Sparrowhawks – Friend or Foe – Allan Hale

From time to time I hear people bemoaning the fact that a Sparrowhawk has killed a songbird in their garden. Or perhaps that Sparrowhawks are a prime suspect in the search to find the cause of the decline of our songbird population. Even more dramatically, there are calls for Sparrowhawks to be taken off of the list of protected species, so that their numbers can be reduced by the legalised culling (i.e shooting) of much of the population.

So,what is the truth? Are Sparrowhawks responsible for declining songbird numbers or is there another cause? Should we be shooting them or is it better that they be left to their own devices? Let’s take the emotion out of the argument and look at some hard facts. But before that, let me say a few words about myself and why I care. I have been a birder as long as I can remember and back in the early 1970s I decided to expand my interest and become a bird ringer. I thought of myself then as a conservationist, and I still do. I reckoned that studying birds through ringing would teach me a lot more about them, and the results of my work might even be of value in a wider context.

How does it all work? Well the British bird ringing scheme is run by the British Trust for Ornithology (under the terms of The Wildlife and Countryside Acts) and after a long period of training they issued me with a licence to work on my own. It needs to be mentioned here that the BTO is a registered charity that collects data so that informed decisions can be taken with regard to conservation issues. It is neutral and collects data for both sides of the Sparrowhawk debate – both those organisations that call for the existing legislation to be strictly enforced and also those that call for the reduction of Sparrowhawk numbers.

So why ring birds? In the early days of the bird ringing scheme, it was simply to find out where birds went, and this was achieved by attaching a small, uniquely numbered metal ring to a bird’s leg, thus enabling it to be identified as an individual. Much has been learnt from such ringing. We know for instance, that our Swallows winter in Southern Africa, and that many of our Starlings move out in spring to breed in Northern and Eastern Europe.

After a hundred years of ringing there is still more to learn about migration routes and wintering areas, information which is often vital for conservation. However, the main purpose of the ringing scheme today is to monitor bird populations. Ringing allows us to study how many young birds leave the nest and survive to become adults each year, as well as how many adults survive the stress of breeding, migration and severe weather. Changes in these birth and death rates are important as they may provide an early warning that a particular species is starting to decline. Ringing allowed us to identify a decline in the survival rate of Sedge Warblers and to link this to the rainfall index in their wintering area in the Sahel desert in Africa. Ringing also lets us work out the stage in birds’ lives which is being affected, and has demonstrated that the dramatic decline in the numbers of Song Thrushes during the 1990s had been caused by a reduction in the survival of young birds in their first two months of life. In my mind, ringing is an essential tool in the conservation of birds, and the country-wide team of bird ringers are at the forefront of the research necessary to establish the facts that are so vital for effective conservation work.

It seems that I digress, but in fact I don’t. Ringing in my garden has taught me much about the relationship between Sparrowhawks and songbirds. My garden is small and on the edge of Beachamwell. I run a feeding station for the birds 365 days a year, and around once a week I operate nets to catch the birds that are attracted to the feeder. In this small garden I catch and ring somewhere around 800 to 1,000 birds a year – an impressive number for such a small area. Yet a pair of Sparrowhawks include my garden in their territory. So why is my songbird population not affected? Yes, I find the evidence of a “kill” fairly frequently; perhaps it’s a Blue Tit or a Blackbird or a Collared Dove. The doves seem to be ‘less bright’ than many of the other birds so perhaps it’s inevitable that they form part of the Sparrowhawks diet. Even so, I’m left with plenty of Collared Doves and songbirds alike.

How can this be? Plenty of songbirds within the territory of a pair of Sparrowhawks! It has to be that the Sparrowhawk is living off the surplus. In the natural world, more are born than can survive. If all individuals and all of their eggs and young could survive and reproduce unchecked, we would soon be overwhelmed by the progeny of a single pair. A single pair of Blue Tits could give rise to a population just shy of 4 million over a time span of only 9 years.** Think about it – a Blue Tit can easily raise 8 young in a season, and if they were all to survive, there would be 10 Blue Tits by the start of the following breeding season, and if they all survived to reproduce then we become knee-deep in Blue Tits. So, even if 8 of the 10 birds die within the year then the population would still remain stable. So each year we have a significant surplus of birds that can be taken by predators without any long term effect on the population of those birds.

It may disturb people to see a Sparrowhawk plucking a Blue or a Great Tit, but the tit is a predator itself, feeding as it does on thousands of caterpillars whilst bringing up its family. So should we control tit numbers? Of course we shouldn’t, even though their diet doubtless includes the caterpillars of several scarce, or even rare, species of butterfly or moth.

During the 1950s and 1960s the population of Sparrowhawks crashed as a result of the use of DDT. The reasons for this have been well documented so I shall not go into them again here. Suffice to say that the use of DDT was banned as a result. So why wasn’t there a problem before DDT? Those that are old enough to remember will recall that before the 1960s there were good numbers of both Sparrowhawks and songbirds. When Sparrowhawk numbers then dramatically declined why didn’t the songbird population rise? It can only be that there is no direct relationship between Sparrowhawk and songbird numbers. Interestingly, research in an Oxfordshire wood showed that during the period when Sparrowhawk numbers declined, Blue Tits and Great Tits got fatter (but with no increase in body length) ie lazier. They were able to store more fat because there was no need to be nimble in order to escape from the predator. As Sparrowhawk numbers recovered, the tits gradually became leaner again.

So what has happened to upset the equilibrium? If the Sparrowhawk is not responsible for the decline in bird numbers, could it be the local cats? We know from surveys that this country hosts around 40,000 breeding pairs of Sparrowhawks. It also hosts around nine million cats. So what kills the most birds, a pair of Sparrowhawks or 225 cats? The answer is not a difficult one – I’m sure we have all seen the local moggie catching birds and then heard its owner say “My cat never takes any birds!” In actual fact although cats kill far more birds than Sparrowhawks it is likely that neither affects the total population significantly.

Research has shown that habitat loss is the prime reason for the fall in songbird numbers. Many of us can remember that when we were young the countryside was far more “wildlife friendly” than it is today. There has also been research done that shows that modern agricultural practices have played their part in this decline. I refuse to use the phrase “farmers are responsible” because it is the remit of farmers to ‘feed the nation’ and if I were a farmer I would want to maximise my profits so that my family could have a better life. Naturally our farmers will strive to get the maximum possible yields from their land. Modern farming methods have resulted in spilt grain in farmyards being a thing of the past. Our farmers have come to rely on insecticides and herbicides to help them achieve higher yields. Yet these sprays are partly responsible for the dearth of the weed seeds and insects that are necessary for our songbirds to flourish.

Take a look at your local field of virtually any crop. Modern farming is so efficient that you are unlikely to see a single weed and virtually no insect life. Is it the farmer’s fault? No, it isn’t, it’s the system that allows it to happen and that’s where central government comes in. Perhaps that’s an article for another day.

I could go on but the point is clear. Many of our songbird species continue to decline, but the situation is unlikely to be helped by the persecution of Sparrowhawks.

** Here are the Blue Tit maths, based on no mortality, immigration, or emigration:

Year 1 – 1 pair raise 8 young Population now 10

Year 2 – 5 pairs each raise 8 young Population now 50

Year 3 – 25 pairs each raise 8 young Population now 250

Year 4 – 125 pairs each raise 8 young Population now 1,250

Year 5 –  625 pairs each raise 8 young Population now 6,250

Year 6 –  3,125 pairs each raise 8 young Population now 31,250

Year 7  – 15,625 pairs each raise 8 young Population now 156,250

Year 8  – 78,125 pairs each raise 8 young Population now 781,250

Year 9 –  390,625 pairs each raise 8 young Population now 3,906,250

In reality, the population after 8 years is still two, so the potential surplus is huge.

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