Apologies for the late posting of the mystery object answer, I’m at a conference in Edinburgh and I didn’t get a chance to write until now.
On Friday I gave you this bird skull to identify:
I thought it might be an easy one, but I was hoping to catch a few people out, which use exactly what happened.
This skull is a nice example of morphological convergence – looking a lot like a Pigeon skull, but it is actually the skull of a Northern Lapwing Vanellus vanellus (Linneaus, 1758).
I’ve written about these birds before, so I’ll keep this answer short, but I think it’s worth mentioning the small scars from the salt glands on the top of the head – which are one of easiest ways of differentiating this skull from that of a Pigeon. These salt glands are normally associated with marine birds (which is also something I’ve talked about before), but Lapwings aren’t really marine. So why do they have them?
As it turns out, that’s not an easy question to answer. The obvious answer would be that the salt glands are a vestigial artefact of the Lapwing’s recent ancestry amongst the shore-foraging Plovers. However, salt glands are quite variable structures that can increase in size if a bird is exposed to more saline conditions. This flexibility (and the relative metabolic expense of maintaining them) suggests that they wouldn’t be a difficult structure to lose, or at least reduce to the point where they don’t leave a scar, over a few generations of disuse. There are certainly other Charadriiformes (like the Snipe) that don’t have salt gland scars, so why do the Lapwings? Perhaps it’s just that the sodium secretion function is still of use in some habitats during their migration.
If you have any thoughts on this please feel free to put them below – it’s a bit of a puzzle for my conference addled mind… More about salt glands here if you’re interested [pdf].