Walia Special Edition on the Bale Mountains (2011) - Zoologische ...

encounters between neighbouring wolves at territory borders were aggressive and involved repeated
chases (102 out of 119 encounters) and the larger group was most likely to win (the larger group won
in 77% of cases, whereas victorious and defeated groups were the same size in 15% of encounters).
Ethiopian wolf packs in Bale occur at saturation density, in a system of highly stable
tessellated territories (Sillero-Zubiri and Gottelli 1995b). Frequent scent-marking, inter-pack
encounters and aversion to strangers’ marks probably constrain each pack to its territory, while
positive feedback keeps each territory boundary adequately marked. A further function of scentmarking
may be to indicate sexual and social status. Wolves in Bale are seasonal breeders and in any
given year mating was synchronised to a period of one to three weeks in the latter part of the rainy
season (August-October), suggesting that a social mechanism triggered mating (Sillero-Zubiri et al.
1998). Scent-marking might allow females to monitor their reproductive condition reciprocally and
synchronise their oestrus. On the other hand, neighbouring packs’ males may gather information on
the receptivity of females. While border encounters occurred throughout the year, peak intrusion
pressure coincided with the mating season. Fifty out of 169 observed encounters between wolves
of neighbouring packs consisted of territorial intrusions by small groups of neighbouring males
attracted by a receptive resident female. Highly seasonal mating may be connected to the occurrence
of a philandering mating system in Ethiopian wolves (Sillero-Zubiri 1994; Sillero-Zubiri et al.
1996a).
Philopatry and the Risk of Inbreeding
Dispersal and philopatry
Lack of suitable habitat places a tight constraint on dispersal in Ethiopian wolves. In Bale immigration
was rare, births and deaths predominated over transfers between packs, and all pack members were
close kin. Relatedness values from microsatellite data were similar for adults (females R = 0.39,
males R = 0.33) and subadults (R = 0.30) (Fig. 1), and approximate relatedness values expected
among half-siblings in this population (Randall et al. 2007). With kin of opposite sex residing in
the same group, natal philopatry provided the potential for inbreeding, in a situation of severely
limited dispersal opportunities (Sillero-Zubiri 1994). Although dispersal was rare, both behavioural
observations and genetic evidence suggest that which occurs is sex biased (Sillero Zubiri et al.
1996a; Randall et al. 2007). In Web and Sanetti, behavioural observations between 1988 and 1992
suggested that 63% of females dispersed at, or shortly before, sexual maturity at two years, some
becoming ‘floaters’ (Sillero-Zubiri et al. 1996a). Under stable demographic conditions Ethiopian
wolf males are philopatric (Randall et al. 2007), however short and long distance male dispersal has
been observed following demographic disturbance due to disease outbreak (Marino 2003b). Pack
fission and males seeking extra-pack sexually receptive females during the breeding season can also
act as male dispersal into neighbouring territories (see below). The population sex-ratio of adults
was biased toward males at 1.9:1 ± 0.07 (SE), with the mean pack sex-ratio of adults at 2.6:1 ± 0.2
(Sillero-Zubiri and Gottelli 1995b).
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 67