Jeremy Madeiros: Checks of nest burrows of Bermuda's critically endangered national bird, the Cahow or Bermuda petrel (Pterodroma cahow) have been carried out all through the month of January, after the birds returned from their 5-week pre-egg-laying exodus, during which they return to the open ocean during the month of December, to feed intensively. This follows the courtship and nest-building phase of the Cahow breeding season in late October and November, when the breeding pairs return from 5 months apart out to sea during the summer months. During the December exodus period, the female develops her single large egg, while the male bird packs on extra weight and fat deposits, to enable him to carry out the majority of incubation duties.
The male birds usually return first at the very beginning of January, so that they are waiting when the females return, usually laying their egg only 1 to 2 hours after their arrival. Although it can vary between individual nesting pairs, usually the female will return to sea again within a day or two, to recover after laying the egg which can weigh 20% to 25% of her body mass. The male will then take the first long incubation "shift", which can be up to 10 - 15 days in length, after which the female returns and the pair starts to alternate shifts every 5 days or so for the remainder of the 53–55-day incubation period.
During the incubation period in January and February, I will try to visit all accessible Cahow nests to carry out checks of body weight, band numbers and sex of the incubating adult birds, as well as weighing and measuring the eggs and using a technique called "candling", where a bright light is used to determine whether the egg is fertile and has a visible embryo, and the age and stage of development of the embryo, and make sure that it is developing normally. This technique has been taught to me by Carla Marquardt, who has had years of experience working with Parrots and Macaws at captive breeding facilities in Florida and accompanies us during this period when her schedule allows.
The pair in the CahowCam 1 nest (nest no. R831) returned first, with the male bird returning at 3am on January 7th 2025, followed by his mate in the evening, which returned at 7pm, laying her egg by 8.11pm. By the 13th January, I carried out a check of this nest which confirmed that the egg was fertile, but it unfortunately had a fairly large "dimple" where the shell has been pushed in. When I checked again with Carla on 18th January, the embryo was still alive, and Carla covered the dimple with clear nail polish, which reduces moisture loss and can sometimes help the egg to finish development and hatch. However, when I checked the egg again with JP Rouja on Sunday, 26th January 2025, the dimple had become larger and the embryo had failed, so we will unfortunately not be seeing a chick in this nest for 2025. This continues this pairs history of producing chicks successfully every other year, as they fledged a robust chick, named "Vega", in 2024.
Things look much more hopeful in the CahowCam 2 nest (nest no. R832), where the male bird "Sampson" had nested with the same mate (named "Susie") since 2010, producing 12 chicks in 14 years. Susie however failed to return for 2023, and is presumed to have died out at sea, cause unknown. However, by 2024, Sampson had attracted a new younger mate, and as is usual with a first-time breeder, her first egg that year was undersized and infertile. Hope is therefore high that her second egg this year would be viable, and after the male had returned around the 10th January, we waited with some anxiety for the return of his new mate. She finally returned on the 17th January and laid a larger-than-average egg. When we checked this egg on the 26th January, it was with relief that we were able to confirm that the egg was fertile and contained a normally developing embryo. We will continue to check periodically on the development of the embryo, which if all goes well, will hopefully hatch sometime between the 9th - 14th March.
UPDATE: Februay 16th J-P Rouja: The CahowCam2 egg as of last check was still fertile with the parents dutifully incubating as can be watched LIVE here, however, the failed egg in CahowCam1 remained intact until February 3rd when one of our volunteers noticed that it seemed to be stuck to the belly of the incubating parent. The weather was not allowing Jeremy and I to get out to Nonsuch at the time, however fortunately, the side/profle view given by Cam1 allowed us to determine that the egg was mostly intact but must have ruptured and leaked through the dimple and then dried and stuck to the parent’s belly feathers. It proceeded to keep incubating and drag it around the nest, including when its mate returned, and then eventually flew out to sea where we assume it bathed and washed it off before returning without it a few days later, all of which was documented by the Cam and can be seen in the attached video.
Failed egg still attached to parent on Feb 3rd
As Jeremy has observed in the past and has now been confirmed by the CahowCam live feeds over the past decade, when an egg fails the parents do not immediately abandon it and the nest. In some cases, the egg will remain intact for several weeks until it eventually explodes and the parents will dutifully keep “incubating” it throughout. One might think that they simply did not know it had failed, however as has been observed in the case of CahowCam1 this season, even after obvious failure and its’ removal from the nest, they will stay on and keep “incubating” the failed egg/empty nest.
As of this writing on February 16th they are both back in the nest today and are continuing to go through the motions of incubating, though there have now been periods where our viewers have observed an empty nest, which will become the norm once they fully abandon it for the season. They will then head out to sea and return to try again in late October, and as Jeremy has observed, pairs with failed eggs, which do not need to keep incubating and then feeding their chick until late May / early June, will have had more time out at sea to fatten up, and generally return heavier and in better health for the next season.
So for this season lets keep watching CahowCam1, whilst the remainder of the Colony is on track for another great year.