Náttúrufræðingurinn - 2006, Blaðsíða 37

Tímarit Hins íslenska náttúrufræðifélags
annarra hrossakynja. Þar eru mest
áberandi tengsl milli móður og af-
kvæma hennar (0-3ja vetra). I sum-
um tilvikum virðist stóðhesturinn
hindra að hryssurnar og tryppin
eigi samskipti við hross úr öðrum
hópi og jafnvel innan hjarðarinnar.
Ef til vill vilja hryssurnar helst vera
með öðrum hryssum sem eru
skyldar þeim þótt slíkt mynstur
komi aðeins í ljós þegar enginn
graðhestur er í hópnum.
Líklegt er því að í stóðum án stóð-
hests hafi hrossin tækifæri til meiri
samskipta og geh frekar valið sér
vini. Fjarvera stóðhests hefur senni-
lega heilmikil áhrif á hrossin. Hugs-
anlega skýrir hún t.d. það að fylfullar
hryssur skyldu hegða sér stundum
eins og stóðhestar. Afskipti af sam-
skiptum annarra, sem stóðhestur
hefur oft í villtum stóðum, sást ein-
nig alloft í rannsókninni á Skáney.
Greinilegt er að það vekur spennu
að ný hross bætist í hópinn og líka ef
hópi er sundrað. Þetta kemur fram í
aukinni árásargimi. Þau virðast ein-
nig vera virkari í að mynda tengsl við
slrkar aðstæður, sérstaklega gelding-
arnir og unghrossin. Fullorðnu
hryssumar voru afhir á móh íhalds-
samar og virtust halda sig mest við
sína fyrri félaga. Áhugavert er að
skyldari hross í sama félagshópi voru
líkleg hl að halda saman, þ.e. kljást,
vera nálægt hvert öðru í haganum og
leika sér saman (þau yngri).
Þakkir
Innilegar þakkir hl Bimu Hauksdótt-
ur, Bjama Marinóssonar og Hauks
Bjamasonar á Skáney fyrir aðstöð-
una og alla hjálpina. Machtzeld van
Dierendonck bar hitann og þungann
af skipulagi vinnunnar á vettvangi
og úrvinnslu gagna. Þórey Ingi-
mundardóthr, Snorri Sigurðsson,
Caroline Kamps, Marilyn Jankevici-
us og Ingimar Sveinsson aðstoðuðu á
vettvangi.
Rannís veitti þriggja ára styrk og
Kennaraháskóli Islands og Land-
búnaðarháskólinn á Hvanneyri
studdu rannsóknina.
SUMMARY
Social behavior of horses. Research
at Skáney, W-Iceland
We report results from studies of social
behaviour of Icelandic horses at the farm
Skáney, West-Iceland in 1997 and 1999.
The groups consisted of adult mares,
many of which had foals during the
study, some adult geldings and many
immature and young horses (Tables 1
and 2.). No stallions were present. The
hypothesis of Feist and McCullough
from 1976 about the effect of a stallion on
the behaviour of herd members, such as
hindering them to form social bond, was
tested. This was done by comparing fre-
quencies of allogrooming and the pattem
of social bonding with results from stu-
dies of wild horses in other coimtries.
Furthermore, we compared pattems of
behaviour in one socially stable and two
socially unstable groups. The stable
group was composed of horses that all
came from Skáney and were all familiar
to each other. The unstable groups were
of two kinds. We introduced unfamiliar
horses into the Skáney group (group III
in 1999) and we had a group (group II)
where half of the individuals in the orig-
inal group (I) were removed. Inbreeding
coefficients between all dyads were cal-
culated allowing us to test if horses for-
med bonds based on kinship. The groups
were observed for 488,166 and 847 hours
respectively in May and June at all hours.
Allogrooming frequencies, playing fre-
quencies, aggressive interactions and
other interactions were recorded. Dom-
inance hierarchies were calculated.
In the stable group where nearest-
neighbour measurements were taken
there was a good agreement between
standing close to each other and affiliati-
ve relationships. This is in an agreement
with some earlier studies but not others.
In all groups the dominance hier-
archies were significantly linear and rank
correlated with age. Ihe adult mares thus
dominated the immature horses and the
younger geldings.
The horses made friends with others
of the same social class, but familiarity
had a strong effect. Males played more
than the sub-adult females and preferred
other males as play mates wliile sub-
adult mares did not discriminate
between the sexes. Compared to the sta-
ble group the sub-adults played more,
allogroomed more and all had more
allogrooming partners than in the soci-
ally unstable groups. Also, the horses
were more aggressive in the unstable
groups.
Earlier findings where it has been
shown that individuals of similar rank
form bonds (based on allogrooming) and
stay close to each other are supported in
this shidy. This undoubtedly stabilizes
the group and reduces aggression.
Interestingly, kinship seems to affect
bonding because the horses were more
likely to allogroom, play with and stay
close to related individuals. Furthermore,
the adult mares formed affiliahve bonds
almost exclusively with other mares, but
not with their offspring. This is an inter-
esting finding which has not been report-
ed before. Thus, the existence of groom-
ing bonds between mothers and young
offspring (1M year old), which has been
described for wild horses and between
donkey mothers and their offspring after
the weaning period, are perhaps not
common in a herd dominated by adult
mares with no stallion.
The social structure of groups of
Icelandic horses, with no mature stallion
but many adult mares, is therefore best
described as being dominated by the
mares which form bonds with each other
and is characterized by strong relations-
hips which are influenced by kinship.
The hypothesis of the suppressing effect
of the stallion on herd members is supp-
orted.
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