EXECUTIVE SUMMARY FOR
RESOURCE MANAGEMENT REPORT 00-3
2000 COMMON LOON SURVEY AT ISLE ROYALE NATIONAL PARK, MICHIGAN
The annual Common Loon (Gavia immer) monitoring program at Isle Royale National Park was completed in 2000 to maintain continuous data on the size and productivity of the island's unique loon population. This is the eleventh consecutive year of the Isle Royale Common Loon monitoring program, and along with the 1998-99 surveys, this year’s work involved a more intensive monitoring effort than previous years. This resulted in a more accurate and thorough account of productivity on individual territories.
Forty-seven of the Island's interior lakes and 45 locations along the Lake Superior shoreline were surveyed between 26 July and 10 September 2000 by boat, canoe, kayak, or walking along the shoreline. The inland lake and Lake Superior data are analyzed both by lake and by individual territory. Sampling methods for 2000 were modified based upon the findings of an atlas, which delineated Common Loon territories at Isle Royale, completed by BioDiversity Research Institute. Data results are organized into two groups: the lake-stratum system used since 1990, and the atlas system used in 1999 and 2000.
According to stratum results, adult loons were recorded on 27 of the 47 interior lakes (57%) and 37 of the 45 Lake Superior sites (82%). Juvenile loons were present on 16 of the interior lakes (34%) and 7 of the Lake Superior sites (16%), and totaled 33. Productivity among 72 recorded pairs was 0.5 young/pair, which is below the 11-year average of 0.6 young/pair. The total of 72 adult pairs is well above the average of 48 for Isle Royale, due to the more precise survey methods. The total of 33 juveniles is above the average of 28. The 2000 productivity rate of 0.5 is barely within the range considered necessary for a loon population to sustain/increase itself (range=0.5-0.79 young/pair). The average productivity of the 11-year loon survey (0.6) is also within the range of sustaining the population, yet seems only marginal when considering the relatively undisturbed aspect of Isle Royale’s wilderness. Only three times in the eleven year period has productivity exceeded the level needed to sustain the population. This raises questions of whether Isle Royale’s loon population is maintaining parameters (i.e. reproduction, adult survivorship) necessary to make it a source for a wider dispersing loon population.
According to atlas results, there are at least 98 confirmed territories on Isle Royale. Lake Superior waters have 35 of these, while inland lakes have 63. There are many more suspected territories as well. Productivity within the atlas system lowers to 0.3 young/territory in 2000, well below the stratum results.
With a total of 203 adults counted, the stratum system would suggest about 71% of the adult population are members of territorial pairs (144 of 203), while the atlas system suggests about 97% of the adult population are in territorial pairs (98 territories = 196 of 203 adults). The 1990-2000 data comparisons show consistently low to marginal productivity. Considering both systems of data analysis, only 30-50% of breeding pairs were successful in 2000. Interesting for its exact correspondence with 2000 productivity numbers on Isle Royale, the 33-50 chicks per 100 pairs has been documented elsewhere as a standard range of success for Common Loon productivity.
Alexander Egan
Biological Technician
Isle Royale National Park
Jack Oelfke
Former Branch Chief, Natural Resources
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