June 2nd, 2012, 01:56 AM
There are one picture of the wing on the picasa site and some more that are not uploaded on the web. I don't have the pics available right here but there should be pics showing upperparts, tail, head etc in my arcive.
In Eilat where the picture is taken hybrids seems to be quite rare but this bird was picked out as an oddie. In SE Sweden, especially on the islands Öland and Gotland, hybridisation is very common where pied and collared are found in the same area.
June 2nd, 2012, 06:55 AM
Originally Posted by Aron
I'm sure you just slipped with your fingers (like I often do), but for the sake of the discussion: The bird was photographed in August and, hence, should be labled as 2cy+ (not 3cy+).
June 2nd, 2012, 07:41 AM
Would be interesting to see the upperparts if you had time to load.
I don't think I'd describe hybridisation as 'very common' on Gotland, even when both species are found in the same area. In the southern part of Gotland the frequency of hybrid males is 2% or so, and the frequency of mixed pairings about the same order of magnitude. On central Öland the rate of mixed pairing is c. 6% (see Vallin et al. 2011 Evolution).
June 2nd, 2012, 08:51 AM
Hi Ben et al.
Here at Ottenby, S Öland (where both Aron and I work) the incidence of hybrids is more or less in accordance with your figures - or perhaps slightly higher. Since 2000 we have caught 72 pure Collared, 5 hybrids and 4 probable hybrids. The population of Collared on Öland have increased rather sharply during the last 15 years as the species have expanded southwards over the island, and most birdwatchers would (probably) agree that Collared nowadays is more numerous than Pied. The latest published (2012) estimation gives 800 pairs on Öland, but in my opinion this figure is too low - I believe that the actual population is 2-4 times as large. However, in the southern 1/4 of the island Collared is still rather scarce and local, and my guess (only a guess) would be that hybidisation is more common in these areas. The frequency of mixed singers (hybrids or not) is high, adding to the impression that the species barriers are rather weak here...
June 2nd, 2012, 09:24 AM
Interesting figures. I've only got second-hand experience of the situation on Öland (although I still have fond memories of my first adult male Collared singing in Ottenby Lund in May 1994 - what a bird!), but on Gotland the proportion of Pieds dropped through the 1990s so that the hybridisation frequency also dropped. I'm a little out of touch with things in Sweden, but I think I'd heard that Collared is increasingly seen on mainland Sweden, which might suggest a general range expansion underway. We found on Gotland that Collareds seem to displace Pieds into forest that had a higher proportion of evergreen trees, so in some sense Aron is right that the hybridisation rate is high when they both occur, because even over a very small scale there is a degree of habitat segregation that keeps many of them apart.
June 2nd, 2012, 04:39 PM
This increase in Scandinavian Collared Flycatchers is welcome but it surprises more that here in the UK we are seeing no signs of an increase in number. We are very lucky to see two records per annum. Perhaps though, we are either overlooking or misidentifying them, especially female/juveniles. In reality, I would expect to see the same correlation as we are seeing with Red-flanked Bluetails (status changing from an extremely rare one every 20 year vagrant to over 30 per annum and in line with the population explosion in Finland and further east). The incidence of hybridisation though, I suspect, is likely to increase
June 2nd, 2012, 07:38 PM
Different overwintering abilities; a bluetail with an anomalous migration route ending up in W Europe has a good chance of surviving and passing its genes (and migration route) to offspring and so setting up a new population using a new migration route, whereas a flycatcher is highly unlikely to survive a W European winter, so west-bound birds have no continuity, relying on further sporadic individual mutations.
Originally Posted by LeeEvans
No reason why it should; hybridisation typically only occurs where individuals can't find a mate of their own species, so happens on the fringes of one of the species' ranges. The fringe may move in location, but needn't cover a larger area and involve more hybridisation events. Comparison: as Syrian Woodpeckers have spread into central Europe, hybrids with Great Spots have only occurred at all regularly at the edge of Syrian Wp's range, not in areas where it is established.
Originally Posted by LeeEvans
June 2nd, 2012, 10:41 PM
The increase in breeding numbers of Collared Fly we're talking about here is, I think, on nothing like the scale of that of Red-flanked Bluetail. With the latter, we're presumably seeing the western expansion of the edge of a huge population that breeds in the taiga forest across Russia. In the case of Collared Fly we're talking about isolated populations on the islands of Öland and Gotland which probably don't number much more than 10,000 pairs at most. They've been on Gotland in good numbers for a long time; it's only on Öland that there is a recent serious population increase. The other records in Sweden relate to a species that is still - I think - a good bird to see on most of the mainland, so they are far from common.
As to the frequency of hybridisation: this has been actually been declining on Gotland in recent years. In any case, it is worth remembering that there are vast numbers of Ficedula flycatchers in Fennoscandia than never come anywhere near a Collared Flycatcher. I don't have an estimate of the population size of Pied Flycatcher in this region to hand, but it will be in the millions. Hybrids are a very tiny drop (perhaps 0.02%?) in that ocean, so there is no reason to expect them to be a common problem for us. Assuming all else equal, you'd probably need to look at something of the order of c. 50 000 Pied Flycatchers and 50 Collared Flycatchers of scandinavian origin in the UK for every hybrid from that region you'd see. People will have problems with the 'all else equal' argument, and it is sometimes suggested that the migration direction of hybrids might make them more likely to occur as vagrants. I don't see any reason to expect them to be more likely. The little we know about the genetic control of migration direction would suggest that a hybrid PF*CF would take an intermediate migration route to the two parental species, although Thor Veen and colleagues looked into this using stable isotopes, and the evidence suggested that hybrids might be more likely to share wintering grounds with Pieds, but I am not aware of anything to suggest they are more likely to occur than the ratios suggested above. Of course, there are plenty of other parts of the range where CF and PF overlap in range in Central Europe. These populations are a bit less well studied, but as far as I know things are broadly comparable.
June 3rd, 2012, 10:56 PM
Many thanks for your comments. By rights, there should be a Collared Fly in the UK in the next week or so.
All the very best