I've blogged about Italian Sparrows before, but I didn't expect to be blogging about one here in Norfolk! On Sunday I popped up to see the sparrow at Northrepps that seems to show characteristics of the Italian form italiae, now treated by many authorities as a new species formed by hybrid speciation (i.e. a population of hybrids, in this case Spanish Sparrow x House Sparrow hybrids, that have become sufficiently reproductively isolated from either ancestor species to be treated as a new species).
Italian-type Sparrow, Northrepps (Norfolk), 18th August 2013
It looks good! But is it really an Italian Sparrow?
Here are the options...
1) Hybrid Tree Sparrow x House Sparrow has been suggested. They occur occasionally so it wouldn't be all that exceptional - certainly more likely than an Italian Sparrow. But other than lacking grey in the crown this bird doesn't really resemble Tree Sparrow. Most (if not all) Tree x House Sparrow hybrids have grey in the crown, most have at least a hint of a dark cheek spot, most show buffier tones on the body, they should probably have a smaller bill than this bird. I don't see anything to suggest Tree Sparrow involvement in this individual.
Italian-type Sparrow, Northrepps (Norfolk), 18th August 2013
2) An aberrant House Sparrow. This bird shows reddish-chestnut extending on to the breast band and the white supraloral stripe is virtually absent. That could be explained by an excess of whatever pigment causes that chestnut colour (is that erythrism?) and if it has that sort of pigment issue then perhaps it could be affecting the crown too, flooding that with chestnut colour? I think this suggestion deserves some merit, but it doesn't convince me. It's not extremely unusual for House Sparrows to show very white cheeks, and perhaps the bill bulbous bill is within range for House Sparrow, but what are the odds of a House Sparrow with erythrism generating a completely chestnut crown like an Italian Sparrow also having white cheeks and a big bulbous bill? I can't rule this option out, but I find it rather unlikely.
Italian-type Sparrow, Northrepps (Norfolk), 18th August 2013
3) An Italian Sparrow, i.e. a vagrant from Italy or neighbouring regions. Some features need explaining for this option, namely the chestnut on the breast, the restricted white supraloral and what looks like grey flecking in the crown. The breast is easy - quite a few photos of Italian Sparrows have this. It's not typical but it's not exceptional either. The restricted white supraloral seems to be more unusual, but there are images online that seem to share this feature. At least some of the grey flecks in the crown are not true plumage features but an effect of moult. The bird has several loose or missing feathers and this seems to be revealing grey feather bases. I'm not convinced that there really are any grey feathers in the crown, although this will perhaps become clearer when the bird has completed its moult. So nothing here rules out Italian Sparrow, but we can't get away from the fact that it's not a completely typical Italian Sparrow. If the odds of any Italian Sparrow turning up in a Northrepps garden are low then I'd have thought that the odds of one with chestnut on the breast and virtually no supraloral stripe are significantly lower.
Italian-type Sparrow, Northrepps (Norfolk), 18th August 2013
4) A hybrid between a House Sparrow and a Spanish Sparrow. There are a few references to hybrids between these species away from Italy. Spanish Sparrow has occurred in the UK several times and some have been long-stayers oversummering with House Sparrows, so one producing hybrid offspring isn't very unlikely. Sparrows tend to frequent places that aren't birding hotspots so it's plausible that even a male Spanish Sparrow could have summered and bred locally without being detected - and most birders would be hard-pushed to detect a vagrant female even if it was breeding in their own garden! It's a pretty subjective call whether a hybrid Spanish x House Sparrow would be more or less likely than an Italian Sparrow to appear in Northrepps, but I am personally inclined to think such a hybrid might be rather more likely than a vagrant Italian. As yet I haven't been able to track down any photos or descriptions of Spanish x House Sparrow hybrids, so I'm not sure how their appearance fits in with that of the Northrepps bird. Given the history of Italian Sparrow it seems reasonable to summise that they look a lot like Italian Sparrows, and given that first generation hybrids between any two species (not in every case) tend to be a bit variable we might expect that it will look a lot like an Italian Sparrow but not necessarily exactly like a typical Italian Sparrow. In other words they might look a bit like the Northrepps bird, perhaps. But all that is guesswork - I don't actually know what Spanish x House Sparrow hybrids really do look like. If you can point me to any references that show such a hybrid (proven or not) please leave a comment or get in touch!
Italian-type Sparrow, Northrepps (Norfolk), 18th August 2013
Whatever it is it's an interesting bird - big thanks to Andy and Carl for finding it, letting us know and allowing me to visit.
Maybe DNA analysis will offer some answers in due course...
I think this is not a hybrid, but just an example of erythrism in the House Sparrow.
ReplyDeleteWonderfull serial shots,and article post, best regard from Belgium
ReplyDeleteTaking a fresh look at this and comparing with other photos taken on other dates, including one when it reappeared briefly in 2014, and I'm still not sure what it was. One thing does strike me though - the pale markings in the forecrown. At the time I got the impression that at least some of these were effects of loose or missing feathers revealing grey feather bases, but looking back at the photos now, especially as it's on all of them taken on different dates too (if anything more obvious on some of the others) I think there must have really been some grey feathering there.
ReplyDeleteWhat difference does that make? Not much really, except that it probably counts out option 3, and it probably reduces any rationale for rejecting option 2.
I'm still not convinced it was a House Sparrow x Tree Sparrow hybrid, which is what many people seem to have concluded, but I think I'm finding myself slightly more open to that possibility than I was before.
It is probably a case of hypoeumelanin leucism. This just means that grey pigment is lacking, leaving the reddish phaeomelanins behind.
ReplyDeleteIt gives us an inside into house sparrow plumage. For this to happen the house sparrow crown must already be brown all over by default (like tree sparrow) before the grey sets in. Interesting stuff and great find!
If this was erythrism then red pigment would have to be added. In this case I see no reason to jump to this because the crown area is already this rusty brown colour normally.
DeleteThanks for your replies. I guess your idea is a variation on my option 2 and it does seem plausible.
DeleteI am still favouring the hybrid theory, but I am not sure. Interestingly it has been published as House Sparrow x Tree Sparrow, which at the time I considered to be incorrect. I'm still doubtful, though a little less convinced it's not right than I was. I remain open-minded as to the solution - we may never know for sure but in time we may develop a better understanding of variation within House Sparrow x Tree Sparrow hybrids and perhaps also House Sparrow x Spanish Sparrow hybrids, and then we may be in a better position to draw a conclusion.