Zino’s Petrel, Pterodroma Madeira
The Zino’s Petrel (Pterodroma madeira) is a little seabird in the gadfly petrel genus which is 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 except for a white triangle at the front edge near the body, and the belly is white with grey flanks. It’s very similar in appearance to the slightly larger Fea’s Petrel, and separating these two Macaronesian species at sea is very difficult. Zino’s Petrel was formerly considered to be a subspecies of the Soft-plumaged Petrel, P. mollis, but they aren’t closely related, and Zino’s was raised to species status because of the differences in morphology, calls, breeding behavior and mitochondrial DNA. Its Europe’s most endangered seabird, with breeding areas restricted to a few ledges high in the central mountains of Madeira.
This bird nests in burrows which are visited only at night, to the accompaniment of their haunting calls. A 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 victimized by 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 which trample the burrows, has given the population a chance to recover to 65 to 80 breeding pairs; it remains Endangered on the IUCN Red List. However, conservation efforts had a major setback in August 2010 when fires killed three adults and 65% of the chicks.
The gadfly petrels in the genus Pterodroma are seabirds of tropical and temperate oceans. Many are little known and their often similar appearance has caused the taxonomy of the group to be fairly fluid. The forms breeding in Macaronesia on Madeira, Bugio in the Desertas Islands, and in the Cape Verde archipelago were long believed to be subspecies of the Southern Hemisphere Soft-plumaged Petrel, P. mollis, but mitochondrial DNA analysis, and difference in size, vocalizations and breeding behavior showed that the northern birds weren’t closely related to P. mollis, and that the Bermuda Petrel or Cahow may be the closest relative of the Macaronesian birds. Sangster suggested establishing Zino’s Petrel on Madeira and Fea’s Petrel on the Desertas and Cape Verde as full species, and the species separation was accepted by the Association of European Rarities Committees (AERC) in 2003.
Nunn and Zino estimated that the two Macaronesian species drifted apart at the end of the Early Pleistocene, 850,000 years ago. An analysis of feather lice taken from Fea’s Petrels, Pterodroma feae deserti, from Bugio Island, and from Zino’s Petrels from the Madeiran mainland displayed that there were marked differences between the two seabirds in terms of the parasites they carried, suggesting that they have long been isolated, since lice can normally only be transferred through physical contact in the nest. The species of Zino’s petrel are most similar to those of the Bermuda Petrel, whereas Fea’s Petrel’s lice are similar to those of Caribbean and Pacific Pterodroma species. This suggests that despite the close physical proximity of the two species of gadfly petrel found in the Madeiran archipelago, they might have arisen from separate colonization’s of mainland Madeira and, later, the Desertas Islands. Although their reproductive isolation permitted separate evolutionary development of the two species, genetic evidence shows the three Macaronesian petrels are each other’s closest relatives.
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 realize that they were different from the Fea’s Petrels he had seen in the Desertas. The species was formerly 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 Portuguese ornithologist, Paul Alexander Zino, who was active in their conservation during the latter half of the 20th century. The genus name Pterodroma comes from the greek “pteron”, meaning “a wing” and dromos, meaning “running”, and it 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 (Nuns Valley) near the breeding site claimed that the nocturnal wailing of the petrels during 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 stays dated at 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 is the product of a seabird wreck in which storms blow birds inland. They do suggest, however, that members of the genus were formerly more widespread.
Zino’s Petrel is a long-winged bird averaging at 12.5 to 13.4 inches long, 31 to 34 inch wingspan and 290 grams. Its grey back contains grey wings with a dark “W” marking across them and has a grey tail. The undersides of the wings are blackish except for a white triangle shape at the front edge near the body and the belly is white with grey flanks. The head has a spotty whitish-brown forehead, a dark cap, and a dark spot below and behind the brown eye. The legs are a flesh-pink, the color continuing into the first third of the feet, the rest of the toes and webs are black-brown and the bill is black. It gives the general impression of a small Cory’s or Great Shearwater, with a speedy flight; in powerful winds it shears high above the surface with angled wings. Nothing is known about the fresh juvenile plumage or the moult sequence, and aging birds is currently not practicable.
This species is much like the Fea’s Petrel appearance, but smaller. The size difference and lighter flight may not be evident at sea, especially with lone birds, but a recent study helped to explain other useful features. Zino’s has a diagnostically small, delicate, often rather long and slender bill, which may be noticeable in the most slender-billed examples, which are probably mostly females, but can be difficult to establish in larger billed, probably male, birds. Another useful attribute is a large whitish panel on the underwing. The wing panel is exclusive to Zino’s but it’s only shown by about 15% of the birds. Zino’s has a more rounded wing tip, but P. feae deserti sometimes shows a rounded wing tip as well, so this feature isn’t diagnostic. Previously suggested criteria such as head, upper wing, and flank patterns were found to be proving nothing. Off the eastern United States and the Azores, both Macaronesian petrels are set apart from the larger Bermuda Petrel by that species’ upperparts, which are uniformly dark but for a pale grey rump.
This species at its breeding sites gives a long mournful call much like the hooting of a Tawny Owl, and a much less frequent sound like the whimpering of a pup. It is silent at sea. The breeding calls are much similar to that of a Fea’s Petrel, and Bretagnolle’s analysis of the calls of the Soft-plumaged Petrel complex led him to suggest in 1995 only a two-way species split, with the northern forms Madeira, feae and deserti all as subspecies of Fea’s 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 large white underwings, but upper wings like Zino’s or Fea’s. This wing coloration does not correspond to any known Pterodroma species. It might have been an unusual variant of Zino’s but it is unlikely since no similar bird has been seen amongst the more than 100 caught at the nest. It may otherwise be a single aberrant individual, a hybrid or an unknown taxon from Madeira or somewhere else. No conclusion is potential on current knowledge.
Zino’s Petrel is endemic to the main island of Madeira, where it breeds on inaccessible and well-vegetated ledges within the central mountains between Pico do Areerio and Pico Ruivo. The usual ledge plants are endemic hemicryptophytess and Chamaephytes, but grasses may also be there. It nests at heights above 5400 ft. It was previously more widespread, since sub fossil remains have been found in a cave in eastern Madeira, and on nearby Porto Santo Island. The breeding ledges need to be inaccessible to introduced goats so that they remain rich in endemic flora. The vegetation makes sure that there is sufficient earth on the edges to allow the birds to burrow and make their nests, and trampling by grazing animals reduces the soil cover.
The petrel is only in attendance in Madeiran waters during the breeding season. Its distribution at sea during the rest of the year is poorly known because of the rarity of the species and how hard it is to separate it from other Pterodroma petrels at sea. Birds identified as either Fea’s or Zino’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, maybe because global warming brings increasing numbers of tropical species into temperate waters. The timing of the reports, mainly in late spring and summer within the western North Atlantic, and in late summer and early autumn in the east, has suggested that birds keep to a clockwise route around the North Atlantic after departing from their breeding sites. However, the few birds that have been identified with assurance have all been Fea’s. Zino’s Petrel may have a similar strategy, since initial results from geolocation studies suggest widespread dispersal over the North Atlantic central ridge during the breeding season, and migration towards the Brazilian coast during the non-breeding period. Pterodroma petrels have been recorded in the Canary Islands and the Azores on surprisingly few occurrences; a claim of possible Zino’s from South Africa is now thought to be mistaken.
Zino’s petrel breeds two months before the Fea’s Petrel on Bugio, only 30 mi away. The birds return from the sea to breeding grounds in late March or early April and courting takes place over the main breeding area during the late evening and early morning hours. The nest is a shallow burrow or an old rabbit tunnel up to 55 inches long in thick soil on vegetated ledges. The length of the burrow is related to the age of the pair that utilizes it, young birds making shorter tunnels, which are extended in following years. The oval white egg is laid from mid-May to mid-June in a chamber at the end of the burrow and incubated for 51 to 54 days, with each parent alternating between sitting on the nest and feeding at sea. The young fledge after about 85 days in late September and October. This petrel is strictly nocturnal at the breeding sites in order to avoid predation by gulls. It remains 2 to 3 miles off shore during the day, coming to land in darkness. It calls from about 30 minutes after nightfall until dawn, including moonlight nights.
This species mates for life, and pairs return to the same burrow each year. The single white egg does not get replaced if it is lost. This is a long-lived species: one bird has returned to its burrow for 10 uninterrupted years, and the lifespan is expected to be about 16 years. The age of first breeding is not known, but it is assumed to be 4 or more years. In spite of the proximity of the breeding sites, Zino’s and Fea’s Petrels have never been found at each other’s nesting areas, and Zino’s is not known to hybridize with any other species.
Zino’s Petrel, just like its relatives, feeds on small fish and squid. The vomited stomach contents of one bird consisted of cephalopods, the bioluminescent fish Electrona risso and small crustaceans. Similar to other small petrels, Zino’s does not normally follow ships.
Their nocturnal approach towards breeding sites means that Zino’s Petrels avoids the attentions of gulls or diurnal raptors, and the only owl on the island, the Barn Owl is a rodent hunter. Other than the bats, there are no native land mammals on Madeira, although there are a number of introduced species, two of which will take the birds or chicks. These are Brown Rats and feral domestic cats. Even the high mountain nest sites of the Zino’s Petrel are unsafe 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.
Zeno’s Petrel has a very restricted range on the mountaintops of a single island, and it is the most endangered European seabird. The birds, already confined to a limited area when discovered, came to be extinct by the mid-20th century. Two freshly fledged juveniles were found within the walls of the governor’s palace in Funchal during the early 1940s, seemingly because they are attracted there by the lights, but the species wasn’t seen again until 1969. In 1969, Paul Zino played a tape of Fea’s Petrel from Bugio to a shepherd from Curral das Freiras; he instantaneously recognized the call, and led the researches to the remaining nesting area. Predation by introduced rats meant that breeding success in the tiny population was low, and no young at all fledged in 1985. The Freira Conservation Project was established in 1986 with the intention of increasing the population of Zino’s Petrel by controlling rats and human interference; the control was extended to cats after the mass predation of 1990.
There are now 130 to 160 known individuals (65 to 80 breeding pairs) incorrigible to breed on just six ledges. There may be some disturbance from visitors at night and from the construction of NATO radar station on the summit of Mt. Areerio, and in the longer term climate change might have an unpleasant effect, since all nests are within 3250 ft of the top of the highest mountain within the breeding area. Formerly, shepherds collected nestlings for food, and egg collectors have ransacked burrows. Currently, the main threats continue to be predation of eggs and chicks by rats, and of nesting adults by feral cats, although at much reduced levels because of trapping.
Zeno’s Petrel is protected under the EU’s Wild Birds Directive, and their breeding sites lie within the Parque Natural da Madeira national park. Following the purchase of about 740 acres of land around the main breeding site, all livestock has been removed from breeding areas, allowing the vegetation to recover, although breeding still only occurs on ledges that were never accessible by grazing animals. The research and predator control by the Freira Conservation Project and the nation park which began in 1986 was expanded in 2001 with added EU funding. The increase in productivity (29 chicks fledged in 2004) meant that this species was downgraded from Critically Endangered to Endangered on the IUCN Red List in 2004. Its population seemed to be stable or increasing slightly up to the summer of 2010.
A disaster hit the colony on August 13, 2012, when a forest fire swept through the breeding site killing three adults and 25 of the 38 chicks. The fire demolished the vegetation and several nesting burrows. Conservation action to protect the 13 remaining chicks included removing dead birds and burnt vegetation, reinforcing the surviving nests, and setting poison bait for rats around the now bare nest sites. In the longer term, the action plan includes the provision of artificial burrows, seed dispersal to aid in vegetation recovery, and the use of anti-erosion materials.
Image Caption: Watercolor pencil sketch of Zino’s Petrel, Pterodroma madeira. Credit: Jimfbleak/Wikipedia (CC BY-SA 3.0)