The Bermuda petrel (Cahow) chick continues to grow and experience all of the challenges that a young petrel chick must go through during the course of its long, 3-month or more development period.
After hatching on March 2nd, the chick was fed by both the female parent on the 6th March, and the male parent, just after hatching and again in the pre-dawn hours of 8th March.
The following week was the period leading up to the full moon, when parental feeding visits often drop off as the extra light discourages the Cahows, which are nocturnal over the breeding grounds, from visiting the nests. As a result, the chick was not visited or fed for 6 days, until the female parent finally returned to the nest in the predawn hours of March 14th, under cover of cloudy, stormy weather, staying over for the day in the nest burrow with the chick and feeding it at least 4 separate times.
Although many viewers have expressed concern about the length of time that the chick was left on its own, this is completely normal for the Cahow and chicks can be on their own for a week or more between visits, with no lasting ill effects.
Cahow chicks, like those of other seabirds in the tubenose seabird family, which includes Albatrosses, Shearwaters and Petrels, are precocious, or quite highly developed when they hatch (which is one of the reasons the egg incubation period is so long), and are equipped with coats of long, dense down which enable them to keep warm and survive on their own in cold, damp underground burrows without needing the adults after the first 2 or 3 days.
The adults indeed have to spend almost all of their time out at sea finding enough food, or the chick will starve. These chicks take about 3 months (about 90 days) to fully develop, and then fledge to sea on their own, with no parental help or instruction. They then must learn to survive, find and catch food, out on the open ocean on their own, in about a 10-day period after fledging before their own fat reserves are exhausted , or they will not survive. Life for the Cahow is not easy, and it is a testament to what tough survivors they are, that they not only survive in one of the toughest environments on Earth (the open ocean), but are also recovering (with a bit of assistance!) from what can only be described as the very edge of extinction.
After the full moon on the 12th of March, we expected to see an increase in adult feeding visits, and that was just what happened. The female parent visiting on the 14th, 17th, 21st and 22nd March, a couple of times staying over the next day with the chick in the nest, while the male adult has visited on the 15th and 20th March.
It appears that the female has located a prey-rich foraging area much closer to the island and so has a shorter return time, while the male is going much further away to gather food on a approximate 5-day rotation.
This male had been fitted with a geolocator tag for 2 years back in 2009-2010, and we know he generally travelled well away from Bermuda, ranging from just south of Nova Scotia to 1500 miles northeast of Bermuda (two-thirds of the way to the Azores Islands!), so I suspect that is the approximate area where he is going now.
All of these feeding visits have enabled the chick to increase rapidly in weight, from just 52 grams on March 13th, to 153 grams just 2 days later on March 15th, and to 192 grams on March 22nd.
This increase/decrease in the chick's weight as it develops is a normal part of it's development, and I expect we will see another temporary decrease in the next full moon period, approximately the 5th to 11th April. However, stormy and cloudy weather may also enable the adults to sneak in, so you never can tell. If the chick continues to develop normally and is adequately fed by the adults, we can expect to see its weight increase to 300 grams or more by the end of April. The current record peak weight for a Cahow chick was 557 grams, almost double the weight of an adult! More normal peak weights for chicks however range from 330-430 grams, and last year's CahowCam chick reached a peak weight of 435 grams on May 18th. After reaching their peak weights, feeding visits by the adults become fewer and the chick completes its development using its fat reserves accumulated earlier in their growth, going through a "slimming down" period before fledging to the open ocean at a normal weight range of 250 - 300 grams.
UPDATE March 26th: The weight of the R831 chick today (Sunday March 26th) was 151 grams, while the wing chord was 40mm. By comparison, on Wednesday (March 22nd), the weight was 192 grams, while the wing chord was 32mm. The most advanced chick on Nonsuch (in the R821 burrow) was 247 grams today with a wing chord of 50mm.