Tag Archives: study

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

(University of Cambridge 18 Dev 2017)

Many animals have evolved to stand out. Bright colours are 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.

The team behind the study, published in the journal Nature Ecology & Evolution, say the ability of great tits to learn bad food choices through observing others is an example of “social transmission.”

The 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 University 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 University of Jyväskylä and University of Zurich 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.

The 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.

The 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.

“The 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.”

Video: https://www.youtube.com/watch?v=87l0Dyte_nQ

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Complex, old-growth forests may protect some bird species in a warming climate

(Oregon State University 15 Dec 2017;Photo:Hankyu Kim)

Old forests that contain large trees and a diversity of tree sizes and species may offer refuge to some types of birds facing threats in a warming climate, scientists have found.

In a paper published in Diversity and Distributions, a professional journal, researchers in the College of Forestry at Oregon State University reported that the more sensitive a bird species is to rising temperatures during the breeding season, the more likely it is to be affected by being near old-growth forest.

Researchers studied 13 bird species that have been tracked annually in the U.S. Geological Survey’s annual Breeding Bird Survey, one of the most comprehensive efforts of its kind in North America. Only two — the Wilson’s warbler and hermit warbler — showed negative effects from rising temperatures over the past 30 years, but actual counts of both species show that their populations are stable or increasing in areas that contain high proportions of old-growth forest.

A team led by Matthew Betts, professor in the College of Forestry, reached their conclusions by analyzing data for bird populations, forest structure and climate across northwestern North America. The researchers used satellite imagery to determine the amount of old-growth forest within about 450 yards of each 25-mile-long bird survey route.

The findings provide an additional reason for old-growth forest conservation, said Betts. “Managers hoping to combat the effects of climate change on species’ populations may now have an additional tool — maintaining and restoring old-growth forest.” He noted that this is important because management recommendations from biodiversity and climate studies have traditionally been sparse. Such studies have tended to focus on moving species to cooler climates or simply reducing carbon emissions.

Wilson’s warbler winters in Mexico and breeds during the late spring and early summer along the West Coast and across northern North America from Alaska to New England and the Canadian Maritimes. Although it occurs in early-stage as well as mature forests, it is declining at a rate of about 2 percent per year in the Pacific Northwest.

The hermit warbler also winters in Mexico but breeds exclusively along the West Coast as far north as Washington. Its populations are relatively stable but declining in landscapes with low amounts of old-growth forest.

Additional research will be needed to identify the specific features of mature forests that buffer the effects of warming temperatures on birds. One possibility, the researchers said, is that the large trees themselves function as “heat sinks” during warm periods and thus moderate temperatures. Multiple canopy layers may also provide climate buffering effects.

Mercury decline in seabirds due to diet, not emissions controls

Mercury decline in seabirds due to diet, not emissions controls
(Kyle Elliott, Mehrnoosh Azodi, 23 November 2017;Photo: CC BY)

For 47 years, biologists have plucked eggs from seabird nests along the British Columbia coast. Many of the eggs were collected from remote rocky islands surrounded by some of the world’s roughest seas.

In all, they collected 537 eggs from six species, including ancient murrelets, rhinoceros auklets and double-crested cormorants. Now these eggs are revealing new information about the way mercury finds its way into the ecosystem.

The eggs of top predators, like these seabirds, are important for researchers who study chemical pollutants. We use these eggs to understand, for example, how mercury levels in seabirds have changed over time. This data helps us understand whether control measures, including international agreements, are reducing mercury levels in the global environment.

Human activities, especially the burning of coal, release mercury into the atmosphere. Mercury levels in the Pacific Ocean are now three to five times higher than they were before the industrial revolution. Our activities have released 1.5 million tonnes of mercury into the air, land and water bodies since 1850.

For wildlife —and humans — mercury is a neurotoxin. High levels in the food chain can have negative impacts on the reproductive health of seabirds, marine mammals and other carnivores that feed on seafood. For example, seabirds with heavy mercury loads are less likely to breed. Mercury also slows down the healthy growth of chicks.

Bacteria plays a fundamental role

Researchers had thought that the seabirds that feed on large predatory fish would have the highest levels of mercury because large fish, which are higher up the food chain, accumulate more mercury in their bodies than the small fish and invertebrates that occupy the bottom of the food chain.

But later studies contradicted these expectations. By studying mercury levels in the eggs of seabirds over many years, researchers found seabirds that fed on invertebrates and small fish had higher mercury levels than the seabirds that ate large fish.

Our research explained why the highest mercury levels occurred in species that ate small fish. We measured mercury levels and a collection of dietary tracers called stable isotopes in the seabird eggs. We studied nitrogen, carbon and sulphur isotopes because these chemicals tell us about the type of food the birds were eating.

We found that the seabird eggs with high mercury levels also had higher sulphate levels. It meant that these birds were eating small fish from areas that were also favoured by a specific type of bacteria.

These bacteria, called sulphate-reducing bacteria, convert mercury to methylmercury, the toxic form of mercury that can move up the food web and harm seabirds. These bacteria tend to be found in deep-water sediments.

Stable mercury levels

The study also showed that mercury concentrations in Pacific seabird eggs have been relatively stable over the past 50 years. This is surprising, given the dramatic changes in mercury concentrations in Pacific waters.

A decline in surface-dwelling fish stocks in the Pacific Ocean has forced some seabirds to feed elsewhere where there are fewer sulphate-reducing bacteria. By changing their diet, these seabirds end up with lower mercury levels.

Monitoring programs have suggested that environmental levels of mercury are in decline, but this research suggests otherwise. Based on our results, we believe monitoring programs need to consider the structure of the food web, including where these birds are foraging.

Human health threat

Although this research focuses on the eggs of seabirds, it has implications for human health. The World Health Organisation has identified mercury as one of the top ten chemicals of major health concern.

Mercury pollution is a global issue since elemental mercury travels over long distance and methylmercury accumulates in the food chain, posing a serious risk to both humans and wildlife who feed on seafood.

The global scale of this issue was the key driving force for a global environmental treaty called the Minamata Convention, which enforces reductions on mercury emissions. The agreement entered into force on Aug. 16, 2017, making it the most recent international law that aims to protect humans and the environment from the threat of toxic mercury.

The current study on avian predators, which feed on marine food webs similar to those we feed on ourselves, illustrates how important it is to consider those food webs when considering the risk of mercury.

Rather than simply considering larger species high in the food chain as being riskiest, we suggest that governments also consider the role of bacteria and reduce the consumption of those fish feeding in food webs with high levels of sulphate-reducing bacteria.

How camouflaged birds decide where to blend in

How camouflaged birds decide where to blend in
(University of Exeter, Physorg 31 July 2017; Photo: Project Nightjar)

Animals that rely on camouflage can choose the best places to conceal themselves based on their individual appearance, new research shows.

The camouflage and concealment strategies of various animal species have been widely studied, but scientists from Exeter and Cambridge universities have discovered that individual wild birds adjust their choices of where to nest based on their specific patterns and colours.

The study looked at nine remarkably hard-to-see ground-nesting bird species (nightjars, plovers and coursers).

“Each individual bird looks a little bit different, and we have shown that they can act individually,” said project co-leader Professor Martin Stevens, of the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall.

“This is not a species-level choice.

“Individual birds consistently sit in places that enhance their own unique markings, both within a habitat, and at a fine scale with regards to specific background sites.”

The study, carried out in Zambia, showed that individual birds chose backgrounds that enhanced their camouflage to the visual systems of their main predators – being better matched to their chosen backgrounds than to other places nearby.

Bird echolocation inspires new engineering

(Birgitte Svennevig 2 August 2017)

All animals use a combination of senses to survive. But where the majority typically rely on one or two especially sensitive sensory systems, the oilbird excels by apparently having keen senses all-around.

In addition to its extremely sensitive vision, the oilbird has the neural foundation for a powerful olfactory sense, bristles by the beak for tactile sensation, and a powerful echolocation sense, normally found in bats and cetaceans.

“This complex sensory apparatus, where the animal has the ability to combine input from so many well-developed senses, is interesting to study,” says Signe Brinkløv of the Sound, Communication and Behaviour Group at the Department of Biology, University of Southern Denmark.

As a biologist, she is interested in understanding how the oilbird uses its senses to achieve the best possible conditions in its natural surroundings. From a more applied perspective, she wants to apply knowledge of animal sensory systems in new engineering.

“We have come a long way towards understanding individual senses. But senses complement each other, and the balance between different sensory inputs affects the behaviour of the animal when tackling various challenges—this becomes a very complex field of study, which is difficult to transfer from laboratory to natural conditions. If we can learn more about it, perhaps we can transfer the knowledge to technological developments,” she says.

An example is the interaction between vision and the sense of hearing, which the animal uses when it echolocates. With echolocation, the animal emits sounds that are returned as echoes from the surroundings and enables it to judge the distance to surroundings or distinguish between food items and other features.

“Today, drones are often controlled manually by a drone operator who is dependent on the video footage from the drone and thus the sense of sight in order to control it. But it quickly becomes difficult to navigate with such a system in darkness or when visibility is poor. If you could combine the sense of sight and echolocation on a drone to navigate based on input from both systems, then more opportunities open up. For instance, it could fly safely and perhaps autonomously in the dark or in between trees in a forest,” says Signe Brinkløv.

Signe Brinkløv and her colleagues have studied the echolocation of oilbirds in Trinidad. Oilbirds are nocturnal and live in caves in groups of up to several thousand individuals. At night, they leave the cave to find food. Their ability to echolocate enables them to navigate to and from their nests without bumping into the rocky walls of the cave, even in pitch black darkness.

The researchers hope that with further study of the interaction between oilbird vision and echolocation, they can develop a model that can be applied by sensory researchers and robotics engineers.

The study was published in Royal Society Open Science. It is based on sound recordings of echolocating cave-dwelling oilbirds at Asa Wright Nature Centre, Trinidad. The authors are Signe Brinkløv, Coen Elemans and John Ratcliffe.

Signe Brinkløv is a biologist at Department of Biology. Apart from birds, she also studies porpoise and bat communication. The oilbird (Steatornis caripensis) got its name because just before leaving the nest, the fledglings become so fat that their weight exceeds that of the adults. Just like whales, oilbirds have been used in the past for extraction of oil. Oilbirds also produce other sounds than their echolocation signals, which has led to several Spanish nicknames, including Guácharo and Diablotin (little devil), reflecting ghostly sounding calls which led the local Indians to compare the entrance to the birds’ caves with that to the land of the dead.

Grown-up gannets find favorite fishing grounds

(University of Exeter, Science Daily  27 July 2017)

Like humans, some birds can spend years learning and exploring before developing more settled habits.

A study of northern gannets has shown adults return to the same patch of sea over and over again to find food.

But younger gannets search far and wide and tend not to return to the same places — even if they find good hunting grounds, University of Exeter researchers found.

The study also compared successful breeding adults with those which failed to breed, and found successful breeders stuck to their feeding grounds more reliably.

“It’s common for birds like gannets to return to the same foraging grounds year after year,” said Dr Stephen Votier, of the Environment and Sustainability Institute on Exeter’s Penryn Campus in Cornwall.

“They disperse widely at sea, and the fact that they return to specific areas is presumably linked to finding good foraging conditions.

“However, gannets don’t breed until they’re four or five years old, and our research shows that this tendency to return to favoured foraging grounds is lacking in birds younger than this.

“This finding suggests that such behaviours are probably learned, and that gannets use their long period of immaturity finding good sites and remembering where they are.

“However, foraging sites in adults are not absolute — when experienced birds had more time on their hands after a failed breeding attempt, some became more exploratory. This suggests that refinement occurs throughout an animal’s lifetime.”

The research team studied gannets on the Welsh island of Grassholm, supported by the RSPB, and used precision global positioning system (GPS) loggers to find out whether individual birds returned to the same foraging grounds time after time.

Successful breeders showed strong attachment to certain areas and took similar routes when travelling to and from them.

Immature birds (aged two or three years) were much more varied both in foraging sites and routes taken.

The results support the “exploration-refinement foraging hypothesis” — that birds explore and slowly improve their foraging with age and experience.

The common cuckoo is an effective indicator of high bird species richness in Asia and Europe

Cuculus canorus2.jpg
(Federico Morelli, Anders Pape Møller, Emma Nelson, Yanina Benedetti, Wei Liang, Petra Šímová, Marco Moretti, Piotr Tryjanowski 29 June 2017)

Introduction

Why is the common cuckoo Cuculus canorus a fascinating bird species for humans? What are the main reasons for the species being known as “a messenger of spring and morality”1, and why is it so conspicuous in human culture? A review of folklore shows clearly that the enigmatic cuckoo has driven the collective imagination of people throughout the world for thousands of years. First and foremost the cuckoo-call is associated with seasonal change. The timing of arrival of the cuckoo and the vigour of its calls were also used as indicators of the weather2, 3. In ancient Egypt, Aristophanes wrote that its arrival was associated with harvest time2. Cuckoo lore is intimately linked with change and metamorphosis1,2,3 and its call reflects the real world passing of time when seeds are transformed into crops, maidens are married and maids become mothers.

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Results

A total of 65,234 observations of bird occurrence in 3,592 sample sites in different environments were collected from ten European and two Asian countries. The maximum bird species richness per point count in all countries ranged from 12 species (Finland), to 28 species (San Marino and Switzerland).

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Sample sites were treated as statistically independent observations because the spatial autocorrelation in all studied countries was not significant

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The temporal trend in common cuckoo populations was positively correlated with the overall trend in bird populations in European countries

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Discussion

Cuckoo as indicator: Extending species surrogacy from Europe to Asia

This study provides new evidence on the common cuckoo as a surrogate of bird species richness, previously tested in some European countries. This suggests that the common cuckoo is potentially a prime bioindicator in Eurasia. Even if related to different host species, and considering that the common cuckoo is not the only parasitic cuckoo in Asia24, we found the same pattern than in Europe: Occurrence of the common cuckoo is positively correlated with bird species richness in both continents. The implications related to finding the same pattern in Europe and in Asia are important from an ecological point of view. First, in Asia, C. canorus has different host species than in Europe. Second, the common cuckoo is not the only brood parasite in China and Japan. So, C. canorus is subject to a greater competitive pressure from other cuckoo species in Asia than in Europe. However, common cuckoo still shows the same capacity as surrogate of bird species richness, highlighting the process linking this particular (and charismatic species) to overall bird diversity.

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Our study shows that the population trend of common cuckoo, as well as climate suitability trend for the common cuckoo, follow the overall trend for populations of all other passerines species and the climate suitability trend in all Europena countries. This result supports the hypothesis that common cuckoo is a suitable bioindicator, making the species also sensible to climate change scenarios. When using proxies of population trends, many aspects need to be considered. For instance if within country variation in population abundance trends of different species is larger or smaller than variation among countries, and also how trends of other bird species can be related to the average community trend.

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