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Tagging expedition: revealing the delicate nursing behavior of humpback whale calves

Written by: Lars Bejder

Every winter, ~10,000 humpback whales migrate to Hawaii, with the main purpose of breeding. The time period during which adult females and their newborn calves spend on the Hawaiian breeding grounds (typically January – March) represents a critical time. Specifically, mothers give birth to their calves in warm and relatively protected waters, while producing a sufficient amount of milk containing the necessary energy for the calves to grow quickly. At the same time, mothers need to ensure that they have enough energy stores of their own to feed their calves and support their own energetic needs. This is particularly important because no feeding occurs during the breeding season so they are reliant on energy stores gained during the feeding season. As such, during the three months on the breeding ground, mothers must ensure that their calves grow strong enough to be able to migrate back up to their summer foraging grounds. Naturally, this puts certain demands on the mother in order to be successful. A critical aspect of being successful is to ensure that calves are provided the necessary opportunities to nurse from their mothers. This is where we come into the picture…

Video: A short video showcasing our tagging expedition and footage captured by the CATS tags, drones and GoPros. Video by Martin van Aswegen.

We have recently commenced an exciting new project that aims to quantify the nursing behavior of humpback whale calves on their Maui breeding grounds. The project is a collaboration between the Marine Mammal Research Program (MMRP) at the University of Hawaii at Manoa, the Goldbogen Lab at Stanford University’s Hopkins Marine Station, and the Friedlander Lab at University of California, Santa Cruz.

For ten days in February 2020, we (Martin van Aswegen, Will Gough and Lars Bejder) deployed non-invasive suction-up CATs cam tags onto seven humpback whale calves. The tag deployments would not have been possible without the generous support of Marc Lammers from the Hawaiian Islands Humpback Whale Sanctuary, Stephanie Stack and Jens Currie from the Pacific Whale Foundation and the Oceanwide Science Institute.

The CATs tags have a built-in camera, pressure sensors and accelerometers that are allowing us to obtain insights into the remarkable behaviors of humpback whale mothers and calves. The camera recordings are providing us with seldom seen nursing behavior (including nursing bout frequency and durations) and social interactions between individuals. The accelerometer data is allowing us to quantify the fine-scale behavior, movement and breathing patterns of tagged individuals. The fieldwork also consisted of flying unoccupied aerial vehicles (UAVs, drones), equipped with altimeters and cameras with undistorted lenses, over the tagged individuals - allowing us to calculate their overall length (and hence age) and body condition. This aspect of the research is coupled to the work by PhD candidate Martin van Aswegen – who will be updating us shortly via a blog on his Winter 2020 fieldwork in Hawaii and Alaska – stay tuned.

Overall, the data collected through these projects will provide important insights into the needs of humpback mothers and calves on their breeding grounds. As for now, we are looking forward to further exploring the data and for our next field season in Jan-March 2021.

Figure: The moment before a non-invasive suction-cup CATS tag is deployed on a surfacing humpback whale calf off Maui, Hawaii.

We are also truly grateful to the following people and organizations for helping us retrieve the tags once they were off the whales: Pete, Art and Trish from Molokai Ocean Tours, Blake Moore and his team at PacWhale Eco-Adventures and Rachel and John Sprague. Thanks also to Abigail Machernis, Grace Olson, Florence Sullivan, Meaghan Jones, Captain Dedrick, Ingelise and Bjarne Bejder and the University of Hawaii at Manoa.

All research activities were conducted in accordance with NOAA permit #21476 and IACUC approval. All drone activities were conducted in accordance with FAA Part 107 regulations.

If you have any questions about this project, please contact:

Lars Bejder (


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