When in Danger, Vomit (if You're a Roller)

When in Danger, Vomit (if You're a Roller)
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Ever picked up a grasshopper? One thing you'll quickly notice is a blackish-brown liquid seeping from its mouthparts. The insect is in fact vomiting, and it's you that's making it "sick."

Most species of grasshoppers vomit a repugnant, bitter bile that's slightly acidic. They do this when handled by a predator. It's a last resort, a "you don't really want to eat me, I taste bad" defense.

Now, fascinatingly, a team of Spanish researchers has discovered that nestlings of an insectivorous bird, the Eurasian roller, do exactly the same thing! When handled, they produce a waterfall of orange, odorous vomit containing hydroxybenzoic and hydroxycinnamic acids, two substances which are slightly toxic and unpleasant to the taste buds.

By maintaining a significant breeding population of rollers, the researchers were able to study the somewhat disgusting behavior over a long duration. The birds appear to gain the ability to vomit at around 6.7 days after birth, and only do so when picked up and shaken. Petting, yelling, or simply seeing a predator did not prompt the regurgitation during the study.

To test the deterrent effects of roller puke, the researchers needed animal subjects that resembled the birds' natural predators. Dogs were the unlucky guinea pigs. After collecting a sufficient amount of vomit, the researchers presented dogs with two choices of chicken breast: one covered in water, and another slathered in roller vomit. 18 of 20 canines chose to first eat the chicken doused in water.  Twelve of those dogs ended up eating the vomit-covered breast as well, but only after two minutes of apparently hesitant sniffing. Six dogs flat-out refused to eat the chicken covered in vomit.

Where did the rollers acquire their deterring vomit? The researchers didn't find any evidence that the birds themselves produced the toxins contained in the bile, so they figured that the substances must be sourced from the birds' food. Can you guess what they ate? Using video surveillance of the nests, the researchers found that 92% of the nestlings' diets consisted of insects of the order Orthoptera, which includes, crickets, weta, locusts, and grasshoppers!

Source: Parejo D, Aviles JM, Pena A, Sanchez L, Ruano F, et al. (2013) Armed Rollers: Does Nestling’s Vomit Function as a Defence against Predators? PLoS ONE 8(7): e68862. doi:10.1371/journal.pone.0068862

(Image: Sumeet Moghe via Wikimedia)

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