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Whispering so predators won’t hear us

on 29 de October de 2019

A recent study, led by researchers at Syracuse University and published in Biology Letters last October, suggests that North Atlantic right whale mothers whisper to their calves to avoid attracting the attention of their predators. But, before going into more detail…

What do we know about this species?

Its scientific name is (Eubalaena glacialis) where Eulabaena means “true whale” and glacialis “from the ice”. They live in coastal waters or near the continental shelf and can reach 17 meters in length, the females being the longest, and about 90,000 kilos in weight [see image 1]. They have no dorsal fin and a very wide back. Their barbs consist of between 220 and 260 plates on each side and can reach a length of up to 2.7 metres. The head area is often covered with rough portions of skin called callosities. These are whitish or creamy in colour due to massive infection by cyamids (also known as whale lice) [see picture 2 and 3]. Its blow is very distinctive as it is V-shaped, both when viewed from the front and the back.

1.- Eubalaena glacialis CC_Lycaon.cl

2.- Eubalaena glacialis

3.- Cyamus boopis CC4.0_Hans Hillewaert

Currently, according to IUCN, this species is listed as “critically endangered” and is seriously threatened. These whales were the first whales of large proportions to be regularly hunted for purely commercial purposes.

Eubalaena glacialis CC_NOAA

During the winter months they are concentrated on the coasts of Florida and Georgia, as this is the breeding season. Females give birth to a single calf every three to five years. The calves at birth can measure between 4 and 4.6 meters and reach a weight of 910 kilos.

 

What have they discovered in this scientific study?

The researchers placed 16 sound recording devices on females and a total of 754 recordings were collected. Once analysed, they discovered that the mothers produced a very soft, short and grunt-like sound, only perceptible at a short distance. In contrast, young and pregnant whales in the same area produced a completely different repertoire of sounds [see picture 5].

5.- Proportion of high and low amplitude sound signals produced by lactating females and non-lactating whales in breeding areas

Susan Parks, a researcher at the University of Syracuse, explains “these sounds can be considered almost as a human whisper (…) they allow the mother and calf to stay in contact without announcing their presence to possible predators in the area”. This strategy is known as crypsis, a camouflage phenomenon in which an organism presents adaptations to pass unnoticed to the senses of other animals. The white sharks (Carcharodon carcharias) are commonly seen in the breeding areas of this species of whale, in addition to having been documented feeding on whales. It has also been documented that killer whales attack right whales and are frequently seen in the southern right whale breeding area.

This is not the only study that suggests this. Two studies in Australia have shown evidence of acoustic crypsis in mother and calf including reduced amplitude sound production in humpback whales (Megaptera novaeangliae) and reduced amplitude sound with low call rates in southern right whales (Eubalaena australis).

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