88 J. T. Ibarra et al.
FIG. 1 Southern South America, showing the Cape Horn Biosphere Reserve (shaded in grey) and Navarino Island, Chile.
which are known to be eaten by mink in other regions of
Chile and Argentina (Medina, 1997).
A total of 414 mink scats were collected over January-
November 2006 along the shoreline of 27 ponds. Faeces
were sorted into seven categories according to their con-
tents: (1) bird, including feathers, bone fragments and egg
shells; (2) mammal, including hair, teeth, and bone frag-
ments; (3) fish, including vertebrae, scales and otoliths; (4)
insects, including appendages and exoskeleton fragments;
(5) crustaceans, incuding appendages and exoskeletal frag-
ments; (6) molluscs, including valve parts; (7) plant matter,
including seeds and leaves. Mammals and birds were iden-
tified to species, if possible, using taxonomic keys and
references. In the case of mammals, teeth and the medullar
and cuticle scale patterns of hairs were compared to pat-
terns described in guides (Reise, 1973; Chehebar & Martin,
1989; Pearson, 1995). For the few bird species, feather colour
patterns were used for identification. We computed fre-
quency of occurrence expressed as a percentage (number of
scats with a prey category divided by the total number of
scats, by season), and percentage of bulk of a prey category
(proportion of volume of a scat with a prey category
multiplied by dry weight of the scat, divided by total dry
weight of scats, by season).
The diet of mink in Navarino Island's wetlands con-
sisted mainly of mammal, birds, insects and plant matter.
Whereas the occurrence of mammals and birds in scats was
similar during summer and winter, the representation of
mammals in the scats in autumn and spring was almost
double that of birds (Fig. 2). Of 272 scats with mammal
remains, 235 comprised fragments amenable to further
identification, including native, exotic and unidentified
mammals (Table 1). Exotic mammals (identified in 86 scats)
were most abundant in the scats during autumn and winter,
whereas native mammal species dominated during the sum-
mer (Table 1). Hair identification showed that muskrat
(n = 78) was the most important exotic mammal prey
followed by beaver (n = 4) and murid rodents (n = 4). Bird
consumption was higher during the summer when 58.5% of
scats contained bird remains (Fig. 2). Bird remains were
identified in 202 scats, but only 11.4% contained remains that
could be identified to species level. Remains of three species
were identified: the ground-nesting upland goose Chloe-
phaga picta, and tree-cavity nesting thorn tailed rayadito
Aphrastura spinicauda and southern house wren Troglo-
dytes musculus. Egg shells were found in only 0.03% of the
scats collected during spring and summer (n = 9) but mink
eat the contents of eggs without necessarily eating the shell
(Ferreras & Macdonald, 1999). Plant matter was more
frequent in winter scats and seemed to compensate for the
decrease in mammal consumption recorded for this season
(Fig. 2). For details of the importance of other prey items see
Fig. 2.
American mink have only recently invaded Navarino
Island and this is the first report of their diet in the early
years of their establishment, with a significant represen-
tation of native wetland and terrestrial birds. The con-
sumption of birds was highest during the warmer months.
Of mammalian prey, introduced species were mainly
consumed during autumn and winter. This demonstrates
that introduced prey species are available for mink when
wild rodents and birds are probably less abundant. The
@ 2009 Fauna & Flora International, Oryx, 43(1), 87-90
