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Wednesday, May 8, 2024

What to consider Hen Harrier numbers – Mark Avery

To make sense of the figures for 2023 UK Hen Harrier numbers, launched at the moment by RSPB, they must be seen in context.  There are 5 essential contextual issues.

  1. There are fairly good estimates of what number of pairs of Hen Harriers might exist in several components of the UK within the absence of unlawful persecution and people recommend that, total, the UK inhabitants is at between a 3rd and a fifth of its potential relying on the 12 months.
  2. Now we have a future of Hen Harrier surveys, carried out in a comparable manner, stretching again over three and a half a long time (see Desk under). There’s little worth in simply specializing in the comparability with the final survey when we now have a run of knowledge. Notably as a result of…
  3. …Hen Harriers have good years and unhealthy years when it comes to whether or not their principal prey within the breeding season are ample sufficient for few or many pairs to settle and breed. Like Brief-eared Owls (however much less so than SEOs) we predict Hen Harriers generally resolve to not settle, or quit very early within the season, if there aren’t sufficient voles of their space. There are good vole years and unhealthy vole years however these fluctuate throughout the UK so there’s a patchy image. Nevertheless, whether or not your survey 12 months is best or worse than common for voles is prone to have an effect on the survey outcomes both a bit, or rather a lot, and with out fairly complicated and costly UK-wide vole information, we now have to grasp that there’s this variation between years.
  4. Hen Harriers transfer round – they will transfer round between years and so they transfer round by shifting from the moors the place they primarily nest to southern components (generally out of the UK) and to lowland and coastal areas in winter. And so the three Hen Harriers I noticed coming in to roost at Wicken Fen in early March would possibly simply conceivably have been single English, Scottish and Welsh birds, and their destiny will likely be decided not simply by the situations on their nesting grounds, or their wintering grounds, however on their journeys between the 2.
  5. Unlawful persecution on grouse moors continues and is a potent consider figuring out numbers.

Listed here are the outcomes:

Hen Harrier Surveys

Potential pairs 1988/89 1998 2004 2010 2016 2023
Scotland c1700 479 436 633 505 460 529
England c330 18 19 10 12 4 50
Wales c250 27 28 43 57 35 40
Northern Eire c150 10 38 63 59 46 34
UK whole c2500 534 521 749 633 545 653

What ought to we make of them?

  1. The UK Hen Harrier inhabitants is at a couple of quarter of its potential degree (examine ‘2023’ with ‘Potential Pairs’) and that’s not good after we imagine that this lack is basically as a consequence of unlawful persecution. Nevertheless, regardless of that, 2023 was…
  2. …total a great 12 months for Hen Harriers throughout the UK; numbers had been good, not simply in contrast with the final survey however in contrast with the 12 months earlier than and the run of surveys going again a great distance. This isn’t true of Northern Eire. It’s true of England the place the variety of pairs was not simply greater, a lot a lot greater, than within the earlier survey 12 months however was additionally greater than the earlier 4 survey years mixed.
  3. Regardless of having an excellent 12 months in 2023 (which we additionally know has been preceded by a run of enhancing years) England continues to be the worst performing nation, in contrast with potential, of the 4 UK nations. Scotland is greatest (regardless of the very fact from earlier surveys that japanese grouse moors are mainly Hen Harrier-free zones), Northern Eire is second greatest (despite the fact that this 12 months was a comparatively poor 12 months there), Wales is second worst and England, regardless of a a lot better 2023 than earlier surveys continues to be worst. If the state of affairs in England had been much like Northern Eire then we’d have one thing like 75 pairs of Hen Harrier in England now. I as soon as supported a lower-league soccer staff and we had good years and unhealthy years however we had been lower-league all the identical – England continues to be lower-league for delivering Hen Harriers. It would take continued enchancment (at a better charge than different nations) for England to get wherever close to Northern Eire on this respect.
  4. That is hypothesis, however knowledgeable hypothesis; I ponder whether the will increase in Hen Harrier numbers in Scotland and Wales are partly as a consequence of lowered spring persecution in England. There have to be lowered spring persecution in England as a result of there are extra Hen Harriers, and harriers passing via England to different nations might profit from this too.


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