Nestling odour modulates behavioural response in male, but not in female zebra finches.

Studies investigating parent offspring recognition in birds led to the conclusion that offspring recognition is absent at the early nestling stage. Especially male songbirds were often assumed to be unable to discriminate between own and foreign offspring. However, olfactory offspring recognition in birds has not been taken into account as yet, probably because particularly songbirds have for a long time been assumed anosmic. This study aimed to test whether offspring might be recognised via smell. We presented zebra finch (Taeniopygia guttata) parents either the odour of their own or that of foreign nestlings and investigated whether the odour presentation resulted in a change in the number of head saccades, i.e. the rapid horizontal turning of the head, with which birds scan their environment and which can be used as a proxy of arousal. Our experiment indicates that male zebra finches, in contrast to females, differentiate between their own and foreign offspring based on odour cues, as indicated by a significant differences in the change of head saccadic movements between males receiving the own chick odour and males receiving the odour of a foreign chick. Thus, it provides behavioural evidence for olfactory offspring recognition in male zebra finches and also the existence of appropriate phenotypic odour cues of the offspring. The question why females do not show any sign of behavioural response remains open, but it might be likely that females use other signatures for offspring recognition.

Social odour activates the hippocampal formation in zebra finches (Taeniopygia guttata).

Experiments from our research group have demonstrated that the olfactory sense of birds, which has been considered as unimportant for a long time, plays a prominent role as communication channel in social behaviour. Odour cues are used e.g. by zebra finch chicks to recognize the mother, by adult birds to distinguish their own eggs from others, or to recognize kin. While there is quite a lot of evidence for the importance of odour for social behaviour, it is not known as yet which brain areas may be involved in the processing of socially relevant odours. We therefore compared the brain activation pattern of zebra finch males exposed to their own offspring odour with that induced by a neutral odour stimulus. By measuring head saccade changes as behavioural reaction and using the expression of the immediate early gene product c-Fos as brain activity marker, we show here that the activation pattern, namely the activity difference between the left and the right hemisphere, of several hippocampal areas in zebra finch males is altered by the presentation of the odour of their own nestlings. In contrast, the nucleus taeniae of the amygdala (TnA) exhibits a tendency of a reduction of c-Fos activation in both hemispheres as a consequence of exposure to the nestling odour. We conclude that the hippocampus is involved in odour based processing of social information, while the role of TnA remains unclear.

Female Zebra Finches Smell Their Eggs.

Parental investment in unrelated offspring seems maladaptive from an evolutionary perspective, due to the costs of energy and resources that cannot be invested in related offspring at the same time. Therefore selection should favour mechanisms to discriminate between own and foreign offspring. In birds, much emphasis has been placed on understanding the visual mechanisms underlying egg recognition. However, olfactory egg recognition has almost been completely ignored. Here, we investigated whether female zebra finches (Taeniopygia guttata) are able to discriminate between their own and a conspecific egg based on olfactory cues alone. Zebra finches are colonial-breeding songbirds. Eggs are monomorphic, i.e. without any spotting pattern, and intraspecific brood parasitism frequently occurs. In a binary choice experiment, female zebra finches were given the choice between the scent of their own and a conspecific egg. After the onset of incubation, females chose randomly and showed no sign of discrimination. However, shortly before hatching, females preferred significantly the odour of their own egg. The finding that females are capable to smell their own egg may inspire more research on the potential of olfaction involved in egg recognition, especially in cases where visual cues might be limited.