̽��ֱ�� of Cambridge - Rose Thorogood

Watching TV helps birds make better food choices

jg533 — Thu, 20 Feb 2020 05:01:00 +0000

Seeing the ‘disgust response’ in others helps them recognise distasteful prey by their conspicuous markings without having to taste them, and this can potentially increase both the birds’ and their prey’s survival rate.

̽��ֱ��study, published in the Journal of Animal Ecology, showed that blue tits (Cyanistes caeruleus) learned best by watching their own species, whereas great tits (Parus major) learned just as well from great tits and blue tits. In addition to learning directly from trial and error, birds can decrease the likelihood of bad experiences - and potential poisoning - by watching others. Such social transmission of information about novel prey could have significant effects on prey evolution, and help explain why different bird species flock together.

“Blue tits and great tits forage together and have a similar diet, but they may differ in their hesitation to try novel food. By watching others, they can learn quickly and safely which prey are best to eat. This can reduce the time and energy they invest in trying different prey, and also help them avoid the ill effects of eating toxic prey,” said Liisa Hämäläinen, formerly a PhD student in the ̽��ֱ�� of Cambridge’s Department of Zoology (now at Macquarie ̽��ֱ��, Sydney) and first author of the report.

This is the first study to show that blue tits are just as good as great tits at learning by observing others. Previously, scientists thought great tits were better, but had only looked at learning about tasty foods. This new work shows that using social information to avoid bad outcomes is especially important in nature.

Many insect species, such as ladybirds, firebugs and tiger moths have developed conspicuous markings and bitter-tasting chemical defences to deter predators. But before birds learn to associate the markings with a disgusting taste, these species are at high risk of being eaten because they stand out.

“Conspicuous warning colours are an effective anti-predator defence for insects, but only after predators have learnt to associate the warning signal with a disgusting taste,” said Hämäläinen. “Before that, these insects are an easy target for naive, uneducated predators.”

Blue tits and great tits forage together in the wild, so have many opportunities to learn from each other. If prey avoidance behaviour spreads quickly through predator populations, this could benefit the ongoing survival of the prey species significantly, and help drive its evolution.

̽��ֱ��researchers showed each bird a video of another bird’s response as it ate a disgusting prey item. ̽��ֱ��TV bird’s disgust response to unpalatable food - including vigorous beak wiping and head shaking - provided information for the watching bird. ̽��ֱ��use of video allowed complete control of the information each bird saw.

̽��ֱ��‘prey’ shown on TV consisted of small pieces of almond flakes glued inside a white paper packet. In some of the packets, the almond flakes had been soaked in a bitter-tasting solution. Two black symbols printed on the outsides of the packets indicated palatability: tasty ‘prey’ had a cross symbol that blended into the background, and disgusting ‘prey’ had a conspicuous square symbol.

̽��ֱ��TV-watching birds were then presented with the different novel ‘prey’ that was either tasty or disgusting, to see if they had learned from the birds on the TV. Both blue tits and great tits ate fewer of the disgusting ‘prey’ packets after watching the bird on TV showing a disgust response to those packets.

Birds, and all other predators, have to work out whether a potential food is worth eating in terms of benefits – such as nutrient content, and costs – such as the level of toxic defence chemicals. Watching others can influence their food preferences and help them learn to avoid unpalatable foods.

“In our previous work using great tits as a ‘model predator’, we found that if one bird sees another being repulsed by a new type of prey, then both birds learn to avoid it in the future. By extending the research we now see that different bird species can learn from each other too,” said Dr Rose Thorogood, previously at the ̽��ֱ�� of Cambridge’s Department of Zoology and now at the ̽��ֱ�� of Helsinki’s HiLIFE Institute of Life Science in Finland, who led the research. “This increases the potential audience that can learn by watching others, and helps to drive the evolution of the prey species.”

This research was funded by the Natural Environment Research Council UK and the Finnish Cultural Foundation.

Reference
Hämäläinen, L. et al, ‘Social learning within and across predator species reduces attacks on novel aposematic prey’, Jan 2020, Journal of Animal Ecology. DOI: 10.1111/1365-2656.13180

By watching videos of each other eating, blue tits and great tits can learn to avoid foods that taste disgusting and are potentially toxic, a new study has found.

By watching others, blue tits and great tits can learn quickly and safely which prey are best to eat.

Liisa Hämäläinen

Nataba, Adobe Stock images

Great tit and blue tit. Credit: Nataba, Adobe Stock images

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Birds learn from each other’s ‘disgust’, enabling insects to evolve bright colours

fpjl2 — Mon, 18 Dec 2017 16:01:33 +0000

Many animals have evolved to stand out. Bright colours may be easy to spot, but they warn predators off by signalling toxicity or foul taste.

Yet if every individual predator has to eat colourful prey to learn this unappetising lesson, it’s a puzzle how conspicuous colours had the chance to evolve as a defensive strategy.

Now, a new study using the great tit species as a “model predator” has shown that if one bird observes another being repulsed by a new type of prey, then both birds learn the lesson to stay away.

By filming a great tit having a terrible dining experience with conspicuous prey, then showing it on a television to other tits before tracking their meal selection, researchers found that birds acquired a better idea of which prey to avoid: those that stand out.

̽��ֱ��team behind the study, published in the journal Nature Ecology & Evolution, say the ability of great tits to learn what to avoid through observing others is an example of “social transmission” of information.

̽��ֱ��scientists scaled up data from their experiments through mathematical modelling to reveal a tipping point: where social transmission has occurred sufficiently in a predator species for its potential prey to stand a better chance with bright colours over camouflage.

“Our study demonstrates that the social behaviour of predators needs to be considered to understand the evolution of their prey,” said lead author Dr Rose Thorogood, from the ̽��ֱ�� of Cambridge’s Department of Zoology.

“Without social transmission taking place in predator species such as great tits, it becomes extremely difficult for conspicuously coloured prey to outlast and outcompete alternative prey, even if they are distasteful or toxic.

“There is mounting evidence that learning by observing others occurs throughout the animal kingdom. Species ranging from fruit flies to trout can learn about food using social transmission.

“We suspect our findings apply over a wide range of predators and prey. Social information may have evolutionary consequences right across ecological communities.”

Thorogood (also based at the Helsinki Institute of Life Science) and colleagues from the ̽��ֱ�� of Jyväskylä and ̽��ֱ�� of Zürich captured wild great tits in the Finnish winter. At Konnevesi Research Station, they trained the birds to open white paper packages with pieces of almond inside as artificial prey.

̽��ֱ��birds were given access to aviaries covered in white paper dotted with small black crosses. These crosses were also marked on some of the paper packages: the camouflaged prey.

One bird was filmed unwrapping a package stamped with a square instead of a cross: the conspicuous prey. As such, its contents were unpalatable – an almond soaked with bitter-tasting fluid.

̽��ֱ��bird’s reaction was played on a TV in front of some great tits but not others (a control group). When foraging in the cross-covered aviaries containing both cross and square packages, the birds exposed to the video were quicker to select their first item, and 32% less likely to choose the ‘conspicuous’ square prey.

“Just as we might learn to avoid certain foods by seeing a facial expression of disgust, observing another individual headshake and wipe its beak encouraged the great tits to avoid that type of prey,” said Thorogood.

“By modelling the social spread of information from our experimental data, we worked out that predator avoidance of more vividly conspicuous species would become enough for them to survive, spread, and evolve.”

Great tits – a close relation of North America’s chickadee – make a good study species as they are “generalist insectivores” that forage in flocks, and are known to spread other forms of information through observation.

Famously, species of tit learned how to pierce milk bottle lids and siphon the cream during the middle of last century – a phenomenon that spread rapidly through flocks across the UK.

Something great tits don’t eat, however, is a seven-spotted ladybird. “One of the most common ladybird species is bright red, and goes untouched by great tits. Other insects that are camouflaged, such as the brown larch ladybird or green winter moth caterpillar, are fed on by great tits and their young,” said Thorogood.

“ ̽��ֱ��seven-spotted ladybird is so easy to see that if every predator had to eat one before they discovered its foul taste, it would have struggled to survive and reproduce.

“We think it may be the social information of their unpalatable nature spreading through predator species such as great tits that makes the paradox of conspicuous insects such as seven-spotted ladybirds possible.”

A new study of TV-watching great tits reveals how they learn through observation. Social interactions within a predator species can have “evolutionary consequences” for potential prey – such as the conspicuous warning colours of insects like ladybirds.

We suspect our findings apply over a wide range of predators and prey. Social information may have evolutionary consequences right across ecological communities

Rose Thorogood

Per Tillmann

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Neighbourhood watch and more: how reed warblers watch out when there’s a cuckoo about

amb206 — Fri, 22 Jan 2016 12:00:00 +0000

It’s a risky business being a reed warbler. Not only do these tiny birds embark on an annual migration of some 5,000 km from their West African winter quarters to breeding grounds in the north, but they are also ‘hosts’ to the cuckoo, a species that lays its eggs in other birds’ nests and takes no further part in raising its offspring. When the cuckoo chick hatches, it pushes the reed warbler eggs and young out of the nest. As sole occupant, it tricks its warbler ‘parents’ into supplying its voracious appetite until it fledges.

Cuckoos are expert tricksters: their eggs mimic those of their hosts in pattern though they are a little bigger. If the reed warbler detects an alien egg in its nest, or spots a cuckoo nearby, it may eject the odd-looking egg. But cuckoos are so swift in laying their eggs (only one is laid per nest and the process is over in as little as 10 seconds), and so clever at disguising their eggs, that warblers are often uncertain whether an odd egg in the clutch is a cuckoo egg or one of their own.

Research into the relationship between cuckoos and reed warblers has to date concentrated on the behaviour of individual birds and their interactions with cuckoos, described as parasites. A new study published today (22 January 2016) in Scientific Reports looks at wider interactions between neighbouring communities of reed warblers, their strategies for coping with cuckoos, and, in particular, how warblers assess levels of risk by gathering information from a variety of sources.

After two years of observation of warblers that spend the breeding season at Wicken Fen in Cambridgeshire, authors Rose Thorogood and Nicholas Davies (Department of Zoology) reveal that a kind of “neighbourhood watch” exists out in the reed beds, keeping birds up-to-date with the latest threats. Using a series of controlled experiments, involving model cuckoos and broadcasts of reed warbler alarm calls, the researchers revealed that reed warblers factored information gathered from close surveillance of the neighbourhood into their decision-making when assessing whether or not to eject an egg.

When reed warblers spot a cuckoo, they may mob it and emit alarm calls that carry up to 40 metres. These alarm calls attract neighbours, who come to investigate the cause of the commotion. But the sound of neighbourly mobbing of a cuckoo alone is insufficient to prompt warblers to eject a suspect egg from their own nests. They also need clues that suggest a more close-up and personal threat.

“We found that warbler pairs ejected an odd egg only when there was strong evidence that it might not be one of their own. For action to be taken, the clues had to add up. ̽��ֱ��warblers needed to be alerted by their neighbours’ behaviour that there was a cuckoo at large in the neighbourhood and they needed to be aware of a more local and imminent threat, by seeing a cuckoo near their own nest. ” said Thorogood.

“Neither personal encounters nor social encounters alone were sufficient to stimulate egg rejection. Instead, information was combined from both these sources. This is fascinating because we have assumed previously that animals favour one type of information over the other – for example, experiments show that some fish species will ignore where their shoal mates forage if they already have information about the location of food themselves, even when it is less profitable. Here we show that combining information is the best way to take the most appropriate course of action.”

̽��ֱ��use of multiple sources of information has important consequences for cuckoos too. With their neighbourhood abuzz with information, cuckoos need to be wary of alarming potential hosts.

“Because the information warfare between cuckoos and their hosts extends well beyond individual interactions, there’s pressure on cuckoos to be increasingly secretive, not only to avoid alerting their target host pair, but also other host pairs in the local neighbourhood” said Thorogood.

Cuckoo numbers have declined by as much as 60% in the past 30 years for reasons that remain unclear. At Wicken Fen, where several hundred warblers arrive to breed each May, between 10% and 20% of reed warblers nests were used by cuckoos. Today only 2% of warbler nests at Wicken host cuckoos. This rapid drop in cuckoo numbers, which contrasts with a stable warbler population, has enabled Thorogood and Davies to track how the warblers have dropped their defences in concert with the dramatic decrease in cuckoo threat.

Davies has been researching cuckoos and their hosts at Wicken Fen since the 1980s. He said: “Reed warblers are much less likely to eject an egg from their nest today than they were in the 1980s. This makes complete sense. They have matched their behaviour to the changing level of risk. Most reed warblers have just one or two summers in which to breed. So every opportunity to mate, construct a nest and raise a clutch of eggs is precious. If a pair of warblers mistakenly identifies one of their own eggs as a cuckoo egg and chucks it out, or deserts the nest, the loss is great. Our work shows how they match their defences to the risk of parasitism.”

A study of reed warbler behaviour reveals for the first time that in assessing the risks posed by cuckoos the birds combine information from multiple sources. An ‘information highway’ provides one set of clues and personal encounters another. Only when both add up, do the birds take defensive action.

Warbler pairs ejected an odd egg only when there was strong evidence that it might not be one of their own. For action to be taken, the clues had to add up.

Rose Thorogood

Richard Nicholl

A cuckoo chick ejects a reed warbler egg from a nest

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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