Hen Harrier checks. Photograph: Gordon Yates

The investigation of brood meddling of Hen Harriers which Pure England has licensed has resulted in 14 chicks being taken into captivity and 13 of them being launched into the wild once more. That sounds fairly good, however how would we assess how good it’s?

Clearly, we are able to’t merely examine the variety of captive-reared chicks with the fledging success of all actual Hen Harrier nests over time.

Why not?

As a result of that may not be a like-for-like comparability as I have mentioned before.

Let’s take 2020 when two nests had been brood meddled: the chicks had been removed on 2 and 6 June from the 2 nests. I don’t suppose now we have been instructed the age of the chicks when faraway from their actual nests however that date of early June suggests the chicks had been pretty younger. However we do know they had been chicks not eggs. So we are able to’t merely take the survival fee of any outdated Hen Harrier nest both in 2020 or every other 12 months as a comparator as a result of we should always solely be evaluating the survival charges of chicks with chicks and never with eggs and chicks.

Simply in case I haven’t made the purpose sufficiently clearly, if the eliminated chicks had been taken once they had been very near fledging (they weren’t, that is for illustrative functions) then they might be in captivity a matter of only a few days. One couldn’t, clearly, examine their survival over these few days with the survival of Hen Harrier nests from egg-laying to fledging, nor with the survival of day-old chicks to fledging – neither could be evaluating like with like.

Ideally, we’d examine the survival of the captive-reared chicks with actual nests in the identical 12 months, over the identical calendar interval, of the identical age, additionally on grouse moors and in the identical geographic locality. That may be fairly taxing and is perhaps not possible. Nevertheless, the truth that every brood-meddled nest has to have a non-intervention nest close by makes it maybe potential. I don’t know, as a result of Pure England may be very secretive in regards to the knowledge from this ‘research’.

Will probably be fascinating to see how Pure England search to do that comparability.

There are a number of different points round assessing brood meddling which I’ll come to later.

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