September 16, 2021

Helping some animals can hurt others — sometimes in surprising ways. A core goal of wild animal welfare research is to understand these tradeoffs well enough to ensure management efforts do more good than harm.

A recent article in Biological Conservation (Shutt & Lees 2021) provides one such example of “killing with kindness.” It explores how well-intentioned UK gardeners may have actually decreased the population of willow tits (Poecile montanus) by stocking their bird feeders through the winter — when the willow tits have flown south but Eurasian blue tits (Cyanistes caeruleus) are still around to benefit.

The researchers proposed two drivers of this effect. First, the blue tits’ population may have increased because they had access to extra food at a time it was otherwise scarce, allowing them to outcompete willow tits for food in the non-winter months. Second, the growing blue tit population may have made it hard for willow tits to secure and maintain nest sites — leaving them vulnerable to predation.

If these hypotheses are true, then deciding whether or not to encourage winter bird feeding requires evaluating the tradeoffs between willow tits, blue tits, and other affected species.

When these decisions are made for the sake of biodiversity conservation, they typically consider effects on populations, species, or ecosystems. For example, which of the affected species face greater risk of extinction, vary more from their historical distributions, or contribute more to ecosystem functions?

But considering the wild animals’ quality of life introduces additional considerations: effects at the level of the individual. How many individuals are affected, how intense are their experiences, and what would they have experienced otherwise?

Predicting the welfare effects of wildlife management decisions often requires digging deeper than population-level metrics. In the case of winter bird food provisioning in the UK, measuring the decline of the willow tit population may be sufficient to inform conservation decisions. But understanding what that means for animals’ well-being requires accounting for causes of death (Hecht 2020). How many more birds than usual are dying from starvation versus predation, and which of those fates causes more suffering? The value of preventing those premature deaths further depends on differences in welfare expectancy between species and age cohorts (Hecht 2019).

Conservation biologists have long been among the most outspoken defenders of members of other species. By calculating the full costs of tradeoffs between species, wild animal welfare research may advance our ability to responsibly defend those interests.