Wednesday, 17 February 2010

Does anything harm birds any more?

First it was squirrels, windfarms, then cats(!), now ravens. The RSPB seems to be on a mission to prove that all the usual suspects have no impact on birds whatsoever.

It can only be a matter of time before we see the society issuing a press release headed: "New research shows gamekeepers no threat to birds".

Meanwhile the GWCT have proper scientific research (c.f. guesstimates and waffle) to prove that sparrowhawks kill up to 40% of grey partridges (a threatened BAP species) overwinter. Expect an RSPB denial imminently.

16 comments:

Andy Richardson said...

The Abernethy Pine Martins did no harm whatsoever to breeding birds so the RSPB told us.

Then someone let the cat out of the bag and stated that out of 20 Capper nests being filmed on the reserve most were destroyed by ?

Yes the Pine Martins.

vicky said...

Unfortunately many of he conservation groups are focused on one animal or group of animals and fail to consider the managed environment as a whole. A balance can be acheived between predaors and prey but only if data on their relationships is collected scientifically and properly assessed and used. Sadly too many times good data is corrupted/ misrepresented to grab headlines or because the truth will be unpalatable to the membership and wider public.

sam_acw said...

.... but pine martins and birds of prey and cats are all cute and cuddly. Surely they can't kill anything? They must be like foxes and live on a diet of slugs and snails and old McDonalds.

alan tilmouth said...

James you must be feeling dizzy by now with all this spin and misrepresentation of good data. Most previous studies on Grey Partridge have found a similar late winter predation rate, the rates are even higher for captive bred birds as they have less well developed predator avoidance strategy. Many bird species with large brood sizes have high winter mortality otherwise we would be overrun with them, it only needs two birds from a brood of 10-12 (i.e 20%) to survive to maintain population levels each year. Other studies such as Potts 1980 & 1986) have demonstrated that the key factor controlling spring density of Grey Partridge is chick survival rate rather than winter predation.The other factor that you make little mention of is the impact of radio-transmitters, various studies have recognised that the fitting of radio transmitters causes individuals to be more susceptible to predation and quote "As a consequence, mortality pattern observed on
radio-tagged grey partridges should be interpreted with
caution and should not be extrapolated to the whole
population."

James Marchington said...

Hi Alan. Not many captive bred greys round my neck of the woods. I'm sure there's more work to be done, but from keepers' experience I'd expect to see 'problem' individual sparrowhawks developing a taste for partridge and cleaning out an area (rather like the one that discovered my mum's bird table served up a regular easy meal of blue tit, and only moved on when he'd scoffed the lot). I'd be surprised if modern radio tags made a real difference, but it would be simple enough to test.

What amuses me is the extraordinary flexibility in interpreting research, and if the facts don't support the predetermined line they just make some up. Politics wags the science dog, and the media don't even bother to question the spin they're fed. See, now you've got me sounding off like a grumpy old git!

James Marchington said...

Interesting idea about radio tags making birds more susceptible to predation, but looking at various studies they appear to acknowledge it as a possibility but observations suggest otherwise.
Chick survival will be crucial, but little use if they then don't make it through the winter - predator control and habitat have got to be part of the equation.

alan tilmouth said...

Yes the references to captive bred birds having higher winter mortality rates (up to 79%) were from an Italian study although the causes were more mammalian than avian. I think as most Grey Partridge disperse from coveys, (which is the key time for predation as they are more vulnerable at field edges and hedges than in the middle of fields) at around the same time Sparrowhawks are establishing territory its unlikely they would 'clean out the area and move on'.Sparrowhawks are opportunist and will feed on what's available within their territory and they simply wont catch all the GP's. You have to question how the two species have managed to evolve and survive in balance together for thousands of years until we began to interfere with habitat, numbers etc in a big way during the 19th century. By the way you mentioned Blue Tit as another victim, that species has an annual mortality rate of adult of 70% and the juvenile mortality rate is higher until November when it then drops to the same figure, again another bird with a large average brood size, a factor presumably evolved to cope with high mortality. We agree that the interpretation of research is becoming ever more flexible, particularly on studies that have a very small scale, the GWCT study you cited as good science only involved 64 radio tagged birds, I understand the reasons why Costs etc but it is then difficult to base sound policy on.

Andy Richardson said...

As an ex wild partridge keeper I have to smile at the science.

Spring is the time to work on the partridge population.

Badgers and Hedgehogs are the main nest predators.

Foxes and Sparowhawks can be a problem as well but without good habitat the little grey bird is doomed.

James Marchington said...

I think the 'evolved and survived in balance' idea is a bit rose-tinted. In any case, the world those species evolved in no longer exists - we've shaped it over the past few thousand years into something quite different (these rewilding enthusiasts would get a shock if they had to live in the landscape they so long for!).

'Predator control' needn't mean killing sparrowhawks, despite what some of my suburban neighbours might wish. I've seen some ingenious methods of protecting game feed hoppers with sheep fencing, and growing the right cover makes a huge difference.

In my experience the sparrowhawk's territory is large enough that it can move on to the next blue-tit takeaway (or etc) on its patch once that source is exhausted (or to be more accurate, the calculation of effort v reward shifts).

I'm sure larger samples would be preferable, but calling for 'more research' is a classic delaying tactic and in the meantime one has to be doing something.

Don't choke on your cocoa, but I ate a grey partridge the other day - absolutely delicious, totally different to those French imposters. It came from one of the big shooting estates that have been so successful at restoring numbers that they are now allowing limited shooting again.

James Marchington said...

Good point Andy. So if a badger eats a hedgehog, is that natural pest control in action? I wonder if sea eagles eat badgers...

vicky said...

OMG. Everyone agrees on something- habitat is the key! If the partridges have good cover need good food sources they'll be less at risk from the sparrowhawks who'll opt for some easier (and less threatened) dinner. Phew. I'm off for a lie down.
This is why shooters and birders must work together; the general public wouldn't be greatly upset if there were no grey partridge BUT WE WOULD! So there needs to be predator management (sometimes lethal, sometimes by using protected feeders etc) AND habitat improvement. Perhaps birdwatching groups could work with local shoots to help them improve their land management for wildlife as well as shooting and get the opportunity to birdwatch in some otherwise private areas? I'm sure both sides can learn from each other...

Charlotte said...

Predation is an issue but it's not the main cause of decline in most species. I'd like to see more attention given to providing healthy invertebrate populations, since they make up over 65% all species on earth and many bird species feed on inverts for at least part of their life cycle...including grey partidge chicks.

The GWCT radio tagged some grey partidge on my parents farm in 2008 - I believe they were all accidently shot that season! The radio tags must have slowed them down. It probably made them easier prey to sparrowhawks too.

Den said...

Lots to be going on with there James.All interesting points,very good information on the losses of Grey Partridge and think like you it would be nice if more cover or something saved the losses as their are not that many Sparrow Hawks and they would move on to easier prey.We certainly need more GP and persoally got doubts about all this tagging as we get information but think it must hinder the birds.Feel sure your bit of fun,Sea Eagles do not eat Badgers in fact I am amazed having seen so many SE and read so much about them no one seems to have seen them catch anything except fish and sea birds.Only my thoughts but honestly given I think if they even caught say live lambs someone would have reported it.Of course like lots of predators they will clear up deadstock,easy meat.

James Marchington said...

Yeah, just pulling Andy's leg about the badgers. We all know sea eagles are really flying billboards for the RSPB. I hear they're training them to flick V-signs at blokes in tweed.

Den said...

Seriously funny James but I bet even guys in tweeds will go wow when they see one even while the Eagle giving them the v-sign.Must say you often make me laugh even when I doubt your intentions.

James Marchington said...

Hi Den, glad to hear you enjoy the blog. I must say, every time I've spotted a sea eagle (or golden eagle, harrier, peregrine, etc) I just stand there open mouthed. They are wonderful birds to watch.