Dear Readers, this is a topic that will be close to all of our hearts, I’m sure. Are we actually helping birds when we feed them in our gardens? Should we be doing it all year round? What are the pitfalls of attracting large numbers of birds to a small space? I was eager to hear what Mike Toms had to say – he wrote the ‘Garden Birds’ volume of the New Naturalist series, one of my favourites, and currently works at the British Trust for Ornithology (BTO), so he’s a man who knows of which he speaks. I’ve given quite a lot of detail here as I found it absolutely fascinating.
Toms started by explaining that the BTO is a research-based organisation that looks specifically at bird populations – changes in distribution and numbers, and the reasons for those changes. The bird that has been studied the longest is the grey heron – BTO have data going back to the 1930s and were able to map a correlation between cold, hard winters and declines in the heron population. Increasingly, though, the BTO studies birds in urban environments. In 2008 the world reached a point where half the population now lives in towns and cities, and this is expected to increase to two-thirds of us in 2050. Urbanisation has consequences not just because of the footprint of the areas themselves, but because of the resources that are needed to support them. Globally, some of the areas that are urbanising most rapidly are also those with the highest current levels of biodiversity, such as south-east Asia and the Horn of Africa.
In the UK, some species can adapt very nicely to the urban environment (Toms showed a photo of two herring gulls looking hopefully at somebody sitting on a bench with a sandwich). Such species have a broad diet, and are not too specific in their requirements, which is one reason why dove and corvid species do so well in our towns and cities. In the garden environment, you’re likely to see a lot of seed eaters, such as sparrows and finches, but far fewer insectivores.
London is particularly well-blessed with green space, however, and although we think about this in terms of parks and woodland, private domestic gardens are by far the biggest space. Taken together, the gardens of the UK cover a larger space than all of the land set aside for nature reserves. At this point, Toms did a survey on whether the live audience thought that gardens were good for birds, and over 90% thought that they were.
Toms then started to look at gardens in more detail. One trend, especially since lockdown, was that people wanted to make their little bit of greenspace more wildlife friendly – he showed a slide of a garden from the Chelsea Flower Show which was contemporary but had a bird feeder, lots of pollinator-friendly plants and some small trees and shrubs – it seemed like a nice combination of the aesthetic and the useful.
The big draw for birds in our gardens is clearly food – Toms had the staggering figure that across the UK we spend £200m per year on bird food (and about half of that is me 🙂 ). For birds to stay in our gardens, and not just use them for food, there need to be nesting opportunities too.
Toms showed an interesting graph which illustrated the reporting rates for robins – volunteers at the BTO record which birds they see in their gardens every week. It showed firstly that reporting rates for rural and suburban gardens are higher than those for urban gardens overall, but that all three types of garden showed a drop off during the breeding season – this seems to indicate that while robins will use gardens during the winter season as a food resource, they prefer not to nest in them.
Why is this? One reason is that most birds feed their nestlings on insects, and these are just not plentiful enough in gardens. Blue tits, for example, will nest in deciduous woodland where there are lots of caterpillars given the choice. This year was particularly devastating for birds as May was so cold, and June so wet, so there were lots of reports of nests failing and nestlings starving in the nest. However, a significant proportion of birds (over 50% of starlings and sparrows, a third of jackdaws and blackbirds and, surprisingly, 25% of song thrush) do breed in gardens, so the habitat is clearly important for these species.
Rural gardens in particular can also be important for birds such as the yellowhammer, tree sparrow and reed bunting, who are seedeaters – Toms showed a graph of farmland birds who visit gardens with a seasonal peak in April, when all the natural food that the birds would normally eat has finished. In days gone by, there would be grain amongst the stubble, but with more efficient farming methods, the birds have taken to visiting feeders. This is especially important in the case of the cirl bunting, a very rare species in Devon, where garden feeding has really helped to reinforce the population.
Turning to blackbirds, Toms showed a graph of the reporting rate of the birds which showed a marked fall-off in the autumn every single year. He explained that this is partly due to the birds becoming more secretive during the moult, but also that they often move out of gardens during the glut of berries that are available in parks and the countryside.
With blue tits, Toms spoke about ringing exercises (where individual birds can be identified), which shows that it isn’t just the same old three or four birds visiting the feeders, but a succession of birds – you could have thirty different blue tits visiting the feeder in the course of a day.
Toms moved on to coal tits – these little birds largely feed on the seeds of coniferous trees, and so have done very well with the planting of sitka spruce plantations (one of the few creatures that have, I imagine). Again, the data from the recorders showed an annual peak and trough, but the peak was supressed in years when the spruces were ‘masting’ (producing their seed) – this only happens every few years, so that there is so much seed that the predators can’t eat it all, and the tree has the best chance of reproducing. In other words, if the spruce seed is available, the coal tits will eat it in preference to visiting the garden, but they will use the gardens if it isn’t so plentiful.
Then, Toms looked at longer term studies. One of them, on goldfinches, has showed a massive increase in the use of gardens by the species. Interestingly, there seem to be two ‘spikes’ in the data, which might indicate that firstly resident birds are using the gardens for food during the breeding season, and then a second wave of migrant birds comes in to take advantage of the resource.
Feeding is not an unalloyed good, however – Toms gave the example of trichomonosis and the greenfinch. This protozoal parasite is spread in saliva and faeces from infected birds, and is a very good reason for making sure that feeders are cleaned regularly. What I hadn’t realised was that the ‘spillover event’ probably came from woodpigeons, who have been carriers of this parasite for years, and one place where pigeons and greenfinches come into contact is at seed feeders in gardens. Greenfinch and chaffinch populations have been horribly affected, with Toms describing the chaffinch population as being ‘in freefall’. It made me think about the last time that I saw chaffinches in the garden, and it’s been quite a while ago.
The ‘pox’ that we sometimes see on blue and great tits seems, according to the BTO research, to have actually come from blackflies which have jumped across from the European mainland, thanks yet again to climate change.
Finally, Toms looked at blackcaps. These birds are increasingly using our gardens in the winter time (probably migrating in from Eastern Europe), and interestingly they prefer urban gardens, which are warmer because of the urban heat island effect (all that concrete stores heat during the day and releases it at night, increasing the ambient temperature). Blackcaps also prefer gardens where food is available every day.
So, it seems that the food that we provide is changing the behaviour of some birds, but by attracting them to our gardens we also increase their exposure to some diseases, and to different predators, such as cats and grey squirrels, which might not be so common in the countryside.
So, what were the conclusions? It’s very clear from the BTO’s studies that the birds who are visiting our gardens have become more diverse over time. We’re also putting out different foods – many of us are feeding not only seeds and peanuts, but suet products. Apparently, too much fat can affect a bird’s feather condition, but the addition of Vitamin E can counteract that. Where do I get suet products with Vitamin E, I wonder?
Living in an urban area brings a whole selection of risks and opportunities. There is pollution in cities that especially affects birds with their delicate lungs, glass windows claim billions of bird lives globally every year, and night time lighting can be confusing and destructive. Some studies have shown that blackbirds living in urban environments have shorter telomeres (the sections of their genetic code that protect the core genes), indicating that they have increased stress levels. Robins have to sing at night because they can’t make themselves heard over the traffic noise. Woodpigeon populations have gone through the roof, and may be contributing to disease in other species.
To sum up, Toms indicated that gardens are probably good for birds on balance, because they provide feeding opportunities and help to offset some of the damage that humans have done elsewhere. But it isn’t straightforward. Toms put in a plea for more research on what birds need, and especially pointed out the BTO’s Garden Bird Watch
To watch the whole talk, click here
