Being an ecologist can result in one taking an opinion that is diametrically opposed to that of simple logic. A classic example is that of the bird of prey populations that have made a spectacular recovery over the past 30 years. Surely more raptors must mean less songbirds? Not according to my understanding!
Studies of predator-prey dynamics have shown that there are often two characteristics of population curves; predator numbers are determined by the abundance of food and they reach a peak later than the prey species. In other words the more that there is to eat the more predators there may be! The total amount of prey in an area will be an important factor in determining the number of predators, but there is a time delay.
The British Trust for Ornithology has presented some important new information that contributes understanding to this model in its BTO News May-June 2010. In a piece entitled Are Predators to Blame? Stuart Newson and Stephen Baillie summarise their research that is published in full in the Journal of Applied Ecology 47.
‘In summary, for the majority of the songbird species examined, there was little evidence that increases in common avian predators and grey squirrels were associated with large-scale depression of prey abundance or population declines. For the majority of declining songbird species with unfavourable conservation status, population declines appear to be due to factors other than predation’.
In Gloucestershire, the numbers of many of our birds of prey have increased dramatically since I have lived in the county. Whilst it is true that species like the house sparrow, yellow hammer, nightingale, turtle dove and many others have achieved the undesirable red or amber status (in trouble), it would seem that the causes are often more complex than their immediate natural enemies. Habitat loss in the
So don’t worry about your local sparrowhawk, buzzard or kestrel, just marvel at their aerial grace and their subtle role in local ecology.
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