Declining Song birds..Farming practises (1 Viewer)

[scampo]

I have heard from an RSPB warden that the sparrowhawk population is now at its maximum and that it might now naturally decline a little to a more sustainable level.

 

[Jane Turner]

I have heard from an RSPB warden that the sparrowhawk population is now at its maximum and that it might now naturally decline a little to a more sustainable level.

It will decline quite sharply if there isn't a recovery in its food, which is now the limiting factor on its population size

 

[scampo]

But that suggests that its (urban?) food source is still in decline - is it? I think it also has several major competing "predators" viz. magpies, crows and grey squirrels.

 

[Jane Turner]

Maybe Sparrowhawks, like foxes... with become an (sub)urban speciality..and yes, as I said I was being simplistic. Sparrowhawks are a special case though since they are so dependant on passerines.

Its more catholic feeders/hunters that tend to pose the greatest long-term risks since they can maintain their populations using other food sources.

 

[Anthony Morton]

No you are not missing something As had been said that was largely due to DDT artificialy reducing the breeding success of Sparrowhawks and other raptors....so again being simplistic about this.. all other things being equal, you could argue that the passerine population in the period was at a higher level than the dwindling resources of the ecosytem could naturally support.

Unfortunately not. What is being forgotten is that the Sparrowhawk ingested the DDT from the bodies of its prey species.The toxins also affected passerines in exactly the same way, causing their populations to decrease as well.

Anthony

 

[Jane Turner]

DDT acts as a cumulative poison that effects egg-shell thickness, which is why it had such a perncius effect on raptors. They ate numbers of small birds with trace ammount of the chemical and concentrated within their bodies.

 

[Jane Turner]

http://www.epa.gov/opptintr/pbt/ddt.htm

http://physchem.ox.ac.uk/MSDS/DD/DDT.html

FYI Anthony

 

[Anthony Morton]

It will decline quite sharply if there isn't a recovery in its food, which is now the limiting factor on its population size

Unless I'm very much mistaken this is exactly the point that pigeon fanciers are making. During the last 10 years or so predation on racing pigeons has increased considerably as the Sparrowhawk's usual prey species have declined. This has enabled them to maintain their numbers at a higher level that the available passerine population would suggest.

Anthony

 

[Jane Turner]

Unless I'm very much mistaken this is exactly the point that pigeon fanciers are making. During the last 10 years or so predation on racing pigeons has increased considerably as the Sparrowhawk's usual prey species have declined. This has enabled them to maintain their numbers at a higher level that the available passerine population would suggest.

Anthony

Well as long as they carry on eating pigeons that ok. Plenty of them in urban envirnments. Mind you Sparrowhawks aren't much good a catching pigeons... big females can just about manage a Collared Dove if they are hungry.

 

[scampo]

I reckon that a problems with racing pigeons is that they seem to have lost the native ability to dodge out of the way of predators. Watching a peregrine go for a wood pigeon is very different from watching a peregrine go for a racer. The latter it never misses; the former is fascinating to watch - there's almost time to put bets on!

 

[Suricate]

DDT acts as a cumulative poison that effects egg-shell thickness, which is why it had such a perncius effect on raptors. They ate numbers of small birds with trace ammount of the chemical and concentrated within their bodies.

I would think that we are all in agreement that after it`s discovery in 1945 it had a negative effect on the environment.
But are the new newer Organochlorines like aldrin or carbamate insecticides as bad if not worse.
There will be the call that many of the new pesticides are banned, but I dont` think so!
Aldicard is used as asystemic pesticide on potatoes, sugar beet carrots and other root crops and is is proven to affect, insects,birds, fish and even bees, this obviously is in part a reason for declining Bee species. Is there a way forward ?.
Suricate

 

[Suricate]

I reckon that a problems with racing pigeons is that they seem to have lost the native ability to dodge out of the way of predators. Watching a peregrine go for a wood pigeon is very different from watching a peregrine go for a racer. The latter it never misses; the former is fascinating to watch - there's almost time to put bets on!

Another possible reason for peregrines catching pigeons easier is the problem of hybrids.
They are bred specifically for the purpose of hunting. Pere/ sakers pere/prairie
pere/ barbary and so on. There are many of these hybrids free in the UK. They can and will adapt and possibly breed with our purer wild birds.
You cannot improve on nature so why do people try. When we get onto Gyr Hybrids thats even more of a problem.
Suricate

 

[Anthony Morton]

http://www.epa.gov/opptintr/pbt/ddt.htm

http://physchem.ox.ac.uk/MSDS/DD/DDT.html

FYI Anthony

Thanks for that. I've looked at both sites and accept that the effects of DDT on raptors was more pronounced due to the build-up of the toxins they were ingesting by being at the top of the food chain.

But are you saying that the same toxins did not have at least some effect on the passerine population and that their system is somehow able to tolerate it?

Given that DDT is carcinogenic to humans, wouldn't it have affected the songbirds in some way as well and is the effect of an amount of toxin linked directly to the bodyweight of the individual host?

 

[Suricate]

Thanks for that. I've looked at both sites and accept that the effects of DDT on raptors was more pronounced due to the build-up of the toxins they were ingesting by being at the top of the food chain.

But are you saying that the same toxins did not have at least some effect on the passerine population and that their system is somehow able to tolerate it?

Given that DDT is carcinogenic to humans, wouldn't it have affected the songbirds in some way as well and is the effect of an amount of toxin linked directly to the bodyweight of the individual host?

Hi Anthony,
Perhaps we will be able to see for ourselves in the future if DDT affects Song birds ( I think it Must Have ) with global warming and more and more pest species thriving in our wet climate someone will remember that DDT is still the cheapest and best effective killer of mosquitos!
There has been a rapid increase in the numbers of birds with Hippoboscid ( flat flies ) and although usually linked to certain Owls and corvids it is affecting Songbirds and in sick birds they are causing death.
There is also an increase in ticks.
Suricate

 

[scampo]

I think I read that it's even been allowed for use, officially, in some countries recently for mosquito or locust control.

 

[Jane Turner]

I would think that we are all in agreement that after it`s discovery in 1945 it had a negative effect on the environment.
But are the new newer Organochlorines like aldrin or carbamate insecticides as bad if not worse.
There will be the call that many of the new pesticides are banned, but I dont` think so!
Aldicard is used as asystemic pesticide on potatoes, sugar beet carrots and other root crops and is is proven to affect, insects,birds, fish and even bees, this obviously is in part a reason for declining Bee species. Is there a way forward ?.
Suricate

DDT had a direct effect on egg-shell inegrity so the effect was obvious. Any pesticide that reduces the amount of edible invertebrates inpacts the whole ecosystem in a smaller but equally damaging way.

Way forward.. yes demand to eat locally grown organic food...

 

[Jane Turner]

Thanks for that. I've looked at both sites and accept that the effects of DDT on raptors was more pronounced due to the build-up of the toxins they were ingesting by being at the top of the food chain.

But are you saying that the same toxins did not have at least some effect on the passerine population and that their system is somehow able to tolerate it?

Given that DDT is carcinogenic to humans, wouldn't it have affected the songbirds in some way as well and is the effect of an amount of toxin linked directly to the bodyweight of the individual host?

My understanding is that the levels of DDT in passerines was insufficient to impact there own reproductive success. The life span of most small passerines is 3 to 10 years, the high end being exceptional. That is insufficient time to accumulate sufficient DDT. Rators with their much lower breeding rate and much longer life expectancies had time to accumulate dangerous levels. You and I are full of the stuff too.

 

[saluki]

Well as long as they carry on eating pigeons that ok. Plenty of them in urban envirnments. Mind you Sparrowhawks aren't much good a catching pigeons... big females can just about manage a Collared Dove if they are hungry.

Sorry Jane, but that isn't correct. I've stated before that a female Spar devastated our pigeon loft when I lived in Argyll. We had a Peregrine nesting site within sight of the property, but they didn't cause anywhere near the amount of damage one particular female Spar caused. I'm not condemning Spars as a species (I've kept Spars, on and off, since I was eleven years old, they're probably my favourite bird) but they are quite capable of taking pigeons. They take Woodpigeons which, if you've ever held one in your hands, you'll know that they are far stronger than the average loft pigeon.

saluki

 

[Jane Turner]

Sorry Jane, but that isn't correct. I've stated before that a female Spar devastated our pigeon loft when I lived in Argyll. We had a Peregrine nesting site within sight of the property, but they didn't cause anywhere near the amount of damage one particular female Spar caused. I'm not condemning Spars as a species (I've kept Spars, on and off, since I was eleven years old, they're probably my favourite bird) but they are quite capable of taking pigeons. They take Woodpigeons which, if you've ever held one in your hands, you'll know that they are far stronger than the average loft pigeon.

saluki

They do vary a lot in size.. Ive held one big female that was Gos-sized...and took a swipe at some crows when released...pigeons are not high in the diet preferences of majority Sparrowhawks though...

 

[Jane Turner]

http://members.lycos.nl/wrn/taksum/tak2-3-22.htm

Will find a better reference tommorow... its late now