Flying with birds

The sound of 20,000 cranes is virtually deafening. But to stand in a field as they soar overhead is a singular experiences. Still, these journeyers represent just a small fraction of their tour group: a half a million migratory birds pass through Israel's Hula Valley each year on the way from Scandinavia to Africa.

And each year hundreds of tourists visit the site in northern Israel bordering Lebanon and Syria to witness the incredible spectacle.

But birds and tourists aren't the only ones to have discovered the Hula Valley. It's also proving to be a real treasure for researchers. At one time the largest wetland in the Middle East, it is now the only one left. For that reason the valley is something of a success story: Since 1900, more than 60 percent of the world's wetlands have disappeared. Those left behind are often in terrible condition.

That ecologist Ran Nathan can now observe thousands of birds with his team in the Hula Valley is down to a somewhat unfortunate coincidence. In the 1950s, the Israeli government drained the habitat to tap into its drinking water. Forty years later, the state realized its mistake and restored the Agamon Lake. It was a success - the birds returned. More than 300 bird species live here, including cranes, songbirds and owls.

The Hula Valley has the greatest population density of barn owls. While in Europe, around 40 pairs of owls will live in 100 square kilometers, in Israel the number is five times as high.

Wild overpopulation often leads to conflict between humans and nature. But the barn owls don't bother the farmers dotted around the valley. On the contrary, farmers voluntarily place nesting boxes on their fields. That's because the birds aren't interested in the peanuts or chickpeas growing there, but are partial to rodents. A pair of barn owls will devour 2000 to 6000 such creatures in a year. It's perhaps the most natural and effective way to fight pests.

The owls remain undisturbed in their nesting boxes. There are no predators to eat them, but every now and then team member Motti Charter sneaks over and fishes the birds out of their homes to fit them with transmitters. "When they bite me, it's my fault" says Charter, who jokes about his alleged clumsiness. "Now she didn't bite me, but pooped on me - that's her revenge."

The transmitter weighs about 13 grams, which is equivalent to 3 to 5 percent of the animal's body weight. "That's the natural variance in body mass over a day," says Charter. It seems the birds don't notice the excess baggage. After a quick preen, the device disappears into the plumage. Only the antenna is visible.

Every two seconds, the transponder sends a signal. The ornithologists can also gather up the devices as they catch most of the birds a number of times.

The collected data provides an overview of the barn owl pair's territory and predatory behavior. And it appears to vary. While one pair of owls tended to hunt in area around its nesting box, another neighboring pair chose a hunting ground further afield and flew each of its prey back to the nest.

Researchers hope to understand behavioral differences amongst the birds with this surveillance. "No one knows how the fledgling process works," says Charter. "We can't seem them at night. We don't know - do they form groups, do they hunt alone, do they learn from their parents?"

The tall grass of the Hula Valley hides many more secrets the researchers hope to uncover.
At dusk, the chirps of the valley's countless songbirds rise. But it's practically impossible to see them with the naked eye or catch them like the barn owls.

To catch these tiny animals, the researchers unfurl nets invisible to a bird's eye along the pathways.

Once caught in the net, a bird can barely move until Yosef Kiat from Nathan's team arrives to carefully free it.

Kiat often recognizes the animals at first glance. He's a been a "bird ringer" for more than ten years and places tiny metal identification rings on their feet. Today, he's also fitting them with small transponders. The researchers hope to learn as much about the songbirds this way as they have with the barn owls.

Even though these tiny birds haven't got the sharpest eyesight, they, like the crane, cover huge distances on their migration. They just take the opposite path: from Lebanon to Turkey or Greece where they spend the winter.

"We can watch them in real-time and in the wild. With the help of technology we can revise and refine our theories, therefore they match reality better," says Nathan. "In the past, we had around 300 data points for an entire research project. Now we collect that many in one hour."

One of the questions the researchers is investigating is the connection between movement and molting patterns. "Different species replace their feathers in different stages and different ways, and we want to understand the variation in this strategy," says Ran Nathan. "Because primary feathers are critical for these lovely flight machines to move, we expect significant differences in movement among different molt strategies."

Hula Valley remains the only place where such delicate processes can be studied. The researchers have built a unique international field lab complete with ground stations and receivers to do the job. Together they make up the Atlas System (Advanced Tracking and Localization of Animals in real-life Systems). Atlas reveals much more than a simple pair of binoculars ever could.

Rather than look at movement patterns in isolation, Ran Nathan's underlying idea is to examine them in conjunction with other biological process in a bird's life.

Even as a child, he observed birds - with binoculars instead of high-tech devices. When he became a researcher, he realized that animal movements were only ever described in isolation and rarely looked at as part of a wider context, regardless of whether the subject was a butterfly, lynx, vulture or elephant.

This prompted him to establish the first ever "movement ecology" working group in the world at Hebrew University of Jerusalem in 2010. As a "birder with a passion for flight" it quickly became clear which animals he would focus on.

In almost complete darkness, Nathan's colleagues start recording the songbirds' tracking signals. As long as the birds remain in the valley, the team's computer will log every flight.

Starting May 2016, Nathan wants to expand the system elsewhere in collaboration with the universities of Frankfurt and Potsdam in Germany. At first, this will cover just ten square meters, which covers the range of many animals. But their vision reaches much further: the monitoring system will in the future span the globe, so researchers can fly worldwide with the birds.