What do shingleback lizards, budgerigars and Mexican grey wolves all have in common? All these animals are monogamous: they generally mate with a partner for a substantial period of time, in many cases to raise offspring together. An obviously important prerequisite to being monogamous is having the ability to recognise your partner, even if you don’t see them for a while.
In many birds, mates recognise each other by the their vocalisation (what their particular call sounds like). For example, colonial seabirds can remember what their partner sounds like even when not seeing them for months at a time.
When hearing the words ‘vocalisation’ and ‘bird’ the first thing that is likely to come to mind is the parrot, possibly Alex the Parrot. Parrots are unusual for birds in that they are able to learn to make new vocalisations throughout their lives, and not just when they are young.
One particular parrot species, the budgerigar (or budgie), is monogamous. Both the male and the female have distinctive calls. When a male and female budgie are together (and love each other very much) they call to each other more often. This indicates that their calls are something to do with keeping pairs close and maintaining their bond. In the early days of courting, the male budgie will imitate the female’s call in order to impress her. The females do not do the same to the males, but prefer males that are particularly good at imitating their own calls (I think it might just freak me out if someone started doing this to me). Once the male and the female have laid eggs, their calls start to become more different again. Therefore, when the next breeding season comes around, the females can’t rely on the males’ calls being the same as their own.
In the lab, it is known that female and male budgies recognise each other after being separated for 70 days. However, it is not known how much of this recognition is based on what the other bird looks like, and how much is based on what they sound like. A recent study looked to see whether females remember the males they have paired with based on what they sound like. To do this, the researchers paired male and female budgies. They were then separated, and not allowed to see or hear one another. The female was then played the sound of her mate’s call and of another male’s call, to see if she would prefer the sound of her mate’s call (measured by how much she called back to it), and thus demonstrate whether she had some memory of it.
As females tend to prefer calls that are similar to their own, and as the males’ call becomes more similar to hers as time went on, the scientists needed to control for this. They did so in three ways: firstly, they paired males and females together at random, so that females were not selecting males with calls more similar to themselves to mate with. Secondly, they recorded males’ calls before they had paired with the females and started to make their own calls more similar to hers. And thirdly, when the researchers were playing back the two calls to the female they made sure that they were equally dissimilar to her call.
The researchers tested the female’s response to her mate’s call and the other male’s call at four different times after being separated (zero, one, two and six months). They found that the female preferred her mate’s call after one month, showing that she did remember what he sounded like after this period of time. However, she did not respond to his call after a longer period of time. A possible reason for this result is that the female has forgotten what her mate sounds like. However, previous work has shown that budgie females are actually very good at remembering calls (for up to 180 days). So, it could be that the female is not forgetting what her mate sounds like but rather she just doesn’t like him any more after this time. Why the females might lose interest after this time is another study waiting to be done…
photo credit: Elektrofisch
Reference: Eda-Fujiwara, H., Kanesada, A., Okamoto, Y., Satoh, R., Watanabe, A. & Miyamoto, T. (2011) Long-term maintenance and eventual extinction of preference for a mate’s call in the female budgerigar. Animal Behaviour. doi:10.1016/j.anbehav.2011.07.030