Bermuda Petrel Pterodroma cahow

  • Order: Procellariiformes
  • Family: Procellariidae
  • Monotypic
  • Authors: Edward S. Brinkley and Kate Sutherland
Sections

Behavior

Behavior

Authors who wrote about Bermuda Petrel in the early days of European exploration and colonization of the New World used much poetic license, but many accounts point to an abundant, highly vocal, and very confiding bird—and one easily captured. Little was published about the species after 1620 and before the species' rediscovery in 1951, but the few who did write about Bermuda Petrel (e.g., Lefroy 1877, Verrill 1902, Bent 1922) had neither type specimen nor careful descriptions of plumage, voice, or behavior.

At sea, normally detected in flight; travels by sinusoidal arcing flight typical of small gadfly petrels, particularly during brisk winds (> 10 kts). Not attracted to ships. Presumably feeds by seizing prey at or just beneath the surface, as do other species of gadfly petrels, though direct observation of foraging Bermuda Petrels has not been reported. When not feeding, foraging, or flying, birds often rest on water; on rare occasions, individuals have been seen resting with other small gadfly petrel species. Birds waiting offshore of breeding islands occasionally gather in small rafts (2-6 individuals); these are thought to be nonbreeding subadults. Adults come to nest burrows only under the cover of darkness; subadults also return to breeding islets during hours of darkness, often vocalizing and practicing courtship flights.

Courtship in adults similar to other gadfly petrels: male and female duet in flight, calling (often antiphonally) while one pursues the other closely. Typically the male selects and prepares the nest site and entices female to inspect the site with him. Both adults spend most of December at sea, the female foraging heavily in preparation for egg-laying, which usually occurs in January.

Behavior at nest widely observed through public "nest-cams," broadcast via internet, and also by conservation officer and staff through tops of artificial burrows. Pair engages in some allopreening when both are at the nest. Female is fed by male when preparing to lay egg; both parents forage at sea to provide food for chick, which fledges by May or early June. Fledgling remains on its own for the last month or so, acquiring juvenile plumage (very similar to adults) and shedding natal down; older fledglings frequently sit at burrow entrance at darkness, appearing to observe the sky for long periods, and exercising wings. As in other gadfly petrels and other small tubenoses, fledgling departs burrow by itself.

Territoriality

Nests in burrows in loose colonies; territorial behavior not observed.

Sexual Behavior

Monogamous but will re-partner in the event of loss of mate or difficulties in reproducing. Courtship in adults similar to other gadfly petrels: male and female duet in flight, calling (often antiphonally) while one pursues the other closely.

Social and interspecific behavior

One of the chief threats to the survival of Bermuda Petrel in the twentieth century, and probably earlier, was its competition for nest sites with White-tailed Tropicbirds (Phaethon lepturus) (Wingate 1960, 1977; Fisher et al. 1969; Zimmerman 1975). In Bermuda, the tropicbirds return to nest in early spring, when Bermuda Petrel chicks are still several months away from fledging. When it was discovered that adult tropicbirds were killing and removing petrel chicks in order to utilize the nest site, biologists devised wooden baffles to cover the nest site entrance, with the smaller aperture preventing the slightly larger tropicbirds from accessing the nest sites. At sea, Captain J. B. P. Patteson has observed apparently antagonistic interactions between White-tailed Tropicbirds and small gadfly petrels, including Bermuda Petrels, on several occasions. Such interactions involved stooping and chasing in the air, but it is not clear whether attempted kleptoparasitism or some other behavior was involved (J. B. P. Patteson, in litt.). Tropicbirds and small gadfly petrels take similar prey species, so competition at sites where prey is concentrated may occur.

Predation

On Bermuda, Peregrine Falcons (Falco peregrinus) are annual visitors, mostly in autumn and early winter (Amos 1991), and David B. Wingate (in litt.) has documented multiple instances of predation of Bermuda Petrels by Peregrines. In December 1987, a Snowy Owl (Bubo scandiacus) reached Bermuda and took 5 Bermuda Petrels before being collected by Wingate (the heads and wings of these birds are in the collection of the Bermuda Aquarium, Museum, and Zoo). At sea, South Polar Skuas (Stercorarius maccormicki) have been observed pursuing and on at least two occasions eating Black-capped Petrels (Pterodroma hasitata) off North Carolina (Brinkley 1994; J. B. P. Patteson, in litt.); presumably, skuas also take smaller species of gadfly petrel as well.

Recommended Citation

Brinkley, E. S. and K. Sutherland (2017). Bermuda Petrel (Pterodroma cahow), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/nb.berpet.01