Hi all,
so it's settled for Antillean then. As I said, I saw the bird flying off, and flying around for a minute or so. While I wouldn't swear that the underparts were entirely buffy, the genral appearance clearly was. Unfortunately I have no photo showing this ... together with Kevin's post, this looks really good for Antillean then. I paste in a copy of his analysis.
Thanks again for your efforts,
Ingo
Response by Kevin Karlson to Antillean Nighthawk? posting on June 14, 2005
This is a response to the photos of the nighthawk from the Dry Tortugas
posted on June 14. This species has been studied by a small number of
people, including myself, for the past 12 years or so in the Dry
Tortugas with hopes of separating them in the field from C.minor
chapmani, the expected race of Common Nighthawk on the Tortugas that
nests in Florida, E. Texas to S. Illinois and nearby southeastern
states. After several years of floundering in the field, I made a few
visits to the Museum of Natural History and studied the small number of
skins available for Antillean Nighthawk, and also referenced the paper
on Common and Antillean Nighthawks of the Florida Keys, by Henry
Stevenson et al. (Oct., 1983). After noting several interesting
structural differences between skins of the two species, I spent several
more years studying all nighthawks in the Dry Tortugas (I spent 150+
days and nights during April/early May in the Tortugas from 1994 -2001).
After years of having little luck separating these birds, I was able to
finally pin down a few field marks, both in plumage and structure, that
are helpful in separating these two very similar species. I was able to
verify my identifications a few times by waiting until dusk and hearing
some birds vocalize as they flew around the fort. Based on my field and
museum studies, I feel that this bird is a male Antillean Nighthawk.
First of all, it would be best to state that Antillean Nighthawks, both
male and female, can show plumage variations that are as extreme as
Common Nighthawks. Based on a number of photographs given to me by Bruce
Hallett from various Bahamian Islands, both male and female Antilleans
can range from very rusty above and buffy below to very gray above with
little or no buff color to the underparts. This is a feature that is
misrepresented in the Sibley Guide, which shows males as only having a
rufous morph, with rusty-marked upperparts and rich buff below, with
only females having a gray and rufous morph. Most of the birds that drew
my attention in the Dry Tortugas, however, exhibited the
"characteristic" rusty markings to the head, neck, mantle and scapulars,
with paler or gray wing coverts and contrastingly paler tertials,
similar to the photos shown by Ingo in his posting. This is also
consistent with skins that I have studied, where virtually all
Antilleans showed bright buff to rust spotting on crown and neck as
opposed to variable amount in C. minor chapmani. The Bahamas population
of Antillean Nighthawks are referred to as C.vicinus in some scientific
literature, which would afford subspecies status to these birds, but
Bond (1956) and Monroe (1968) "regarded them inseparable at the
subspecific level from gundlachii." According to the photos of about 8
different Bahamian birds(vicinus) sent to me by Bruce Hallett, these
seem to average grayer in appearance than all Antillians that I have
seen on the Tortugas. The separation of two subspecies of Antillian
Nighthawk is not embraced by everyone in the scientific community, but
might be a starting point for understanding these problematic birds in
ID terms.
One structural field mark, however, that seems consistent with all
Antilleans that I have seen (both live and skins) is a noticeably
smaller headed appearance (both males and females) with a smaller, more
"petite" body structure. Some Common skins were small in comparison to
Antillean, but the head size in relation to the body was noticeably
larger. This difference can be subtle, depending upon your angle of
viewing, but is helpful. Common's seem to have a larger head and thick
neck, along with a bulkier upper body than Antillean, which often look
'pigeon-headed' when at rest, with a narrower neck than Common.These are
all field observations of mine, and not backed up by measurements.
The wing/tail ratio can be helpful on some birds, especially when the
wings fall noticeably short of the tail, like the bird in the phots.
Male Antilleans have a wing measurement of 150-183mm, while C.minor
chapmani males average 178-195mm. Tail measurements for Antillean males
average from 106-119mm, while C. minor chapmani males average 98-111mm.
The average longer tail on Antillean could account for most wings
falling short of the tail, especially with the much shorter average wing
length on Antillean. However, there is overlap on both wing and tail
measurements, so only extreme examples would be useful in the field.
However, virtually all Antillean Nighthawks that I have been able to
successfully ID in the Tortugas (after hearing calls), had primaries
that fell short of the tail. Some were noticeably short of the tail,
while others fell just short. Most Common's that I have photographed in
the US have primaries that extend from the tail tip to noticeably beyond
the tip of the tail.
Another observation that seems to hold true is the shape of the
primaries. Antilleans have primaries that, when viewed at rest, are
broader and more rounded than Common. This might account for their
shallower wing flap. I once had a single Antillean flying side-by-side
with 5 Commons, and the flight seemed less buoyant with wing strokes
that were not as deep as Common. The length and more rounded shape of
the primaries probably affected this subtle difference. The bird in
question has short wings in relation to its tail, which are very broad
and rounded in shape. Most Common primaries that I studied in
photographs and in the field are more tapered and somewhat narrow in
relation to Antillean.
If we could see the underparts, the narrower bars and distribution of
buff color would also be helpful. Male Antilleans of subspecies
gundlachii average brighter buff coloration to the vent and lower belly,
with paler coloration to the upper breast, and rich buff color under the
chin. However, males of the subspecies vicinus, which range throughout
the Bahamas, are grayer overall, with some birds showing no buff
coloration to underparts and very little to no rufous markings on the
upperparts. This makes analysis of plumage alone a dangerous gamble with
nighthawks seen in the Dry Tortugas or extreme S. Florida. However, a
complete picture of stuctural field marks combined with wing/tail ratio
and plumage can usually result in a fairly accurate conclusion.
Based on the bright rufous markings to head, neck, mantle and scapulars,
with pale contrasting tertials; small-headed look with slender neck and
lack of "bulk" to upper body; and very broad, rounded wings that fall
well short of tail, I suspect that this bird is a 'typical' male
Antillean Nighthawk. The underparts are shaded so much that any buff
color to the vent is hard to pick out, but I would like to see that
field mark go along with the others above to further seal the ID.
, Niels, perhaps?
