We’ve all been told to hush up by our parents. Whether that was usually an act with our safety in mind rather than one of irritation we can probably guess, but how alarm signaling works in animal species has been a topic of interest to scientists to discern how this might be different (or the same) in the animal world.
Previously, primates have been very much at the center of these alarm call studies. It has been shown, for example, that male Blue monkeys give more alarm calls when a predator is closer, and that Thomas langurs will alarm their group continuously until all group members have called in response. A study published in Biology Letters, thus, is the first of its kind to document adjustable alarm calling behaviors not in primates, but in something very different. Birds!
White-browed scrubwren babies beg to be fed, and in a very loud way at that. Australian researchers recorded these pleas and used playbacks of the recordings to imitate noisy versus quiet hatchlings as well as models to mimic predators. They observed that parents only hushed their young with alarm calls when the model predator was nearby, but did not give calls when they were simply being loud without the predator present.
What’s more, when the predator model was replaced with a control model, parent birds did not give alarm calls, even when the nestlings were making a racket. (It seems that white-browed scrubwren parents may have more noise tolerance than their human counterparts).
“I think it’s quite cool to show that birds that are usually thought of as not nearly as smart as primates can do this as well,” says Haff, the PhD student on the project.
Photo by Ben Pitcher
The issue that has been at the heart of alarm signaling studies is well summed-up in part of the name of the paper published by Haff and Magrath: to call or not to call? While the benefits of silencing young can include hiding them from predators (and probably to give the parent a second of peace and quiet), there are potential costs as well. Namely, an unnecessary alarm call could actually endanger young by alerting the predator to the location of the nest.
“Parents were sensitive to the trade-off between silencing young and alerting predators to the presence of nests,” says Haff. Considering these costs and benefits is obviously of value to the parents. This study is the first to show that birds are not only able to adjust when they make alarm calls, but that they also assess the rowdiness level of their young before making the call to get the best of both worlds.
Not only has this study broken ground by expanding beyond the taxonomic group of primates, it has sprung some new ideas on old theories about alarm signaling.
Traditional assumptions have suggested that the costs of alarm calling is only paid by the caller, which aligns with observations of primates that relatedness and mating potential are good indications of whether an alarm call is made if needed.
In this study, however, it is apparent that the costs of the alarm signal are in fact more borne on the young, who receive the call, rather than the parent, who is the caller. Since the significant cost of the alarm would be the attraction of a predator, this will be a bigger deal to the helpless nestlings rather than to the parent itself.
Thus, observations of these little birds may have big implications. Their ability assess predator threat, offspring vulnerability, and then to signal an alarm when conditions are just right may be a Goldilocks skill more common in the animal world 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.
Salleh, Anna. “News in Science–Birds decide when to call and not to call.” ABC Science. ABC, 16 Oct 2013. Web. 12 Nov 2013.