Hi all,
Further to the previous emails, here’s the photos of the chroicocephalus gull with only two mirrors from the Wollongong pelagic trip on 25/06/2011. I’d been very busy with a job interview in Adelaide (my apologies to anyone who I didn’t manage to reply to – many thanks to everyone who gave me information on birding there!) so I’ve only just got round to writing this up. I’ve not included all the thoughts I’ve had on this as I didn’t want to sway anyone. http://www.tonykeenebirds.co.uk/random/gull_wollongong.html Three of the photos can be enlarged by clicking on them and there’s a schematic of the primaries on the port wing. Any suggestions, ideas, IDs, general frowning, etc, feel free to let me know! Cheers,
Tony
Photos, paintings and drawings of Australian, NZ, Swiss and British Birds www.tonykeenebirds.co.uk ===============================
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Hi Elizabeth, Silver gulls are indeed common and very easy to identify, so birders don’t give them much attention. It is not necessarily easy to identify a similar vagrant gull from overseas amongst them (say Red-billed or Black-billed from NZ, Hartlaub’s from Africa, Black-headed or Brown-headed from north, etc). If you want to find and identify rare birds it is best to know the common birds really well. Gulls are also great subjects for learning how plumages and moults work because they are tame, easliy bribed, and their feathers are bigger than those nervous little waders. It’s not everone’s cup of tea, so no to “should look at Silver Gulls” and yes to “must look at Silver Gulls”!
David James, Sydney burunglaut07@yahoo.com ==============================
Sent: Tuesday, 5 July 2011 9:56 AM
Does this mean I should be looking at Silver Gulls more closely? I thought they were an easy bird to identify – and they’re everywhere here! Elizabeth Shaw Phillip Island Victoria
Does this mean I should be looking at Silver Gulls more closely? I thought they were an easy bird to identify – and they’re everywhere here! Elizabeth Shaw Phillip Island Victoria
Hi Tony, It’s great to see someone taking a second look at Silver Gulls. I must confess to neglecting them for many years. I haven’t seen any comments on your “two-mirrored” gull so far, it’s not a well studied subject. Sorry, but I reckon it is an Australian Silver Gull (C. novaeholandiae) and not an NZ Red-billed Gull (C. novaeholandiae scopulinus). Firstly, some comments on taxonomy. Sibley & Monroe (1990) were the first to split them as separate species. Their justification for it was a pers. comm. from Dick Schodde, without any reasons. It has to be said that gulls are not one of Dick’s specialties, and he has not published any taxonomy on the group, either before or in the intervening 2 decades. Splitting doesn’t get much lamer than that, with no science that I am aware of to support a split. Neither Johnstone nor HANZAB found any reason to split them. That some field guide authors follow such splits does nothing to strengthen the lack of arguments in support. The reality is that they are not very different. The identification of Silver and Red-billed Gulls is a tough issue. As far as I am aware it is entirely theoretical, as it has never really been done (in field or museum) except on geography. Johnstone recognised that scopulinus usually has 2 mirrors and novaehollandiae usually has 3. However, the main theme of Johnstone’s paper was that in Australia there is a huge amount of variation within and between populations. Regrettably, the HANZAB plumages text for Silver Gull was not as thorough as it was for some other species in the same volume. It did not have enough detail on the differences between scopulinus and novaehollandiae (my fault, but that was all I could do at the time). However, it did acknowledge the marked variation between ages, sexes, geographical populations and individuals. These different types of variation frequently combine and interact to mask specific types of variation. It does note that some individual adult Silver Gulls in south-eastern Australia have only two mirrors. I have a photo of an adult Silver Gull from Hobart with two mirrors and just a tiny spot on p7; it is very similar to this subject bird. I doubt that the presence of only two mirrors can be used even to rule out an origin from the nearby Five Islands. The bill does not look particularly short or stubby or heavy. There is a subtle average difference between the two forms, but that does not mean that an individual can be identified by this character. Males have heavier but longer bills than females, adults larger than juveniles, big-billed individuals bigger than small-billed individuals, etc. Someone suggested that scopulinus has brighter more crimson coloured bareparts than novaehollandiae. I would ask, is that males, v males and females v females, alternate v alternate and basic v basic plumages across the two forms? Subtle average differences do not really help to identify individuals in highly varied groups. So we come to about the only character that might be concrete – the shape of the mirrors. Admittedly there has not been much study so you can bet that there is a lot more variation than is realised. However, Johnstone and HANZAB indicated that on scopulinus the mirrors have a rather square-cut or perpendicular demarcation at the basal part edge of the mirror, whereas in novaehollandiae this demarcation tends to be tapered or angular. This bird appears to have angular demarcation. Given our lack of knowledge, without square-cut variation, there is not much of a case to prove it isn’t a NSW novaehollandiae with a dark p7. Hope this helps. Hope someone has more to add, one way or the other.
David James, Sydney burunglaut07@yahoo.com ==============================
Sent: Saturday, 2 July 2011 12:09 PM
Hi all,
Further to the previous emails, here’s the photos of the chroicocephalus gull with only two mirrors from the Wollongong pelagic trip on 25/06/2011. I’d been very busy with a job interview in Adelaide (my apologies to anyone who I didn’t manage to reply to – many thanks to everyone who gave me information on birding there!) so I’ve only just got round to writing this up. I’ve not included all the thoughts I’ve had on this as I didn’t want to sway anyone. http://www.tonykeenebirds.co.uk/random/gull_wollongong.html Three of the photos can be enlarged by clicking on them and there’s a schematic of the primaries on the port wing. Any suggestions, ideas, IDs, general frowning, etc, feel free to let me know! Cheers,
Tony
Photos, paintings and drawings of Australian, NZ, Swiss and British Birds http://www.tonykeenebirds.co.uk ===============================
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