Oystercatchers are among our favourite birds, being among the most charistmatic characters of the Charadriiformes. They
occur on most of the world’s coastlines, with 11 living species globally. All belong to the Haematopus genus and are easily recognisable, following the same familiar oystercatcher design: all have much the same shape and size; a long, straight orangey-red bill and a bright orange or yellow eye-ring; fleshy-looking pink legs (Haematopus meaning ‘blood foot’, refers to the colour of the legs); and all advertise their presence with loud, excited piping calls. Six of the species have boldly pied plumage, four have all-dark plumage, and one indecisive species can have plumage that is either pied or all-black (we’ll be looking at that one very shortly).
With three endemic species of Oyc, New Zealand is rather a Haematopus hotspot, although the Chatham Island Oystercatcher occurs only on that remote island group and we won’t really talk about it here. The two species that are found on the main NZ islands are the Variable Oystercatcher and the South Island Pied Oystercatcher, our Stickybeak mascot. Arriving in NZ, we could see that both of these look strikingly similar to their Australian counterparts, the Sooty Oystercatcher and the Australian Pied Oystercatcher.
The SIPO (as we call it for short) breeds mainly inland on the South Island of NZ, and migrates to the coast of both North and South Islands for the winter. Breeding inland is quite unusual among the world’s oycs, as the Eurasian Oystercatcher is the only other species that often does so. As a migratory species, the SIPO occasionally wanders off course and we were lucky enough to see one turn up in Sydney earlier this year.
The Variable Oystercatcher is much more strictly coastal, and occurs all around the edges of NZ’s main islands. Our first impression of the VO, other than that it appeared exactly the same as the Sooty Oycs we were used to seeing in Australia, was that they didn’t seem to be variable at all. For several weeks, every VO we saw looked just like this:
In fact, the vast majority of VOs on South Island are boringly all-dark, but a small percentage are fully pied and strongly resemble the SIPO. The proportion of pied VOs does increase greatly the further north in NZ you go, and they may even outnumber the dark ones in the far north. There are also some intermediate, blotchy individuals that mainly just have an irregular white belly patch.
A few more tips on how to tell a pied morph Variable from a South Island Pied Oyc. VOs can be larger, noticeably bulkier birds than SIPOS, with shorter and thicker bills. SIPOS often look oddly small-headed and have proportionately long, skinny beaks. Shape may be the easiest way to spot one of those sneaky pied morph VOs that masquerade as SIPOs. But there are other clues to look for. Where SIPO plumage is neatly divided into areas of black and white, VOs are a bit scruffier and tend to have a smudgy border to their white belly. SIPOs usually have a big white patch that extends from the belly up in front of the folded wing, while this is comparatively indistinct or lacking in VOs.
If in doubt, you can always wait for your mystery oystercatcher to fly. SIPOs have much more white in their wings than any VOs do, and have a big white wedge up their back.
Finally, here’s a curious oystercatcher feature to look out for: iris flecks, or iridial depigmentation if you want to sound very academic. If you get a very close look at an oyc’s eyes, you may notice that the pupil seems to be a funny shape, bulging out into the iris on one side. Here’s a SIPO with a large iris fleck:
Iris flecks have been studied in the Black Oystercatcher of North America and found to be a pretty good way to tell the bird’s gender: those with big flecks were almost always (94%) females; those with little or no flecking were almost always males. Similar results have also been found in American Oystercatchers. Looking at pics on the web, all oyc species seem to have eye flecking sometimes, and we’ve certainly noticed it on both of New Zealand’s species. We don’t know if anyone’s actually looked into it for these birds, but check out these Variable Oystercatchers we found near Kaikoura:
These two were certainly a pair, and you can see that one has big iris flecks and the other doesn’t. What’s more, the flecked one has a proportionately longer bill, which strongly suggests that it is the female.
Here’s another pair we had a close look at, SIPOs in Timaru this time:
In this pair, both birds had iris flecks but one had a much larger fleck than the other. This bird also had the longer bill of the two, so again we think this is the female. So, on what we’ve seen so far, we think iris flecks could be useful for sexing oycs of both these New Zealand species too. We’ll be interested to have a close stickybeak at more oyc pairs to see if this is always the case.
To read more about oystercatchers of the world, check out Wader Quest’s nice posts on the subject starting here.