The mild heroism of providing water for birds in summer

For garden birds – and for many other birds in temperate latitudes – the warmer temperatures and longer days of summer create what biologists would recognise as optimal conditions for procreation. All of which is to say: summer, for birds, is go time. The extended periods of daylight have shaped birds’ evolutionary history, in such a way that changes in the amount of light trigger a hormonal response that prompts them to mate. Insects, fruits, and nectar are all most abundant in summer, making it the optimal time to raise young. And because cold temperatures are energetically costly and decrease survival in chicks, the warmth of summer is ideal for incubating eggs and reducing the already energy-intensive task of raising young.

At the garden scale, the technical jargon above translates into a period of high bird activity – an orchestra of songbirds searching for mates or defending territories, and the constant comings and goings of parents feeding their chicks and themselves. Summer, for the garden birdwatcher, is certainly peak programming.

But along with summer, comes heat. And with heat, heatwaves. And with heatwaves a reminder: water is critical for garden birds! They do not sweat, but they do lose water constantly: via respiration, via their faeces, and via evaporative cooling mechanisms that are mostly centred around panting or ‘gular fluttering’, neither of which are efficient if there’s no water coming in.

Passerines (the taxonomic group that includes most of the singing, flapping, garden-variety species we love) have especially high rates of water-loss and must replenish fluids frequently. And if you’ve ever seen a House Sparrow or a Robin in your garden birdbath, you might have seen them scooping water with their beaks and tilting their heads backward, relying on gravity to drink water. A recent study of European birds found that most garden species drink water from garden features when available, even those species that get some moisture from their food. Just like in humans, it turns out, water is not optional.

Beyond hydration, water is critical for plumage maintenance – which is less about grooming and more about structural performance. Birds rely on their feathers for flight, insulation, waterproofing, and camouflage. When feathers get dirty or infested with mites or fungi, they lose integrity. Birds bathe to fix that. And after bathing, they preen, applying secretions from the uropygial (‘preen’) gland, which sounds vaguely mythological but is real and is located on the rump near the tail. If denied water, studies show, birds exhibit underdevelopment of this gland. Their feathers deteriorate, their flight becomes less efficient and, ultimately, their odds of survival go down.