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Origin & age of banded Nazca Booby in San Diego County waters June 10, 2018

On the last San Diego Pelagics
trip this past Sunday June 10, 2018 we had the good fortune to
find a subadult NAZCA BOOBY sitting on the water about 8:20am.  Per GPS
readings the exact location 5.5NM west of Imperial Beach and 1.1NM from Mexican
waters to our south.  The booby was spotted just as we motored up very
close to it, maybe somehow it was hidden behind a swell, and we immediately
stopped the boat and got very close looks at the bird.  The bird
was so close in fact that when it took off flying, luckily towards us and along the
starboard side in front of assembled photographers, from the many photos taken
a metal band could be clearly seen on the right leg.  You have to marvel
at modern camera sensors because images so detailed a
partial band number could be read.


The information on the band appeared
to show a number or alphanumeric either "734.." or "73A.."
visible.  You can see the photos on our eBird checklist here


I checked in with Kimball Garrett
about the rehabbed Nazca/Masked Booby that had been released at San Pedro, Los
Angeles County on Oct 9, 2015 but should have read his original email to the
LACOBIRDS listserv first since this bird banded with USGS metal band on left
leg.  The San Diego
bird, a subadult evidenced by some dark speckling on the white upperparts, also inconsistent
considering age.  Kimball confirmed the band did not match that of the San
Pedro released bird with USGS band (with number 1038-26057).


A second photo of the San Diego
Nazca Booby then surfaced showing the band even more clearly and with an upper
line possibly showing word "ANDER…".  I had a hunch about
where the band may have come from and reached out to Professor Dave Anderson at
Wake Forest University who has been studying Nazca Booby and other seabirds in
the Galapagos for the past 35 years.


Sure enough, Dave confirmed the band
originated from his lab and he could trace the partial number (734xx) of this
Nazca Booby to an immature banded on Isla Espanola, Galapagos Islands, in the
first half of 2017.  He estimates the bird's age at 1 3/4 years old at time
of sighting here in San Diego.  He told
me they have banded about 25,000 youngsters (Nazca Booby) and this is the
71st report of one of their banded birds
but the most northerly by 7 degrees of
Dave noted that most band returns are of 1-2 year old
birds from the Pacific coast of Central America.


The age estimate, 21 months, seems low
perhaps.  You can see P7 or P8 growing,
at least on the right wing, and this would seem to peg the bird, in 2nd-prebasic primary molt, in a 25–26
month age range using a Masked Booby molt pattern shown in Howell, 2010, Molt
in North American Birds.  I looked in Howell
et al. 2014, Rare Birds of North America, and it states, under Nazca Booby, pp.
9, 2nd-prebasic primary molt starting about 14 months
after fledging, i.e. about 18 months of age.  Considering
the six or seven visible grown primaries, at about a month apiece, this would get us to
24–25 months.  Maybe the discrepancy can be accounted for with individual variation or the original estimate is a bit lightweight. 
I will have to look around for Nazca Booby molt publications to understand the variation and check on this again with Dave Anderson.


I will be submitting these complete
details to the CBRC along with photographs showing the band number and plumage
details of the booby. A credit due photographers Matthew Binns and Todd McGrath capturing images of the band.


We have three more pelagics out of
San Diego planned for 2018.  Details can
be found at the website
and space is still available but August is filling up fast.  In addition to Nazca Booby last Sunday we
also found the much sought-after TOWNSEND’S STORM-PETREL – photos here
– our next trip in August a good opportunity for this species.

Gary Nunn
Pacific Beach
you can find me on twitter, @garybnunn

Source: SanDiegoRegionBirding Latest Reports