The Bermuda Petrel (Cahow) Biomonitoring Project is an ongoing collaborative effort, started in 2019 with a number of international researchers led by Letizia Campioni, and locally by the DENR’s Jeremy Madeiros, and Nonsuch Expeditions Founder / BioQuest CoFounder J-P Rouja. These first projects continue to bear fruit with a wealth of new information on the biology, feeding & foraging strategies and at-sea range of Bermuda's critically endangered national bird, as well as levels of Persistent Organic Pesticides (POP) in these long-lived seabirds.
Jeremy Madeiros: “In June 2025, we published another peer-reviewed research article in the journal "Ecology and Evolution" titled "Fine-Scale Movement Data Reveal Primarily Surface Foraging and Nocturnal Flight Activity in the Endangered Bermuda Petrel" (Cahow). I believe this is the fourth article or paper to come out of this project. Authors include Paolo Becciu (Dept. of Ecology and Evolution, University of Lausanne, Switzerland), Allison Patterson (Wildlife Research Division, Dept. of Environment and Climate Change, Canada), Carina Gjerdrum (Canadian Wildlife Service, Canada), Jeremy Madeiros, (Terrestrial Conservation, Dept. of Environment and Natural Resources, Flatts, Bermuda), and Letizia Campioni (MARE - Marine and Environmental Sciences Centre, ISPA - Instituto Universitario, Lisboa, Portugal & ARNET - Aquatic Research Network).
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This project was carried out during the egg incubation period of the Cahow's breeding season in January and February 2023, and involved deploying 25 miniaturized multi-sensor biologgers of 3 different types, ranging only 2.5 to 5 grams in weight, attached to the back feathers or central tail feathers of selected adult Cahows, using tesa tape, which can be safely removed with no loss of feathers at the end of the deployment period. Biologgers have also previously been fitted on adult Cahows during the early chick-rearing period, and for periods up to a full year to also see oceanic range during the non-breeding period. Fitting these loggers on the Cahows is necessary because the huge area and remote nature of their feeding / foraging grounds makes direct observation of foraging behavior impracticable, requiring the use of remote tracking technology. Briefly, some of the findings are as follows:
During the egg incubation period GPS tracking data showed extensive foraging trips lasting an average of 10.3 days, with Cahows travelling an average maximum distance of 1207 Km, +/- 305 KM from the breeding colony in Bermuda, in consistent directions, over remote oceanic regions. The at-sea distribution encompassed 3,303,963 square kilometers of the western North Atlantic, during the egg incubation period.
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During these foraging trips, Cahows spent over 75% of their time in flight, mainly in dynamic soaring flight. Dynamic soaring is a very energy-efficient flight technique used by petrels such as the Cahow and was the most common flight behavior used under all conditions. Flight increased during dusk and at night, showing greater activity at night compared to the day, while water surface behaviors were more common during the day.
Evidence showed that Cahows engaged in very limited diving activity. Less than 0.001% of depth measurements from 8 Cahows exceeded 0.1 m, with the maximum depth recorded at 1.57m. There were only 5 dives deeper than 0.5m. Dives were brief, with the deepest dive to 1.57m lasting 4 seconds. 99.99 % of depth readings recorded by tags were shallower than 0.1m. The results show that Cahows are overwhelmingly nocturnal surface feeders, only rarely engaging in shallow diving during their extensive feeding trips on the open ocean.
1/ One of the most important findings from this study dovetails nicely with a previous paper that looked at the diet of Cahows: ("Combining Bio-logging, Stable Isotopes and DNA Metabarcoding to Reveal the Foraging Ecology and Diet of the Endangered Bermuda Petrel Pterodroma cahow". Marine Ecology Progress Series, 2023). Adult and fledgling Cahows sometimes rarely regurgitate their stomach contents when being handled, and advanced techniques such as DNA Metabarcoding were used to identity up to 16 species of deep-water bathypelagic fish and 9 species of Squid that were being eaten by the birds. The mystery was that these fish and squid spend the day up to 1000 metres deep in the dark zone, so how were the Cahows able to reach and feed on them? The results from the project show that Cahows feed and are active primarily at night, and they are also surface feeders. Well, it happens that these deep-water fish & squid migrate to the surface at dusk, to feed during the night on plankton that live in the upper surface layer of the Ocean but are sparse or absent at greater depths. Cahows, with their superb night vision (up to 100 times better than humans, similar to Owls) and many keen sense of smell, are perfectly adapted to locate and feed on these deep-water species, many of which are bioluminescent, as they feed on plankton at the surface at night. Few other seabirds, except those in the same family, can exploit this food resource from an otherwise unreachable layer of the Ocean.
2/ The findings also help to explain how Cahows are able to travel such long distances, in such a short time, by spending over 75% of their time at sea in flight, mainly using dynamic soaring, which is one of the most energy-efficient forms of flight. This flight strategy allows these birds to travel through vast oceanic areas with a minimal expenditure of energy and is the real "superpower" of the Cahow. There is also strong evidence that Cahows actively seek out favorable wind conditions, such as the strong winds around winter storm systems, to enable them to cover huge distances and improve their foraging success.
This project has brought together both Bermudian and overseas researchers, with expertise in deploying data loggers, which I can then recover, and hand them over to other researchers who can extract and analyze the data collected by these devices. The advance in technology over the 25 years that I have worked with the Cahow, and the range of information being gathered, would not have been possible a short time ago and help us to make informed decisions on the future management of our national bird. This will be essential in the future as large-scale ecosystem changes which are being observed, such as increasing Sea-Surface Temperatures, marine heatwaves, alterations in the Gulf Stream or changes in wind patterns, could disrupt the availability of food items and the energy balance for our far-ranging, and endangered national bird. “
J-P Rouja Nonsuch Expeditions Founder: “This collaboration is yet another example of how global partners and the latest technologies are being leveraged to unlock insights into their secret lives. Another offshoot of this project is a Genomic Population Study being conducted with local partner BioQuest, initiated using left over “remnant” blood samples, sent back to Bermuda after originally being drawn for the Persistant Organic Pesticides (POP) portion of this study. These are being sequenced locally in the BioQuest lab at the Bermuda College, a groundbreaking first for Bermuda and the Caribbean region. Stay tuned for updates that will include the answer to the “Who’s the Daddy” drama from this past Cahow nesting season.
Photos by Kirk Zufelt, Letizia Campioni and J. P. Rouja.