A problem of bird relations

The species are multiplying throughout Israel, affecting local birds and harming agriculture. What makes them such successful invasive birds, and could it be that despite their negative image they actually help the birds of our country?

By Racheli Vox, Angle, Science and Environment News Agency

It is very possible that you have already noticed the species, even if you do not know its name: a brown-black songbird that boasts artistic touches of orange and white and chirps with varied sounds that are pleasant to the ear. In recent years, the minnow has been observed more and more in Israel, walking proudly in the human environment.

However, behind the impressive appearance hides a smart but aggressive bird, which belongs to a people List of the hundred most harmful invasive species in the world. An invasive species is a species of animal that was spread as a result of human activity to an area outside of its natural range, and managed to survive there and even thrive there. Invasive species are the second most acute cause of extinction of natural species (after loss of habitats): among other things, they compete with local species for resources, prey on them and spread diseases among them.

The myna was first observed in Israel (out of captivity) in 1997, when, according to the hypothesis, it escaped from the safari in Yarkon Park. Since then, it has multiplied and spread throughout the country, and its great impact includes damaging agricultural crops in deciduous orchards and vineyards, alongside harming local species of birds, including some species at risk, partly by competing with them for nesting sites or directly preying on them. There are countries in the world where the bird was even involved in the extinction of species.

Despite the minnow's wide distribution, surprisingly, not much is known about its impact as an invasive species. Two new studies presented this week at the Israel Zoology Association conference at Tel Aviv University shed new light on the unique mechanism that allows species to be such successful invaders, and also raises the question of whether it is possible that the species also help the local birds, and not just harm them.

New techniques for obtaining food

The myna is a bird of the starling family, which originates from the tropical regions of South Asia. It is an omnivorous bird and its food is very diverse - it includes, among other things, fruits, eggs, insects, chicks of other birds and even rodent pups. Like parrots, the meena is able to imitate the sounds in its environment and even human speech. In recent years, the type has become more and more common throughout the country, and it has reached the fifth place in the bird count conducted in 2015, when it precedes the nightingale, the raven and the nightingale. They nest in various places in the human environment, including trees, houses, traffic lights and light poles.

One of the questions that preoccupy scientists who study the invasion of new species is why certain invasive species manage to establish quickly and successfully in their new destination, while others fail. In a study conducted as part of Tali Maguri-Cohen's doctoral thesis under the guidance of Dr. Roi Dor from the School of Zoology at Tel Aviv University, it was examined whether the species that invaded Israel were so successful thanks to the ability to develop new techniques for obtaining food, and thus adapted better to the new environment.

The researchers set a task that required innovation in obtaining food for species that live at the source of the invasion - that is, in the Tel Aviv area - and for those that live at the front of the invasion, that is, in areas where the birds have only recently invaded: southern Mount Hebron, Nahariya, and other places in the north of Israel and in the south.

In the zoological garden at Tel Aviv University, the researchers placed in front of them a wooden board to which was connected a transparent tube open on both sides, inside which was a transparent test tube with a caterpillar. A string was attached to the test tube, so the only way the species could get the test tube and the juicy larva inside was to pull the string and thus get it out of the tube - innovative thinking, by all accounts.

According to the initial results of the study, of the species that managed to solve the task and obtain the food, almost 80 percent were from the front of the invasion, that is, species that recently invaded new places throughout Israel. The birds from the invasion front also showed more motivation to solve the task (that is, they pecked at the clear tube, hoping to reach the larva, at a higher rate). As the number of years that had passed since the invasion of the site was greater, the time that passed until the species from that site began to try and solve the task was longer, and their motivation to solve it was lower.

That is, according to the results of the study, it seems that the trait of innovation in obtaining food characterizes individuals that are at the forefront of invasion, and it is possible that it helps them invade a new area successfully. How is it possible that there are such differences in the trait between individuals of the same species living in different regions? And how can wines that are actively invading "suddenly" become more innovative than their sisters who live at the source of the invasion? "There are two possibilities for this," Maguri-Cohen explains. "One possibility is that it is a certain genetic variation, and then there is a selection of the more successful individuals, meaning that the individual will succeed or fail to survive depending on how he was born. A second possibility is that the individual has in his genome the ability to behave in both ways, but he 'chooses' a way of behavior according to the environmental conditions."

According to the researchers, a better understanding of the behaviors that enable biological invasion, such as that provided by the research findings, is important in order to develop better strategies for the prevention and treatment of invasive species.

Do the species keep the sparrows?

In another study presented at the conference, and conducted as part of the doctoral thesis of Itai Berger from the laboratory of Prof. Tamar Dayan from the Department of Zoology at Tel Aviv University, the researchers tried to understand more about how species affect the local species in Israel. The researchers examined the way in which wines affect the acquisition of food and nesting, two traits that are very important for survival, in the house sparrow - a well-known local species.

In order to test the effect of species on the sparrows' food-getting behaviors, the researchers videotaped sparrows looking for and gathering food in urban lawns, when there are tzuzales (the well-known brown birds of the dove family that are common throughout Israel) or sparrows in their surroundings. In the cases examined, there were not those in which the species competed with the sparrows for food or tried to devour them, but rather those in which the species were simply present near the sparrows. The researchers measured the amount of time that the sparrows' heads were above the grass, that is, the time that they scanned their surroundings - a condition that indicates alertness and attention to threats such as predators, and comes at the expense of eating. To the surprise of the researchers, the sparrows showed less vigilance precisely when there were birds around them, that is - the sparrows were less on guard when the birds were around them, and could focus on the task of searching for food.

In another experiment carried out by the researchers, in which the sparrows were given the opportunity to choose whether to eat next to a cage with other sparrows or next to a cage with birds of a different species, birds of prey or tzuzales, the sparrows preferred to eat next to the species rather than next to members of their own species.

"There is an apparent positive effect of an invasive species," says Berger. According to him, it is possible that the sparrows allow themselves to be less alert to threats in their environment because they rely on the vigilance of the species, which will "warn" the appearance of a predator. "It may be that the vision of the species and their ability to identify a predator is better than that of the sparrows," he says. "Studies have been done on the vision of starlings, which are birds that are close to species, and starlings can definitely detect a predator from a greater distance than sparrows."

Another possibility is that the species function as the "bodyguards" of the sparrows. "It could be that because the minnow is such an aggressive species, potential predators avoid hunting in the areas where it is found, and thus the minnows create a safer environment for the sparrows," Berger says.

In order to test the effect of the species on the nesting behaviors of the sparrows, the researchers raised sparrows in six colonies in the zoological garden at Tel Aviv University, with five pairs nesting in each colony. In half of the colonies there was a cage with a minnow and in the other half a cage with a tzuzalat. The warbler or myna could not have any interaction with the sparrows: they and the sparrows could only see each other. After one nesting cycle, the species were replaced by warblers and vice versa, so that all sparrows nested near the other two bird species.

The researchers found that the chicks that lived near mines were smaller and fewer of them survived. When the sparrows were exposed to the maine, about 4.5 chicks on average survived to at least fledging age from the nest, compared to 7.5 that survived when the sparrows were exposed to the tsetla. In another experiment, the researchers found that sparrows fed their chicks less when the researchers placed a stuffed myna in their environment, compared to the situation where a stuffed toad was placed.

These experiments show that, despite the advantage in food consumption, the reproductive capacity of the local bird is affected by the presence of the species. According to Berger, there are two possible reasons for the change in the nesting behaviors of the sparrows. "It could be that the sparrows see the species as those who might prey on the chicks, and they don't want the predator to recognize the nest. We know from testimonies that minnows prey on sparrow chicks", he says. A second reason that may cause sparrows to invest less in their offspring is the fear for their own safety. "Birds that nest in holes, such as sparrows, may expose themselves to increased predation as adults once they are trapped inside the nest, which, unlike an open nest, can be a trap," Berger explains.

The findings of the studies on the species are particularly important considering that there are still many information gaps regarding the characteristics and effects of the species invasions in Israel. "If the decision makers wait until we find all the findings on the invasive species - it could be too late," says Berger. "For this reason, when it comes to invasive species, one should act according to the precautionary principle and try to prevent biological invasions ahead of time as much as possible, even before their impact is proven."