Sperm whales have a problem.  They find most of their food in the mesopelagic zone, typically at depths more than 600m deep,
but their calves are unable to dive this deep for very long (the youngest cannot even reach these depths).  This means that
whilst the adults and sub-adults from a social group are foraging the calves have to remain on or near the surface where
they are vulnerable to predators. To help protect them but also probably to help prevent the calves from getting lost older
members of the social group take it turns to baby sit.  Adult females in the group will also give milk to any calf seeking
it not just their own offspring (see also our blog entry on ´peduncle diving´).  This means that a calf does not have to
struggle to keep up with its mother whilst she is diving for food.  A calf can get all the milk it needs by simply moving
between any of the groups females as they surface between dives.

The forehead and blow-hole of a baby Sperm whale seen as it passes close by our boat. 

Yesterday during our afternoon whale watch we saw an excellent illustration of baby sitting in Sperm whales but also perhaps
how they sometimes chose to communicate at the surface by breaching.  In the course of the trip we had already seen a
variety of different females and sub-adult males from one group surfacing between dives but also two very young calves.
After an interlude when none of the whales were at the surface we suddenly saw one sub-adult bull breach twice in the
distance.  We immediately moved the boat to where this whale lay at the surface and there, almost certainly in response to
his signal, we witnessed the two calves speedily swimming to his side (see photo). An amazing sight and a noteworthy
observation too – at least good anecdotal evidence of why Sperm whales sometimes breach and that in their social groups not
only mothers take responsibility for the care of their young.  

Two Sperm whale calves being 'baby sat' by a sub-adult bull.