Zino's petrel (Pterodroma madeira) or the freira, is a species of small seabird in the gadfly petrel genus, endemic to the island of Madeira. This long-winged petrel has a grey back and wings, with a dark "W" marking across the wings, and a grey upper tail. The undersides of the wings are blackish apart from a triangle of white at the front edge near the body, and the belly is white with grey flanks. It is very similar in appearance to the slightly larger Fea's petrel, and separating these two Macaronesian species at sea is very challenging. It was formerly considered to be a subspecies of the soft-plumaged petrel, P. mollis, but they are not closely related, and Zino's was raised to the status of a species because of differences in morphology, calls, breeding behaviour and mitochondrial DNA. It is one of Europe's most endangered seabirds, with breeding areas restricted to a few ledges high in the central mountains of Madeira.
Zino's petrel nests in burrows which are visited only at night, when they give their haunting calls. The single white egg is incubated by both adults, one sitting during the day while the other feeds on fish and squid at sea. Eggs, chicks and adults have been subject to predation by introduced cats and rats, and in the past have been taken for food by local shepherds. Predator control, and other measures such as the removal of grazing animals that trample the burrows, have enabled the population to recover to 65–80 breeding pairs; the species remains listed as endangered on the IUCN Red List. However, conservation efforts had a major setback in August 2010 when fires killed three adults and 65 percent of the chicks. The population eventually recovered and was stable at 160 individuals by 2018.
Taxonomy
The gadfly petrels in the genus Pterodroma are seabirds of temperate and tropical oceans. Many are little-known, and their often similar appearance have caused the taxonomy of the group to be rather fluid. The forms breeding in Macaronesia on Madeira, Bugio in the Desertas Islands, and in the Cape Verde archipelago were long considered to be subspecies of the Southern Hemisphere soft-plumaged petrel, P. mollis, but mitochondrial DNA analysis, and differences in size, vocalisations, breeding behaviour, showed that the northern birds are not closely related to P. mollis, and the species split was accepted by the Association of European Rarities Committees (AERC) in 2003.
Nunn and Zino estimated that the two Macaronesian species diverged at the end of the Early Pleistocene, 850,000 years ago.
The petrels breeding in the high central mountains of Madeira were first recorded in 1903 by German naturalist and priest Ernst Johann Schmitz, who failed to realise that they were different from the Fea's petrels he had seen in the Desertas. The species was formally described as a race of soft-plumaged petrel by Australian amateur ornithologist Gregory Mathews in 1934. Following the recognition of the Madeiran birds as a full species, they were named after the British ornithologist, Paul Alexander Zino, who was instrumental in their conservation during the latter half of the twentieth century. The genus name Pterodroma is derived from Greek πτερον, pteron, "a wing", and δρομος, dromos, "running", and refers to the bird's swift erratic flight. The specific madeira refers to the island on which it breeds. The Portuguese name Freira means "nun"; the inhabitants of Curral das Freiras (Nun's Valley) near the breeding site claimed that the nocturnal wailing of the petrels in the breeding season were the calls of the suffering souls of the nuns. The sisters had taken refuge in the valley from attacks on the island by French pirates in 1566 that lasted for 15 days.
Pterodroma petrel remains dated between 60,000 and 25,000 years BP were found in two cave sites in Gibraltar. They consist of a more abundant form similar in size to Zino's, and a larger, less common type. It is uncertain whether they represent the site of a former breeding colony, or are the result of a seabird wreck in which storms blow birds inland. They do suggest, however, that members of the genus were formerly more widespread.
Description
thumb|Illustration of species
This long-winged petrel is long with an , It has a grey , grey wings with a dark "W" marking across them, and a grey upper tail. The undersides of the wings are blackish, apart from a triangle of white at the front edge near the body, and the is white with grey . The head has a mottled whitish-brown , a dark cap, and a dark spot below and behind the brown eye. The is black and the legs are flesh pink, the colour continuing onto the first third of the feet, the rest of the toes and webs being black-brown. It gives the general impression of a small Cory's or great shearwater, with a fast flight; in strong winds it shears high above the surface with angled wings.
This species at its breeding sites gives a long mournful call like the hooting of a tawny owl, and a much less frequent sound like the whimpering of a pup. It is silent at sea.
"Snowy-winged petrel"
The Hadoram Shirihai expeditions to the Madeira archipelago in 2008, 2009, and 2010 each had sightings of a Pterodroma petrel (possibly the same bird) with largely white underwings, but upper wings like Zino's or Fea's. This plumage does not correspond to any known Pterodroma species. It may have been an unusual variant of Zino's but this is unlikely since no similar bird has been seen amongst the more than 100 caught at the nest. It may alternatively be a single aberrant individual, a hybrid or an unknown taxon from Madeira or elsewhere. No conclusion is possible on current knowledge. It nests at heights above . It was formerly more widespread, since subfossil remains have been found in a cave in eastern Madeira, and on nearby Porto Santo Island. The breeding ledges have to be inaccessible to introduced goats so that they remain rich in endemic flora. The vegetation ensures that there is sufficient earth on the ledges to allow the birds to burrow and make their nests, and trampling by grazing animals reduces the soil cover. Birds identified as either Zino's or Fea's have been recorded from both sides of the North Atlantic, and in Ireland and Britain there has been a large increase in the number of reports, perhaps because global warming brings increasing numbers of tropical species into temperate waters. The timing of the reports, mainly in late spring and summer in the western North Atlantic, and in late summer and early autumn in the east, has suggested that birds follow a clockwise route around the North Atlantic after leaving their breeding sites. However, the few birds that have been identified with certainty have all been Fea's.
Feeding
Zino's petrel, like its relatives, feed on small squid and fish. The vomited stomach contents of one bird contained cephalopods, the bioluminiscent fish Electrona risso and small crustaceans.
Predators and parasites
Their nocturnal approach to the breeding sites means that Zino's petrels avoid the attentions of gulls or diurnal raptors, and the only owl on the island, the barn owl, is a rodent hunter. Other than bats, there are no native land mammals on Madeira, although there are a number of introduced species, two of which will take birds or chicks. These are brown rats and feral domestic cats. Even the high mountain nest sites of the Zino's petrel are not safe from these adaptable predators, ten adults being killed by cats in 1990. Feather lice found on Zino's petrels include Trabeculus schillingi, Saemundssonia species and an unnamed species of Halipeurus.
Conservation status
Zino's petrel has a very restricted range on the mountaintops of a single island and is one of Europe's most endangered seabirds. The birds, already confined to a limited area when discovered, were thought to be extinct by the mid-twentieth century. By 2018, the colony had recovered and was stable at 160 adults.