Hey Mom – It’s Dinner Time!
New Research Sheds Light on Humpback Whale Nursing Behavior
By Anne Smrcina
Ask any mother and she’ll tell you that nursing a baby takes a lot of work. Lactation uses energy stores that need to be renewed. Trips to the store and preparing the food adds to the daily burden.
Whales share a similar maternal task load. A humpback whale mother who reaches her feeding grounds undertakes those two very important tasks – nursing her calf and gathering her food. A recent study provides a better look at how calves nurse, as well as at how mothers and calves behave together during this period. Through the use of new technologies, scientists are gaining new insights into these underwater activities.
“Stellwagen Bank National Marine Sanctuary and Monterey Bay National Marine Sanctuary are both hot spots for mothers raising calves,” says Dr. David Wiley, Stellwagen Bank research coordinator. Wiley is a co-author on a new paper published in PeerJ entitled From a calf’s perspective: humpback whale nursing behavior on two U.S. feeding grounds. “By better understanding whales’ behaviors, we have a better chance of protecting them.”
Researchers used suction cups to attach tags to humpback whale mothers and calves. The tags recorded video, as well as many hours of movement data – information on the whales’ direction, depth, pitch, and roll, and their up-and-down fluke strokes. “Fluke strokes indicate an action that requires more energy. It’s like a floating beachgoer suddenly kicking,“ Wiley notes.
The researchers found that mothers use fewer fluke strokes when nursing, and calves seem to increase fluking and overall body acceleration when feeding. When her calf is nursing, a humpback whale mother aligns herself with her young and squirts a thick, rich milk into the calf’s mouth.
“Most of our ideas about whale nursing were formerly based on surface sightings,” says lead author Jennifer Tackaberry, who spent many years studying whales in Stellwagen Bank National Marine Sanctuary. Researchers had assumed that whenever they saw calves near their mothers, they were feeding or preparing to feed, rather than just staying close to their caregiver. “The amount of time [nursing] was probably overestimated. We now believe the majority of surface time the calf spends close to the mother’s ventral or bottom side is not spent nursing.”
Data indicate that feeding can occur anywhere from a depth of about 12 feet – which would be visible from the surface – to about 200 feet. “At Stellwagen Bank, they’re using all of the water column and can even be at the seafloor,” says Wiley.
From tag videos, the researchers observed nursing events that averaged 23 seconds in duration, often interspersed between the mothers’ foraging forays. “The mothers balance their needs with the needs of the calves,” the researchers report. They also note that calves remain in close proximity to their mothers, and even nurse, while she is engaged in higher overall activity states, such as foraging.
Although data from this study came from daytime recordings, the researchers hypothesize that nursing may be more common at night when there may be fewer opportunities to forage. However, exceptions always arise. Stellwagen Bank National Marine Sanctuary researchers have documented bottom-feeding at night. “Hopefully, when video tags come with night vision, we’ll get a complete picture of mother-calf nursing,” says Wiley.
Anne Smrcina is the education and outreach coordinator at Stellwagen Bank National Marine Sanctuary.