Social Recognition in Newly Weaned Grey Seals
(Halichoerus grypus)
Kelly
1*
Robinson ,
Sean
2
Twiss ,
Neil
1
Hazon ,
Simon
1
Moss
& Paddy
1**
Pomeroy
Abstract
Study Behaviours
Recognising individuals and behaving appropriately towards them is a crucial ability for many species. In pinnipeds, mother/pup recognition is well documented, but the existence of other social bonds on
breeding colonies and haul-outs remains poorly understood. Aspects of pinniped reproductive behaviour, such as breeding site fidelity, mean that individuals may encounter the same animals repeatedly
within and across seasons. However the ability to recognise non-related individuals has never been tested in pinnipeds outside of studies on recognition between territorial males.
To investigate the recognition capabilities of grey seals, 12 weaned pups were penned in 2 groups of 6 during the 2010 breeding season on the Isle of May, Scotland. Over 14 days each pup took part in a
series of paired pen trials with either individuals they had previously co-habited with (familiar) or ones they had never encountered before (stranger). As declines in investigative behaviour indicates
familiarity in paired pen trials, the number of visual and olfactory ‘checks’ and the number of interactions between pups were recorded. Plasma samples were also taken to look for peaks in the
neuropeptide hormone oxytocin, which is released during positive social interactions with familiar individuals. Trials with paired strangers had significantly more ‘checks’ (mean increase: 22.4 checks/trial,
p=0.026) and interactions (mean increase: 17 interactions/trial, p=0.034) than trials with familiars. Four individuals in familiar trials also exhibited a significant rise in plasma oxytocin (basal: 11.1pg/ml,
trial: 192.8pg/ml, p<0.01) whilst none in stranger trials had such a response. Previous studies show evidence of breeding female grey seals consistently affiliating over successive seasons, with potential
energetic rewards for associating with animals that recognise and adjust their behaviour towards each other. This study begins to unravel the mechanism behind this, showing that even newly weaned
pups can recognise familiar individuals and respond differently to them.
3. Results
Fig. 4
Fig. 5
1.Introduction
Fig. 6
• In pinnipeds, many species aggregate in large numbers to breed or to haul out to rest/moult.
• The ability to recognise individuals would be useful to reduce costly aggressive interactions (Ruddell et al.
2007).
Clockwise from top left;
Fig. 2 Two study animals in a low level aggressive interaction, with the animal on the left as
the aggressor. Hisses and ‘flippering’ (scratching or hitting the other animal with a fore
flipper) are common threat displays that preclude lunges and biting.
• This study used paired pen trials (Bielsky and Young 2004) to investigate whether newly-weaned grey seals
on the Isle of May, Scotland, change their behaviour towards individuals they have previously co-habited
with.
Fig. 4 Number of Interactions between the two
trial animals in familiar and stranger trials.
• Analysis included using levels of the neuropeptide oxytocin as an indicator of positive social experiences.
Fig. 5 Number of visual and olfactory ‘checks’
between two trial animals in familiar and stranger
trials.
2. Methods
Fig. 6 Oxytocin levels during the two trial types
and the basal level for free roaming weaned pups
on the Isle of May colony in 2010.
Fig. 1 The 5x5m trial pen
during a familiar trial.
The two holding pens were
10 x 15m and were
separated by 10m to
prevent interactions
between ‘stranger’ animals
outside of the trials.
•In familiar trials, there are fewer interactions (p=0.034) and fewer ‘checks’ (p=0.026) than in stranger trials (see
fig. 4 and 5).
•Mean basal oxytocin levels for free-roaming weaned pups was 12.6pg/ml, and the mean basal oxytocin levels of
the study group (11.1pg/ml) were not significantly different (p=0.29), nor were they affected by time of day, time in
captivity or time taken to obtain a plasma sample.
•Oxytocin levels in the stranger trials (mean = 12.7pg/ml) were not significantly different to basal levels in the
study group or free-roaming animals (p=0.2).
•Four out of twelve animals in familiar trials had very high oxytocin levels (189.5-197.2pg/ml), making the mean
(70.9pg/ml) significantly higher than the basal and stranger trial levels (p<0.01) (see fig 6).
• 12 weaned pups were penned in 2 groups of 6, producing animals that have cohabited prior to the pen trials
(familiar) and animals that have never previously interacted (strangers).
4. Conclusions
•Individuals were then paired with either a familiar animal or a stranger for a 1 hour pen trial (fig. 1).
Fig. 3 Two study animals in an olfactory ‘check’. Sniffing the facial or anogenital areas and
specifically looking at the other animal frequently occur between individuals that encounter
each other on a colony.
•Observations and videos were taken during the trial to detect any behavioural differences between the two
types of trial (fig. 2 and 3).
•Plasma was taken after a subset of stranger and familiar trials (n=12 each), before capture and throughout
the seal’s time in captivity to establish basal oxytocin levels for those animals.
Thanks to:
We wish to thank the field teams from North Rona and the Isle of May for 2009 and 2010 including Paddy Pomeroy, Sean Twiss, Ross Culloch, Wully Paterson, Simon Moss, Matt
Bivins, Paula Redman and Theoni Photopoulou. For invaluable guidance on the plasma analysis, we would like to thank Neil Hazon and Ailsa Hall. This work was funded by NERC
and SMRU.
•Additional plasma samples were taken from non-study animals on the Isle of May colony to establish basal
oxytocin levels for this species and age class.
Contact information:
1
Sea Mammal Research Unit, Scottish Oceans Institute,
University of St Andrews, St Andrews, Fife, KY16 8LB
2 School of Biological and Biomedical Sciences, Durham
University, South Road, Durham, DH1 3LE
* kjr33@st-andrews.ac.uk
** pp6@st-andrews.ac.uk
References
Ruddell, S., Twiss, S. and Pomeroy, P. (2007) Measuring opportunity for sociality: quantifying social stability in a colonially
breeding phocid. Animal Behaviour vol 74, P1357-1368
Bielsky, I. and Young, L. (2004) Oxytocin, vasopressin and social recognition in mammals. Peptides vol 25, P1565-1574
Hall, A., McConnell, B. and Barker, R. (2001) Factors affecting first year survival in grey seals and their implications for life
history strategy. Journal of animal ecology vol. 70, No. 1, P138-149
Neumann, I., Wiggler, L., Torner, F., Holsboer, F. and Landgraf, R. (2000) Brain oxytocin inhibits basal and stressinduced activity of the hypothalamo-pituitary adrenal axis in male and female rats: partial action within the paraventricular
nucleus. Journal of Neuroendocrinology vol 12, P235-243
•There is a difference in the behaviour grey seals express towards familiar animals over stranger ones,
suggesting that recognition between animals in this species is possible and that reduction of aggressive
behaviours does occur in these circumstances.
•For animals fasting on a breeding colony, it would be beneficial for neighbours to minimise the energy they
expended in aggressive interactions, reducing the risk of injuring themselves and dependant pups nearby.
•Pup survival in the first year of life is positively correlated to its mass at weaning (Hall et al. 2001). Therefore
maximising the energy invested in feeding dependant pups and reducing other behaviours would be a beneficial
strategy for a female to maximise her lifetime reproductive output.
•Oxytocin release is only associated with positive social interactions. This suggests that the individuals with high
levels in familiar trials not only recognised the other individual but received a physiological benefit from
associating with them, as oxytocin acts on the hypothalamo-pituitary-adrenal axis to reduce anxiety and stress
responses (Neumann et al. 2000).
•Therefore this study provides strong evidence that grey seals can recognise and adjust behaviour to other
individuals they have co-habited with, as well as linking this reduction to a physiological pay off.