Why do birds sing in the morning?

by Colin Beale in Safari Ecology

Ruppell's Robin-chat: an impressive mimic. Lake Duluti I enjoyed a walk around Lake Duluti yesterday morning and came across a couple of wonderfully singing Ruppell's Robin-chats. These are great birds, with an amazingly varied song hat's gull of mimicry (of you want to hear one, listen here!). For me, one of the best things about camping in the bush is being able to lie in bed and listen to the birds waking up while it's still too dim to see them properly. The dawn chorus is a worldwide phenomenon and I'm often asked about bird song, so I thought it would be worth exploring some of the theories behind bird song, and - particularly - why birds sing in the morning. It's something that's interested me since I was introduced to the question by a friend of mine who did a PhD on the subject some years ago, and I know he reads the blog so I'm hoping he'll make sure I get the answers right!There are two parts to the question, of course: why do birds sing? And why do they sing in the morning more than at other times of day? The first I think we've had a pretty good idea about for a long time, and there are two main reasons: to attract mates, and to claim their territory. In general the two actions aren't mutually exclusive - as a male bird you can sing to both let the other males around know that you're still in your territory, and you can at the same time let females know that you're around and looking for a mate. For some species by listening to the song you can tell what the bird is actually trying to say  - Nightingales are well known in Europe for their beautiful song, but it's not uncommon to hear them singing down here during the non-breeding season too (they seem to be more territorial than many migant species). The difference is that here, I've almost never hear the typical long whistle notes that are so frequent in the breeding areas during the early breeding season (listen to them here). They also use even more of these whistles during the middle of the night before they find a mate, and it seems that these whistles are particularly for attracting females, which obviously isn't relevant when not breeding. As females might be flying over at night, singing in the midle of the night and whilsting a lot, might be a very good way to attract a female to your territory.Yellow-vented Bulbul - nesting all year round in my garden (March 2012), both sexes sing far too early in the morning for comfort...For some species song is probably more important for attracting females than in other species - particularly, I would suggest, for species where mimicry is very important. Like my Ruppell's Robin-chat, many birds are accomplished mimics, and observations suggest that the more varied an individual male's repertiore, the more attractive the male. The most impressive example of this that I'm aware of is the Marsh Warbler, a species that we mainly see on passage here in Tanzania from time to time - though it is another than sometimes sings during the non-breeding season. In what's become one of the classic studies of song mimicry, 30 individual males were recorded during the breeding season and the songs then analysed and mimicry identified. The total diversity of song mimmiced by these 30 males was 212 species, 113 of which were African species! On average, each male knew the songs of 76 different species, mostly African - one male included identifiable fragments of 84 species - an astonishing variety of songs and calls! Why do they do this? Well, it seems most likely that females prefer the males that have the most varied songs - males that can learn lots of different songs have clearly got some good mental abilities, whilst - the hypothesis goes - must be tied to their ability to find food, avoid predators or otherwise help around the nest. So there's not only a chance to let a female know that you're around like the nightingales do, but there's a real competion going on to be the best singer of all.As I said before, there's also plenty of evidence that it's not only about attracting a female: even after findinga  female and her sitting on the nest many species keep singing for a while - this is clearly about territory defence. And the first example of how effective this is comes from a nice experiment where birds were removed from their territories and the time it took other birds to come and occupy the patches was recorded: it's pretty quick, but if you play a tape recording of the song of the resident male even though he's been removed, it takes a lot longer. Clearly birds looking for a territory recognise individual songs and as long as the territory holder is still around and still singing they won't bother trying to take over - an efficient system of defence if ever there was one.Usambiro Barbet, a typical African species with duets. Serengeti, Dec 2011.Now, that's the general answer to why birds sing. But here in Africa there's an additional complication we should consider: here, many female birds sing too. This isn't unknown in the north, but it's fairly unusual. And we've already seen that a whole load of African birds engage in complex duets too, with both male and female taking part. Why is it that many more females take part in song here in Africa and the rest of the tropics than they do elsewhere? There's no good answer to this one yet, but a couple of interesting theories are being developed that are worth mentioning. Firstly, as we've already talked about, birds in the tropics tend to be rather long lived - they do things slowly, and they have a rather tougher time raising young in many ways than in more temperate regions. So here they're often also with their partner longer, and often holding territories year-round - lots more reason for females to be involved in territory defence as well as males, so that's one possible reason. The other theory is that here in Africa the seasons might be harder to define (at least in the forests), with breeding possible much of the year (certainly the bulbuls in my garden think it's fine to nest all year around). But birds don't tend to keep their ovaries or other bits of breeding equipment large and ready to breed year round - it would be a waste energy to carry around fully developed genetalia if you're not going to use them, and flight is tricky. So in a less seasonal environment, how do both male and female make sure they're in breeding condition at the same time? Well, perhaps, by singing to each other - there's certainly some evidence that song can help bring on breeding condition in some birds. Interesting thoughts though, and (yet) another area of tropical ornithology where we're well behind on theory and experiment.So. Having tried to answer why birds sing, let's tackle why we think they sing most in the morning. There are a number of (not mutually exlusive) theories here too. They all start with the assumption that singing is good (for the reasons we've covered above) - but it's costly in terms of time and energy (another reason why females might like males that sing more: they're showing honestly h... Read more »