New publication: Energetic benefits of resting behaviour in humpback whale mother–calf pairs revealed by biologging and UAS-photogrammetry
- Gussie Hollers
- Jul 10
- 6 min read
We are excited to share our newest publication in Conservation Physiology on humpback whale mother-calf energetics written by PhD candidate Gussie Hollers and coauthors! Link to the full paper: doi.org/10.1093/conphys/coag041
Background motivation
Every winter, humpback whales travel thousands of miles from their feeding grounds in Alaska to the warm, calm waters of Hawaiʻi. For lactating mothers, this is an extraordinary physiological feat: they sustain their own metabolic needs and produce rich milk for a rapidly growing calf, all while fasting for months on end. Tightly managing their energy budgets during this time is incredibly important for calf survival, maternal health, and the long-term growth of the population.
Humpback whale mothers and calves in Hawaiʻi rest for long stretches of time to conserve energy, but we don’t know how much energy these resting dives are actually saving. If mothers and calves are disturbed while resting, nursing behavior could be interrupted, or important maternal energy reserves could be used up swimming away.
Contrasting calf behavior from a CATS tag perspective. On the left, a mother and calf rest at depth. On the right, a calf repeatedly breaches and swims quickly near the surface.
Members of the MMRP have been working to answer a deceptively simple question: how much energy do humpback whale mothers and calves actually use, and how could that change when humans share their space?
Fieldwork methods
Accurately measuring metabolic rate in large, free-swimming whales is challenging. We can’t put a whale on a treadmill in a lab, so we have to get creative with new technology to measure metabolic rate in wild whales. To collect non-invasive data on humpback whale bioenergetics, we used a combination of UAS (Unoccupied Aerial Systems, drone) photogrammetry, and suction-cup movement tags. Our Customized Animal Tracking Solutions (CATS) tags recorded the whale's movements, depth, sounds, and video perspective in extraordinary detail. After attaching each tag to a whale, we flew the drone overhead, capturing photogrammetric measurements from the air to estimate important parameters like body mass and calf age.
Video compilation of tag deployments on humpback whales in Hawaiʻi
This fieldwork was a collaborative effort spanning multiple institutions, donors, and volunteers, and we are grateful for all the support we have received. On any given field day, our small team would head out before dawn, locate a mother-calf pair, and carefully approach to deploy a suction-cup biologging tag on the mother or calf. Over seven field seasons (2020-2026), we deployed 123 tags for a total of 527 hours of detailed video and movement data!
Results: resting dives save significant amounts of energy
We divided each deployment into two general behavioral categories, resting dives and all other behavior, and calculated the difference in energy use between behavioral states. We used two independent methods to calculate energy expenditure: one based on the tailbeat thrust power required for swimming, and one based on breathing frequency.
Example dive profiles we get from the tag depth sensor of a mother and calf pair tagged off of Lahaina in 2023. The mother’s dive profile is on the top, and her calf’s dive profile is on the bottom. The x-axis shows time, and the y-axis shows depth. Resting dives are highlighted in blue. These dives are easy to identify because of their longer length, uniform depth, and low movement.
One of the most striking findings was just how much energy resting dives saves. During resting dives, mothers used on average 45% less energy than during active swimming, and calves 35% less. For an animal that is not eating, every calorie matters, and resting behavior appears to be a critical energy conservation strategy. We also found that calves spent more time resting as they aged, in line with previous boat-based behavioral observation studies.
Boxplots comparing the calories per minute used in resting dives (blue) and other behavior (red) across two methods in both mothers and calves.
Using these behavioral state-specific energy rates, we also simulated daily energy expenditure across the range of body sizes observed in Hawaiian humpback whales. Daily energy use ranged from around 92 MJ for the smallest, youngest calves to 452 MJ for the largest and oldest, and from 817 MJ for small mothers to over 2,000 MJ for the largest females. In human terms, mothers burn the caloric equivalent of 350 cans of spam for 1,400 malasadas every day just to sustain her own metabolism! The average calf would use about 60 cans of spam or 240 malasadas per day. These numbers underscore just how much fuel these animals require to sustain themselves through the breeding season.
Simulated calories used per day for mothers and calves. For mothers, the x axis is body mass and the y-axis is Calories. The predicted daily energy expenditure across body masses is the blue line, and the black dotted lines are 1,2, and 3 times the predicted mammalian basal metabolic rate. The red dots are the predicted daily energy expenditure for the tagged whales. For calves, the x axis is days since birth, and the y axis is Calories. The different colored lines are the predicted daily energy expenditure for calves born to mothers of different lengths, because larger mothers give birth to heavier calves.
Results: disturbance to resting behavior could cost mothers
These estimates also let us ask a conservation question that has been difficult to answer quantitatively: how much energy could it reasonably cost a mother-calf pair when vessel disturbance interrupts their resting behavior?
To explore this, we built simulations grounded in both our empirical data and published studies of how cetacean mother-calf pairs respond to vessel presence. Using a representative Hawaiian mother-calf pair and realistic scenarios of resting time reduction, we found that even a moderate, daytime-only reduction in resting behavior, the kind that might occur on a day with repeated whale-watching vessel encounters, increased daily pair energy expenditure by about 64 MJ, equivalent to an additional 2.5 kg of maternal blubber burned per day. That might sound small, but for a fasting animal with no ability to eat more to compensate, these costs accumulate. Across 60 days of such disturbance, the cumulative additional blubber loss reaches approximately 150 kg. For smaller mothers with lower absolute energy reserves, even modest accumulations may begin to constrain milk production, calf growth, and ultimately reproductive success.
These simulations are not intended as precise predictions of disturbance costs, but they demonstrate something important: the detailed, individual-level energy estimates we collected in the field can be directly scaled to ecological consequences, providing exactly the kind of inputs that complex models need to connect behavioral observations to population health.
Video from CATS tags on mothers during resting dives, showing one reason calves didn't save as much energy during resting dives
A collaborative effort to protect humpback whales
Humpback whales have made a remarkable recovery since commercial whaling, and Hawaiʻi hosts one of the most important breeding concentrations in the North Pacific. Understanding population health in the face of vessel traffic, climate-driven changes in prey availability, and other stressors requires quantitative, mechanistic understanding of energy budgets that this study begins to provide. We hope it serves as a foundation for more refined assessments of disturbance costs, and ultimately, for more effective protection of this population and their environment.
We would like to especially thank the field team at the Marine Mammal Research Program (MMRP) at UH Mānoa’s Hawai‘i Institute of Marine Biology, Pacific Whale Foundation, and Alaska Whale Foundation, for their invaluable assistance with tag data collection for this project. We would also like to thank the members of the MMRP for their substantial feedback on the structure and content of this work. All data were collected under appropriate NOAA NMFS permits (nos 21476 and 27548) and university IACUC protocols. UAS flights were operated by Part- 107 authorized pilots in compliance with standards set by the Federal Aviation Administration. We would like to thank our corporate and philanthropic funders for making this research possible, includ- ing Our Oceans’ Netflix, Wildspace Productions, Freeborne Media, PacWhale Eco-Adventures and PWF donors, Young Brothers and Dolphin Quest, the Omidyar Ohana Foundation, Brook Byers, Paul and Elle Stephens, Barbara and Duncan Chapman, Peter Beck, Benjy Garfinkle, Thomas Griggs, Thomas Tierney, Owen Williams, Deepak Srivastava, Bernard Alpert, Patricia Cahill, the Schwab Foundation, JP and Dalia Maheu, Denise O’Leary and Kent Thiry, Kristin and Larry Link and Brion Applegate.
If you’d like to support our research, please click the blue button below — any donation, big or small, makes a meaningful difference in helping us protect these incredible animals. Mahalo for being part of this work!
Citation: Hollers A, Gough WT, Aswegen M, Szabo A, Evans L, Currie JJ, Blawas AM, Fahlman A, Goldbogen JA, Bejder L (2026) Energetic benefits of resting behaviour in humpback whale mother–calf pairs revealed by biologging and UAS-photogrammetry. Conserv Physiol 14(1): coag041; doi:10.1093/conphys/coag041.
If you would like to read more about related tagging projects, please visit the following blogs:
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