Great tit pairs discuss at the nest during breeding, but what are the functions of this communication?
LINKED PAPER
Interactive vocal communication at the nest by parent Great Tits Parus major.
Boucaud, I.C.A., Valère, P.A., Aguirre Smith, M.L.N., Doligez, B., Cauchard, L., Rybak F. Vignal, C. 2016. IBIS: DOI: 10.1111/ibi.12374 View
Although most bird species show monogamous pair bonds and bi-parental care, little is known on how mated birds coordinate their activities. Whether or not partners communicate with each other to adjust their behaviours remains an open question. In this study we describe great tit pairs’ communication at the nest and made some hypotheses on the functions of this communication.
Pairs’ communication in birds has been actually poorly described. It is probably underestimated in many species because it may be difficult to observe and record. Indeed, communication around the nest is often very discrete, probably to avoid attracting predators. The zebra finch is a good example of these hidden conversations because it is the most studied bird in captivity and vocal exchanges at the nest were not described until recently (Elie et al. 2010). Using microphones inside and around the nests allowed studying these private conversations and in a recent study we demonstrated that, in this species with bi-parental incubation, vocal communication allows the pair to negotiate incubation sharing (Boucaud et al. 2016).
Based on these first results, we made the prediction that pair communication at the nest is widespread in birds and might be a key factor in future studies on the adjustment of parental effort between males and females. But is there also pair communication in species whose partners do not share the same duties during breeding? And if so, what could be the functions of this communication? To answer these questions we studied vocal communication at the nest between mates in great tits.
In the great tit, the female builds the nest, incubates the eggs and broods the hatchlings alone. Males are known to address songs to their mate located in the cavity, and females respond to these songs (Gorissen et al. 2004, Gorissen and Eens 2005, Halfwerk et al. 2011, 2012). Great tit mates thus discuss at the nest, but it remains unknown what pieces of information are exchanged and whether this communication participates in coordinating partners’ activities.
In this study, we recorded the vocalizations and observed the behaviour of great tit pairs in spring 2013 and 2014 in France. To do so, acoustic recorders were positioned near the nest boxes and connected to two microphones: one inside the nest and one outside. In addition, an observer sat under a camouflage net at 10-15 m from the nest box recorded partners’ behaviour (e.g. birds’ entrance and exit from the nest). We thus recorded pairs’ communication during laying, incubation and early nestling period. Our observations allowed us to make different hypothesis on the functions of pair communication.
Figure 1 Pictures of the set up showing the acoustic recorder as well as the microphones outside (fixed on the recorder, left) and inside a nest box (right) © Ingrid Boucaud
We observed vocal exchanges between the female inside the nest and her male outside in three contexts with different outcomes:
- the female left the nest and may be fed by the male outside,
- the male entered the box with food,
- mates stopped calling but did not move out/in the nest.
We found only the third outcome during the laying period but all three kinds of vocal exchanges were observed during incubation and early nestling period.
During incubation, we found that the probability that males would deliver food in the nest to the incubating female increased with the number of vocalisations and the tempo of the exchange, but also with the frequency spectrum of calls (their pitch). This suggests that females could indicate their energetic needs to their mate both in the structure of their calls and in the temporal structure of the vocal exchange.
Vocal exchanges consisted of alternated male and female vocalisation bouts. Females responded to male vocalisations more rapidly than the reverse suggesting that females matched males’ tempo. This temporal coordination between male and female is often considered as a marker of pair bond strength and mates’ commitment in pair bond activities (Hall 2004).
Figure 2 Spectrogram of a vocal exchange between a male (M) and a female (F). This figure clearly shows the alternation of male and female vocalisation bouts © Ingrid Boucaud
We occasionally observed that females sang during vocal exchanges. In female great tits, song is very uncommon and its function is poorly known (Hinde 1952, Gompertz 1961). Because this vocalization has higher amplitude than the other calls used by the female inside the nest cavity, female song may participate in extra-pair communication by signalling ownership of the nest cavity and thus play a role in nest or territory defence.
Finally, we observed that some males used alarm calls in vocal exchanges and, interestingly, females never emerged from their nest in this case. This suggests that vocal exchanges can be used as an anti-predator strategy: the male could signal to the female when it is safe or not to go out of the nest cavity.
To sum up, this study has shown that great tit pairs’ communication may fulfil different functions such as signalling females’ need, strengthening the pair bond, participating in territory defence and signalling predators. More studies are now needed to confirm these hypotheses and find out if there are other possible functions. More generally, pair acoustic communication may be a key factor in future studies to understand bird monogamy and bi-parental care.
References
Boucaud, I. C. A., Mariette, M. M., Villain, A. S. and Vignal, C. 2016. Vocal negotiation over parental care? Acoustic communication at the nest predicts partners’ incubation share. Biol. J. Linn. Soc. 117: 322–336. View
Elie, J., Mariette, M., Soula, H., Griffith, S., Mathevon, N. and Vignal, C. 2010. Vocal communication at the nest between mates in wild zebra finches: a private vocal duet? Anim. Behav. 80: 597–605. View
Gompertz, T. 1961. The vocabulary of the Great Tit. Br. Birds. 54: 369–417. View
Gorissen, L. and Eens, M. 2005. Complex female vocal behaviour of great and blue tits inside the nesting cavity. Behaviour. 142: 489–506. View
Gorissen, L. and Eens, M. 2004. Interactive communication between male and female great tits (Parus major) during the dawn chorus. The Auk. 121: 184–191. View
Halfwerk, W., Bot, S., Buikx, J., Velde, M. van der, Komdeur, J., Cate, C. ten and Slabbekoorn, H. 2011. Low-frequency songs lose their potency in noisy urban conditions. Proc. Natl. Acad. Sci. 108: 14549–14544. View
Halfwerk, W., Bot, S. and Slabbekoorn, H. 2012. Male great tit song perch selection in response to noise-dependent female feedback. Funct. Ecol. 26: 1339–1347. View
Hall, M. 2004. A review of hypotheses for the functions of avian duetting. Behav. Ecol. Sociobiol. 55: 415–430. View
Hinde, R. A. 1952. The behaviour of the Great Tit (Parus major) and some other related species. In: Behaviour . 2 (Supplement) pp. 1–207. View
Image credit
Featured image: Great Tit Parus major at nest © Ingrid Boucaud
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