There have been several claims that the lone Kelp Gull at cottontree is a male
because of the deep bill. It probably is, but I don't think you can relaibly
sex an individual bird this way.
Here is what I wrote on the subject for HANZAB vol 3.
Bill depth (at base) ranges from 18.5-23.5 mm in males and 16.5-20.0 in fmeales
Bill depth (at gonys) ranges from 19.5-23.5 mm in males and 18.0-21.5 in
females
SEXING Males considerably larger than females, specially in bill, but
overlap in all measurements. Breeding pairs can be reliably sexed on
measurements or by observation if side by side (Kinsky 1963). Brooke and Cooper
(1979) used NZ data on weight and Bill F from Kinsky (1963) to sex live birds
on Marion I.: Weight > 975 and Bill F > 50 taken as male, smaller birds as
female; no validation reported. Nugent (1982) produced a discriminant function
for NZ birds using total head length and bill depth (taken at shallowest point,
about half-way between loral point and nostril): 0 = (0.126 * THL) + (0.289 *
depth) - 19.707; females negative, males positive; 156 (99%) of 158 birds used
to derive the function and 25 (96%) of 26 independent birds were correctly
classified.
What are the bill depth measurements of the Cottontree bird?
David James,
Sydney
==============================
________________________________
From: Paul Walbridge <>
To:
Sent: Monday, 5 December 2011 8:18 AM
Subject: Kelp Gull on Sunshine Coast.
Hi All, Brian Russell and myself journeyed up to the Sunshine Coast yesterday
hoping to get some good shots of the visiting Kelp Gull. On arriving early at
Cottontree we quickly located the bird some 300-400 metres away on one of the
sand banks with an ever dropping tide. Hopeless, no way we could get close and
the minutes were ticking by and that up turned Canadian canoe nearby was
beginning to look very tempting especially as no-one seemed to know at the
caravan park as to who owned it! Mind you there were no paddles and you've all
heard the one about being up a certain creek without a paddle!! Exactly how we
felt.
However after a few quick flights around the sand bar and a few quick naps the
Kelp Gull took off with a few Silver Gulls and headed south. After a few
hurried flight shots we quickly took off to try and track it down. First stop
Alexandra Headland, where there wasn't much save for a Wandering Tattler, 3
Ospreys, loads of White-throated Needletails and lots of very tame (and large)
Eastern Water Dragons.
Next stop Pt. Cartwright, where there was even less, not even wandering Tattler
and just 3 Sooty Oystercatchers. So after a fruitless search there we decided
to take a different way out from there to our usual route and drove slowly
along Harbour Parade along the southern edge of the Mooloolah River looking out
for congregations of Silver Gulls. Sure enough, on pulling up at the Kawana
boat ramp there was a fish cleaning station with a few Silver Gulls in
attendance, right opposite to the main trawler and long lining fleet ( gull
heaven). The first house to the left had several silver Gulls festooned on the
gangway to the pontoon and above them just 15 metres from us was the big bopper
resting on a pylon.
So for the next hour or so we got some great close-up shots as it rested and
fed on offal being thrown from one of the trawlers, unlike the Silver Gulls
though wasn't interested in our Big Rooster chips or sausage roll from our
favourite local Danish pie shop. This is my 4th Queensland record of Kelp Gull
and going on the deep bill it would be an adult male bird. Cheers - Paul W.
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