During a stay on Middleton Island (59°29’N, 146°28’W, 7x2 km in size, some 120 km south of mainland Alaska) in the Gulf of Alaska in 2005, the nest of the sole pair of Northern Harrier on the island was located during the early chick stage. Although a second male roamed the island for some time, this individual was not seen anymore after 21 May. By erecting poles near the nest (hence providing sitting- and plucking posts) and frequent nest visits, diet and breeding performance were recorded. The nest contained six downy chicks of 1-11 days old on 23 June, of which four fledged (after 17 July). The male provided most of the food throughout the nestling stage, but as he apparently disappeared from the island after 15 July, the female took over and intensified her hunting effort from then on, essentially covering the same home range as the male’s (a radius of about 3 km, i.e. covering about 60% of the island). By 19 August, when the author departed from the island, the chicks were still present. The diet is described by means of prey remains, pluckings and pellets found underneath sitting posts and on the nest (Table 1). The absence of mice and voles on Middleton Island is reflected in a diet composed by small birds and Rabbits Oryctolagus cuniculus. Passerines dominated the diet during the nestling period, mainly Savannah Sparrow Passerculus sandwichensis (and to a smaller extent Fox Sparrow Passerella iliaca and Common Snipe Gallinago gallinago). These were almost exclusively captured by the male. After the female started hunting, from fledging onwards, Rabbits started to become a major portion of the diet (Table 1). As the local Rabbits produced at least three litters year-1, this prey species may play a key role in the breeding success of Northern Harriers on Middleton Islands. Rabbits were supposedly introduced on Middleton Island in 1952.