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SITE NAME
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Herschel Island, Yukon Territory, Canada
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| Contact details
(phone/fax//e-mail//address): |
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PROJECT DETAILS |
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Start of survey:
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End
of survey: |
Team
size: |
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26.05
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26.09
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WEATHER
CONDITIONS
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| Season phenology: |
average
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Weather conditions: |
Observations were carried out from 26 May to 26 September 2007.
A generally late snowmelt was observed in the northern Yukon, which proceeded very quickly (within 10 days) once the warmer weather arrived. One snow transect in wet lowland of 25 stations, 10 m apart was run from 29 May through to full melt (8 June). Substantial areas of the well incised topography had very deep drifts with snow lasting well into July.
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| Date of ice-break on
rivers: |
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| Date of final loss of
snow: |
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BIOTIC
CONDITIONS
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| Rodents abundance evaluation: |
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Breeding conditions:
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Abundant and diverse arthropod fauna is characteristic of the area. The Arachnid abundance seemed to be in advance of fledging. Arachnids dominated early, with coleopterans, dipterans and crane flies dominant in July. There was an increasing rate of capture, with strong variability related to weather from 15 June to 5 August.
Only two fox dens appeared active. One close to camp being used by two adult Arctic Fox (reproduction uncertain); the second was far from camp and species unknown. Dynamic balance between fox species is ongoing - Arctic Fox was occupying a den used by Red Fox in 2005. Remains of at least 3 Arctic Foxes and 1 Red Fox were found, having died in winter. Fox density appeared quite low in the eastern half of island. Seven Least Weasels were captured in June in lemming traps on small mammal grids. These were adults and recently weaned juveniles. Five Weasels captured in September on small mammal grids gave evidence of summer breeding. Quick numerical response of winter breeding Weasels to lemming abundance may have curtailed an increase in lemming populations. But Weasels were unable to curtail summer population growth of lemmings despite continued breeding. Direct observations indicate some Wolverines were resident. There were also indications that at least one Grizzly Bear was present on the island periodically, but the animal was not observed. One Polar Bear was observed in September apparently investigating lemming burrows.
The eastern half of the island (c. 50 km2) was searched for nests of avian predators. There were found 4 nests with eggs of the Rough-legged Buzzard, 5 of the Peregrine Falcon, one of the Short-eared Owl, and 4 of the Long-tailed Skua. Two nests of Rough-legged Buzzards and one of Peregrine Falcons failed. Snowy Owls did not breed, although 80 birds were estimated on the island, which suggested that lemming densities had not been high enough. Apparently, the island is a good area to sustain owls in years without breeding opportunities elsewhere. Peregrine Falcon densities are on increase historically, and may have influence on densities of other raptors.
The majority of the island is not productive shorebird habitat, and very few shorebirds were nesting in the upland areas (only the American Golden Plover on two plots established). Most upland nesters were Lapland Buntings, Savannah Sparrows and Buff-bellied Pipits, with scattered Greater White-fronted Geese and Rock Ptarmigans. The alluvial fan habitat was the most productive for shorebirds (but no plot was monitored this year); the Semipalmated Plover and Semipalmated and Baird sandpipers were breeding there. A sample of at least 70 shorebird and passerine nests were tracked from some time during incubation through hatching, and some to fledging. Data indicated earlier mean hatching dates for prominent species (e.g., the Semipalmated Sandpiper and Lapland Bunting) compared to mid-1980s.
Foxes had a high local impact on bird nesting success, based on direct observations at the alluvial fan and a spit near the camp. Wolverine should be also considered a potentially powerful ungulate, small mammal, and avian nest predator.
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Rodent dynamics:
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For small mammal abundance two upland 9 ha grids and one 2 ha alluvial fan grid were trapped in mid-June, mid July and early September. Also winter nests were counted on all grids. Relative abundance index lines from 2006 were re-trapped in June, and yielded low catches. New "Upland" index lines were established in early July, and yielded moderate catches. All lines re-trapped in mid September showed increased catches. Shrew population was growing during summer. Lemmings and voles were abundant in spring, decreasing in mid summer, but often increasing thereafter: upland grids had from 6 to 9 animals/ha and from 8 to ca. 11 animals/ha; alluvial fan grid had from 15 to ca. 12 animals/ha. 2006/2007 winter nest densities were high compared to other data sets collected historically. A relatively high proportion (15-30%) of winter nests were found with signs of weasel predation.
VHF radio-telemetry was applied on 25 adult females (mix of small mammal species) to quantify September survival and home range use (prior to snow fall). Moderate mortality rate recorded was due to fox and weasel activities.
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Rodent species recorded:
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Summary
of fauna studies: |
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