May 21, 2018, University of Chicago Medical Center

Cooperation among different species of birds is common. Some birds build their nests near those of larger, more aggressive species to deter predators, and flocks of mixed species forage for food and defend territories together in alliances that can last for years. In most cases, though, these partnerships are not between specific individuals of the other species—any bird from the other species will do.

But in a new study published in the journal Behavioral Ecology, scientists from the University of Chicago and University of Nebraska show how two different species of Australian fairy-wrens not only recognize individual birds from other species, but also form long-term partnerships that help them forage and defend their shared space as a group.

“Finding that these two species associate was not surprising, as mixed species flocks of birds are observed all over the world,” said Allison Johnson, Ph.D., a postdoctoral scholar at the University of Nebraska who conducted the study as part of her dissertation research at UChicago. “But when we realized they were sharing territories with specific individuals and responding aggressively only to unknown individuals, we knew this was really unique. It completely changed our research and we knew we had to investigate it.”

Variegated fairy-wrens and splendid fairy-wrens are two small songbirds that live in Australia. The males of each species have striking, bright blue feathers that make them popular with bird watchers. Their behavior also makes them an appealing subject for biologists. Both species feed on insects, live in large family groups, and breed during the same time of year. They are also non-migratory, meaning they live in one area for their entire lives, occupying the same eucalyptus scrublands that provide plenty of bushes and trees for cover.

When these territories overlap, the two species interact with each other. They forage together, travel together, and seem to be aware of what the other species is doing. They also help each other defend their territory from rivals. Variegated fairy-wrens will defend their shared territory from both variegated and splendid outsiders; splendid fairy-wrens will do the same, while fending off unfamiliar birds from both species.

“Splendid and variegated fairy-wrens are so similar in their habitat preferences and behavior, we would expect them to act as competitors. Instead, we’ve found stable, positive relationships between individuals of the two species,” said Christina Masco, Ph.D., a graduate student at UChicago and a co-author on the new paper.

Many songbirds can recognize familiar members of their own species on the basis of the unique songs each bird sings. However, in this research the investigators believed this recognition occurred across species. How could they be so certain?

Birds from different species recognize each other and cooperate

From 2012-2015, Johnson, Masco, and their former advisor, Stephen Pruett-Jones, Ph.D., associate professor of ecology and evolution at UChicago, studied these species at Brookfield Conservation Park in South Australia. The first unusual observation Johnson made was that when playing a recorded vocalization of one species, the other species would respond and fly in to investigate what was going on.

To follow up on this observation, the researchers monitored both fairy-wren species in the darkness before dawn and captured clear recordings of their signature songs. After sunrise, they broadcast the recorded songs from a speaker to simulate an intrusion by a particular bird into a group’s territory. The objective was to see how territory owners reacted to the songs of familiar and unfamiliar members of the other species.

The researchers placed a speaker about 30 meters away from a subject fairy-wren and played the songs of four different individuals: a fairy-wren that occupied the same territory (a co-resident or “friendly” bird), a fairy-wren from an adjacent territory (a neighbor), a fairy-wren from an area five or more territories away (an unknown bird), and a red-capped robin, a common species in the park that doesn’t pose a threat to the fairy-wrens (as a control group).

Both splendid and variegated fairy-wrens demonstrated the ability to recognize their co-residents’ songs despite the species difference. Socially dominant males of both species responded more aggressively to songs of neighbors and unknown birds of the other fairy-wren species than they did to friendly birds sharing their territory, or to the red-capped robin. When they heard songs from friendly birds, they didn’t respond, suggesting they didn’t see them as a threat.

By forming and keeping these associations with another species, fairy-wrens can better defend their nests from predators and their territories from rivals. There is also evidence that interacting with the other species has additional benefits besides territorial defense. While the splendid fairy-wrens didn’t change their behavior when associating with the other species, the variegated fairy-wrens spent more time foraging, were less vigilant, and had more success raising their young.

Johnson, Masco, and Pruett-Jones believe the fairy-wrens associate with the other species as a form of cooperation. By interacting with other species that share the same territory instead of working against them, these already social species create a larger group to help defend their territory and ward off intruders. In other words, if you can’t beat ‘em, join ‘em.

“Although our discovery that individuals of different species recognize each other was unexpected, it is likely that something similar occurs whenever species of non-migratory birds live on overlapping territories,” Pruett-Jones said. “Recognition facilitates sociality within species, and it follows that it could also facilitate associations between species.”

Task1 Find words/expressions meaning the following.

1.  To stop somebody from doing something by making them realize it will be difficult or have bad results.

2.  To continue;

3.  Reacting;

4.  very noticeable or unusual;

5.  whole;

6.  to partially occupy the same area as the other thing;

7.  to have knowledge - of a situation or fact;

8.  aim, purpose;

9.  to be dangerous;

10. to make easier

Task2 Say whether the following is true, false or not mentioned.

1.  It is often enough that birds form a sort of symbiosis with other species of birds.

2.  Nobody knows how long this partnership may continue: it may end

in a month or it may continue for a dozen years, at most.

3.  What surprised scientists was that two different species shared the same territory interacting with each other.

4.  It is usually a more numerous species that benefits from such cooperation.

5.  The only aim of such interaction is territory defence.

6.  Birds react more aggressively to songs of birds belonging to their species but from a different place than they react to songs of birds of the other species they cooperate with.

7.  This cooperation makes interspecies friendship and also communication of birds of the same species easier .

8.  The two species sharing the same territory can help each other rearing each other’s young.

Task3 Answer the following questions.

1.  Bird cooperation has been known for a long time. What made the cooperation discovered by scientists different?

2.  What do the two species mentioned here have in common?

3.  How do they cooperate?

4.  How do they benefit from this cooperation?

5.  Which species benefits more?

6.  What does the fact that birds recognize each other result in?

-Ravens can plan for future as well as 4-year-old children can

By Anil Ananthaswamy

Ravens can plan for future events at least as well as 4-year-old humans and some adult, non-human great apes.

The birds did this in tasks they wouldn’t encounter in the wild, so it isn’t an adaptation to an ecological niche, but rather a flexible cognitive ability that evolved independently in birds and hominids, whose lineages diverged about 320 million years ago.

Planning for future events requires the use of long-term memory for some anticipated future gain. For a long time, it was thought to be a uniquely human trait. Children begin showing such abilities when they are about 4. But it turned out that chimpanzees, bonobos and orangutans have this ability too, making tools to use later on.

In 2007, researchers at the University of Cambridge showed that scrub jays can cache food in places where they anticipate being hungry the next morning.

While the behaviour is flexible and requires planning, some argued that it might be an adaptation specific to caching food, which scrub jays and other members of the crow family do habitually, says Mathias Osvath of Lund University, Sweden.

Osvath and his colleagues wanted to see if ravens could plan for the future in tasks that aren’t their natural behaviours, such as tool use and bartering with humans.

In one experiment, the ravens were first trained to use a stone to dislodge some dry dog food from a box. Later, the birds were shown a collection of objects, including the tool, without the box in sight. The researchers let the ravens select an object and 15 minutes later showed them the box at a different location with the reward in it. The birds had to drop the stone into the box to collect the food. The ravens succeeded, on average, in 11 of the 14 trials.

The birds also took part in a bartering test. Again, they were first trained, in this case to exchange a token for a reward. Later, they had to select the correct token from a batch of objects, hold on to it for 15 minutes, and then exchange it with an experimenter to get a reward. The birds picked the correct token 143 out of 144 times, and were able to exchange about 77 per cent of the tokens for the reward.

The researchers then increased the delay between the tool or token selection and its use to 17 hours. The ravens succeeded in the task nearly 90 per cent of the time.

Crucially, the ravens were planning from the first trial onwards, suggesting that their success wasn’t due to habituation, says Osvath. “They can perform at the same levels as great apes, making a decision in the immediate situation for a future that will occur at another place,” he says.

“This is new, very exciting evidence which we didn’t have before,” says Markus Boeckle at the University of Cambridge. “[It’s evidence] that general intelligence has also developed in birds. This is very important for understanding how intelligence evolves.”