Australasian Science Magazine

An experimental bird feeder in New Zealand. Credit: Josie Galbraith

By Josie Galbraith

Bird feeding is a popular way for people to interact with urban wildlife, but what are the consequences for birds, bird populations and native biodiversity as a whole?

Food is a critical necessity of life, a shared need for all of us life-forms living on the planet. It can be hard work finding enough food to survive, or, in our case, earning the money to pay for our groceries each week.

We humans are an odd bunch, though. Many of us choose to spend some of our hard-earned resources providing food for other animals, particularly wild animals that give us nothing tangible in return. Birds are by far the most popular group of animals to feed. Estimates of participation rates from New Zealand (https://goo.gl/tNsyyt), Australia, the USA, the UK and Europe range from one- to two-thirds of the population. In the USA alone around 60 million Americans feed wild birds, with the activity more popular than fishing by about 25 million people (https://goo.gl/qPg48E).

Equally as impressive is the amount of food being served up. In Aotearoa, New Zealand, an estimated 5.1 million loaves of bread goes to hungry birds instead of people every year. A 2002 estimate put the amount of seed being fed to wild birds in the USA at 500,000 tonnes/year – a figure that has undoubtedly grown since then. By any measure, the scale of this seemingly benign pastime is absolutely staggering.

Why people choose to feed birds is still poorly understood, but it is likely to be driven by a complex array of factors. The most common reason people give for bird feeding is that the activity brings them great pleasure and enjoyment. There is increasing scientific evidence that connecting with nature generates some pretty powerful psychological benefits, quantifying a phenomenon we have had some understanding of for millennia (think of health retreats located in beautiful wilderness locations). But urban dwellers are increasingly disconnected from the natural world, and have fewer opportunities to experience and interact with nature (this is known as the “extinction of experience”), so perhaps the rise in bird feeding popularity is a response to counter this disconnect.

Whatever the underlying reasons, people undoubtedly gain some benefit from bird feeding. But what about the birds?

Many people believe that by feeding birds they are helping them, or the environment, in some way. On the surface it may certainly seem logical to think that providing more food in your backyard for the birds is good for them. After all, you’ve just made their little lives a bit easier for a short while by giving them free food they don’t have to spend energy searching for.

But “easy” doesn’t equate to “good”. Think of backyard bird feeding as opening up a fast food restaurant at every street corner – it might be convenient but probably not beneficial if you ate there everyday. In the same way, supplementing the food available for birds at every second or third house is likely to have some impact on birds using that food. From the growing number of studies on urban bird feeding, that certainly appears to be the case.

Every aspect of a bird’s ecology or biology could potentially be affected by supplementary feeding. For instance, it can alter their chances of survival and of successfully raising chicks, which in turn may affect population size. It can also affect their health, increase the risks of disease transmission, heighten aggressive behaviour, lead to increased predation, and even influence large-scale migratory patterns. Some of these effects may be beneficial to the birds, and some may be detrimental. Whether these effects are desirable is another matter again, and this all hinges on who is coming to the food.

Understanding who is visiting these backyard fast food restaurants, and what influences this visitation, is critical for predicting the impacts of feeding so we can make decisions on whether they are impacts we want. In other words, birds that make frequent use of feeders are more likely to gain any benefits but also suffer any direct detrimental effects, and identifying who these feeder-addicts are (i.e. which species and individuals) will help us work out if the outcomes of this feeding are desirable.

A 2-year experimental study of bird feeding has help to illustrate this (https://goo.gl/Fr6c74). The primary aim of the study was to investigate the ecological impacts of typical bird feeding practices in Aotearoa. Twenty-three suburban householders generously volunteered to be part of our study; in the backyards of 11 of these we established supplementary feeding stations, while at the remaining 12 properties no extra food was put out for birds. Feeding stations were refilled with bread and seed every morning for 18 months – these are the two most popular food types fed to birds in New Zealand. With these feeders set up, we collected data on which bird species were using these feeders and what effects these practices were having.

With the help of motion-activated wildlife cameras, we found that 11 species of bird were using our feeding stations. Supporting 11 different species in an urban habitat sounds pretty good, but only one of these species was a native bird (the silvereye Zosterops lateralis). The rest were introduced species.

Two introduced birds overwhelmingly dominated – house sparrows (Passer domesticus) and spotted doves (Streptopelia chinensis) – present at the feeder in 65% and 58% of photographs taken by the wildlife cameras, respectively. In comparison, silvereyes were only present in 4.6% of photos. House sparrows and spotted doves were also the two most abundant species at feeders, both in terms of mean and maximum group size using the feeder simultaneously. The mean group size for house sparrows was 5.2 ± 0.12 individuals, with a maximum of 45 sparrows recorded at the station at one time!

Within a few months of starting the feeding experiment, we saw the overall abundance of these two species in the local vicinity skyrocket (https://goo.gl/VKRnhq). There were two-and-a-half times more sparrows around feeding properties than around non-feeding properties during the feeding experiment, and three-and-a-half times more spotted doves.

While our feeding regime certainly seemed beneficial for these species, this outcome was not a desirable one overall. These species came to dominate in the local bird community as well as at the feeders themselves. That isn’t good for populations of native bird species in our cities. In fact, we found evidence that the number of one city-dwelling native bird, the tiny grey warbler (Gerygone igata), decreased by 50% as a consequence of the feeding regime.

You may think: “That’s not a problem in my backyard – where I live we only have native birds hanging around.” But even among an assemblage comprised of all native birds, one species may benefit from feeding over and above the others, and will similarly come to dominate that bird community at the expense of others. So the lessons we have learned from our feeding experiment in this urban bird community in New Zealand are absolutely crucial to consider wherever feeding is taking place.

One of the most common questions I get asked is: “Is it OK to feed birds?” I get the impression that people suspect it may not be, but that they’d very much like me to allay their fears and give my full endorsement anyway. However, there isn’t a simple one-size-fits-all answer to this question.

While our research has provided some pretty clear evidence that bird feeding can have serious impacts on urban bird communities, the potential social and psychological benefits of bird feeding are too important to ignore. Furthermore, what food, how much and how often will influence the impacts of feeding.

So the better question is to ask how can people feed birds without causing harm to urban bird communities. Better yet, how can bird feeding work to enhance native biodiversity?

Bird feeding could well be a powerful tool in helping bring nature back to our cities. With urban ecology and environmental movements taking off around the world, it is an opportune time for further research to explore this potential.