THE BIOLOGY OF AN ENDANGERED SPECIES, THE PARK-RUMPED PETREL (PTERODROMA PHAEOPYGIA), IN THE GALAPAGOS ISLANDS MICHAEL P. HARRIS Edward Grey Institute Botanic Garden Oxford, England The Hawaiian or Dark-romped Petrel (Pterod- species was far commoner and bred down to rcma phaeopygia) is restricted as a breeding 180 m, but these areas have now been cleared species to the Galapagos Archipelago (Pt. p. for agriculture. phaeopygia) and to <theHawaiian Archipelago On San Cristobal (= Chatham) the species (Pt. p. saruh&Amwis), but it is a common was reported as breeding by Leveque ( 1963) member of the avifauna of the tropical eastern and birds are still heard calling at night. There Pacific Ocean. As with most species of this is no information as to the numbers present large and widespread genus, little is known of or the breeding area, but as most of the high- its breeding biology. Loomis (1918) sum- lands have been cleared for cattle raising it is marized the scant data available at that time, unlikely that the island is a stronghold for the and LCv&que ( 1963,’ 1964) gave details of dis- species. tribution and some breeding information and San Salvador (= James or Santiago) is drew attention to conservation problems. Lar- thought by some of the local settlers to have son (1967) has recently given a few details the largest population of any of the islands. of breeding in Hawaii. Although this island has no resident human From November 1965 to July 1967 I was inhabitants, there are very large numbers of resident in the Galapagos, and in <thebreeding pigs which destroy the petrels and the tor- seasons of 1966 and 1967 was able to study a toises. small nesting colony of this species in the up- Local people on Floreana (= Charles) report lands of Santa Cruz ( = Indefatigable). After numbers of calling birds in the highlands, and I left, the latter seasons’ observations were it undoubtedly nests there. completed by Tj, de Vries and Miguel Castro. It is possible that the petrels nest on all five Little time was available for the work and the of the volcanos of Isabela (= Albemarle), but difficulties involved meant that many of the they have been reported regularly only from data were incomplete. However, because of Santo Tomas, where they have the local name the paucity of information on this genus and of “10s vaqueros” as they are most active at the unlikelihood of obtaining any better on about 94:09 when the cowboys are awakening this species in the immediate future, it is ad- (J. Gordillo, pers. comm.). Otherwise in the visable to place the details on record. Galapagos they are known as “pata pegada” (= foot stuck together, or webbed). During a DISTRIBUTION IN THE GALAPAGOS crossing of Volcan Alcedo in September 1966, In the Galapagos the Dark-rumped Petrel I spent two nights on the mountain and heard breeds only in the humid and thickly vegetated only a single petrel call in flight. However, uplands of the main islands (fig. 1). Nowhere D. Weber (pers. comm.) heard birds calling is it known to breed below about 180 m in early in the morning of 1 August 1967 and altitude. At least at present, it prefers thickly found an area suitable for nesting, but no vegetated areas with sufficient soil for burrow- actual nests, on the southeastern slopes. There ing, but it may possibly have been eliminated is no information relating to ’ Cerro Azul or in some other areas. The highlands of many Volc&n Darwin and Voldn Wolf. of the islands are unexplored, and knowledge Leveque ( 1963) cited Fernandina (= Nar- of the breeding distribution is fragmentary borough) as a breeding area but he never actu- and based largely on calling birds. ally visited the highlands. Roger Perry, who On Santa Cruz the first nest was recorded has been to the crater of Femandina on four by R. H. Beck in July 1906 in the forest on the occasions, has never seen the Dark-rumped northwest of the island at about 370 m (Loomis Petrels there, and the only record appears to 1918). The main nesting areas are, however, be a bird seen by A. Root and W. McCrory at on the south and southeastern parts of the dusk in July 1966. My visit to the summit was island above about 250 m. Formerly the in the first week of April, which would have The Condor, 72 :76-84, 1970 1761 BIOLOGY OF THE DARK-RUMPED PETREL 77 SANTA CRUZ SAbJ CI2kYTO~AL FLOREANA k5~6Ei-A q 92O 91° 90” FIGURE 1. Breeding colonies of the Dark-rumped Petrel in the Galhpagos. been too early for breeding birds, but there STATUS ON HAWAII are some rather restricted but suitable areas The species apparently once bred on Hawaii, for burrowing. Maui, Molokai, Oahu, Kauai, and Lanai but Marchena (= Bindloe) was mentioned by has been exterminated or drastically reduced Leveque (1963) as a possible breeding area, by mongooses, pigs and man ( Munro 1944). but a crossing of the island in December 1966 It is at present known to breed only on Maui showed it to be entirely unsuitable. I have no and Hawaii; it possibly also breeds on Kauai information on Pinta (= Abingdon) but it ap- and Molokai in small numbers (Richardson pears suitable for the species. and Woodside 1954; W. B. King, R. L. Walker, None of the other islands appears to be D. H. Woodside, pers. comm.). The popula- suitable for nesting, although petrels may visit tion in Haleakala Crater (Maui) probably them. For instance, I found the remains of numbers 100-1000 pairs (Larson 1967); an petrels killed by ,the Short-eared Owl (Asia undetermined number, but probably more flammeus galapagoensis) on Tower (= Geno- than on Maui, breed on Hawaii (W. B. King, vesa) and Cowley. In this connection it should pers. comm. ) . It is considered to be in danger be mentioned that on Plaza (off Santa Cruz) of extinction on all islands. on 19 September 1966, I found remains of a Wedge-tailed Shearwater (Puffinus pacificus) THE STUDY AREA which had been eaten by a Short-eared Owl. The colony observed was at the base of a This shearwater has not been previously re- weathered and overgrown parasitic tuff crater corded from the islands. known locally as Media-Luna or La Copa. At 78 MICHAEL P. HARRIS FIGURE 2. General view of the upper Mimnia zone at Media Luna, Santa Cruz. 560 m, this is at the upper limit of a vegetation earthen banks (fig. 3). A few nests were above zone of Miconia robinsonianu, a 1-3-m-tall en- the Miconiu zone in open areas. The burrows demic bush of the family Melastomaceae (fig. were as deep as 2 m but many were far shorter 2). During the breeding season the area is or ran parallel to the bank so that inspection almost permanently shrouded in mist. holes could be made into the nesting chamber. The majority of the nests were in the steep The nesting habitat is different from that of banks of a watercourse which is usually empty many Dark-rumped Petrels in Hawaii where or contains a mere trickle but which fills very some colonies occur in almost barren areas of infrequently in years of heavy rain when the lava and others in clearings in scrub thickets area would be unsuitable for nesting. The (Larson 1967). The birds there may have been vegetation of Miconiu bushes, the tree fern driven in recent years from the lower thickly Hemitelia multiflora, and bracken Pteridium vegetated areas, as Bryan (1908) found birds sp. is extremely dense and dripping with in habitats similar to those now used in Gala- water. A few nests were under boulders but pagos, or perhaps the remaining colonies are the majority were dug by the birds in the relicts. In 1967, outside the study area, Castro re- corded successful breeding by three pairs of Dark-rumped Petrels in a cave in Bellavista farmland at 180 m. Although soft soil was present, there was no burrowing and .the eggs were on the surface. In the study area, 80 occupied burrows were found in the two seasons combined, but only half of these were accessible. The whole rather scattered colony probably numbered about 120 pairs. During 1966 the colony was checked on 46 days between 21 May and 16 December, and in 1967 on 17 days from 8 May to 12 Decem- FIGURE 3. Nesting burrow of a Dark-rumped Petrel ber. The majority of nests were inspected in the steep bank of a rarely filled water course. at every visit, any young and some adults BIOLOGY OF THE DARK-RUMPED PETREL 79 TABLE 1. Weights (g) of adult Dark-rumped Petrels. Local settlers in the highlands report that the birds are usually first heard calling, ap- z Range SD II parently as they first return to land, at the end Before laying 10 385 350-470 34.5 of April. The first records I have for the two $ d incubating 16 430 380-500 28.9 seasons were 5 May 1966 and 23 April 1967, 365480 32.5 0 9 incubating” 8 429 but birds were heard calling on Floreana on Unsexed incubating 16 425 380-490 29.2 15 March 1968 and on San Salvador on 4 April With large young 1 345 1968 (Sr. Cruz, R. Perry, and T. de Vries, pers. Failed breeders 15 375 350410 16.8 comm. ) . This calling continued until mid- * Not including two birds (330, 385 g) which had just laid. September but was most intense from May to July.