Bottlenose dolphins that work together with humans to catch fish have their own distinctive whistle, one that may help them recognise each other.

Off Laguna, Brazil, fishers stand in a line in waist-deep water or wait in canoes while, farther out, chase shoals of mullet to the shore. The fishers can’t see the fish in the murky water, so they wait for the dolphins to give a signal — like an abrupt dive or tail slap — then cast their nets.

Fishers catch larger and more fish when they work with dolphins. “Dolphins likely reap similar benefits,” says of the Federal University of Santa Catarina in Brazil – it might be easy for them to gobble up fish disoriented by the nets.

But only some dolphins, working alone or in small groups, cooperate with humans. To explore the differences between helpful and unhelpful dolphins, Cantor and his colleagues recorded the sounds made by both types while they foraged either on their own or with people.

Whistle while you fish

Surprisingly, the whistles of cooperative dolphins were different from those of non-cooperative ones, even when foraging alone. For instance, they used fewer ascending whistles.

Dolphins from different regions often whistle differently, Cantor says, but “it is much less common to find such acoustic differences among dolphins of the same population that inhabit such a small area”.

Since cooperative dolphins also whistle differently when fishing solo, the researchers don’t think these calls carry specific messages about fishing with people. Instead, the whistles may be a way for dolphins to label themselves as members of a particular social group, Cantor says.

Alternatively, the dolphins may be using dialect or slang. Cantor says it is “as if they speak the same language but use some ‘expressions’ that are exclusive to their social community”.

Dolphins also use clicks to communicate during feeding, says of the Italian National Research Council. Researchers will need to examine clicks as well as whistles to better understand the dolphins’ communication styles.

Full control

In south-western Morocco, acrobatic goats climb argan trees to eat their fruit and leaves. A tree full of goats is a striking sight, but the goats’ widely overlooked habit of regurgitating and spitting out the nuts may be important to the life of these forests.

Goat herders lead their flocks through the argan (Argania spinosa) forests, where the animals can clamber up trees 8 to 10 metres high and strip them nearly bare. Popular accounts say the goats defecate the nuts of argan fruits, which can then be retrieved from the goats’ manure.

Cracking these nuts open is the first step in making argan oil, a valuable export to richer countries where it is used in beauty products and foods. People may also harvest the fruits directly, but the goats save them a step.

“Some scientists have accepted the defecation hypothesis, probably because they did not speak to the herders,” says Miguel Delibes, a biologist at Doñana Biological Station in Seville, Spain.

The herders say the goats mostly spit the seeds out.

Seed of a thought

“Goats do not usually defecate large seeds,” Delibes and his co-authors write. This made them sceptical that argan nuts, about 2.2 centimetres long, took this route through the animals.

So they fed Spanish domestic goats fruits with seeds of various sizes, including olives, hawthorn fruits, and carob tree pods. The researchers didn’t have access to argan fruits as the tree doesn’t grow in Spain.

Despite not being able to find all of the seeds afterwards, the authors note, they recovered spat-out seeds from every type of fruit. The largest seeds — still smaller than an argan nut — were most likely to be spat out. Smaller seeds more often wound up in faeces.

Food that a goat swallows travels to the rumen, the first of four stomach compartments. Like other ruminants such as cattle or deer, the goat regurgitates material — the cud — from this compartment for extra chewing.

“The time in the rumen is very variable,” Delibes says, because goats may chew foods several times. A goat might spit out a swallowed seed hours or days later — up to six days in the study.

The researchers tested the viability of regurgitated seeds and found that more than 70 per cent could still grow. That means spitting goats might be an overlooked ecological factor, helping to scatter the seeds of plants they eat.

Spitting is good

Delibes says researchers already knew tropical grazers could spit seeds in their cud, but this shows that the spit of temperate ruminants might be important too. In fact, he thinks all ruminant species, wild and domestic, probably do the same thing — not just goats.

Ecological research that focuses on animal dung might miss the seeds that spread via spit, especially seeds that wouldn’t survive a trip through the intestines.

Ahmed El Aich of the Hassan II Agronomic and Veterinary Institute in Rabat, Morocco, says argan nuts spat out by goats represent up to 60 per cent of the nuts used to make argan oil. “Farmers use goats on purpose to collect argan nuts, since some argan are very far from the habitations,” El Aich says. He adds that the arrangement isn’t risk-free — some goats break their legs falling from the trees.

Read more: Shawl thing: Cashmere could soon come from gene-edited goats

Frozen fish