Breeding of the Leachos Petrel Oceanodroma leucorhoa in the Rgst archipelago, northernNorway TYCHO ANKER-NILSSEN AND PER G. ANKER-NILSSEN Anker-Nilssen, T. & Anker-Nilssen, P. G. 1993.Breeding of the Leach's PetrelOcea- nodroma leucorhoa in the Rost archipelago,northern Norway. Fauna norv. Ser. C, Cinclus I6: 19-24. On29 August 1989, a Leach's Petrel nest was found in a Puffin burrow 80 m abovesea level on the island of Hernykenin the municipality of Rost, county of Nordland. The nestcontained an egg and two adult birds and was locatedat night by provoking the birdsto respond vocallyto a tape-lure. This is the first confirmed breeding recordof the species in Norway. Various evidence indicates that significantnumbers of Leach's Petrels breed in the upper slopes of the five highestislands in the Rost archipelago. During 1964-1992, 389 Leach'swere ringed at Rost. Most birds were caught in mist-nets with the use of tape-lures, which wereintroduced in 1983. Ringingdata, as well asobservations made at Hernyken and at sea off Rsst, indicate that the Leach's is a far less abundant breeder than the Storm Petrelat Rgst. Tycho Anker-Nilssen, Norwegian Institute for Nature Research, Tungasletta 2, N-7005 Trondheim,Norway. Per Anker-Nilssen, Erling Skjalgssonsgt. l6 A, N-0267 Oslo, Norway. INTRODUCTION The Leach's Petrel (Leach's Storm-petrel) Oceanodroma leucorhoa is widely distri- buted in the Pacific and Atlantic Oceans. with the largest populations breeding in Newfoundland and Alaska and one largeco- lony in Japan (Croxall et al. 1984,Sklepko- vych & Montevecchi 1989). The world popu- lation is in the orderof 10-15 million pairs, of which only about l% or lessare found in Europe. Most of the known European po- pulationbreeds in Scotland where7 colonies have been discovered, but breeding has also been confirmedin NW lreland, Icelandand the Faeroelslands(e.g. Cramp & Simmons 1977 , Lloyd et al. l99l ). Sincethe early 1960s, it hasbeenassumed that the two Hydrobatidae species found in Norwegian coastalwaters breed in seabird colonieswithin the Rost archipelago in the county of Nordland. On 10-11 August 1961, Helling (1962)caught both the Leach's Petrel and the Storm PetrelHydrobates pela- gicus in burrows on Trenyken (67'26'N 11o53'E), one of the five major bird cliffs in Rost (Fig. 1). Since then, breeding of the Storm Petrel at Rgst has been documented repeatedlyon the neightbouringisland of Hernyken (67'26'N I1"52'E), both indi- rectly (e.g. by the mist-nettingin August of Fauna nory. Ser. C, CinclusI6: 19-24. Oslo 1993. adultslaying eggs while kept shortly for rin- ging, and in November-December of adults and newly fledged young) and directly by observing adult birds sittingon the nest or by hearingthe begging calls of a chick (G. Lid and others, pers.comm.). Farther north, the z b o N @ Rsst 0 1 2 3 km / o0 ^ 4?.JQ "r*t4slo -,4 n "^ 7 n" 6rp veaovffp ,.1 o 6 (,f stoti"a"t 4 Eilelsnyken " OTrenyken Ob Hernyken Dv o Skomver ffi -{/ Nortn 'U Norway 11"50'E 1r00'E 1 2"1 0'E Fig. 1. Map of Rost, showingthe locations of the five highest islands(which are the major bird cliffs of the acrhipelago) and the much lower island of Skomvrer (which has a famouslighthouse). T9