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Acknowledgements Oliphant, L. W 1985. North I would like to thank Allan Harris American Merlin Breeding and Barry Atkinson for helping Survey. Raptor Research 19(2/ with the survey, Derek Parkinson 3):37-41. and Bill Climie for the Oliphant. L. Wand E. Haug. 1985. photographs, and Stuart Houston Productivity, population density, for references. and rate of increase of an expanding Merlin population. Literature Cited Raptor Research 19(2/3):56-59. Allin, A.E. 1949. Field notes from Peck, G.K. and R.D. James. 1983. Canada. Thunder Bay Field Breeding of Ontario. Naturalists Newsletter 3(5):2-5. Nidiology and Distribution. Escott, NO. 1977. Marathon Volume I: Nonpasserines. Life notes. Thunder Bay Field Sciences Miscellaneous Publi­ Naturalists Newsletter 31(4):58. cation, Royal Ontario Museum, Houston, c.s. 1981. History of Toronto. 321 pp. Richardson's Merlin in Smith, A.R. 1978. The Merlins of Saskatchewan. The Blue Jay Edmonton. Alberta Naturalist 39(1):30-37. 8(4):188-191. Johnson. D.H 1982. Raptors of Minnesota-nesting distribution and population status. The Loon 54:73-104. Are Red-eyed and Philadelphia Always Interspecifically Territorial? by Ross D. James and Mark K. Peck

After an extensive study of evidence that the two species Philadelphia Vireos ( maintained mutually exclusive philadelphicus) and Red-eyed territories in any particular year Vireos (V olivaceus) near Englehart, (Rice 1978a). Experimental and in Timiskaming District, Ontario, observational findings indicated Rice (l978c) presented evidence that neither species was at a that the two species used disadvantage in territorial disputes, essentially identical habitat and so that despite size differences, would even occupy the same each could exist adjacent to the territorial area in successive years. other without overlapping terri­ But, he also provided clear tories. However, we made casual Ross D. James and Mark K. Peck, Department of Ornithology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6

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observations during the summer of Philadelphia Vireo. As I stood 1986 that suggested to us that watching and waiting, I noticed a interspecific territoriality is not female Red-eyed Vireo fly in with always achieved or necessary. nest material and place it on the Our observations were made 15 beginnings of a nest only about 3 to 25 km south of Gogama in m above the ground and almost Sudbury District, only slightly directly below the singing bird. I south of the latitude of Englehart, thought immediately that I must but where Red-eyed Vireos were have been wrong in my much more numerous than identification by song and that the Philadelphia Vireos. In the first bird singing above me was a Red­ instance we heard a Philadelphia eyed Vireo. But within a few Vireo singing near our cook tent in moments a male Red-eyed Vireo an aspen grove, and on 25 May flew silently to the nest as the noted a pair building a nest. The female left. When I eventually saw birds gathered nest material right the bird singing above this nest it beside our tent and could be heard was indeed a Philadelphia Vireo. morning and evening as we were Why then, in either instance, if preparing and eating meals. The these two species maintain birds were incubating in early mutually exclusive territories as June, and after that time we found by Rice (l978a), did one of scarcely ever heard the male sing. the birds not chase the other from The nest was about 18 m high in its territory? the crown of an aspen. When the In the first instance, although Philadelphia Vireos were the Philadelphia Vireo may not incubating, however, we regularly have responded as strongly to the heard Red-eyed Vireos singing in Red-eyed Vireo during incubation the same aspen grove, well below as at other times (Rice 1978b), and the Philadelphia Vireo nest. There the Red-eyed Vireo likewise might was only one pair of Philadelphia not have responded strongly to Vireos detected in this location, but what seemed to us to be an several pairs of Red-eyed Vireos unusually quiet Philadelphia were present. Vireo, there still appeared to be In the second instance, on 10 simultaneous occupation of at June, after completing a transect least part of the same territory by census, RDJ returned to an aspen the two species. grove about 14 km east of our In the second instance, although camp to verify the identity of the Red-eyed Vireos are supposed to vireos heard singing on the count. respond strongly to Philadelphia Two Philadelphia Vireos were Vireo song (Rice 1978a,b), the Red­ detected among much more eyed Vireo made no move to chase numerous Red-eyed Vireos. For the apparent intruder from its about 10 minutes I followed a bird territory complete with nest. that was singing continually, high Although the observations were in the aspens, trying to get a look casual, the situation with Red-eyed at the bird to confirm that it was a and Philadelphia Vireos in the

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Gogama area seemed similar to Literature Cited the vertical separation of vireos Hamilton. TH 1962. Species noted elsewhere, rather than one of relationships and adaptations interspecific territoriality. Yellow­ for sympatry in the avian genus throated Vireos (V. jlavifrons) may Vireo. Condor 64:40-68. occupy the upper parts of forests Hoiberg, A.J 1954. Breeding-bird above Red-eyed Vireos (Hamilton census: oak-pine stream bottom­ 1962; Williamson 1971; James land. Audubon Field Notes 1979); Red-eyed Vireos have been 8:369. noted above White-eyed Vireos (V. James, R.D. 1979. The comparative griseus) (Hoiberg 1954) or Bell's foraging behavior of Yellow­ Vireos (V. bellii) (Hamilton 1962); throated and Solitary Vireos: the Warbling Vireos (V. gilvus) may be effect of habitat and sympatry. above Hutton's Vireos (V. huttom) In Dickson, J.G. et al., The Role or Solitary Vireos (V. solitarius) of Insectivorous Birds in Forest (Hamilton 1962). There are no Ecosystems. Academic Press, obvious habitat differences New York, pp. 137-163. between the Gogama and Rice, Ie. 1978a. Behavioural Englehart study sites; both had interactions of interspecifically groves of tall aspen (and birch) territorial vireos. I. Song with an understory shrubs. of If discrimination and natural anything, the Englehart site has interactions. Behaviour older and taller aspens than at 26:527-549. Gogama. Does the interspecific territorial Rice, Ie. 1978b. Behavioural response of these species break interactions of interspecifically down where one species is much territorial vireos. II. Seasonal more numerous than the other? If variation in response intensity. Red-eyed Vireos are continually Animal Behaviour 26:550-561. concerned with intraspecific Rice, Ie. 1978c. Ecological competition and the very few relationships of two inter­ Philadelphia Vireos present are specifically territorial vireos. largely confined to a stratum of the Ecology 59:526-538. forest above the Red-eyed Vireos, Williamson, P. 1971. Feeding is there much reason for either ecology of the Red-eyed Vireo species to engage in costly (Vireo olivaceus) and associated interspecific territorial disputes? At foliage-gleaning birds. Ecologi­ what population densities or in cal Monographs 41:129-152. what circumstances are these two species induced to invoke interspecific territoriality? Clearly additional fieldwork is necessary to understand the relationships of these broadly sympatric species.

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