Willow Tits in Britain - inbreeding & partial albininism (1 Viewer)

halftwo · Mar 10, 2017

If inbreeding is the cause then why don't tiny populations on isolated islands exhibit the most albinism?
Having just returned from Philippines I'm thinking of , e.g. various Scops Owl species (Mantanani, eg.) occupying tiny islands around the world, which, presumably, have been interbreeding for maybe thousands of years, which show no such signs.

lewis20126 · Mar 10, 2017

halftwo said:
If inbreeding is the cause then why don't tiny populations on isolated islands exhibit the most albinism?
Having just returned from Philippines I'm thinking of , e.g. various Scops Owl species (Mantanani, eg.) occupying tiny islands around the world, which, presumably, have been interbreeding for maybe thousands of years, which show no such signs.

Have a look at the Pacific Reed-warblers...

You've also got to think about dispersal mechanisms, eg Scops Owls (and indeed many species) are very mobile / dispersive so limited populations on "small" islands may be subject to a high degree of mixing from the whole range. In most cases the islands are actually not that small whilst on the smallest islands, the birds are very very common (eg Ryukyu = Lanyu Scops Owl is a classic) so the populations are not that small.

Edit- you've mentioned Mantanani - a classic inter-island tramp species, look at its range..

It has always been speculated that Willow Tit is very poor at dispersing - I haven't checked UK ringing recoveries but this is surely the case.

cheers, alan

lewis20126 · Mar 10, 2017

stonechat1 said:
Sorry but I doubt that, Alan.
If that would be true all not migrating birds living all islands must be white since decades, they aren´t. E.g the Golden-shouldered Parrot, an endemic of the Cape York Pen. in Australia with only 2500 birds. I assume there´s inbreeding too.

Regards,
Roman

2500?? I've only just noticed that.

That's a huge population in the context we're talking about with small isolated WT populations, perhaps just a few isolated pairs, with no in/out migration.

cheers, a

Paul Chapman · Mar 10, 2017

OK. To say that I am trespassing on areas that I know nothing about is this week's understatement of the week!

I think that the suggestion is not necessarily that the inbreeding causes albinism but that if there is the relevant mutation gene within the population that the inbreeding can increase the likelihood of its occurrence within both parents and that is the trigger?

Maybe the small populations to which reference is made simply do not have the gene at all in which case the increased level of inbreeding will have no effect or the incidence of the gene is more prevalent in some families than others eg the attached where the highest incidence was in American Robin in the States matching our experience with Blackbird on this side of the pond?

I suspect that my comments may simply be a load of turdus.

All the best

Paul

lewis20126 · Mar 10, 2017

Paul Chapman said:
OK. To say that I am trespassing on areas that I know nothing about is this week's understatement of the week!

I think that the suggestion is not necessarily that the inbreeding causes albinism but that if there is the relevant mutation gene within the population that the inbreeding can increase the likelihood of its occurrence within both parents and that is the trigger?

I don't know the mechanisms, which themselves are likely to vary from case to case, but very small populations and the consequent breeding with relatives causes incidences of abnormality which are higher than would be expected in larger unrelated populations. This is true for humans, captive tigers and I suggest small isolated populations of Willow Tits.

cheers, alan

lewis20126 · Mar 10, 2017

lewis20126 said:
I don't know the mechanisms, which themselves are likely to vary from case to case, but very small populations and the consequent breeding with relatives causes incidences of abnormality which are higher than would be expected in larger unrelated populations. This is true for humans, captive tigers and I suggest small isolated populations of Willow Tits.

cheers, alan

Captive Bald Ibises in Turkey with short bills? I have some distant memory that this was suggested as due to in-breeding?

cheers, alan

Jos Stratford · Mar 10, 2017

Paul Chapman said:
OK. To say that I am trespassing on areas that I know nothing about is this week's understatement of the week!

I think that the suggestion is not necessarily that the inbreeding causes albinism but that if there is the relevant mutation gene within the population that the inbreeding can increase the likelihood of its occurrence within both parents and that is the trigger?

Maybe the small populations to which reference is made simply do not have the gene at all in which case the increased level of inbreeding will have no effect or the incidence of the gene is more prevalent in some families than others eg the attached where the highest incidence was in American Robin in the States matching our experience with Blackbird on this side of the pond?

I suspect that my comments may simply be a load of turdus.

All the best

Paul

Reflects my suspicions too, though I might well fall in the same category as your last sentence.

lewis20126 · Mar 10, 2017

Inbreeding; focus on humans, but useful on mechanisms:

https://en.wikipedia.org/wiki/Inbreeding

cheers, alan

Xenospiza · Mar 10, 2017

halftwo said:
If inbreeding is the cause then why don't tiny populations on isolated islands exhibit the most albinism?
Having just returned from Philippines I'm thinking of , e.g. various Scops Owl species (Mantanani, eg.) occupying tiny islands around the world, which, presumably, have been interbreeding for maybe thousands of years, which show no such signs.

In addition to the Pacific Reed Warblers, I can think of the white Ravens of the Faeroes (shot to extinction) and the white Swamphen of Lord Howe (likewise). I believe the mostly extinct Pomarea monarchs also exhibit(ed) variation that can be explained by leucism.

Melanistic populations occur in e.g. Japanese Tit (Ryukyu), Blackcap (Canaries) and Bananaquit (Caribbean).

lemonskinny · Oct 10, 2018

Hi

I started a thread today asking for help id-ing a tit at Fairburn Ings, Yorkshire, and it appears to be a Willow Tit with plumage aberration ie more white on the head:

http:// https://www.birdforum.net/showthread.php?p=3774000#post3774000

Muppit17 · Oct 11, 2018

lewis20126 said:
I've finally caught up with Hampshire's first (?) Willow Tit with abnormal white bits, the same bird as linked above, see attached for my pic this morning.

cheers, alan

Only just came across this thread.

"Facing extinction" book expounds the possible causes of the gene disruption and then plumage aberrations.

The Willow tit that Alan photographed was on territory in spring of this year as well. Seemed not to have a pure song as well as the plumage issues.

Willow Tits in Britain - inbreeding & partial albininism (1 Viewer)

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