Not so bird-brained after all! Avians quickly learn to avoid plants that host toxic insects, study finds 

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  • In the wild, British researchers test birds with artificial cinnabar caterpillars
  • Birds were more likely to go for the insects if they were on a non-poisonous plant
  • This suggests that birds learn to avoid poisonous plants, as well as poisonous insects

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It is already well known that animals such as birds learn to avoid eating poisonous insects that could potentially kill them.

Now, researchers from the University of Bristol have found that birds can also learn to avoid plants that host these poisonous insects.

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In the wild, academics have exposed several wild bird species to artificial cinnabar caterpillars, which are known for their yellow and black stripes.

They found that birds were less likely to visit the fake caterpillars if they sat on ragwort — a poisonous plant — than a non-poisonous plant.

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The larvae of cinnabar feed on ragwort. The bold yellow and black stripes of the moth species (Tyria jacobae) make it easy to identify in the wild

Cinnabar Catpillar and Ragwort

Cinnabar moth caterpillars can be found in their hundreds of munches on the yellow-flowered ragwort.

As well as being the main food plant for cinnabar caterpillars, ragwort supports more than 40 other insect species and is an important source of nectar.

It is also toxic and is particularly known for its ability to poison horses and other livestock when eaten through contaminated hay.

The toxins within the growing plant make it so bitter and unpleasant that it is usually avoided—but cinnabar caterpillars feast on ragwort with no effect.

They actually benefit from its toxicity, ingesting it in sufficient quantities to become toxic themselves, and their colorful stripes are a warning to predators.

Source: Sussex Wildlife Trust

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Insect species such as caterpillars, ladybirds and moths have distinctive or colored markings and bitter-tasting chemical defenses to deter predators, including birds.

These predators therefore must find out whether their potential prey is edible or likely to be poisonous, and therefore capable of killing them.

The new study used an artificial mock-up of the cinnabar caterpillar (Tyria jacobae), which is striped black and yellow before becoming an attractive red and black insect.

As a caterpillar, its colorful yellow and black stripes serve as a warning to predators – ‘I am venomous and taste terrible, so don’t try to eat me’.

‘The cinnabar caterpillar has this really recognizable, striped yellow and black appearance,’ said study lead author Callum McClellan, a graduate student in Bristol’s School of Biological Sciences.

‘We have shown that birds learn that ragwort flowers are danger signals, so can avoid going anywhere near venomous prey.

‘It is more efficient to avoid the whole plant than to make decisions about individual caterpillars.’

Cinnabar caterpillars live and feed only on ragwort, which is native to Britain and other parts of Europe with distinctive yellow flowers.

As well as being the main food plant for cinnabar caterpillars, ragwort supports more than 40 other insect species and is an important source of nectar—but it is poisonous to birds and other animals.

Tyria jacobaeae changes from a yellow and black caterpillar to an attractive red and black insect.  Pictured, an adult cinnabar moth on a ragwort stem

Tyria jacobaeae changes from a yellow and black caterpillar to an attractive red and black insect. Pictured, an adult cinnabar moth on a ragwort stem

McClellan explains that eating poisonous ragwort provides a form of defense to cinnabar caterpillars.

‘I’m not sure of the mechanism, but through evolution it has gained the ability to sequester its host’s pyrrolizidine alkaloids harmlessly into its tissues to use as its own defense,’ he said. ‘ They said.

‘This probably comes at some metabolic cost to the caterpillars.’

In sufficient amounts, the pyrrolizidine alkaloids in ragwort can be very harmful to birds if ingested.

‘But the toxicity of cinnabar need not be fatal to the birds so that they cannot eat them; They just have to taste bad, or create a bad impression, that the birds don’t bother eating them again.’

For the study, the scientists fabricated waterproof paper tubes containing mealworms to act as a proxy for the true caterpillars.

There were two designs – ‘artificial cinnabar caterpillar’ (with a yellow and black striped pattern) and ‘Non-signaling mock caterpillar target’ (brown).

‘Non-signaling refers to their brown coloration,’ said McClellan, while targets such as our Cinnabar had a yellow and black striped warning sign.

The researchers did not use real cinnabar caterpillars because they needed the target to stay in place and change their distinctive coloration.

The researchers created two designs - 'artificial cinnabar caterpillars' (with yellow and black striped patterns) and 'non-signaling simulated caterpillar targets' (brown).

The researchers created two designs – ‘artificial cinnabar caterpillars’ (with yellow and black striped patterns) and ‘non-signaling simulated caterpillar targets’ (brown).

In the picture is ragwort, a plant that is poisonous to birds and other animals.  Cinnabar caterpillars feast on ragwort with no ill effects, despite its toxicity

In the picture is ragwort, a plant that is poisonous to birds and other animals. Cinnabar caterpillars feast on ragwort with no ill effects, despite its toxicity

They feed on fake caterpillars on ragwort plants, as well as bramble, a non-toxic plant that is not a natural host of cinnabar.

The study relied on wild, local birds to feed the target, but the researchers did not identify the specific bird species that were the eaters.

McClellan told MailOnline: ‘The most likely predators were passers-by – likely robins, tits and blackbirds.

The ‘caterpillar’ survived better on ragwort than bramble when experienced hunters were abundant – suggesting that the birds are not known to snort for poisonous ragwort.

The most likely predators in the local vicinity were passers-by, such as robins, tits and blackbirds (pictured)

The most likely predators in the local vicinity were passers-by, such as robins, tits and blackbirds (pictured)

The researchers were also interested in whether birds use the ragwort’s bright yellow flowers as a cue to escape.

They cleverly tested this by removing spikes of ragwort yellow flowers and pinning them to brambles, then recording target survival on any plant.

‘We put it on our target ragwort by removing its flowers, and on the ragwort with it…

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