Birds learn to avoid plants that host dangerous insects

Date:
October 7, 2021
Source:
University of Bristol
Summary:
Scientists have discovered that birds know to avoid the plants
where toxic animals dwell.



FULL STORY ========================================================================== Young birds that eat insects with conspicuous warning colouration to
advertise their toxicity to would-be predators quickly learn to avoid
other prey that carry the same markings. Developing on this understanding,
a University of Bristol team have shown for the very first time that
birds don't just learn the colours of dangerous prey, they can also
learn the appearance of the plants such insects live on.


==========================================================================
To do this, the scientists exposed artificial cinnabar caterpillars, characterised by bright yellow and black stripes, and non-signalling
fake caterpillar targets to wild avian predation by presenting them on
ragwort and a non-toxic plant -- bramble, which is not a natural host
of the cinnabar. Both target types survived better on ragwort compared
to bramble when experienced predators were abundant in the population.

They were also interested in whether birds use the bright yellow flowers
of ragwort as a cue for avoidance. They tested this by removing spikes of flowers from the ragwort and pinning them onto bramble, then recording
target survival on either plant. In this second experiment, only the non-signalling targets survived better on plants with ragwort flowers,
compared to the same plant type without the flowers. The survival of
the cinnabar-like target was equal across all plant treatments.

Lead author Callum McLellan, a graduate student at the School of
Biological Sciences, said "Cinnabar caterpillars have this really
recognisable, stripey yellow and black appearance. They also only live
and feed on ragwort, which itself has distinctive yellow flowers. We have
shown that birds learn that the ragwort flowers are a cue for danger,
so can avoid going anywhere near toxic prey. It's more efficient to
avoid the whole plant than make decisions about individual caterpillars." Co-author Prof Nick Scott-Samuel of the School of Psychological Science,
said "Our findings suggest that insect herbivores that specialise on
easily recognisable host plants gain enhanced protection from predation, independent of their warning signal alone." Prof Innes Cuthill, who
conceived the study, added "Interestingly, any camouflaged caterpillars
living on the same plant also benefit from birds' learnt wariness of
ragwort, despite being perfectly good to eat.

"Our results provide the opening to a brand-new discussion
on how toxicity initially evolved in insect prey, and the
conditions under which warning colouration is, or is not, favoured." ========================================================================== Story Source: Materials provided by University_of_Bristol. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Callum F. Mclellan, Nicholas E. Scott-Samuel, Innes
C. Cuthill. Birds
learn to avoid aposematic prey by using the appearance of host
plants.

Current Biology, October 07, 2021 DOI: 10.1016/j.cub.2021.09.048 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211007122053.htm

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