They’re a friendly kind of bat, not the ones that spread COVID-19. Despite bat myths, they don’t get stuck in one’s hair or suck blood but a type that beneficially spread seeds and live mostly fruits, especially in Israeli cities. To date, 33 species of Israeli bats have been identified, of which 32 feast on insects, while fruit bats like dates and other fruits.
Fruit bats also live in rural caves such as those near the city of Beit Shemesh mentioned in the Bible on the border between Judah and Philistia where Canaanites worshipped a pagan deity and mentioned in the Book of Joshua in connection with the return of the Ark of the Covenant by the Philistines, who had captured it in the battle of Eben-Ezer.
Despite the saying “blind as a bat,” they are far from blind. In completely separate research projects, zoologists at the Hebrew University of Jerusalem (HUJI) and Tel Aviv University (TAU) studying this aerial, nocturnal mammal species in search of a meal have – for the first time ever – discovered that these bats navigate just like humans. They do so not with the Israeli-invented Waze navigation system but using their excellent eyesight and a cognitive map of the landscape.
The two separate groundbreaking articles comprise the cover story of the just-issued Science, the most prominent science journal in the world, that has a large photo of a fruit bat on the front.
When wild Egyptian fruit bats set out at night to find food in Israel’s Hula Valley, they do so using advanced spatial memory and a flexible cognitive mapping of the fruit trees and other goals scattered in their foraging area. They rarely search randomly, and their foraging patterns cannot be explained by simpler navigation mechanisms, a research team headed by Prof. Ran Nathan of HUJI’s Movement Ecology Lab has found. Nathan’s study is titled “Cognitive map–based navigation in wild bats revealed by a new high-throughput tracking system.”
The HUJI study, co-authored with Prof. Sivan Toledo of TAU, HUJI doctoral candidate David Shohami and other members of Nathan’s group, details the bats’ cognitive map – the animals’ mental representation of their own position relative to the surrounding environment. This helps them move efficiently from any location to any of the many goals within their foraging area, even if the goal is out of their sight or smell range.
The existence of a cognitive map allows the bats to remember and return to trees with an abundance of fruit, roosting caves and other targets, using their mapping and memory skills rather than relying on path directions or simply finding these targets by chance.
To track the animals, the researchers had to overcome the limitations of global positioning systems (GPS) and other available wildlife tracking technologies. Although scientists have achieved key insights into animals’ navigational capabilities from experiments on rats and other lab animals, limited battery size and the need to remotely retrieve data from GPS trackers prevented researchers from collecting large sets of data on wild animals in their natural habitats.
Alternative tracking methods such as radio telemetry have been used to track small wild animals, but they do not provide sufficiently detailed, long-term information on the movements, leaving researchers at an impasse.
“Our discovery doesn’t have an immediate application or cure cancer, for example. But it increases our understanding of nature, which is a very important value. Up to now, the technologies we had could not be used to track small wild animals in their natural habitats with enough detail required to test the existence of a cognitive map,” added Nathan.
To solve the dilemma, Nathan teamed up with Toledo to develop an advanced “inverse-GPS” tracking system they called ATLAS. After a few years of development and refinement, Shohami used the system to collect a large dataset of 172 foraging Egyptian fruit bats comprising more than 18 million localizations collected over 3,449 bat-nights over a period of four years.
ATLAS movement data provided the means for detailed track analysis combined with translocation experiments and mapping of all fruit trees in the study area, spanning 88,200 hectares. The system provided researchers with detailed, accurate information from many individuals for relatively long periods at relatively low cost, showing that wild bats seldom search for food randomly, but instead repeatedly forage in goal-directed, long, and straight flights that include frequent shortcuts. The team also ruled out alternative, non–map-based strategies by analyzing simulated tracks, time-lag embedding, and other analyses of the trajectory data.
The results present the most comprehensive evidence for a cognitive map from any wild animal studied since scientists first hypothesized the existence of a human-style cognitive map in 1948, stressed Nathan. Furthermore, the study marks a landmark for movement ecology, the academic discipline that Nathan pioneered in 2008 to study life on the move. “Movement ecology has benefited from advances in tracking technology, but new ideas and novel insights have lagged behind. ATLAS has given us the keys to unlock previously unanswerable questions and will continue to shed light on a range of enigmatic natural phenomena,” he said. Asked about the TAU bat study, Nathan said: “We are good friends with their team, but we didn’t work together. It was parallel, each with its own technology.”
The TAU researchers, led by zoology Prof. Yossi Yovel, together with students Amitai Katz, Lee Harten, Aya Goldstein and Michal Handel of the Sensory Perception and Cognition Laboratory found that for long-distance navigation, fruit bats in Tel Aviv rely on conspicuous landmarks such as the Azrieli Towers, the Reading Power Station and Dizengoff Center. Their article is entitled: “The otogeny of a mammalian cognitive map in the real world.”
They tracked fruit bats from birth to maturity, trying to understand how they navigate when flying long distances. The surprising results was that fruit bats, just like humans, build a visual cognitive map of the space around them, making use of conspicuous landmarks.
In this case, bat pups raised at TAU came to know the city by looking for towering unique structures. “How animals are able to navigate over long distances is an ancient riddle,” explained Yovel. “Bats are considered world champions of navigation – they fly dozens of kilometers in just a few hours and then come back to the starting point. For this study we used tiny GPS devices – the smallest in the world, developed by our team…, tracking bat pups from the moment they spread their wings until they reach maturity so as to understand how their navigation capabilities develop. No such study has ever been conducted on any living creature, and the findings are very interesting.”
The researchers monitored 22 fruit bat pups born in a colony raised at TAU – from infancy to maturity, tracking them as they scoured the city for food. The results show that Tel Aviv bats navigate the space around them in much the same way as the city’s human inhabitants.
“Bats use their sonar to navigate over short distances – near a tree, for example,” continued Yovel. “The sonar doesn’t work for greater distances. For this, fruit-bats use their vision. Altogether, we mapped about 2,000 bat flight-nights in Tel Aviv. We found that bats construct a mental map: They learn to identify and use salient visual landmarks such as the Azrieli Towers, the Reading Power Station and other distinct features that serve as visual indicators. The most distinct proof of this map lies in their ability to perform shortcuts.”
Like humans, Yovel continued, “bats at some stage get from one point to another via direct new routes not previously taken. Since we knew the flight history of each bat since infancy, we could always tell when a specific bat took a certain shortcut for the first time. We discovered that when taking new, unknown routes the bats flew above the buildings. Sending up drones to the altitude and location where a bat had been observed, we found that the city’s towers were clearly visible from this high angle. Here is another amazing example of how animals make use of manmade features.”
When the fruit bat lives in urban regions, residents often get upset by the mess they leave behind with their droppings on cars, sidewalks and walls. When they live in agriculture areas, only a small minority scavenge farmed dates, lychees, berries and other fruits, which in the past led to efforts to poison them. For a while, bats were a state-protected animal, but this did not last.