The Debate on Feeding Wild Birds
Recently, while browsing social media, I stumbled upon an account discussing the significance of placing feeders with food for wild birds. Common in several European countries and North America, this practice has long been regarded as advantageous for birds.
The post explained that there might be some negative effects, but they are outweighed by the positives. Some reports indicate that populations frequenting feeders fare just as well or better than those without extra food. However, if this were true, it would pose a problem as we’d be benefiting bird species more likely to approach artificial structures.
Scientific Perspectives on Bird Feeding
For instance, a study involving blue tits (Cyanistes caeruleus) showed that winter supplementation reduced breeding success in the following spring. Chicks from supplemented parents were smaller and had lower survival rates compared to those of parents without extra food. The hypothesis suggests that adults feeding excessively on feeders might be in poorer physical condition due to the lower quality of the provided food compared to their natural diet.
Interestingly, another study where birds ate peanuts did not show such negative effects. The researchers from the first study also discussed how the overall effect might be due to winter supplementation favoring the survival of lower-quality individuals, who, when reproducing (without the aid of feeders in spring), achieve poorer results.
In another study examining blue tits and great tits (Parus major), no clear effects of supplementary feeding on individual reproduction were found. However, it was detected that food facilitation increased the survival and subsequent reproduction of less competitive birds. As they joined the breeding population, competition for resources increased.
The authors suggested that feeders might facilitate breeding in marginal territories or the reproduction of lower-quality individuals, as juveniles in their study used supplementary food more frequently than older birds.
Expert Opinions on Bird Feeding
More experts argue that providing extra food for wild birds is likely more harmful than beneficial. A 2021 study highlights the consequences for non-target species. These include more common and adaptable species that use feeders more often, which can expose the intended recipients to higher predation and competition rates.
In fact, in the UK, it was discovered how a protozoan parasite of the genus Trichomonas jumped from pigeons to various finches, sparrows, and wagtails feeding at bird feeders, causing a Trichomoniasis epidemic—a significant threat to birds.
This work also demonstrates how population trends of species frequently feeding at bird feeders are favorable, while those not usually visiting them tend to be negative in most cases. This raises the question of whether feeder use is responsible for these differences: could massive, predictable food provision in UK gardens be causing less common, subordinate species that don’t use feeders to be unable to compete with abundant, dominant species that do?
The Case of Scavenger Birds
Supplementary feeding is a tool used to improve the situation of threatened populations, especially when natural food scarcity is a threat factor. However, this often successful practice has also taught us that supplementation does not exclusively have positive effects.
In Spain, potential negative consequences of this practice on scavenger birds have been investigated. The decreasing population sizes of vultures and other species in the Iberian Peninsula led administrations to provide food at so-called carcass sites, areas traditionally left with domestic animal carcasses.
Read more: The challenge of managing carcasses for scavenger conservation
Carcass sites proved crucial for vulture population recovery, but closer inspection revealed that the way administrations managed feeding points could have less positive effects. Carcass sites transformed into “vulture restaurants,” with large amounts of food concentrated in a few points and predictably over time, altering the habitat regarding food resources for scavengers.
If, at carcass sites, food is provided at predictable times and locations, it favors the monopolization of carcasses by a few dominant and aggressive species, like the Egyptian vulture (Gyps fulvus). A study in northern Spain found that carcass diversity depended on the number of Egyptian vultures attending carcass sites: more vultures meant less species diversity feeding.
When carcasses appear in the environment unpredictably in time and space, more species utilize them, and they are more frequently used by smaller birds (like vultures or owls, some of which are endangered).
From these studies, it’s deduced that managing feeding points is essential. Experts suggest that supplementation should be considered only when maintaining populations based on unpredictable carcasses from wildlife or extensive livestock (unpredictable in time and space) is compromised.
In any case, feeding points should be established as a series of locations where food is sporadically provided to avoid resource and scavenger concentration.
Although it’s true that for certain cases, feeders and supplementary feeding can be beneficial, their use should be limited to scenarios where populations face demographic issues. Moreover, they should target birds that might need them rather than being available for most species prone to using them.
In other words, if we genuinely care about nature maintaining its balance, we must avoid massive, indiscriminate use of these practices.
