Now I know where my sparrows go to sleep

I've long had a special interest in the sleeping habits of small birds. In fact, as you'll know if you read the article I published here back in September 2008*, I've covered this issue before. In that article, I noted that at least some passerines secrete themselves away in crevices or thick foliage. I first became really interested in this subject after making one of my greatest natural history 'discoveries': a sleeping Blue tit Cyanistes caeruleus that I encountered while it was tucked deep beneath the broken bark of a tree, just the tip of its tail betraying its presence. I didn't have a camera with me at the time. And, yes, I (and a colleague) were creeping around in the woods, at night.

* I frequently find myself regarding an article as 'recent'. On finding it online, I'm then consistently surprised when it's actually, like, three years old or so.

Other passerines form huddles inside tree holes and nest boxes: cases where Eurasian wrens Troglodytes troglodytes pack tightly into nest boxes and hirundine mud nests during the winter are well known, with the record being 63 individuals found in the same box. Unsurprisingly, birds at the bottom of such deep piles sometimes suffocate to death. House sparrows Passer domesticus have been reported to use streetlight interiors as winter roosting locations. Still other species roost on branches, but typically huddled close to friends or relatives and mostly hidden by surrounding foliage.

There are also passerine species that roost in caves (Diamond 1983), and then there's the fact that various tits, kinglets, buntings and others excavate and roost in snow burrows (e.g., Bagg 1943, Lagerström 1979, Helle 1980). Then there are species that sleep in nests. Some species sleep on their nests prior to the laying of their first egg (e.g., phoebes) but don't use the nest as a roost at other times of the year. The Curved-billed thrasher Toxostoma curvirostre [shown here, by Peter Wallack, from wikipedia], which builds its nest in thorny cacti, is apparently unique in sleeping on its open-topped nest outside of the nesting season (Skutch 1960a).

Other passerines that sleep in their nests outside the nesting season use covered nests. The use of such nests year-round is particularly well known for various tyrant flycatchers (e.g., Sulphur-rumped flycatcher Myiobius sulphureipygius) (Skutch 1989). In some areas, the use of covered nests as roost sites is probably opportunistic and not really a necessity, but in others it may be necessary if the birds are to survive through the cold night (Skutch 1960a, Merola-Zwartjes 1998). Some passerines (e.g., Eye-ringed flatbill Rhynchocyclus brevirostris, House sparrow, Bananaquit Coereba flaveola, various wrens) are known to construct special dormitory nests or roost nests (Skutch 1960a, b, Jansen 1983, Merola-Zwartjes 1998). [Costa Rican bananaquit nest shown here by Steven G. Johnson, from wikipedia].

The immediate surrounds of my house are home to a small colony of House sparrows. It can't be easy for such birds to persist in sub-urban habitats given the committed efforts of local humans to remove all and any foliage. Anyway, my interest in passerine sleeping habits got me wondering: where do my sparrows go at night? I became determined to find out.

As I've spent the last year or so discovering, determining exactly where small birds go as the sun starts to go down is surprisingly difficult. On several occasions I stayed out, watching the birds and waiting to see exactly where they go during dusk. This didn't work; they simply flew around the building and out of sight. Given that they nest in my neighbour's roof (but not mine), could they roost in my roof? I crept, as quietly as possible, hidden in darkness, deep into the darkest recesses of the loft one night, armed only with a torch and a camera. Small apertures around one of the gables allow birds to enter the roof in a particularly inaccessible region. Turning the torch on only when I'd reached said inaccessible region, I found a lot of grass and feathers that perhaps indicated a previous nesting effort. But, alas, no sleeping birds.

Then, some months later, I began to notice that small birds would sometimes fly off into the darkness whenever I left the house (at night) via the front door. I never got to see them, only hear them. Associated droppings [see adjacent pic] revealed that an area right above the front door was being used as a roost site, and apparently on a regular (probably nightly) basis. To cut a very long story short, I eventually learnt that some of the local sparrows were spending their nights under the porch roof over my front door, perched on dead jasmine branches and pressed right up under the slanting roof. At times, at least three sparrows (one male and two females) shared the roost. I became determined to photograph them while minimising disturbance; alas, photographing them without one, two or all of them flying away proved just about impossible. The photos you see here are the result. Finding sparrows roosting under the roof of my front porch isn't exactly a revelatory scientific discovery, and I don't plan to write it up for attempted publication in a technical journal. But it's a very satisfying personal little discovery.

The end of the story is somewhat sad, however. For various reasons I had to remove a dead tree from the garden adjacent to the porch. This was several metres away from the porch, but it seems that its position still provided cover or protection of some sort. With the tree removed, the sparrows moved on. They roost somewhere else now, but where I do not know... Sleep well, little sparrows. [UPDATE: I was wrong, the sparrows are still using the site as a roost. Good, I feel less guilty.]

Thanks to Dartian for digging out the snow-roosting citations.

PS - in totally unconnected news, I just joined twitter. Find me at TetZoo.

For previous articles on sleep, roosting, nesting and other connected aspects of bird behaviour, see...

• Dead baby birds: why here, why now?
• Why can't my readers be dumber? Or: replica owls
• A stork in ice and snow
• Sleep behaviour and sleep postures
• Why do some owls have ear tufts?
• Raptor makes killing in university grounds
• The pigeon in the fireplace

Refs - -

Bagg, A. M. 1943. Snow buntings burrowing into snowdrifts. The Auk 60, 445.

Diamond, J. 1983. Melampitta gigantea: possible relation between feather structure and underground roosting habits. Condor 85, 89-91.

Helle, P. 1980. A great tit Parus major roosting in snow. Ornis Fennica 57, 175-176.

Jansen, R. R. 1983. House Sparrows build roost nests. The Loon 55, 64-65.

Lagerström, M. 1979. Goldcrests Regulus regulus roosting in the snow. Ornis Fennica 56, 170-172.

Merola-Zwartjes, M. (1998). Metabolic rate, temperature regulation, and the energetic implications of roost nests in the Bananaquit (Coereba flaveola). The Auk, 115, 780-786

Skutch, A. F. 1960a. The nest as a dormitory. Ibis 103, 50-70.

- . 1960b. Life Histories of Central American Birds II: Families Vireonidae, Sylviidae, Turdidae, Troglodytidae, Paridae, Corvidae, Hirundinidae and Tyrannidae. (Pacific Coast Avifauna No. 34). Cooper Ornithological Society: Berkeley.

- . 1989. Birds Asleep. University of Texas Press, Austin.