WHO REALLY BENEFITS FROM FEEDING GARDEN BIRDS? (Part 1 of 3)
Charles and Julia Botha
Charles and Julia Botha are the authors of Bring Nature Back to your Garden and Bring Butterflies Back to your Garden. Both their books have won book prizes from the University of KwaZulu-Natal. With their kind permission, we reproduce an article written and adapted by them for Environment from one by the same authors entitled Food for thought; who benefits from feeding birds? Africa Birds & Birding, 2009, 14 (3) 36-41.
The article will appear in our Newsletter in three parts. Here is the first.
Most people derive immense pleasure from watching birds devour food they have supplied. Feeding birds also has the undeniably positive spin off that it may start many people on a life-long interest in birds. In our own case, it was birding that awakened our interest in South Africa’s indigenous flora, as we realized how important local plants are to birds. But, in reality, is feeding birds doing them a favor or does it merely serve to gratify our own human pleasure?
There are many overseas studies regarding the consequences of feeding birds. With households in the USA and UK together estimated to purchase about 500 000 tons of bird seed annually, Robb et al. have reviewed the relevant scientific literature to try and understand the overall influence of this enormous food subsidy. While the studies which were included varied in design, form of supplemental feeding and species involved, the review gives an indication of the potential impact.
One concern is that regular bird feeding may create a population level that cannot be sustained by the natural food supply in the area. Thus birds are encouraged to settle where they cannot support themselves once feeding stops. Supplementary feeding often improves breeding results and causes earlier egg laying, which is of benefit to some species. However, in others, breeding too early brings negative results, because chicks are in the nest before the period when the maximum natural food becomes available. As a result, extra food supplements on offer during times less favorable for raising chicks can lead to a decrease, rather than an increase, in the survival rate of offspring.
With some surveys estimating that as many as 75% of UK households provide food for birds, this human influence on the ecology of birds is undeniable and is more than likely causing considerable disruption of the natural selection process. Studies in some species have shown that an unnatural abundance of food can even alter the male to female ratio of hatchlings. Research further indicates that feeding could affect returning migratory birds which have to compete with more well-fed, abnormally strong resident species. If it has not done so already, this could affect species currently in decline, such as the Willow Warbler, a summer visitor to this country. Certainly in the UK an alarming drop in the numbers of migrants has been recorded. Researchers are still gathering evidence from a variety of possible sources, but the excessive feeding cannot yet be ruled out as a contributor to the dramatic decline, which is as high as 88% in some previously common garden species.
Still further overseas experience has shown that certain waterfowl chicks, which have been fed by their parents from human handouts, fall victim to a wing deformity which renders them flightless. Considering the unsuitable food, such as refined white bread that is not even healthy for humans, which is often put on feeding trays, would the situation be any different with birds’ offspring in this country? Are we not perhaps responsible for the survival of weaker birds that Mother Nature will ultimately eliminate, in a cruel starving end, when their human benefactor ceases to pamper them and they lose the battle for scarce resources against their more hardened competitors of the same species?
This is a matter of speculation until ornithologists conduct more research on the subject in this country. But what cannot be disputed is that uneaten food, left behind by the birds, will attract unwanted pests that may harm the very creatures intended to be the beneficiaries. Almost certainly at the top of the list of culprits are alien rodents, especially rats. Probably the main villain is the Norway Rat or Brown Rat (Rattus norvegicus), but there is no reason to believe that the ubiquitous House Rat (R. rattus), also known as the Black Rat, is not equally detrimental to the well-being of smaller wild birds and their nestlings.
Since the elimination of feral cats from Gough and Marion Islands, albatross chicks have been viciously attacked by the introduced House Mouse (Mus musculus). Probably the world’s most widespread pest mammal, it is quite likely that it is silently just as destructive in gardens all over the country. Garden birds have not evolved with these fierce foreigners and so have no natural defence. Introduced predators have been shown to kill female birds when they are incubating eggs on their nests. This is one of the reasons for ornithologists reporting that in most adult bird species there are more males than females.
The article continues next month when we read about possible negative consequences of using bird feeders and what naturally occurring and indigenous alternatives we can use to attract birds to our gardens.