Data from: High suckling rates and acoustic crypsis of humpback whale neonates maximise potential for mother–calf energy transfer

1. The migration of humpback whales to and from their breeding grounds
results in a short, critical time period during which neonatal calves must
acquire sufficient energy via suckling from their fasting mothers to
survive the long return journey. 2. Understanding neonate suckling
behaviour is critical for understanding the energetics and evolution of
humpback whale migratory behaviour and for informing conservation efforts,
but despite its importance, very little is known about the details, rate
and behavioural context of this critical energy transfer. 3. To address
this pertinent data gap on calf suckling behaviour, we deployed
multi-sensor Dtags on eight humpback whale calves and two mothers allowing
us to analyse detailed suckling and acoustic behaviour for a total of 68·8
h. 4. Suckling dives were performed 20·7 ± 7% of the total tagging time
with the mothers either resting at the surface or at depth with the calves
hanging motionless with roll and pitch angles close to zero. 5.
Vocalisations between mother and calf, which included very weak tonal and
grunting sounds, were produced more frequently during active dives than
suckling dives, suggesting that mechanical stimuli rather than acoustic
cues are used to initiate nursing. 6. Use of mechanical cues for
initiating suckling and low level vocalisations with an active space of
<100 m indicate a strong selection pressure for acoustic crypsis.
7. Such inconspicuous behaviour likely reduces the risk of exposure to
eavesdropping predators and male humpback whale escorts that may disrupt
the high proportion of time spent nursing and resting, and hence
ultimately compromise calf fitness. 8. The small active space of the weak
calls between mother and calf is very sensitive to increases in ambient
noise from human encroachment thereby increasing the risk of mother–calf
separation.