Common Tern ID

["Mike Carter" <>]

 

Hi Jill,

 

I agree your bird is a Common Tern, possibly of the nominate subspecies hirundo. However, because on the breeding grounds in Siberia, there is a wide area of overlap between the races, this is not certain. In the this area, individuals may more closely resemble either that form or the far eastern longipennis. In Victoria, although typical longipennis out number other forms, birds resembling hirundo are not uncommon. When I was 'studying' Common Terns back in the 60's, we reckoned we were getting two intermediate races, minussensis and turkestanica. These have now been absorbed into the other two as there are no clear demarcations. Thus only extreme individuals can reliably be assigned to a subspecies. A third subspecies, tibetana from central Asia is said to occur in HANZAB region. Plumage and size are as longipennis whereas bill and legs are like hirundo so have much red.

 

ID to race is further complicated because the species takes three years to achieve full adult plumage, the three ages moulting in different periods. This is very detailed in HANZAB but unfortunately doesn't show when bare part colours change. 

 

The day Jill posted her query, I received a letter with photos from Rob Drummond with a similar problem. They were terns taken at Ricketts Point in Port Phillip Bay on 4.02.02. Rob was confident that a black billed, red legged bird with black primaries, dark carpal bar and partially black, irregular shaped, non-breeding plumaged, crown (not extending to nape), was a Common Tern. This, I understand, was typical of others present. His query bird had a black bill, black (possibly tinged red) legs, white forehead but remainder of crown to nape black, no carpal bar, grey, not black primaries and long tail streamers extending to tip of folded wings. I consider this was an adult Common Tern of the race longipennis in almost full breeding plumage, needing only a black forehead, a darker belly and perhaps some moderation in colours of bare-parts to complete the process.      

    A bird so nearly in breeding plumage in early February is very advanced. According to fig. 1 in HANZAB, head moult should not start till February and one might assume that the outer primaries should be in moult rather than complete. Perhaps the data used was more relevant to hirundo than longipennis.

 

Hope this helps.

 

Mike Carter
30 Canadian Bay Road
Mt Eliza    VIC     3930
Ph:  (03) 9787 7136
Email:  

  

----- Part of Original Message -----

From: jilldening <>

To: birding-aus <>

Sent: Sunday, January 12, 2003 11:37 PM

Subject: [BIRDING-AUS] Tern, not sure which, SEQ

Hi Everyone,

Jill Chamberlain
spotted an unusual tern in the final ten minutes of our time at the sandbanks,
after the first
load had started back to shore. At the time she came to me
and said she
thought she had a Common Tern in her scope, except it had red
legs and bill.
It was preening vigorously with its head mostly away from us.
It was partly
obscured all of the time in a flock of about a thousand or two,
and I never
saw its primaries or tail. Then the flock lifted, and we couldn't
relocate it.

For the record, this is what I did see:
Bill part bright
red, part black
Legs bright red
Very strong carpal bar
Stronger cap
that Common Terns present (which are still showing no cap
movement from
non-breeding), but not full cap
Otherwise like a Common Tern, same
size

I feel that it was most likely a Common Tern. But I think there is
the
possibility that it might be the first time I have ever seen (and 
I
emphasise the MIGHT) the  nominate species of Sterna hirundo. There
has been
the odd record of a nominate on the east coast, but the usual place
for
these to turn up is on the west coast of Australia.
However, they do
breed as far east as western Siberia. From east of this
point the subspecies,
our subspecies, longipennis, takes over.

I just wonder if it could just
be one of our regular longipennis with more
red that is usual. Not sure. I
have seen Commons before showing dark red
legs and dark red on bill, but this
was bright red, somewhat like the red on
the bill of a Caspian
Tern.

Cheers,

Jill