Most avian brood parasites reproduce by laying eggs in nests of other species (e.g., Hamilton and Orians 1965, Payne 1977), but some may lay in nests of conspecifics. Intraspecific brood parasitism has been reported for over 50 species of birds, mostly ducks (YomTov 1980). For passerines, however, intraspecific brood parasitism has been reported far less frequently, although several well-documented cases do exist (see Yom-Tov et al. 1974, Manwell and Baker 1975). In this note we provide the first evidence for intraspecific brood parasitism in a small, cavity-nesting passerine, the House Wren, Troglodytes aedon. Between 1984 and 1987 we conducted a study of the House Wren breeding ecology in Presqu'ille Provincial Park (hereafter the Park) and in the Mer Bleue Bog (hereafter the Bog) near Ottawa, Ontario (description of these study sites can be found elsewhere; Belles-Isles and Picman 1986a, Belles-Isles 1987). In the 4 years of this study we have made observations on a total of 123 nests and obtained evidence for five probable cases (about 4% of the total) of intraspecific parasitic egg laying. Because we could find no previous reports of intraspecific brood parasitism for this species, below we provide a description of these cases. Cases 1, 2, and 3-Appearance of two eggs per day. First, late in June 1985, we found a nest in the Park, where three eggs were laid in two consecutive days. The final clutch laid in this nest consisted of seven eggs and of these six young fledged. Second, in 1986 in the Bog we recorded a case where the first egg was laid on 22 June, and 4 days later (on 26 June) the nest contained six eggs. The further breeding history of this nest is not known. Third, in one House Wren nest that was under observation in the Bog, six eggs were laid between 16 June and 19 June 1987. This nest successfully fledged all six young. Since passerines normally lay only one egg per day, the appearance of more than one egg per day can be used as evidence for parasitic laying (see Yom-Tov 1980). Case 4-Appearance of a new egg after completion of the clutch. In May/June 1986, we observed the irregular appearance of an egg in a House Wren nest located in the Bog. In this nest seven eggs were laid between 20 and 26 May. During the next visit on 31 May the nest still contained seven eggs. However, on 2 June, we discovered a new egg near the entrance of the nest box. This nest eventually fledged seven young. The irregular time interval between laying of the seventh egg and the last egg, along with an unusual location of the last egg at the box entrance away from the nest depression, strongly suggest that the last egg was laid by a parasitic female. Case 5-Abnormally large clutch. On 25 June 1987, in one of the boxes used for breeding by House Wrens in the Bog, we found a clutch consisting of nine eggs. Most House Wrens in our study areas, however, laid between four and seven eggs (for 1984 to 1987 mean clutch size ? 99% CI = 6.1 ? 0.2; n = 123). The abnormally large clutch in this case thus suggests parasitic laying by another female. The five above cases provide strong evidence for intraspecific nest parasitism in the House Wren, although this mode of reproduction appears to be infrequent (about 4%) in our wren populations. However, ' Received 28 October 1987. Final acceptance 4 January 1988. 2 Present address: Departement de Biologie, Universite Laval, St. Foy, Quebec GIK 7P4, Canada. SHORT COMMUNICATIONS 513