Sparrow hawks (1 Viewer)

[Anthony Morton]

No, but in your post at 20.29 yesterday, you said the BTO did.
And you'll have a long one, since I don't have that information.
If you think that, you must be looking out of the back of your head. My only purpose in posting was to ask you to be precise in order to avoid misrepresenting the position. At least your reply to nirofo was precise, for which I thank you.

My apologies, 'Bluetail' is right - I did type 'kill' instead of 'consume' by mistake in one of my earlier postings. So in the interests of accuracy, I will re-state the quote made by Jeremy Greenwood, the BTO's Director General, in the February 2003 edition of 'The Field', where he wrote that '...It is also true that the British sparrowhawk population probably consumes food equivalent in weight to 107 million sparrow-sized birds.'

As 'Bluetail' admits that he is unable to convert this into the exact number of individual birds this represents (I'm not surprised as I've never seen a figure for it either!) can we agree to base our debate on Jeremy Greenwood's comment at least until we can prove otherwise?

Anthony

 

[Bluetail]

OK. I've done some calculations with the most up-to-date info I could find on the BTO's website. However, I don't claim any expertise with statistics so I hope others will improve the following where necessary.

In 1993 there were an estimated 34,655 breeding pairs of Sparrowhawks, since when the population has stabilised, or even declined. That’s 69,310 birds.

Not all Sparrowhawks breed in their first year and the non-breeding population has been calculated as 0.28 of the breeding population – another 19,407 birds.

Mean brood size has been growing, the latest figure being a mean of 3.93 birds per pair. That’s another (34,655 x 3.93 =) 136,194 birds, but the figure includes the 19,407 non-breeders, suggesting that 116,787 die before their first spring, late summer and autumn being the peak mortality period for juveniles. Let’s say for the sake of argument that these doomed birds survive on average for 6 months (this may be a bit generous, but I can't find any information). That would be the equivalent of 58,394 birds surviving a year. That gives the equivalent of an annual population of:

Breeding individuals: 69,310
Non-breeding individuals: 19,407
Doomed juveniles: 58,394
Total: 147,111

Now if these 147,111 individuals take the equivalent of 107 million sparrows a year, that equates to (107,000,000 / 147,111) / 365 = 2 birds per Sparrowhawk per day.

We do get some wintering Spars from Scandinavia, but it seems that numbers are not high; others pass through in autumn and spring (does the Migration Atlas say anything about numbers?)

Even so, the equivalent of 2 sparrows a day seems a bit on the high side to me, especially since a proportion of young birds die of starvation (a study gave it a figure of 11% of all mortalities). Perhaps female Sparrowhawks, which feed mainly on starlings and thrushes, might require this much (I don’t know how long will a thrush sustain a Spar for), but I wouldn’t have thought a male would.

In any case, the actual number of birds taken is clearly not a problem since, as has been pointed out already, the patterns of the year-to-year population changes in songbirds show no difference between sites with Sparrowhawks and those without.

 

[Spar]

Bluetail,
Sparrowhawks require 25% of their body weight per day unlike eagles which require 5-6% per day.

Lol Spar(hope this helps)

 

[Bluetail]

Thanks, Spar. This is one of those occasions when I wish I was a ringer. I've no real idea about birds' weights, but at a guess I'd say that, in this case, Greenwood's figure looks about right.

 

[Edward woodwood]

Blimey boys why all the arguments?

as any fule kno it's agricultural change (and the bloody cats) that have done for our songbirds

cheers B
Tim

 

[Spar]

Not the sparrowhawks then Tim :news:
Lol Spar

 

[Edward woodwood]

don't get me involved Spar
I want a chilled evening........

 

[Anthony Morton]

In an earlier posting, I mentioned the book 'The Sparrowhawk', written by Dr. Ian Newton, an acknowledged authority on the species. It was first published in 1987 as Number 16 in the Shire Natural History series - ISBN Number 0 85263 857 4 refers, but I'm not sure if it's still in print. My copy (in booklet form) cost £1.95 and is crammed full of relevant information, plus some incredible colour pictures for the slower readers amongst us - that's if you can still obtain a copy!

Anyway, the following quotes are all taken from it:-

'The larger female measures about 35 cm (14 inches) from head to tail and weighs around 300 grams (10 ounces) while the smaller male measures about 30 cm (12 inches) and weighs around 150 grams (5 ounces).'

'The average food consumption has been measured at around 40 to 50 grams (1.4 to 1.8 ounces) per day for males and 50 to 70 grams (1.8 to 2.5 ounces) per day for the larger females, depending partly on their activity.'

'The number of carcases needed to provide this ration varies with their size, but it is equivalent to about two and three sparrows per day respectively for each sex. Over a whole year total food intake amounts to around 16.5 kg (36 pounds) of meat for a male and 22 kg (48 pounds) for a female.'

'Added to the needs of breeding, a successful Sparrowhawk pair could account for 55 kg (121 pounds) of meat in a year. This is equivalent to about 2200 House Sparrows, or 600 blackbirds, or 110 Wood Pigeons.'

'... the average mortality over the first year of life has been estimated at 69 per cent for cocks and 51 per cent for hens. ... In later life the death rate is lower and more similar between the sexes, at 33 per cent per year for cocks and 29 per cent per year for hens.'

It's easy to calculate from the first two quotes that the answer given yesterday (sorry - I've forgotten who posted it) that Sparrowhawks require a daily food intake equivalent to 25% of their body weight is spot-on for the female, but the male seems to require slightly more at around 33% - I wonder why?

And if the combined weight of a successful breeding pair of Sparrowhaks is 15 ounces (hen 10 ounces and cock 5 ounces) and between them they consume 121 pounds of meat in a year, they will have eaten the equivalent of 129 times
their combined body weight - much of it songbirds!

Finally (stand up the boy who said 'At last!') the Sparrowhawk is on The Population Status Of Birds In The UK 'Green' list as not being in any conservation danger, while the House Sparrow, Tree Sparrow, Song thrush, Starling, Skylark etc.,etc. are all now on the 'Red' list as being of 'high conservation concern.'

Anthony

 

[Bluetail]

...while the House Sparrow, Tree Sparrow, Song thrush, Starling, Skylark etc.,etc. are all now on the 'Red' list as being of 'high conservation concern.'

Indeed, but of course we shouldn't therefore infer that Sparrowhawks are to blame.

 

[Elizabeth Bigg]

The Sparrowhawk, by Ian Newton is cerainly still available - I had a copy for Christmas. The Amazon price is £2.95. (It has not been revised since it was first published in 1987).

 

[Sleeper]

http://www.virginbooks.com/go/Books_72188.htmlGot mine hear. Good info involved if a little outdated(probably)

 

[Spar]

Olde hat,
Lol Spar :C :C

 

[Anthony Morton]

http://www.virginbooks.com/go/Books_72188.htmlGot mine hear. Good info involved if a little outdated(probably)

Dr. Ian Newton's book 'The Sparrowhawk' outdated? - I don't think so!

As far as I can see the only statistic that has changed is the number of breeding pairs, which has risen from 32,000 to 34,655 based on the BTO's latest figures.

Anthony

 

[Anthony Morton]

Indeed, but of course we shouldn't therefore infer that Sparrowhawks are to blame.

Agreed - that wasn't the point I was making. What puzzles me is that according to the BTO the Sparrowhawk is (quote) '...on the Green List and therefore not in any conservation danger', with the prediction that the Long Term Trend for the UK anticipates a further 'Rapid Increase' in numbers. Despite this, the Sparrowhawk enjoys TOTAL legal protection along with all UK raptor species.

In contrast, however, The Population Status Of Birds In The UK shows 40 species on the 'Red List' (only two, the Hen harrier and the White-tailed eagle, are raptors) while around three quarters of them are potential prey species for the Sparrowhawk. These include such once common species as Bullfinch, House Sparrow, Linnet, Skylark, Song Thrush, Starling, Yellowhammer etc., yet none of them receive the same level of protection as Accipiter nisus.

Why not?

 

[Spar]

Is it not a case all raptors have a certain HIGH PROFILE and as a consequence they would be a public outcry if Total legal protection is withdrawn,and rightly so.

Lol Spar

 

[Jasonbirder]

I haven`t had the opportunity to read all of this thread so I apologise if i`m restating points that have been already made.

I have never come across such arrant rubish as the inference that the Sparrowhawk Poulation is in any way responsible for population declines in small passerines.

Like any predator the Sparrowhawk population is limited by available prey numbers along with many other factors it is quite simply not possible for it to increase to the point where it starts to wipe out its prey species - as soon as prey numbers begin to decline brood size and survival decrease to match.

With such obvious and far more damaging factors such as Cat Ownership, Pesticides/Herbicides etc etc are taken into account I feel we don`t have to look much further for factors affecting Passerine populations - any suggestions to the contrary are just ignorant or wifully malicious distractions.

 

[Ranger James]

Agreed - that wasn't the point I was making. What puzzles me is that according to the BTO the Sparrowhawk is (quote) '...on the Green List and therefore not in any conservation danger', with the prediction that the Long Term Trend for the UK anticipates a further 'Rapid Increase' in numbers. Despite this, the Sparrowhawk enjoys TOTAL legal protection along with all UK raptor species.

In contrast, however, The Population Status Of Birds In The UK shows 40 species on the 'Red List' (only two, the Hen harrier and the White-tailed eagle, are raptors) while around three quarters of them are potential prey species for the Sparrowhawk. These include such once common species as Bullfinch, House Sparrow, Linnet, Skylark, Song Thrush, Starling, Yellowhammer etc., yet none of them receive the same level of protection as Accipiter nisus.

Why not?

The red, amber or green status reflects a bird's population dynamic, raptors are by-and-large increasing in numbers after catastrophic loss through human persecution and this, to me, explains why they don't have red list status (2 exceptions).
However, the raptor's potential for persecution if removed from protected status is much greater than those species without the history of human persecution. Which accounts for thier protection.

But above and beyond this, surely we should be trying to control the factors that have lead to the recent decline of woodland and farmland birds per-se, rather than spending so much effort concentrating on a predator-prey relationship that has been coexisting for many millennia.

 

[Ranger James]

I haven`t had the opportunity to read all of this thread so I apologise if i`m restating points that have been already made.

I have never come across such arrant rubish as the inference that the Sparrowhawk Poulation is in any way responsible for population declines in small passerines.

Like any predator the Sparrowhawk population is limited by available prey numbers along with many other factors it is quite simply not possible for it to increase to the point where it starts to wipe out its prey species - as soon as prey numbers begin to decline brood size and survival decrease to match.

With such obvious and far more damaging factors such as Cat Ownership, Pesticides/Herbicides etc etc are taken into account I feel we don`t have to look much further for factors affecting Passerine populations - any suggestions to the contrary are just ignorant or wifully malicious distractions.

Here-here

 

[Andrew Rowlands]

SNIP
These include such once common species as Bullfinch, House Sparrow, Linnet, Skylark, Song Thrush, Starling, Yellowhammer etc., yet none of them receive the same level of protection as Accipiter nisus.

As far as I am aware, Skylark (and most of your 'etc.' species), DO enjoy the same level of protection as the Sparrowhawk.

Andy.

 

[simondix]

All birds are protected by law. Some are more protected than others. Thanks to George Orwell for the misquote.