It’s not only humans and primates who can assess when it’s most appropriate to hush their noisy young; a new study shows birds can do it too. Parents assess the vulnerability of their brood and only make alarm calls when it is most beneficial to the safety of their offspring, Australian researchers say.
When a parent bird gives an alarm signal to warn her offspring that a predator is nearby, there are potential costs and potential benefits. The signal could cue the young to be silent and avoid catching the attention of the predator, or it could instead lead the predator to the nest.
“Parents were sensitive to the trade-off between silencing young and alerting predators to the presence of nests,” says Haff. Haff was involved in the research for her PhD.
The best option in this trade-off for parents is to only call to their young when they are most at risk. This study showed that in fact, parents do just that, and do not simply call more frequently when their offspring are being most noisy. Instead, both the presence of the predator and the noise level of the offspring are taken into account.
The study used recordings to imitate noisy young as well as to model predators. Researchers observed that parents only hushed their young when the model predator was nearby, but not when a control model was put in the model predator’s place.
Additionally, it was shown that parents did not give more calls when their young were simply being noisier; calls were only increased in frequency with the threat of a predator present.
Photo by Ben Pitcher
Previous studies have been done on the value of alarm signaling, and have shown that the audience, who the signaler is warning, has an affect on if the alarm call is made or not. How closely related the receivers of the signal are to the signaler, as well as their mating potential to the signaler, can positively affect the benefits of the alarm to the caller.
Signals can be costly to produce for the caller, thus this relationship seems logical and in accordance with the evolutionary benefits of protecting closest related individuals. Most theoretical models of this caller and receiver relationship have been based on assumptions that the caller sustains the direct costs of an alarm signal.
This study, however, is contrary to that traditional assumption. The receivers in this case, the young, are more likely to bear the costs if their parent’s alarm signal attracts a predator.
Moreover, the great majority of these alarm call studies have been done with primates. Older studies have shown that male Blue monkeys give more alarm calls when a predator is closer, and that Thomas langurs alarm their group until all of the group members call in response to the signal.
This study on the white-browed scrubwren shows that the ability to accommodate information on predator threat and offspring vulnerability to adjust alarm calling is not limited by taxonomic group. In fact, it suggests that this ability may be much more widespread than previously thought.
Haff, Tonya M., and Robert D. Magrath. “To call or not to call: parents assess the vulnerability of their young before warning them about predators.”Biology Letters. 9.6 (2013): n. page. Web. 12 Nov. 2013.
“Research School of Biology—Research Snapshots” Australian National University. N.p., 21 Oct 2013. Web. 12 Nov 2013.