DISTRIBUTION

The owl invasion of , , January-April 1979

A report from the owl capital of the world of the parliament of winter, 19 79

Gary P. Bell, Frank J. S. Phelan and Ron C. P. Wypkema. Photographsby the authors.

LTHOUGHNORTHERN OWLS moved into easternNorth America in large Short-eared Owl on Amherst Island. Photo/ numbers in the winter of 1978-79, the Frank J. S. Phelan. invasionof owls in the Kingston, Ontar- io, Canada area was unique. Over the course of the winter, thousands of bird- watchers from across Canada and the United States visited Amherst Island. 3 miles southwestof Kingston. to view an unusualassemblage of owl species. Amherst Island is an isolated rural community lying 2 miles south of the north shore of , at 44ø10'N, 76ø40'W.The 25-squaremile islandpro- vides a variety of habitats including active farmland, old field pasture, woods and marsh. During the latter part of 1978the pop- ulation densityof meadowvoles (Micro- tus penns.vlvanicus) became very high. Great Gray Owl on Amherst Island. Photo/ The isolation of the island, and the lack Gary P. Be!!. of terrestrial predators such as foxes intensifiesthe natural population cycles Saw-whet Owl on Amherst Island. Photo/ of small mammals. Extreme population Frank J..S. Phelan. "outbreaks", then, are regular occur- rences.Large incursionsof raptorshave long been associatedwith such out- breaks of voles, and periodically raptor densities on Amherst Island and , 2 miles to the east, increase dramatically in responseto abundances of meadow voles (Phelan. 1976; Phelan and Robertson,1978). These raptor den- sity increasesare easily predicted, but along with this increasein numbers of raptors, comes a highly unpredictable increasein the numbers and diversity of raptor species. This past winter, most of the raptors present on Amherst Island were owls. Ten species were recorded, including Great Gray, Long-earedand Snowyowls Hawk Owl on Amherst Island. Photo/R. in great abundance,with other species Boreal Owl on Amherst Island. Photo/Gary Wypkema. present in varying nfimbers.Table I P. Be!!.

Volume33, Number3 245 Coincidentwith the springdispersal of Table I. Owl observationsfrom the recordsof the KingstonField Naturalists, the northernraptors, the volepopulation January1,1979 - April 15,1979 on AmherstIsland, Ontario on Amherst Island crashed.It probably will not peak again for another3-4 years. Date of First Date of Highest Date of Last Owl Species Sighting Count Sighting When it does,raptors on their searching migrationswill again be attractedto the GreatGray Owl Jan.20 (1P Mar. 10 (18) Apr. 8 (2) island. It would, however. be unusual to Long-earedOwl' Feb. 11(1) Mar. 17(29) Apr. 13(1Y' find soon again a diversity of owls as SnowyOwl Jan. 1 (5) Mar. 4, 17 (21) Apr. 8 (1) Short-earedOwl c Jan. 5 (1) Mar. 4 (10) Apr. 13 (1} high as that which was experiencedon Saw-whetOwl Feb. 17 (1) Mar. 7 (6) Apr. 1 (1) Amherst Island in the winter of 1978-79. BorealOwl Feb. 25 (1) Mar. 7 (4) Apr. 1 (1} ScreechOwl' Feb. 19(1) (only1 eachcount) Mar. 18 (1) Literature Cited Great HornedOwl c-d Feb. 17 (1) (only1 eachcount) Mar. 24 (1) Hawk Owl Jan.3 (1) (only1 eachcount) Mar. 25 (1) BELL, G. P. 1979. Summer habitat use and Barn OM ß Feb.22 (1) (only2 sightings) Mar. 3 (1) responseto food patchesby insectivorous Numbersin parenthesesindicate count data for datespecified. bats in a desert community. M.Sc. thesis, Long-earedOwl on nest with 2 eggsthis date. Carleton University,Ottawa. Residentspecies. GALUSHIN, V. M. 1974. Synchronousfluc- on nestFebruary 22, anothernest March 17. tuationsin populationsof someraptors and May be residents,although very seldom seen. their prey.Ibis, 116:127-132. PHELAN, F. J. S. 1976.The responseofavian predators to population cyclesof small summarizes the records for Amherst food resourcesof the island. Despite the mammals(especially Microtus) on Amherst Island from the KingstonField Natural- incredible density of potential compet- and Wolfe Islands,near Kingston,Ontario ists'files for the periodJanuary I - April itors, few interspecificinteractions were (Canada). M.Sc. thesis,Oueen's University, noted. Kingston. IS. 1979. The first owls, Snowies, were PHELAN. F. J. S. and R. ]. ROBERTSON presenton the Island from mid-October, Table 2. Total owl populationestimates for 1978. Predatoryresponses of a raptor guild long beforethe first snowfall.The first Amherst Island. to changesin preydensity. Can. J. Zool. 56: report of a Great Gray Owl on Amherst 2565-2572. Island came January 20, six days after Species Number --Department of Biology, Queens the first report for the Kingston region. Great Gray Owl 34 Universi.tv,Kingston, Ontario K7L 3N6. By February 17 it was evident that a Long-earedOwl 50 major influx was occurring, when IS SnowyOwl 30 Short-eared Owl 20 Great Gray Owls were seenin one wood- Saw-whet Owl 9 lot. Large numbersof observers.comb- Boreal Owl 8 ing the island. soonlocated Long-eared. Screech Owl 3 Short-eared. Saw-whet. Screech. Great Great Horned Owl 4 Horned. Boreal. Hawk and Barn owls. Hawk Owl Barn OM 1 Maximum numbers for all species occurredin a 14-dayperiod March 4-17. Total 160 By March 18 most of the Great Gray Owls had left the island. The last two Suchopportunistic response to super- wereseen on April 8. and appearedto be abundant, patchy food sourcesseems to engagingin courtshipbehavior. be a commonstrategy in manypredatory animals (Bell, 1979). The great mobility ScreechOwl playing dead. Amherst Island. OSTOBSERVER ACTIVITY was con- of raptors makes local, temporary incur- Photo/R. Wypkema. centrated around two woodlots at sionspossible (Galushin, 1976). the west end of Amherst Island where IS Great Gray Owls were present from at least February 17 - March 17. Although many small or inaccessiblewoodloLs went unexamined. most sizable woodlots inspected showed some signs of owl activity. With this in mind, and using our information about the movements of observers.we have produced a conserv- ativeestimate of the total owl population of Amherst Island {Table 2)for the peak period. Other raptors present on the island at this time included Rough- leggedHawk (SO),Red-tailed Hawk (18), Marsh Hawk (2), American Kestrel (6), gray-phaseGyrfalcon (1) and Northern Shrike (4); thus at least 230 birds of prey were utilizing the samehighly available Long-earedOwl on AmherstIsland. Photo/R. Wypkema.

246 AmericanBirds, May 1979