are the main predators found on Bylot Island and their
favourite preys are small rodents called lemmings. Lemming
populations are however cyclic, meaning that they go
through phases of really high to really low densities,
every 3-5 years (see Lemmings).
When lemmings are abundant, Arctic Foxes can survive by mainly
feeding on them, but in period of low lemming densities, foxes
have to put more effort in preying upon alternative preys such
as goose eggs and goslings. Since geese fiercely defend their
nests against predators, catching eggs and goslings is however
a more difficult and risky task than catching lemmings.
Even though Bylot Island Arctic
Foxes can rely on alternative preys when there are few lemmings,
their population remains largely driven by lemming abundance.
In fact, fox reproductive effort (number and size of litters)
seems to be closely related to lemming availability. In years
following high peaks in lemming populations, foxes are in better
physical condition, so many fox litters are found and the number
of pups in each litter is high. In contrary, in years following
very low lemming abundance, only few litters are found and litter
sizes are small.
Arctic Fox populations as been an important part of the
Bylot Island ecological monitoring project. Every year since
1993, Arctic Fox breeding activity has been monitored. This
is done by searching and monitoring Arctic Fox dens in the
Qarlikturvik Valley as well as in the vicinity of the goose
nesting colony (30 km south of Qarlikturvik Valley). Each
year, all known dens (51 in 2002) are visited at least once,
in late June or early July, to identify traces of fox activity.
Dens that have shown activity signs are then visited later
in the summer to determine the presence and number of fox
in each litter. During these visits, the presence of Red
Foxes has been observed. Therefore, their breeding activity
has also been incorporated in our fox monitoring program.
From 1996 to 2000, relationships
between Arctic Foxes, lemmings and geese were more thoroughly
investigated. As a result, many questions related to the
impact of Arctic Fox predation on Bylot Island Greater Snow
Geese population were elucidated.
During the summer 2003, the den survey
and monitoring was also expanded to an area covering 600
km². This allowed us to increase our number of know
dens to a total of 98 (48 more than in 2002). Some of the
foxes observed were captured and marked with collar emitting
radio frequencies, which alllows us to study fox activity
and diet around dens.
Relation Between Lemming Abundance
and Fox Breeding Activity
As it was previously mentioned, the breeding effort of Arctic
and Red Foxes seems to be closely related to lemming abundance.
However, since the expansion of our den monitoring area in 2003,
this relationship seems less visible and little is known yet about
the lemming abundance in these new areas. It may be different
or non-synchronized with that observed in the traditionally surveyed
areas (see Lemmings).
Fox Denning Activity
The percentage of known dens that present signs of activity
(either diggings or fresh prey remains) greatly vary from year
to year and can be considered as an indicator of fox abundance.
However, the variability of reproductive foxes is not similar
but may be explained by the cyclic nature of lemming populations.
Years with the lowest percentages of dens with pups are years
when lemming abundance was the lowest as well.