Dolphins that are free-roaming but are fed by hand become less socially involved with their peers. As a result, their calves may grow up lacking vital social skills 鈥� which could explain, at least in part, why they are twice as likely to die before reaching adulthood.
鈥淒olphins are a very social species that rely on the social group to protect them from predators and for courtship [in breeding situations],鈥� says at Murdoch University in Perth, Australia. 鈥淭here鈥檚 a lot of alliance behaviour, and there鈥檚 a lot of learning that has to be done by observing other dolphins.鈥�
Some tourist centres and even recreational boaters train Indo-Pacific bottlenose dolphins (Tursiops aduncus) to approach beachside public sighting areas or boats by hand-feeding them small amounts of fish every day. Because hand-fed males aggressively attack each other over the food 鈥� putting themselves and nearby humans in danger 鈥� tourist centres focus their hand-feeding only on female dolphins, says Senigaglia.
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But recent studies have shown that only 38 per cent of the calves of hand-fed wild dolphins survive to 3 years of age, which is much lower than the average 77 per cent survival rate for wild calves in general. To better understand why, Senigaglia and her colleagues evaluated the social behaviour of dolphins along the Bunbury coast in Western Australia.
In particular, they observed the individual behaviour and movement of 35 dolphins, including 13 that had been hand-fed. Using a small boat, they regularly followed each of the 35 dolphins for periods lasting from 20 minutes to 3 hours for two years in a row, for a total of 180 hours.
The researchers found that hand-fed dolphins explored much less and kept to home ranges that were almost half the size of those of dolphins that weren鈥檛 fed by hand 鈥� marking an average of 11 square kilometres as opposed to 21 square kilometres, says Senigaglia.
Socially speaking, hand-fed dolphins actually swam in relatively large groups, but more readily broke away from them to join different ones. In general, they created weaker ties with other group members.
鈥淵ou can be solitary in a room full of people, and it鈥檚 the same for dolphins,鈥� says Senigaglia. 鈥淗and-fed dolphins are the ones that interact less or for shorter time with other individuals and do not care so much who is around. They get along with everyone but have no 鈥榖est friends鈥�.鈥�
When the hand-fed females had calves, these offspring ended up socialising with other dolphins for only an hour a day, instead of the usual 3 hours seen in calves that aren鈥檛 fed by hand.
What鈥檚 more, on average, the hand-fed dolphins spent 8 hours of their day hunting and begging for food. Dolphins that haven鈥檛 been fed by hand spend less than 5 hours a day hunting for food, on average. 鈥淸Hand-fed dolphins] spent a lot of time at the beach, waiting for the fish,鈥� says Senigaglia, adding that this was generally time spent alone.
There are prohibitions on feeding wild animals in Australia, but local governments allow exceptions for certain tourist companies that want to encourage regular dolphin visits. These companies generally keep the amounts of hand-fed food low, limiting them to just 500 grams per dolphin per day, in an effort to encourage natural hunting behaviour.
However, even with the limits on hand feeding, the dolphins still devote plenty of time to begging, which leaves them with less time for socialising. The findings suggest that hand-fed dolphins become 鈥渕ore loosely connected鈥� to social groups and lack real-world opportunities to teach calves how to live in the wild, says Senigaglia. Consequently, these well-meant feeding activities are leading to poor survival of the species, she says.
鈥淲e all want the same thing, which is protecting these dolphins and having them there for as long as possible,鈥� she says. 鈥淏ut I don鈥檛 think dolphins come to the beach because they think it鈥檚 fun to interact with humans. I think dolphins come to the beach because we鈥檙e like vending machines. So we need to do things in a smarter way.鈥�
Animal Behaviour
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