Corvid cull looming

An old thread, which I'll admit to only having scanned very quickly through after reading the new post from Tiggywinkle - so I apologise if I've everything I say is a repeat of what has been said already...

Unknown said:

It has been observed over a period of 60 years in this area that at the beginning of this period there were many many hedgehogs. In fact at night it was impossible not to see some around this estate which borders a very large parkland. Although badgers were in attendance in small numbers they did not seem to prey on the hedgehogs so as to reduce their numbers for quite a number of years but it changed long ago. For around 40 years there have been no hedgehogs at all. Badgers however have multiplied to the extent that regular sightings are seen of them througout the estate in fact there is a sett under my shed. I am fully aware that foxes that are prevalent as well as badgers will kill hedgehogs and I firmly believe that between them the predators have made the hedgehogs extinct in this area. Therefore whilst these predators are the hierarchy in the food chain they do not have the intention or the intelligence to realize they have extinguished their food supply.  

The important thing to remember here is that correlation does not necessarily demonstrate causation.

It often seems to be automatically assumed that if an increase in predatory species A is seen at the same time as, or before, the decline of species B (which species A is known to predate to some degree), then the decline of species B is because of the increase in species A. In some cases this might actually be true, but you will usually find that there are numerous other possible reasons for the decline of species B. For example, in the Hedgehog versus Badger numbers mentioned above, I would not be at all surprised if as well as a correlation between increasing Badger numbers and declines in Hedgehogs, there are also found to be correlations between lower Hedgehog numbers and at least some of the following (as well as a variety of other potential reasons): an increasing number of cars/vehicles on our roads; declines in invertebrate numbers; changes in management of gardens and parkland (including concreting/paving gardens, and changes in pesticide/herbicide use).

When predatory species are generalists it is possible for them to cause some of the species they prey on to decline even to the point where they become extinct, but more typically a balance will be reached, just with the prey species at a lower population level than has previously been the case. In the UK we have become used to a balance involving a unnaturally low populations of many predatory species as a result of centuries of persecution keeping the populations of these species down. In all likelihood we are now returning to a more natural balance for most species (although mans influence on the environment is so great that nothing in the UK is now truly "natural"). The problem is that people tend to value certain species above others, depending on their personal preferences.

Unknown said:

I believe that this trait is abundantly clear as regards the Crow and Magpie species in regard to the fact that they have intelligence but they are not intelligent enough to prevent the extinction of their prey species. The habitat locally has not changed since 1927 so this fact cannot be blamed upon the reduction which is quite alarming in  the small bird species. The food source has increased due to many people especially since the war ,feeding the birds.  It is difficult to not direct blame to the Corvids that seem to be the most abundant species locally. There is a difficulty with culling the corvids in the surrounds to the Park because the Parkland has a reservoir of some 250 Carrion Crows and plenty of Magpies. If culling were carried out it would be found that this would be  very  very time consuming indeed.  It seems obvious that if the Corvids are kept within reasonable numbers the small bird population may well return to what it was before the Corvid explosion because locally nothing else seems to have changed.

No animal is intelligent enough to prevent the extinction of prey species (including humans, who have caused the extinction of numerous species that they have exploited - and will sadly continue to do so for the foreseeable future). However, what tends to happen is that predators take whatever is most readily available and can be taken with the least effort - this invariably means that they will feed on the more common species within a given area (unless a scarcer species is particularly ill suited to evading predation, which can be the case when 'new' predators have been introduced by man).

I will definitely contend your assertion that the habitat in your area has not changed since 1927. There have been considerable changes in farming in more recent years, as well as changes in the maintenance of gardens, parklands, and road verges. Simply changing the frequency, or timing, of the cutting of road verges and hedges can greatly change the ecology of these habitats, as can changes in farming, including changes in crops or the maintenance of grazing land for livestock (and changes in the farmland surrounding a town can affect the species within the town). The levels of pollution, and types of pollutants, have also changed with largely unknown effects.

Any attempt to link corvid numbers with declines in "songbirds" (scientifically corvids are songbirds) ignores the fact that a large number of songbird species have actually shown noticeable increases in their numbers - examples including well known garden visitors like Blue Tit, Long-tailed Tit, Robin, Blackcap, and Chaffinch.

Removing predatory species would often be expected to result in an increase in the populations of the species that they prey on, but could potentially ultimately weaken the population (predators typically remove the weaker individuals from the gene pool). It is also not a solution, any increase seen will only be maintained for as long as culling of the predatory species is maintained and relies on the predators being controlled in all areas that may lead to immigration into the 'controlled' areas. The only sensible answer is to work to eliminate all other risks to the declining bird species and allow them to reach a balance with un-culled populations of predators (as well as potentially limiting the other food sources available to scavenging predatory species, such as by working to reduce food available from sources like refuse tips).

Unknown said:

Observations have been made in the farmlands of North Wales and have been compared to this urban area. The situation re plenty of Corvids in Wales and also  numerous and abundant species of small birds there seem to suggest the farmland habitat is the most nurturing for all birds. The urban area seems to require the Corvids to be kept to a ballance if the small bird population is to continue to be enjoyed.

I would suggest that the "problem" in urban areas is that there is increasingly a lack of habitat for most small bird species to find food and nest sites in, while corvids (specifically Carrion Crows really) are more than able to survive in built up areas - living off discarded food, and nesting on buildings, pylons etc.

The lack of suitable nest sites for the smaller birds that do attempt to nest then makes their nests easier for crows to locate - so people see crows predating smaller birds and assume that this is the main reason for the smaller birds declining numbers.

Sometimes culling can be advantageous for conservation purposes, but in general it should be seen as no more than a temporary 'fix' while more permanent solutions are being worked on. Suggesting what would need to be large scale culling on a permanently ongoing basis is not a solution to the declines of some songbirds - and (IMO) the continued 'arguments' for this detract from the serious research that is taking place to find real solutions.

Unknown said:

The problem is that people tend to value certain species above others, depending on their personal preferences.

It is a great pity that there should be a group that is for and another that is against. This however is what the situation has become. I can assure you that this estate has not changed a great deal over 40 years and that is what I refer to re the downfall of the hedgehogs not since 1927.

Regarding the Corvids in this area what you seem to be suggesting is that 200 Carrion Crows are good for the small bird population locally as well as hoards of Magpies that have occured in the last 15 years or so. I and others think that these large numbers have had a detrimental effect in that the small bird species in certain local areas have dwindled especially Green finches, sparrows,starlings. These three species are virtually none existant. When there was a healthy number of starlings the Sparrow Hawks had plenty to prey on but not now so what is this species feeding on ? whatever it can catch is the answer.

The truth is that as Jon says in certain areas certain species require a balance but unfortunately this balance will not happen on its own it requires a helping hand even if this helping hand is deemed to be cruel.   Cruel to be kind ?

Interesting contribution Roy well worth reading and very balanced.

Unknown said:

I can assure you that this estate has not changed a great deal over 40 years and that is what I refer to re the downfall of the hedgehogs not since 1927.

I'd like to say that I wouldn't mind betting that the amount of roadkill we see and the litter and waste everywhere has contributed to the very healthy corvid numbers.   They perform a useful service with both - and magpies go a step further in clearing up dog poo that irresponsible dog owners can't be bothered with.

Unknown said:

reading a copy of the Field saw a letter referring to the incident of the Buzzard taking the Osprey chick (that is nature) but the author turned it into a diatribe against the RSPB for protecting raptors

We often get letters in this vein in our local papers blaming the release of Red Kites for the demise of the local song bird population,always from the same few people.

Unknown said:

It is a great pity that there should be a group that is for and another that is against. This however is what the situation has become. I can assure you that this estate has not changed a great deal over 40 years and that is what I refer to re the downfall of the hedgehogs not since 1927.

Although I cannot know how things might have changed on the estate that you are talking about over the last 40 years, I would be very surprised if things haven't changed - and there have definitely been changes in the wider countryside during this period, and these wider countryside changeswill have had an effect on the populations of wildlife even in areas that have had comparatively little change.

I am afraid that any argument that there have been no changes in land management/habitat in any given area, so changes in the numbers of certain species can't be linked to this type of change, just doesn't hold water. One of the problems with studies investigating species declines is that the effects of changes of this sort can be very difficult to quantify.

Unknown said:

Regarding the Corvids in this area what you seem to be suggesting is that 200 Carrion Crows are good for the small bird population locally as well as hoards of Magpies that have occured in the last 15 years or so. I and others think that these large numbers have had a detrimental effect in that the small bird species in certain local areas have dwindled especially Green finches, sparrows,starlings. These three species are virtually none existant. When there was a healthy number of starlings the Sparrow Hawks had plenty to prey on but not now so what is this species feeding on ? whatever it can catch is the answer.

If you are referring to my comments, I am certainly not suggesting that increasing numbers of corvids is good for the populations of small birds, however, in the vast majority of cases the effect will be neutral - unless there is something else that is adversely affecting the populations.

People do think that increased numbers of Carrion Crows and Magpies have had a detrimental effect on small bird numbers, but to date no one has been able to produce any evidence that this is actually true. There is evidence that corvid numbers can have an effect on the productivity of some ground nesting species in certain circumstances, but not that they affect the numbers of passerine species (in fact the available evidence suggests that there has been no real link between corvid numbers and passerine populations).

For the three species you mention, Greenfinch numbers were actually increasing until trichomoniasis started to affect the population a few years ago, no cause for sparrow declines has yet been found, and there is good evidence that declines in Starling numbers may be linked to changes in farming, and the invertebrate numbers in pasture.

I don't see the relevance of Sparrowhawk prey choice at all. Sparrowhawks are opportunistic hunters that will take any bird species, of a manageable size, that is available, which tends to mean that they largely feed on the more common bird species in their area - and many of the most favoured prey species (eg. Blue Tits, Chaffinches, Collared Doves etc.) are increasing in number, and have been for many years.

Unknown said:

The truth is that as Jon says in certain areas certain species require a balance but unfortunately this balance will not happen on its own it requires a helping hand even if this helping hand is deemed to be cruel.   Cruel to be kind ?

I'm afraid that this is simply not true - nature will always reach a balance without any kind of involvement from humans whatsoever. The only consideration is whether or not the balance reached will be one that most humans consider to be the "right" one. The balance that would naturally be sustained by the environment that humans have created in the UK might be one with numbers of corvids and passerines similar to those that we have now (the evidence is that Magpie numbers, and the populations of many passerines, including House Sparrows, have more or less stabilised, and Carrion Crow numbers are stabilising). The problem is that people have been used to lower numbers of corvids (largely because of widespread former "control"), and higher numbers of many common passerine species (for a variety of reasons, including prior farming practices that favoured some species), and these are the population levels that they consider to be 'natural".

Unknown said:

I think that Roy has made a very balanced comment but there is one thing that Tiggywinkle says that I do agree with and that is 'It is a great pity that there should be a group that is for and another that is against. This however is what the situation has become.'.  I think that is absolutely right.  Over the years I have noticed both sides drifting away from each other and it is joint dialogue that is needed to deal with the decline in wildlife generally.

I agree entirely. I am not against culling when the reasons for it can be justified, and are backed with suitable scientific evidence - what I am against is taking action such as culls without valid evidence that it will have the desired effect. Active campaigning for culls of corvids and raptors because of the unsubstantiated belief that this will change the fortunes of the small bird species that have declined, or are declining, does very little other than distract from valid research which might help to find real solutions that could help to reverse their fortunes.

It is difficult not to alienate some groups, if they have opinions that are already fixed, but there is nothing at all to be gained from stalemates where neither "side" will consider what is being said by the other. In my opinion the only thing that is really worth considering is the evidence - not opinions that are not supported. I will happily consider any evidence that suggests that culling corvids is the best way to help declining small bird populations, and because there is evidence that localised culling can help waders and other ground nesting species, have no issues with limited culling of corvids intended as a short term "helping hand" for these species (although it should never be seen as something to be carried on in the long term - only as a short term fix to get species away from "the brink").

Unknown said:

The only consideration is whether or not the balance reached will be one that most humans consider to be the "right" one.

Unknown said:

I can assure you that this estate has not changed a great deal over 40 years ..........................................

Have you any idea what happens in people's back gardens ? How many lawns have been replaced with easy maintenance gravel or decking ? What area of gardens has been lost under patios and conservatories ? What plants do people grow today compared to 40 years ago ? How many people use chemical fertilisers and slug deterrents etc ? It really is preposterous to make such a sweeping statement about something you cannot possibly have researched in any detail.