Biology of Wintering Northern Shrikes in Central Minnesota
Northern Shrikes (Lanius excubitor invictus Grinnell) wintering in central Minnesota were observed from 3 January 1991 to 10 April 1993. Wintering shrikes were monitored to determine: population size, density and age structure, territory size, extent of daily and seasonal movements, habitat preferen...
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The Repository at St. Cloud State
1996
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| Online Access: | https://repository.stcloudstate.edu/biol_etds/70 https://repository.stcloudstate.edu/context/biol_etds/article/1094/viewcontent/Final.pdf |
| Summary: | Northern Shrikes (Lanius excubitor invictus Grinnell) wintering in central Minnesota were observed from 3 January 1991 to 10 April 1993. Wintering shrikes were monitored to determine: population size, density and age structure, territory size, extent of daily and seasonal movements, habitat preferences, hunting behaviors, diet composition, intra and interspecific interactions, vocalizations, night roost site locations, arrival and departure dates, and effective trapping methods. Shrikes began to arrive in central Minnesota from sub-arctic breeding areas in early October. Density of birds continued to increase into late November when the population leveled out at an estimated 110 - 140 birds in the 750 square mile study area. Most of the birds sighted were adults, three of which had been captured on the same territory the previous winter. Of 54 birds captured, only 11 (20.4%) were in their first-winter plumage. Territory size varied from one to two square miles where suitable habitat existed. Prey availability was a major factor in territory selection. Shrikes spent most of their time in the scattered frozen marshes, meadows, and brushlands. where small mammals and birds were concentrated. Unharvested agricultural fields and road ditches were important hunting areas as well. Hunting accounted for much of a shrike's daily activity. Small mammals formed 90.1 % of a shrike's winter diet. Meadow voles accounted for 64.5% of mammalian prey followed by deer/white-footed mice at 25.5% and masked shrews at 6.7%. Small birds made up 6.6% of the diet while insects accounted for 3.3%. The night roost sites of nine shrikes were located. Each bird alternated between several roost trees. Size, shape and species of tree and its proximity to other woody vegetation was important in roost selection. Fifty-four shrikes were banded and marked with colored leg bands. Eight of th~se birds were fitted with radio transmitters. Shrikes were captured with a variety of trap designs and bait items. These were tested in various combinations ... |
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