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Fylingdales Moor- why not more raptors?


Tanya Eyre:
At the talk Tanya gave the Whitby Naturalists on 15th October on Managing Fylingdales Moor, I was asked at the end:
"Why aren't there more raptors on the moor?"
On asking the Conservation Manager for Fylingdales Moor, Professor John Edwards, this is his reply:
"How many should there be?" As with all species, the numbers able to live in any particular area will depend on the suitability on habitat, the density of prey, and the level of disturbance. I have previously calculated that Fylingdales Moor could hold between 0.5 and 2 pairs. In fact, we have at least 3 regular pairs (possibly more), so on that basis we are doing well for Merlins. For other species there are similar limitations on population size.

Expanded explanation from John
    How much moor does a Merlin need? 
Many factors will determine how many Merlins will be present on a given area. Suitable habitat is important (and something that we can do something about - by heather management), but so is food supply, lack of disturbance, etc. Wilf Norman has some good information about preferred nesting locations. As for the question "how many Merlins can we expect to have if the management is good?" - this is more difficult to answer. It is a question that interests me greatly because we too need to be able to judge the effectiveness/success of our moorland management in relation to Merlin breeding success.  My own view is that one can best judge how well management is doing by aiming to get what might be judged a "high" Merlin density on your patch. What is a high density of Merlins? For the whole of northern England, Bibby and Nattrass (1986) estimated mean density of 2.3 breeding pairs per 100 square km of heather dominated moorland, but unpublished studies by Nattrass in Durham and the North York Moors indicate that this density can go as high as 8 pairs per 100 sqkm in some areas. It seems reasonable to take a figure somewhere in between these - say 5 to 8 pairs per 100 sqkm of moorland - as a "high" density, and 2 to 4 pairs as a "good" density. Of course, this assumes that there is sufficient "suitable" heather, food, etc., to sustain such a population. Calculations of the "nearest neighbour" distance (Wright, 2005) gave a mean of 1.75km between nests (range 0.35 - 4.7 km), and in the Fylingdales area in 2006 we had two nests that were almost exactly 1.5 km apart. I use the lower of these approximations as "target" densities for Merlin on Fylingdales Moor. Thus, Fylingdales Moor occupies about 25 square kilometres (most of which is potentially suitable for Merlins) so we could expect to have 0.5 to 1 pairs if the density was "good" and 1.25 to 2 pairs if the density was "high". Of course, these are guidelines - not rules. In any case, I doubt that Merlins know about these values! It is quite possible that in really excellent conditions of habitat and food supply, etc., one could exceed 8 pairs per 100 sqkm. Fortunately for monitoring, Merlins tend to return to the same nesting area year after year – so once you have found your Merlins, you can (usually) keep an eye on them. The difficulty is finding all of your Merlins in the first place (Wilf is fantastic at this, but it isn’t easy). So I believe that monitoring is very important – otherwise

Johns reply when I asked about buzzards:
“Lack of trees on the moor will contribute to the paucity of buzzards compared to Harwood Dale area.”
Also, read John’s comments below-
from the Fylingdales Moor Bird Surveys Report 2008

Buzzard (Buteo buteo)

The Common Buzzard is one of the species which (surprisingly) we have not recorded in our previous surveys in 2005, 2006 and 2007. This is surprising because the Buzzard is a species that has shown remarkable population increase and range expansion in recent years – especially in Eastern England (Clements, 2002). Thus, it was with some delight (and relief) that 2008 produced the first record of a buzzard (on NZ 96/00) obtained during the formal surveys. Outside the formal surveys, another record was obtained from a different square (NZ 91/04). Subjectively, the Buzzard is becoming more common in North Yorkshire, and has certainly increased over the 12 years that I have lived here. However, the population in this region remains lower than that in many other parts of the country.

Up until about 1800, it seems that the Buzzard was one of the most widely distributed and abundant of our larger birds of prey (Moore, 1957; Nelson, 1907). However, by about 1900 there had been a dramatic change, and in 1907 Nelson commenting on its status in Yorkshire wrote “confined to one or perhaps two pairs; also an irregular spring and autumn migrant”. Following some recovery during the period of the two World Wars, the UK population was again badly hit by the introduction of the Myxoma virus in the early 1950s and the consequential reduction in rabbit numbers. Latterly, several factors have resulted in a general increase in the numbers and distribution of Buzzards in the UK. First, the rabbit population has largely recovered from myxomatosis – rabbits being an extremely important part of the bird’s diet (Brown, 1976; Graham et al., 1995). Second, even ‘though Buzzards may have succumbed less to the harmful effects of organochlorine pesticides (because their diet is predominantly mammalian) than many other birds of prey (especially those whose diet is predominantly seed-eating birds), the withdrawal of such toxic and persistent chemicals will have done buzzard populations no harm at all. Finally, the (slow) spread of a more enlightened attitude towards birds of prey among farmers and gamekeepers has probably reduced the impact of persecution on Buzzards in many parts of the country (Sim et al., 2000). However, such persecution persists in some areas as recorded by the RSPB review of Buzzard persecution (Elliott and Avery, 1991). In this review of the period 1975 to 1989, 283 buzzards were illegally killed in Britain, mostly in spring, and the deaths were largely attributable to the misuse of pesticides. Why would anyone wish to kill a Buzzard?  Neither those with sporting interests on commercial grouse moors, nor those who rear and release pheasants or other gamebirds for shooting, or those who rear livestock have much to fear from the predation of their animals or gamebirds by Buzzards. Analysis of the diet of the Common Buzzard (Table 4) shows that Lagomorphs (rabbits and hares) and other small mammals form a very substantial part (48.8%) of all vertebrates in the Buzzard’s diet. By contrast, the number of gamebirds recorded represents only a tiny proportion (0.67%) of the diet. In a different study, of 20,725 juvenile pheasants released in 1994/95, gamekeepers attributed only 4.3% of deaths to Buzzards (Kenward et al., 2001). 

Table 4. Numbers of prey items in the diets of British Buzzards.

Numbers based on data from several studies. Data taken from Brown, L. (1976).
Key: Lagos. = Rabbits and Hares; S. Mams. = small mammals (voles, shrews etc.); Carns. = carnivores (mustellids, etc.); Carrion = carrion (including sheep); Game Bds. = Pheasant, Grouse, etc; Non pas. = other non passerine birds; Corv. = corvids; S. Pas. = small passerines; Unid. = unidentified birds; Rep/Amph = reptiles and amphibians; Inverts = invertebrates (worms, insects, etc.).     

Lagos.   S. Mams.   Carns.   Carrion   Game Bds.   Non pas.   Corv.        S. pas.    Unid.   Rep/Amph.   Inverts
  319             695             7           18            14            201             394         168    44           215                    >3000

Despite the lack of any evidence that Buzzards do any real harm to farmers or to those with shooting interests, it seems that there is still an element of persecution that may hinder the future increase and spread of this most attractive large bird of prey. Continued persecution is even more surprising when one considers that rabbits and Corvids (both considered to be pest species) feature heavily in the diet (Table 4). Within the North York Moors National Park there would appear to be plenty of suitable habitat and abundant food resources for Buzzards. Hopefully, if persecution can be eliminated, Buzzards will continue to increase, and we can look forward to hearing the enigmatic and characteristic “mew” over our moors and wooded valleys more frequently in future.

david cunion:
That is a really interesting and comprehensive analysis. It would be nice to see the comments about buzzards being no threat circulated to local estate managers and their gamekeepers....

Dave Perry:
There are other more complex reasons and it is not always simple to predict. 

For example Hen Harriers are considered a moorland bird here but in Eire and Scotland they'll also nest in young forestry, but mainly hunt over the nearest available  habitat whether it is heather moorland or rough grazing land.  I'm not aware of them nesting in forestry in north yorkshire.  All the hunting Hen Harriers I've seen have been using a combination of moorland and/or the heads of dales or marginal farm land.  They also require mature heather here to nest  and like many larger birds prefer a site with a good view of the surrounds.

Now, if you manage the moorland to provide a large number of prey items you'll create a better food source for harriers and in many cases will also provide an increase in possible nesting sites for prey items also.  Golden Plover for example will ONLY nest on bare recently burned moorland.  Grouse will only nest in pretty dense heather.  Equally removing anything that eats young grouse or their eggs increases the opportunity for other smaller moorland specialist birds to  successfully rear young.  This includes snipe, golden plover, curlew, meadow pipit and so on.  This variety of heather stands (burnt, new growth & mature) need carefully managed rotated burning every year over a 15 to 20 year period are ideal habitats for these smaller birds too.

Compared to 'commercially managed' moorland the birds mentioned above are generally at much lower densities on flylingdales moors.  (I've carried out surveys on both and have made general observations since the 1960's)

It is no coincidence therefore that the areas on the north yorks moors with the highest density of these 'prey' birds are those estates which are heavily managed towards grouse shooting and employee gamekeepers who remove stoats, hedgehogs, foxes, weasels, crows, magpies and anything else they consider a danger to grouse.  Therefore you would expect that Hen Harriers would be in abundance.  The reason they are not is pretty obvious.  They are removed at any opportunity for the simple reason they will eat young grouse. 

And they probably won't nest on Fylingdales moor in any appreciable numbers until the moorland is managed to allow large areas of mature old heather to be left along with heather rotation on the remaining areas in the same way a shooting estate is managed. 

Alas a lot of our moorland is confined to narrow ridges and other higher ground (unlike say Scotland or the dales, where you'll find plenty of areas where you can often be completely surrounded by large areas of continuous moorland)  So a 'Harrier, even if it did nest successfully on Flylingdales would almost certainly stray off the moor onto other areas of land where shooting is  commercially managed.  As many of you know, many of the moorland dales are heavily populated by artificially reared pheasants and french partidge.  Thus it might be safe on the moor but if the harriers flew off it .............!!!

So it isn't just about creating a 'safe haven' and leaving it to 'nature'


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