Brant


CarolC7529@...
 

To: the group
From: John Roser

For those who are interested, here's an update on the Morro Bay Brant
population and a brief summary of some of my findings over the past 3 years:

Spring migration out of Morro Bay has been on in earnest the past few weeks.
Numbers have been as follows: 2,700 3/11, 2,200 3/17, 1,600 3/23, 1,300
3/30, 700 4/7, 170 4/12. This years population peak was 3,800 Brant during
the first week of February. Last year the population peaked at 2,400 and the
year before it was 1,700. The bay's Eelgrass beds were in very poor
condition 3 winters ago and have since slowly recovered to the approximate
acreage seen preceeding the fall of '94 Hwy 41 fire and spring of '95 floods
(which brought heavy sediment loads to the bay and led to a severe depletion
of Eelgrass). The Brant numbers seen this year are probably more indicative
of the bays current true carrying capacity. Brant counts from the '60s were
typically from 6,000 to 8,000 with a count in the '50s of 11,000. Band reads
obtained in Morro Bay represent all of the Black Brant banding localities
from Russia and Alaska to Banks and Victoria Islands in Canada. One
individual of the 'western high arctic' or 'gray bellied' race was observed
last year, and several were observed this year. Their breeding range is
Melville and Prince Patrick Islands and they winter in Puget Sound. They
currently are recognized as a distict race but they have no subspecies
designation. These birds look more like the eastern hrota race in plumage
(very pale, almost white bellies with a thin necklace that is typically
incomplete in front), but they are observably larger than our nigricans race
(as opposed to the hrota race being smaller).

This year I got over 1,100 band reads over the six month season. Once again
band read data showed that our wintering population seemed to consist of a
core of family groups that spend the entire season. Of the family groups in
which juveniles are banded as well as their parents, data shows that many of
them spend the entire season here from Nov. through Mar. or Apr. Family
groups typically stay intact until they leave on migration. Strong site
fidelity has been observed over the 3 year study. Many pairs have returned
to spend the entire season 3 years in a row. In January northward movement
from Mexico picks up. Many birds were observed all three years with their
first sightings here occurring roughly at the same time each year (for
example, if I first picked it up in Feb. the first year, odds are that's when
I first would pick it up in subsequent years). Some of these birds stay a
month or two, some seem to move on more quickly.

First arrivals in the fall are heavily weighted by family groups with a large
influx of what are probably failed breeders or non breeders arriving later in
mid to late Nov. During the 97/98 season a dramatic Eelgrass crash occurred
in January. At that time the population abruptly went from 1,700 to 600
individuals with many family groups remaining and the failed or non breeders
departing. At that time the birds fed in the salt marsh on algae and
vascular plants all day (both high and low tide) for several weeks (you may
have noticed this). This behavior did not occur during the past two seasons
due abundant Eelgrass availability.

It is estimated that about 80% of the 130 - 140 K population of Black Brant
now winters in Mexico. Of the approximately 40 radioed brant that were
radioed in their breeding sites in Alaska and were tracked migrating straight
to Baja, only one was detected using Morro Bay as a northward stopover this
year. Most Mexican migrants fly right by and I believe many don't even know
Morro Bay exists due to low flight elevations over Estero Bay and the dunes
of the spit obscuring their view of the bay. Some of these northward
migrants will stop briefly at intertidal sites along the coast to eat Ulva
(sea lettuce).