and Brown Lemmings
of lemmings are found on Bylot Island: the Collared
Lemming (Dicrostonyx groenlandicus) and the
Brown Lemming (Lemmus sibiricus). The Brown
Lemming is typically found in wetlands where it feeds
on plants such as sedges and grasses. In contrast, the
Collared Lemming prefers a dryer habitat (uplands) where
it mainly feeds on forbs and shrubs.
Both lemming species found on Bylot Island play major ecological
roles in the terrestrial ecosystem. They are the main preys of
many arctic predators such as Arctic Foxes, Weasels and Snowy
Owls, which largely depend on them. Brown and Collared Lemmings
also influence tundra vegetation by dispersing seeds or devastating
plants when overgrazing them.
A particular characteristic of these two lemming species is the
cyclic nature of their populations. Simply, this means the Brown
and Collared Lemming populations go through phases of very low
to very high densities, depending on food availability. If conditions
are good, lemmings can reproduce and have many large litters every
year. As a result, their population grows and grows until it reaches
a point at which there are not enough plants anymore to sustain
all the animals. At this point the population crashes, the vegetation
regenerates and the cycle starts over again. On Bylot Island,
3 to 4 years can pass between two peaks in the lemming population.
Because lemmings have important ecological roles, cycles in their
populations have large impacts on arctic ecosystems (see Arctic
Fox and Snowy
Owl sections). For this reason, the Bylot Island environmental
monitoring project participates in the small-mammal survey coordinated
across the Northwest Territories and Nunavut (Canada) by the Renewable
Resources office in Yellowknife, a governmental agency.
Each year since 1994, lemming trapping-censuses are carried out
in two study plots of the Qarlikturvik Valley (one in wetlands,
one in dryer uplands). Since 1997, another census is carried out
at a third study plot in an upland habitat nearby the main geese
nesting site (see Snow
Goose section). At each study plot, 50 snap-traps are baited
during a period of 10 to 11 days, for a total of 500 to 550 trap-nights
(50 traps x 10-11 nights) per plot. The lemming abundance index
is determined by calculating the number of lemmings caught per
In 2004, we initiated a new sampling program based on live-trapping
of lemmings. This program will enable us to estimate seasonal
and annual variations in abundance, reproductive activity, and
survival of lemmings, which will improve our knowledge of their
population dynamics. In order to do so, we are using 2 grids laid
out in the Qarlikturvik Valley (one in wetlands and one in a drier
habitat), each with 144 live traps baited with apples. We monitor
these traps during 4 periods of 5 days from early June to mid-August.
All trapped animals are identified, sexed, weighed, marked with
electronic PIT tags (or checked for the presence of such tags)
Fluctuating Lemming Abundance (snap-traps
In the Qarlikturvik Valley, we observed that Collared and Brown
Lemmings are synchronised, but the Brown Lemming cycle is more
accentuated than that of the Collared Lemming.
Considering both the Qarlikturvik Valley plots and the upland
plot of the main geese colony, we observed a delay of one year
between the population peaks of 2000 and 2004 (Qarlikturvik) and
the peaks of 2001 and 2005 (main geese nesting site). Interestingly,
the year of peak abundance usually followed the year of lowest
abundance since the previous peak. Thus, abundance appears to
build up abruptly (i.e. within one year) whereas the decline,
though rapid in the year following the peak, was not complete
until at least two years after the peak, and was thus more gradual.
Population Dynamics (live-trapping
Results from our 2004 and 2005 field season
showed that the density of Brown Lemmings declined markedly between
the two years while that of Collared Lemmings was relatively constant.
For Brown Lemmings, 2004 appeared to be a peak year in their cycle
and 2005 a decline phase.
The proportion of juvenile Brown Lemmings
in the population was lower during the decline phase (2005) than
in the peak phase (2004), but did not differ between years in
the Collared Lemmings. The proportion of juveniles in the population
increased seasonally in both species.
Based on the weight and age of Brown Lemmings
captured during the summers 2004 and 2005, we were also able to
infer the distribution of their birth seasons. Results showed
that during the 2004 peak most births occurred during the summer
while in 2005 (decline phase) most of the lemmings captured over
the summer were born during the previous winter and spring.
* GRUYER, N. 2007. Étude comparative de la démographie
de deux espèces de lemmings (Lemmus sibericus
et Dicrostonyx groenlandicus), à l’Île
Bylot, Nunavut, Canada. M.Sc. thesis, Université Laval,
Québec, QC, Canada.