in June is probably responsible for many of the 21 nest
failures we witnessed in ’01. Despite all these nests that produced no young,
we estimate that 1.03 young were fledged for each nest where eggs were laid.
While this is the lowest productivity from the Vineyard Ospreys since 1998, it
is still above the “break-even” value of 0.88 that Osprey researchers
believe is necessary to keep a population stable.
Four pairs were “house-keeping” – a not-so-technical terrm that
describes the behavior of young birds that are getting ready to breed but
don’t quite have it all together yet. These housekeepers usually breed after a
year or two of practice.
Changes
Several “old faithful” nests were unoccupied in ’01, including nest
#8 out on Squibnocket, which had been continuously active for nearly 20 years.
One of the Oyster Pond nests “downgraded” from breeding to housekeeping,
suggesting that at least one of the old pair from this long-active nest had not
survived the winter and was replaced by a young bird. A pair at Scrubby Neck
also dissappeared. After this nest pole was blown to smithereens by a lightning
bolt in ’00 (with eggs or young in the nest), the pair set up a nest on a
power line near the old nest pole
in ’01. Their nest failed that year, and in ’02 they were not among those
present and accounted for. Two neighboring pairs to the west also disappeared in
’01. Nearby, a pair of ’00 housekeepers at the end of Oyster-Watcha Rd. laid
eggs in ’01 but did not raise any young.
On Chappy, the unofficial Opsrey capitol of the Vineyard, a pole out at
Shearpin Pond (at the north end of the island) had housekeepers as did a pole
across the water on the west shore of Poucha. On the Katama Bay side, a pair of
‘00 housekeepers just north of Wasque on Katama Bay laid eggs (but failed),
and late in the season a pair showed up north of Litchfield Rd and started
building a nest on a power line on perhaps the highest ground on Chappy. Another
(or maybe the same) pair put some sticks on the short pole on the northeast
corner of Caleb’s Pond.
Along the north shore, a pair built a nest and laid eggs on a chimney at
Mink Meadows. At Paul’s Point, where we had a housekeeping pair on the
Guiney's property in ’00, a pair built a nest on a powerline not far from the
housekeeping nest of the year before—these were probably the same birds.
Fledging
Success in 2001
As previously mentioned, 2001 was a relatively poor year for Osprey
productivity on the Vineyard. Ospreys are long-lived, however, often breeding
well into their teens, so one, or even a series of off years is no reason for
concern. An adult Osprey might attempt to raise young in as many as 10 breeding
seasons and only has to successfully rear one young that will survive to
breeding age (3-4 years) in those 10 years to keep the population stable.
In mid May we completed our annual grand tour of all the known nesting
sites on the Island for a head count of this year’s breeders. And a “head
count” it really is. By the middle of May, all the birds that will lay eggs
will have done so, and the females are busy incubating. When they are
incubating, often all that’s visible from the ground is the female's mostly
white head. This is very conspicuous, so just a glance up at the nest is usually
all that is needed to confirm that a pair is breeding.
We found 58 pairs incubating eggs—four pairs fewer than last year—and
five housekeepers. As last year, a few “old faithful” nests went unoccupied.
Changes
The pole overlooking the Menemsha Pond herring run at Squibnocket has
"downgraded" from active to housekeepers and is apparently having
trouble getting a nest started. On Menemsha Pond a pair is housekeeping on James
Taylor's pole (finally). Whit Manter's nest on Tisbury Great Pond is empty after
a long run. A pair has resumed residence at the summer parking area at Long
Point. A pair on the Jones farm that has tried off and on for the past few years
has apparently given up. At Sippiessa Pt/Clam Cove, the nest near the boat
landing is unoccupied after several years of failures. The south shore nest
occupied by HX and KD, the satellite tagged birds we followed on migration last
fall, is inactive. A neighboring nest on Oyster Pond is active again after a
year off. Other nests inactive this year include Mohu, the pair at the end of
Oyster-Watcha Rd., and Little Neck (Shearpin Pond on Chappy).
A housekeeping pair has taken up residence on a pole at Eel Pond in
Edgartown, while over on Chappy, a pair is back at the Self's nest on Cape Pogue
Bay. The 2001 housekeepers on the power line on Litchfield Rd are incubating.
Migration
and Satellite Tracking
In the last newsletter I reported on the fall migration of a breeding
pair of Ospreys banded on the Vineyard’s south shore in 2000. The male, “HX,”
made it to his wintering grounds in Venezuela, while his mate, “HW,”
apparently died in Pana-ma. “HX” returned in the spring of ’01 and found a
new mate.
2001 was our second year of collaboration with The Raptor Center of the
University of Minnesota’s satellite tracking program. Thanks to very generous
contributions, in 2001 we were able to capture and tag three breeding
Ospreys—the replacement mate at HW’s south-shore nest and both adults at the
Felix Neck nest.
Both these nests failed—the south shore nest had actually lost their
young a few days before we captured the female (HX’s replacement mate). We
later learned from the satellite data that on the day we were trapping the
south-shore female, her mate (HX), still wearing his transmitter from the year
before, was already in Connecticut. While it was disappointing to have these
nests fail, we learned that it is not uncommon for failed breeders to leave the
Island and wander around southern New England before they head south in the
fall. We were surprised to see one of the birds tagged in ’00 do this after
her nest failed that year, but subsequently not so surprised when in ’01 three
of the tagged birds commuted back and forth between the Vineyard and central
Massachusetts, Connecticut, and NYC for the duration of the summer. Only the
Felix Neck male (KC) stayed around his nest until he migrated.
In September, our birds stopped their wandering and headed south in
earnest. The two males, HW and KC, followed the typical migration route through
Florida, Cuba, and Hispaniola to their wintering grounds in Venezuela. HW
returned to exactly the same area where he spent the previous winter on the
delta of the Orinoco River. KC spent the winter in central Venezuela and
returned to the Island on April 9th, more than three weeks after the first of
the Vineyard Ospreys returned to the Island. By the time he returned, a young
male had already laid claim to his territory. KC wasted little time in
reestablishing his ownership of the Felix Neck pole and finding a replacement
mate.
Unfortunately, neither of our two females, KD and KB, completed their
migration. Both landed on boats while crossing the Caribbean south of Hispaniola
and were never heard from again. We
can only speculate as to what happened. While it is not unusual at all for birds
crossing large bodies of water to stop to rest on boats, they might have done so
because they were exhausted and were unable to complete the 500 mile, open-water
crossing to Venezuela. Ospreys are not good at fishing in deep water, so if they
were undernourished, they simply might not have been able to stock up for the
rest of the trip. Alternatively, they might have been shot on the boats.
And while we're on the bad-news-bandwagon, HX, the male tagged in the spring of 2000, did not return from his wintering grounds. We lost his signal a month or so before he should have started the 2001 spring migration, and he did not appear at his nest this spring.
Summary
of Productivity-1998-2001
| '98 | '99 | '00 | '01 | '02 | |
| Active nests | 66 | 63 | 63 | 63 | 58 |
| Housekeepers | 4 | 6 | 6 | 4 | 5 |
| Successes |
38 | 41 | 52 | 41 | |
| Fa |
18 | 12 | 8 | 21 | |
| Fledglings: | |||||
| Total | 65 | 64 | 96 | 64 | |
|
Per active nest |
1.16 | 1.21 | 1.6 | 1.03 |
During the last week of July and the first half of August, James Mason, a
graduate student at UNC-Charlotte, will be on the Vineyard checking on fledging
success at this year's active nests.
"Fledging," occurs when a young bird becomes capable of fully
powered flight and leaves its nest. This is not the same as reaching
independence--the fledglings will be fed by their parents for several weeks
after they begin to explore the skies around their nest--but it does offer
researchers an objective benchmark that can be compared between different study
areas and, as such, has become the "industry standard" in monitoring
the success of a bird population.
In previous years, despite the careful observations made by Vineyard Osprey watchers and my trips to check on nests in the remote corners of the Island, we've never been able to check all the Island's nests. Jim's work, supported by a very generous donation from a Vineyard Osprey watcher, will enable us to assess this year's Osprey productivity more accurately than in any previous year.
As this newsletter goes to press (months after most of it was written), James
reports from the field that many nests have already fledged (by late July). It
seems that we will have fewer nest failures than last year, but the average
number of young per successful nest may be somewhat low.
We were surprised and disappointed to learn that the Conservation Program
at the Raptor Center of the University of Minnesota has been shut down due to
the University’s budgetary problems. Our tracking of Vineyard Ospreys was
accomplished under the auspices of the Raptor Center, and it is not certain that
we will be able to tag more birds in the future. We will at the least continue
to track the one bird still wearing a transmitter (the Felix Neck male, KC) as
long as he survives and consider tracking more birds if we can find sponsors.
Tracking
Osprey Migration via the Web:
Two websites track the Vineyard Ospreys' migration. For detailed maps
along with a running play-by-play description of their movements, log on to the
Carolina Raptor Center's webpage: http://www.birdsofprey.org
and click on "Migration." The travels of the Vineyard birds
will also be displayed on the Minnesota Raptor Center's webpage http://www.raptor.cvm.umn.edu
(follow the link to the "Highway to the Tropics" page and then click
on "migration data"). At this site you will be able to compare the
Vineyard birds to all the other
Ospreys tagged by Mark Martell and his collaborators.