It seems Natural England has some (more) explaining to do.
In the latest NE update on satellite-tagged hen harriers published last Friday, buried amongst the spreadsheet notes and carefully not mentioned in NE’s accompanying blog, I found the following information:
Two sibling hen harriers, both hatched in the same nest in 2020 (nest site: BM R2 Cumbria) and both brood meddled as part of NE and DEFRA’s sham conservation project, apparently ‘bred successfully‘ in Co Durham in 2021 (see lines 43 & 46 in the March 2022 spreadsheet).
The two incestuous individuals are Male R2-M1-20 and Female R2-F3-20.
Isn’t that interesting? Two young hen harriers, removed from their nest (along with two other siblings), raised under artificial conditions in captivity, released back to the wild just after reaching fledging age, pair up the next breeding season and produce offspring.
I don’t know what Natural England means by ‘bred successfully‘. I wouldn’t call an incestuous breeding attempt ‘successful’ by any stretch of the imagination. I’d call it deeply concerning, at the very least.
I haven’t heard of incestuous hen harriers before. Quite a bit has been written by several authors on the intimate details of the hen harrier’s love life (which is why we know that polygyny can be common) but I haven’t been able to find any reference to incest.
I spoke about it this morning to my colleague Mark Avery, who said that incestuous relationships are probably very common in the uplands of England but I don’t think he was referring to hen harriers.
I wonder how Natural England will explain this behaviour? It’s clear they’re not that keen to explain anything, because otherwise they would have already drawn attention to this incestuous pair.
One for the brood meddling scientific committee to answer, perhaps.
Meanwhile, standby for more news of vanishing hen harriers; yet another indication that this brood meddling trial is utterly futile.
Raptor Persecution UK 
Perhaps an indication of scarcity of available partners ? I have no knowledge of sibling mating in birds and how common it is – I’d imagine the usual autumn dispersal of immature birds is nature’s way of trying to avoid it.
Interesting paper on close breeding in wild peregrines
Click to access close_inbreeding_1998.pdf
I am totally appalled by NE’s actions with regard to these Hen Harriers. It is far better not to ‘brood meddle’ even if convinced it is for the best. Other bodies would probably be prosecuted if they behaved like this. The consequences have been dire to say the least, so I hope NE have learned from their actions.
Harriers are both monogamous and polygamous. Polygamous males usually have two or three mates. This is nothing to get your knickers in a twist! Certain species siblings will also help out with food provisions, common buzzard being the obvious but also peregrine.
Thanks, Tom, but the issue is not about cooperative breeding (part of the subject of my PhD as it happens), nor polygyny. The issue is about inbreeding between full siblings, in a declining population, and those two siblings just happening to have been brood meddled. There’s a lot to question there.
Patronising comment. Especially on International Women’s Day. Or had that passed you by?
When the resident peregrine Tiercel disappeared a two year old son took his place. Mother and son fledged a number of young until she was replaced.