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

[Jane Turner]

Oh John, you must have realised by now that it matters not a jot that everywhere you look you can find well-documented and rigorously recorded temporal-spatio data from sites where Sparrow declined or become extinct despite their being no breeding Sparrowhawks and other areas where Sparrows are increasing where there are Sparrowhawks.

Re a parallel study You mean like in the US, where they seem to be surviving the savage attentions of Sharpies

 

[AlfArbuthnot]

Oh John, you must have realised by now that it matters not a jot that everywhere you look you can find well-documented and rigorously recorded temporal-spatio data from sites where Sparrow declined or become extinct despite their being no breeding Sparrowhawks and other areas where Sparrows are increasing where there are Sparrowhawks.

Re a parallel study You mean like in the US, where they seem to be surviving the savage attentions of Sharpies

House Sparrows actually have TWO small-medium Accipiter hawks to avoid in the US - Sharp-shinned and also Cooper's Hawk, which occur together across much of the country including cities. But they can't have heard of CPBell's ideas of predator aversion and predation-induced declines, seeing as sparrows are ten-a-penny in Boston and New York.

 

[Jane Turner]

Looking for something else,I found this...

Density-dependent decline of host abundance resulting from a new infectious disease
Wesley M. Hochachka and
André A. Dhondt



"Here we are able to demonstrate a causal relationship between high disease prevalence and declining house finch abundance throughout the eastern half of North America because the epizootic reached different parts of the house finch range at different times. Three years after the epizootic arrived, house finch abundance stabilized at similar levels, although house finch abundance had been high and stable in some areas but low and rapidly increasing in others. This result, not previously documented in wild populations, is as expected from theory if transmission of the disease was density dependent."

Which I thought was interesting

especially when combined with this

Sickness behaviour acting as an evolutionary trap? Male house finches preferentially feed near diseased conspecifics

Karen M. Bouwman and
Dana M. Hawley*

+ Author Affiliations

Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA

*Author for correspondence ([email protected]).

Abstract

Host behaviour towards infectious conspecifics is a crucial yet overlooked component of pathogen dynamics. Selection is expected to favour individuals who can recognize and avoid infected conspecifics in order to reduce their own risk of infection. However, evidence is scarce and limited to species employing chemical cues. Here, we experimentally examine whether healthy captive house finches (Carpodacus mexicanus) preferentially forage near a same-sex, healthy conspecific versus one infected with the directly transmissible pathogen Mycoplasma gallisepticum (MG), which causes lethargy and visible conjunctivitis. Interestingly, male house finches strongly preferred feeding near diseased conspecifics, while females showed no preference. This sex difference appeared to be the result of lower aggression rates in diseased males, but not in females. The reduced aggression of diseased males may act as an ‘evolutionary trap’ by presenting a historically beneficial behavioural cue in the context of a new environment, which now includes a recently emerged, potentially fatal pathogen. Since MG can be directly transmitted during feeding, healthy males may inadvertently increase their risk of contracting MG. This behaviour is likely to significantly contribute to the continued persistence of MG epidemics in wild populations.

 

[Wildmoreway]

Hi, I am a newbie and this is my first comment on any posting. Regarding House Sparrow declination, I think the main problem lies with the lack of access into buildings for breeding rather than the Hawks. Practically all the houses built today have boxed-in eaves, the area below the roofs and house brickwalls generally being boarded up to constrain heat loss. My Cottage is over 100 years old with 'open' eaves, and I am privileged to have a colony of Swifts and Sparrows nesting together. The Sparrows seem to provide all the bedding materials for nesting and they live in harmony. The fault/blame must surely be with the Controlling legislative bodies, Construction industry, Designers & Architects, and the builders. What is now our task in life, is it to 'Conserve Energy' or 'Preserve Nature'. ????

Welcome aboard, this point has been made before and yes I think that it is part of the issue along with all that anti pigeon netting on public buildings. Another problem I think is that the house sparrows have adapted to new habitats that have made them less visible and less easy to count, another issue is that many people seem to be far too immersed in statistics and in simply observing that they have vanished from their old habitats to have adapted their own methods of observing them (i have certainly guilty of the latter). In simple terms I don't think that the house sparrow population was ever as high as most people suppose and I don't think that it is at present as low as most people suppose.

 

[KenM]

I've only been serious (and had the time each day) about observing my garden for the last 8 years, so I'd guess that the numbers are pretty meaningless over such a short period of time. However, there are not less than 100 Starlings and not less than 50 Sparrows in my garden each year. I'll only see those numbers in my garden a few times a year, but the birds are visible in trees and bushes nearby. So I might have 40 Starlings in the garden tomorrow, but I'll see loads more locally while those 40 are in the garden.

There appears to an 8 year ''occurence consistency'' to your observations, and there is probably no reason to assume that the situation has not been any different over a much longer period of time? My personal (abode) Passer decline began sometime during the '90's (wish I could be more exacting!)

However....then as now, I am able to walk from my abode to colonies circa 800m - 1500m distant, that were there then and now..still tenanted!..as I can, with small colonies in Central London.

 

[MJB]

Looking for something else,I found this...

Density-dependent decline of host abundance resulting from a new infectious disease. Wesley M. Hochachka and André A. Dhondt



"Here we are able to demonstrate a causal relationship between high disease prevalence and declining house finch abundance throughout the eastern half of North America because the epizootic reached different parts of the house finch range at different times. Three years after the epizootic arrived, house finch abundance stabilized at similar levels, although house finch abundance had been high and stable in some areas but low and rapidly increasing in others. This result, not previously documented in wild populations, is as expected from theory if transmission of the disease was density dependent."

Which I thought was interesting.

I've followed the work of André Dhondt for over 20 years, from the time he moved from Belgium. He's one of the heavyweights in his field, but perhaps we stand to be re-educated by a certain contributor to this thread...:eek!:
MJB

 

[Nightranger]

Another problem I think is that the house sparrows have adapted to new habitats that have made them less visible and less easy to count, another issue is that many people seem to be far too immersed in statistics and in simply observing that they have vanished from their old habitats to have adapted their own methods of observing them (i have certainly guilty of the latter).

It is a very interesting point but to be honest, I have not seen any evidence of this and I noticed house sparrows disappearing from sites long before the RSPB/BTO illustrated the fact. Indeed, this now seems likely to have happened all over the UK and in different habitats but a lot of casual observers (including me, at the time) probably assumed it was a localised phenomenon. Population trends are assessed almost on an annual basis these days but in the days before computers, it had to be done over a much longer period (25 years). The alarm bell would only sound (figuratively speaking) when the trend hit a certain consistent decline rate. Alarmingly, this means declines could start decades before they were noticed or went over at a steeper angle. House sparrows are a classic example of this because the decline began before computers came into regular use and it just underlines how difficult conservation was only a few decades ago. By the time the decline became critical for the national population, we were already looking back on events that triggered the trend. As the population then settles to a lower level we would not be absolutely sure that we were looking at the correct threat if we looked at the figures and the changes in a contemporary light. These days, populations can be assessed every five years (although I think the index still stands at 25 years for data listing colour) and this makes it easier to flag up early changes.

In simple terms I don't think that the house sparrow population was ever as high as most people suppose and I don't think that it is at present as low as most people suppose.

I would only agree (in principle) with the second part of your conclusion although I would add the caveat that it is possible the population is not as low as some people suppose. Indeed, to reflect this, the BTO has produced revised guidelines for surveying house sparrows. What we still do not kn ow andcannot possibly know in hindsight is what the proportion of non-breeding to breeding birds is in a typical house sparrow colony and by extension, what a typical house sparrow colony is. Due to the way house sparrows were surveyed traditionally (much as other species still are) would mostly tell us about breeding birds and the opportunity to determine what the nb v b proportions were prior to decline is long gone. Clearly, the data shows a decline over several decades and this is far outside the longevity of individuals so it seems certain that the original surveys were accurate enough and the nb v b proportions have not changed. Indeed, I suspect that had CP looked at this side of things he may have got a very interesting result.

Note on edit: IMO the BTO were right to look at a different survey methodology for house sparrows but this does not necessarily invalidate earlier data. What it is designed to do is give a better baseline model for future assessment of the population.

 

[Kentbloke]

noise

 

[Jane Turner]

Does anyone have the source study?

 

[RoyW]

Does anyone have the source study?

Assuming you mean the "noise" one in the post above yours:
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0039200

 

[Jane Turner]

Thanks... that's looking quite compelling, and a nice and easy theory to test.

 

[KenM]

According to the D.Telegraph today...noise is possibly the cause of London's cockney sparrow decline. So Accipter nisus cannot be the only protagonist!...Perhaps the proponents of this latest theory have never been to ''the city that never sleeps.'' On the urban ''richter scale'' of noise..NYC is certainly streets ahead of London, and Passer domesticus along with Sturnus vulgaris..is positively thriving!

 

[ZanderII]

According to the D.Telegraph today...noise is possibly the cause of London's cockney sparrow decline. So Accipter nisus cannot be the only protagonist!...Perhaps the proponents of this latest theory have never been to ''the city that never sleeps.'' On the urban ''richter scale'' of noise..NYC is certainly streets ahead of London, and Passer domesticus along with Sturnus vulgaris..is positively thriving!

and urban Accipiters?

 

[Wildmoreway]

According to the D.Telegraph today...noise is possibly the cause of London's cockney sparrow decline. So Accipter nisus cannot be the only protagonist!...Perhaps the proponents of this latest theory have never been to ''the city that never sleeps.'' On the urban ''richter scale'' of noise..NYC is certainly streets ahead of London, and Passer domesticus along with Sturnus vulgaris..is positively thriving!

The NYC sparrows haven't read the report yet, that's why.

 

[Jane Turner]

Johnson (1930) 'The Nature World of London' does not mention Sparrowhawks, but says of kestrels (largely predators of birds in urban areas) "the evidence points to the existence of many individuals, which continue to live amongst us [in London]".

Lilford (1895), Sparrowhawk: "very common in the Peterborough area".

Chislett (1952), Yorkshire, Sparrowhawk: "there are areas near to large towns where Sparrow-Hawks suffer little molestation". Second only to the Kestrel in abundance (Nelson 1902).

Chislett (1952), Yorkshire, Kestrel: "can often be seen hovering above rooftops in many lowland towns".

Hudson (1924) 'Birds in London' describes massive predation on London sparrows by cats, which he often witnessed destroying whole broods shortly after fledging, and with injured birds being common in the parks.

So it appears that predators were not absent from London prior to the 1990s. These predators were avian (Kestrels at least) and mammalian (cats). Yet Hudson counted 118 sparrow nests on his walk through a London park. So 'predator aversion' must have also been present at that time, yet they were still super-abundant.

Sparrowhawks were clearly present about other large towns prior to 1950, as were Kestrels, but again sparrows were still super-abundant.

So CPBell's theory would require sparrows to lose this predator aversion in the 20 years between about 1960 and 1980 when predation from raptors was rare due to organochlorine poisoning (but note that cats would still be present in London and other towns, so sparrows would still need to be wary - in fact the cat population has increased), but not having regained predator aversion in the 30 years since 1980 and rebounded back to their former numbers.

That doesn't sound very plausible. If they can 'unlearn' something in 20 years then why can't they 'relearn' it in 30?

But as CPBell he says, he is "assuming" that this ever happened. Just like he assumed that no house-building happened between 1970 and 2000 in his model, the whole idea of a house of cards. The empirical evidence clearly shows he is wrong - from house-building spikes and urban sprawl in the 1970s and 1980s to the presence of urban raptors prior to 1990.

In BB this month - Breeding birds of inner London.

1900-50
No Sparrowhawks
Kestrel & House Sparrow breeding (numbers not quoted)

1951-1965
Sparrowhawk, Kestrel & House Sparrow breeding

1968-72
Sparrowhawk not mapped, Kestrel 7 pairs, House Sparrow 23 pairs

1988-94
Sparrowhawk 3 pairs, Kestrel 18 pairs, House Sparrow 24 pairs

2008-12
Sparrowhawk 8 pairs, Kestrel 5 pairs and House Sparrow 12 pairs

 

[AlfArbuthnot]

I was surprised to see that House Sparrows are still recorded as being present in almost every tetrad (91%) in London in the new atlas (p.452 of BB).

News & Comment (p.492) also notes the sudden acceleration of decline in the middle of the last decade (00s) which coincided with the trichomoniasis outbreak (which caused a slump in Greenfinch numbers).

 

[KenM]

In BB this month - Breeding birds of inner London.

1900-50
No Sparrowhawks
Kestrel & House Sparrow breeding (numbers not quoted)

1951-1965
Sparrowhawk, Kestrel & House Sparrow breeding

1968-72
Sparrowhawk not mapped, Kestrel 7 pairs, House Sparrow 23 pairs

1988-94
Sparrowhawk 3 pairs, Kestrel 18 pairs, House Sparrow 24 pairs

2008-12
Sparrowhawk 8 pairs, Kestrel 5 pairs and House Sparrow 12 pairs

FWIW I believe that the presence of Passer domesticus within the inner London area for 2008-2012 has been underestimated. I am aware of 6 sites that have birds that could match/surpass the total given for this period, and obviously I would not know all of the ''known'' sites.

 

[AlfArbuthnot]

In BB this month - Breeding birds of inner London.

1900-50
No Sparrowhawks
Kestrel & House Sparrow breeding (numbers not quoted)

1951-1965
Sparrowhawk, Kestrel & House Sparrow breeding

1968-72
Sparrowhawk not mapped, Kestrel 7 pairs, House Sparrow 23 pairs

1988-94
Sparrowhawk 3 pairs, Kestrel 18 pairs, House Sparrow 24 pairs

2008-12
Sparrowhawk 8 pairs, Kestrel 5 pairs and House Sparrow 12 pairs

Jane, these numbers are not 'pairs' but the number of tetrads where breeding was confirmed in Inner London.

 

[Jane Turner]

that makes more sense.... I was speed reading.

Does rather knock a hole in Dr Bell's slightly odd predator aversion theory either way

 

[MJB]

That makes more sense.... I was speed reading. Does rather knock a hole in Dr Bell's slightly odd predator aversion theory either way

But who would notice one more in the Emmental?:-O
MJB