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Sparrowhawks responsible for House Sparrow decline says scientist (1 Viewer)

CPBell

Well-known member
Anyone who's read enough of this thread will be aware that I first became interested in sparrows while working at London Zoo, which had the last large sparrow colony in central London - about 150 of them. It's recently become apparent that the population has grown considerably over the last 5 years, and has recolonized parts of the zoo from which they've been absent for decades. Why could this be? Decking going out of fashion? Off-road parking spaces infra-dig in NW1? Maybe because the RSPB have planted some wildflower patches on Primrose Hill? Or could it be because Sparrowhawks have stopped breeding in Regent's Park?

Join me here on my day out at the zoo!

http://www.cpbell.co.uk
http://www.youtube.com/CultoftheAmateur
 

Amarillo

Well-known member
Why could this be? Decking going out of fashion? Off-road parking spaces infra-dig in NW1? Maybe because the RSPB have planted some wildflower patches on Primrose Hill? Or could it be because Sparrowhawks have stopped breeding in Regent's Park?

Sounds like its definately the sparrowhawks, I wouldn't even bother with the other possibilities;)
 

hinnark

Well-known member
The House Sparrow decline (same phenomenon over here as well) is caused by sterility of their environment. The sparrows need insects for the youngs, places to build their nests, a place/shrubs to hide with their family and clan and open sand areas for bathing. Once one of these four basic needs falls under a certain threshold of availabilty, the decline is going on.

Steve
 

Dimitris

Birdwatcher in Oz
This study was definitely on Great Tits.

As to predators having an effect on population size. Of course they do. They're an extra pressure, remove them and the population (may) increases (or even explode: e.g. Rabbits in Australia). Its more that the population will reach a new optimum population threshold accommodating this extra pressure (assuming we're not dealing with extremes of course like say introduced non native predators)

Having a large population though is not always good news as it encourages disease, starvation, territorial disputes etc.

Sorry to bring this up again. But I stumbled on the paper I was referring too:

"Predation Risk and the cost of being fat" Gosler, Greenwood, and Perrins, 1995, Nature pp 621-623
 

hampers

Hampers
How representational of the country as a whole is the BTO Garden Bird Feeding Survey, is it the same results as the RSPB Survey?

Interesting debate, no problem in my garden with house sparrows and sparrowhawks, sparrow numbers steady and daily sparrowhawk. I'm in an urban area of 1930 -1950 properties with oldish roof's in the main.

Phil
 

AlfArbuthnot

Well-known member
How representational of the country as a whole is the BTO Garden Bird Feeding Survey, is it the same results as the RSPB Survey?

Once you start breaking it down into 'zones' of Sparrowhawk recovery, it isn't very representative at all. That's one of the big criticisms that Bell was trying to duck (sample sizes), where in some cases he had literally 4 or 5 gardens (sample points) to cover an area of several thousand square km. When pressed in this thread on how many misclassified gardens it would take for his model to give a different result, his answer was an enigmatic yet revealing "very few". Misclassification is very likely to have happened, when his methods were scrutinised, as they were very 'rough and ready'.
 

hampers

Hampers
Once you start breaking it down into 'zones' of Sparrowhawk recovery, it isn't very representative at all. That's one of the big criticisms that Bell was trying to duck (sample sizes), where in some cases he had literally 4 or 5 gardens (sample points) to cover an area of several thousand square km. When pressed in this thread on how many misclassified gardens it would take for his model to give a different result, his answer was an enigmatic yet revealing "very few". Misclassification is very likely to have happened, when his methods were scrutinised, as they were very 'rough and ready'.

Thank you, I'm neither a scientist or statistician and can understand your response. I do understand that you need an accurate and representative basis on which to base statistics though.
I only asked for my personal clarification.

Phil
 
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Oxeye

Member
Lack of sparrows

The reason I feel for the lack of sparrows, is the lack of hedges.
We have a public footpath near us, that has hedges on both sides, of bramble, hawthorn, elder etc, it is alive with house sparrows.
When I was young most houses had privet hedges, & again the sparrow would chirp away in them.
Most front gardens now are used to park the car, & paved over. Bye bye sparrows.
 

Jack Dawe

Well-known member
The reason I feel for the lack of sparrows, is the lack of hedges.
Could be. There were very few sparrows in our neighborhood until I planted a hawthorn hedge. Got loads now. And that's despite the resident pair of Sparrowhawks that have always been in the area.
 

pianoman

duck and diver, bobolink and weaver
Possibly one reason for the constant debate about this subject is that people seem to have either lots of House Sparrows, or none at all. In my sister's case about 5 miles away in an inner suburb, they are the commonest bird by far in her garden. In my case, further out, there are none - except that for a year or two, a couple of years back, they were the commonest bird in my garden too.

It's a strange thing, perhaps explained by some mathematical formula rather than the presence of Sparrowhawks.
 

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