杏吧原创

The world is a dangerous place for young birds, but it seems that even as embryos, some can take measures to hide from hungry predators.

Late in their embryonic development, many bird species will communicate with their parents through the eggshell by chirping. Kristal Kostoglou at Deakin University in Melbourne, Australia, wanted to know if these talkative embryos already have the predator-avoiding instincts of hatched chicks, which hide and fall silent when threatened.

Kostoglou and her colleagues exposed the eggs of two Australian shorebird species 鈥� 56 red-capped plover (Charadrius ruficapillus) eggs and 299 masked lapwings (Vanellus miles) eggs 鈥� to different signals of a predator approaching, like predator calls, parental alarm calls, increased parent heart rate sounds or changes in light level from a parent bird moving off the nest. The team then recorded how often the embryos called under these conditions.

The researchers didn鈥檛 find any effects from a change in light or heart rate, but the embryos of lapwings went from calling just over once per minute under white noise, to once over three minutes when exposed to the sounds of egg-eating little ravens (Corvus mellori), suggesting they were hushing up to avoid predators. The plovers鈥� call rate was about four times per minute under white noise, but dropped to twice per minute with the predator noises.

Jose Noguera at the University of Vigo in Spain says these findings and earlier research on prenatal birds 鈥渃learly show that embryos are not passive agents to external cues鈥�.

Noguera says he is surprised that the embryos didn鈥檛 also call less in response to parental alarm calls. 鈥淎larm calls may serve as a more reliable cue of predator presence, as some predators can be very silent,鈥� he says.

Kostoglou points out that parental calls might be less reliable signs of predators if the calls have multiple uses. It is also possible she and her team weren鈥檛 adequately replicating real parental alarm calls, she says.

Martin Bulla at the Max Planck Institute for Ornithology in Germany is less convinced by the findings, pointing out the small sample size for the plovers, where only 29 of 56 eggs were used for all the bird call treatments. Also, the embryos鈥� rate of sounds often only differs between treatments by a few times per minute, making Bulla wonder if the differences are 鈥渆ven biologically relevant for evading predators鈥�.

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