83-98 OB Aug 2020 38-2.Pdf

83-98 OB Aug 2020 38-2.Pdf

Feeding niche overlap and segregation among three grouse species wintering in Hudson Bay Lowlands of northern Ontario Vernon G. Thomas Male Rock Ptarmigan. Photo: Gregory Smith Abstract The HUdson BaY LoWlands of northern for Sharp-tailed GroUse. WilloW Was Ontario (comprising tUndra and taiga) eaten primarilY bY WilloW and Rock proVide Winter habitats for WilloW Ptarmigan. The proportions of ingested Ptarmigan and Sharp-tailed GroUse as WilloW and birch parts differed greatlY Well as Rock Ptarmigan that occasionallY (P< 0.001) among the three groUse flY in from arctic and sUbarctic regions. species bUt food niche oVerlap did eXist Winter food niche segregation/oVerlap among all three. Morisita's IndeX of food Was measUred among these three species niche oVerlap, based on nUmbers of in - to inVestigate potential feeding competi - gested items, Was least (0.452/1.0) for tion; tamarack and berries Were qUanti - WilloW Ptarmigan and Sharp-tailed fied bY nUmber and mass in the crops of GroUse, intermediate (0.669/1.0) for groUse collected from the VicinitY of the WilloW and Rock Ptarmigan, high former commUnitY of Winisk, Ontario (0.957./1.0) for Sharp-tailed GroUse and (noW PeaWanUck). All groUse species fed Rock Ptarmigan, and greatest (0.996/1.0) on birch and it Was the principal food for Sharp-tailed GroUse at PeaWanUck Volume 38 Number 2 83 and Moosonee. Resident WilloW Ptarmi - 1963). Arctic-breeding Rock Ptarmigan gan and Sharp-tailed GroUse maY be (Lagopus muta ) migrate irregUlarlY across segregated partiallY bY habitat. IrrUption Years into this region for the Winter of Rock Ptarmigan occUrs irregUlarlY months (LUmsden 1964). Their flocks across Years, thUs loWering feeding com - contain a majoritY of immatUre and petition for birch parts With Sharp-tailed adUlt females (Thomas and Popko GroUse, and WilloW parts With WilloW 1981). AdditionallY, WilloW Ptar migan Ptarmigan. that breed north of the HBL are knoWn to migrate into this region dUring the Introduction Winter (SnYder and Shortt 1936) and The northern part of Ontario that bor - aUgment local nUmbers of this species. ders HUdson BaY and James BaY is a dis - While the breeding habitats of these tinct ecological formation, the HUdson species are dissimilar and segregate the BaY LoWlands (HBL) EcoZone (Crins et species ecologicallY, theY appear to eXist al . 2009, RileY 2003, also knoWn as the sYmpatricallY dUring the Winter months. HUdson Plain EcoZone, Abraham and These three species of groUse contain McKinnon 2011). Crins et al. (2009) VerY loW bodY reserVes of fat dUring the described different regions Within the Winter (Thomas and Popko 1981, HBL: Ecoregion 0E is the HUdson BaY Thomas 1982) and mUst feed continU - Coast Ecoregion and contains Ontario's allY to maintain their energY balance. tUndra heath, Ecoregion 1E is the The principal foods consUmed are parts Northern Taiga Ecoregion and contains of WilloW ( Salix spp.) and dWarf birch fens, bogs, riVer margins and eXtensiVe (Betula pumila ), especiallY the dormant conifer forest edge, Ecoregion 2E is the leaf bUds and catkins. These are the James BaY Ecoregion and contains eXten - species and parts of Vegetation reported siVe open and treed fens, bogs, and riVer to be consUmed regUlarlY bY WilloW and margins in addition to conifer forest. Rock Ptarmigan dUring the Winter in The HBL is Well-knoWn for the staging other parts of the species range in Alaska habitats of manY species of migratorY and EUrope (West and Meng 1966, birds and breeding habitats for WaterfoWl Weeden 1969). Despite the common (Thomas and PreVett 1982, Abraham name, WilloW Ptarmigan are not obli - and McKinnon 2011). The HBL also gate feeders on WilloW parts as sUggested contains the habitats of seVeral groUse bY West and Meng (1966). WilloW does (AVes: FamilY Phasianidae, SUbfamilY not comprise part of this species Winter Tetraoninae) species, aboUt Which little diet in NeWfoUndland (Peters 1958), is knoWn compared to the migratorY and in Scotland, heather ( Calluna spp.) bird species. Sharp-tailed GroUse ( Tym - is a major part of the annUal diet of the panuchus phas ianellus ) and WilloW sUbspecies ( L. l. scoticus ) (SaVorY 1978). Ptarmigan ( Lagopus lagopus ) are com - Weeden (1969) indicated that these tWo mon permanent residents of this region ptarmigan species shoW feeding segrega - (Manning 1952, Hanson 1953, Aldrich tion dUring Winter in Alaska. GiVen that 84 Ontario Birds August 2020 Hudson Bay N er iv ECOREGION Winisk R Cape n 0E r • Henrietta e v e Maria S Winisk River•Peawanuck ECOREGION 1E James Bay Attawapiskat • Fort Albany ECOREGION 2E r • ive ONTARIO R y n ba Al Moosonee • QUEBEC 0 100 200 km Figure 1. The Hudson Bay region of northern Ontario showing the collection areas around Peawanuck and Moosonee. Map adapted from Ontario location map by Nord Nordwest ( CC-BY-SA- 3.0 ). J. Shore both ptarmigan species and Sharp-tailed eXpanded oesophagUs (or crop) in Which GroUse share similar Wintering range in hUndreds of food items can be stored northern Ontario, the qUestion of feed - temporarilY Until digested. Collections ing competition or, alternatelY, food of these three groUse species in 1977 niche segregation arises (Weeden 1969, from a region aroUnd the former com - Moss 1974, BeloVskY 1986). mUnitY of Winisk (relocated in 1986, Each daY, Rock and WilloW Ptarmi - the commUnitY is noW named gan and Sharp-tailed GroUse emerge PeaWanUck and referred to as PeaWanUck from their snoW bUrroWs to feed dUring hereafter), Ontario (55° 16' N, 85 °11' W) the earlY morning and late afternoon. (FigUre 1) for energY reserVe stUdies After tWo to three hoUrs of feeding, the (Thomas and Popko 1981, Thomas birds retUrn to their snoW bUrroWs to di - 1982) enabled the crops and their con - gest their food. These species possess an tents to be retained and preserVed for Volume 38 Number 2 85 for fUtUre analYsis. The nUll hYpothesis flocks as encoUntered. A collection of adVanced is that there is no Winter food Sharp-tailed GroUse Was made (13 JanU - niche oVerlap among Rock Ptarmigan, arY – 14 March) in the forested region WilloW Ptarmigan and Sharp-tailed north of Moosonee in the Winter of 1978. GroUse in northern Ontario. Each groUse species Was collected seVeral Sharp-tailed GroUse are also common hoUrs after daYlight feeding to ensUre that permanent residents of the soUthern part eXtensiVe feeding had occUrred. All birds of the HBL (Ecoregion 2E) aroUnd collected Were froZen and sent to the Uni - Moosonee (51 °16 'N, 80 °38 'W) (Han - VersitY of GUelph for analYsis. son 1953). Rock Ptarmigan are not The entire crop With its contents Was knoWn to freqUent this region in Winter remoVed from each bird and freeZe-dried. and WilloW Ptarmigan occUr here onlY The indiVidUal food items Were identified rarelY in Winter. Collections of the crop bY species Using a reference collection of contents of Sharp-tailed GroUse from this Vegetation from the PeaWanUck region. soUthern ecoregion in Winter, 1978, WilloW items Were diVided readilY into enabled a comparison of the food niche bUd and stem categories. Stems com - With Sharp-tailed GroUse from PeaWan - prised aboUt 10-12% of the WilloW parts, Uck, Where potential competition eXists and for pUrposes of this stUdY, Were With other species. The hYpothesis ad - inclUded With bUds for analYsis. DWarf Vanced is that the food niche WoUld be birch items comprised dormant catkins narroWer in the birds from the VicinitY of and leaf bUds and comprised a single PeaWanUck than from Moosonee. groUp. Tamarack ( Larix laricina ) dor - mant leaf bUds Were present in crops Methods from some Sharp-tailed GroUse. Parts of Direct obserVations of the feeding behaV - Vegetation that coUld not be attribUted to ioUr of the three species bY this aUthor anY species Were labelled “Unidentified.” indicated that parts of WilloW and birch For each plant groUp, the drY mass Was Vegetation Were selected as indiVidUal recorded along With the nUmber of items bites from the plants at snoW leVel (FigUre in that groUp. The difference betWeen 2). Each species Was encoUntered in flocks species in the nUmber of items ingested of approXimatelY 10-30 birds, and each is a measUre of selectiVitY, Whereas the flock comprised onlY one groUse species. mass of those items is indicatiVe of their Collections of each species Were made bY oVerall contribUtion to the energY/nUtri - shooting With rifle dUring the Winter ent intake. SeVeral hUndred discrete food months in 1977 (Sharp-tailed GroUse, items coUld be foUnd in the crop of anY 13 JanUarY – 14 March: WilloW Ptarmi - bird. HoWeVer, onlY the crops of those gan, 17 FebrUarY – 15 April: Rock birds that contained more than 100 food Ptarmigan, 28 March – 15 April) from a 2 region of approXimatelY 1,400 km Figure 2. Sharp-tailed Grouse feeding on birch aroUnd the commUnitY of PeaWanUck. catkins and buds near Moosonee. Illustration: Birds Were collected randomlY from C. McManniman, (1980). © V.G. Thomas. 86 Ontario Birds August 2020 Volume 38 Number 2 87 items Were Used in this analYsis, Validat - Results ing the Use of percentages to compare The three groUse species relied Upon amoUnts of a plant species ingested With - parts of the WilloW and/or birch for their in and betWeen groUse species. principal foods both at PeaWanUck and The data sets Were tested for normal - Moosonee (Table 1). The WilloW Ptarmi - itY of distribUtion, and all data sets Were gan data set Was diVided into a collection distribUted normallY. Differences in the from 17 FebrUarY – 25 March and 26 amoUnt of WilloW and birch parts con - March – 15 April, the later collection sUmed bY each of the three groUse species coinciding With the marked presence of Were tested bY t-tests.

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