Cahow season two chicks short of breaking record
Bermuda’s cahows enjoyed a near record-breaking year of a total of 78 chicks fledging in the 2024-25 season across all the colonies, just two shy of the most successful season, 2023-24.
The nesting season started earlier than expected this year and while breeding numbers were looking to exceed previous years, the cahows faced a potentially devastating threat from the passage of Hurricane Melissa.
The new Nonsuch colonies are now growing from strength to strength with 23 chicks fledged from 41 breeding pairs in 2024-25, just two off the record of 25 chicks fledged in the previous season.
Jean-Pierre Rouja, the founder of Nonsuch Expeditions, said: “This makes the Nonsuch colonies the second-largest subpopulation of cahows in Bermuda and thus the world.”
He highlighted Nonsuch as it is the primary focus of management efforts and the only growing colony at this point, soon expected to take over from the largest natural colony on neighbouring Horn Island. The 23 chicks were laid by 41 nesting pairs.
He added: “In the 16 years since the first Nonsuch Island chick fledged, these colonies have produced a total of 185 successfully fledged chicks.
“With so many prospecting younger birds and new pairs seen returning, we expect it to take the lead this coming year or next.
“This will require a big boost in the building of new cahow burrows to speed up the process and avoid conflicts.
“Things are definitely looking positive for Nonsuch. However, elsewhere in the original nesting colonies, on the smaller lower lying outer islands, we are now facing the increased sea-level rise and hurricane threats that the 25-year Nonsuch effort was designed to counter.”
Mr Rouja said anyone interested in helping with the creation of the burrows should keep an eye on Nonsuch Expeditions updates.
The groundbreaking Nonsuch Island “translocation” nesting colonies, where the cahow — Bermuda’s national bird — had not nested since the 1620s, saw the first in nearly 400 years hatch in 2009 as a result of the pioneering translocation projects in 2004 to 2008 and 2013 to 2017.
These projects were led by Jeremy Madeiros, the chief terrestrial officer for the Department of Environment and Natural Resources, following on the work of David Wingate, Bermuda’s first government conservation officer who in 1951, at the age of 15, was part of a team that found the endemic Bermuda petrel, which had been thought extinct for centuries, nesting on islands in Castle Harbour.
Historically, based on decades of meticulous records kept by Mr Madeiros, the cahows have been known to return for nest building, courtship and mating for the month of November, go back to sea for December to feed and recharge whilst the female develops her single egg.
They return to land in early January for egg laying and the start of the two-month incubation process.
If all goes well, this is followed by the chick hatching in early March and fledging in late May or early June.
On October 14, a camera, the CahowCam1 which runs a live stream, recorded the earlier-than-expected arrival of what was confirmed to be a male from a well established resident pair, the earliest return on record to be logged by Mr Madeiros.
This was then followed by the early return of several other individual cahows and pairs throughout the colony, and the return of the CahowCam1 mate the night of October 21.
The season’s first video health check shot earlier that day can be viewed at youtu.be/8HoFfJ7e9Xc.
Mr Rouja said: “The longtime pair failed to fledge a chick last year due to a cracked egg, but were able to head back out to sea early and have had more time to recover and build up fat reserves, putting them in better condition for this coming season.
“They successfully fledge a chick roughly every other year, so hopefully this year will be a good one.”
He and Mr Madeiros were finally able to land on Green Island on November 21 for an assessment after Hurricane Melissa and confirmed that there was very little damage, with only one nest lid having been washed off.
Cahows usually arrive to Bermuda in November, return to sea in December and come back to land in January to lay their egg.
Jean-Pierre Rouja, founder of Nonsuch Expeditions, said: “This timing has evolved over millennia to be during the winter, as opposed to during the summer as in most bird species, and is theorised to have developed so as to avoid the hurricane season which runs from June through October. It also conveniently falls during the school year, so is perfect for our educational outreach purposes.
“More recently though, likely triggered by climate change, many of the cahows have been documented returning earlier and earlier in October, with this year’s October 14 return of the CahowCam1 male being the earliest on record.
“Whilst not as much of a concern for the Nonsuch Island colonies that were built 50-plus feet above sea level for this very reason, some of the burrows on the original nesting islands get completely overswept during hurricanes and are under major threat not only from physical damage to the concrete burrows, with concrete lids routinely being swept off, but even more of a concern when early returning birds overlap with late season hurricanes, as we faced when Melissa passed.
“In 2014, late season Hurricane Gonzalo impacted Bermuda with large ocean swells which overswept Green Island and drowned several cahows that had returned early and were already in their nests in late October.
“After a rather frustrating late summer/early fall, Bermuda has felt the effects of three near-miss hurricanes, Erin, Humberto and Imelda, but fortunately none of the cahows were back yet.”
Mr Rouja said as Hurricane Melissa passed Bermuda overnight as a Category 2 storm in late October, the accompanying swells were predicted to be as high as 35ft feet.
He added: “These, depending upon their direction, could have completely overswept the Green Island and Long Rock colonies which would have been a disaster, as many of the pairs on those islands were back and hunkered down in their nests.
“We can only hope that Melissa's path to the west of Bermuda reduced the size of its accompanying swells and surge, which generally are larger if a storm passes to the east or southeast of the island, but as the worst effects were predicted to be around midnight we were not able to document this.”
On October 29, a cahow also returned to the neighbouring CahowCam2 burrow where last season there was a paternity scandal after an interloping male spent a few days with the new resident female prior to the original male’s return.
To answer this question, Nonsuch Expeditions and the DENR are collaborating with BioQuest, CariGenetics’ conservation NGO spin-off, using blood work drawn with help from the Ettrick Animal Hospital, which the local CariGenetics Lab is using to produce a genetic paternity test to determine who the father is of the resulting chick.
The results are due to be announced during a presentation on December 3 at the Bermuda Underwater Exploration Institute discussing their “pioneering collaborative use of genomics in studying and protecting Bermuda’s signature critically endangered species” including the cahow, Bermuda cedar, and Bermuda skink.
• For updates, visit www.nonsuchisland.com/live-cahow-cam
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