It has been two and a half years of collecting data for my oxymoronically entitled study, “An assessment of consistent individual differences during human-animal interactions in the pre and post-natal period in rangeland ewes”. Ewes are female sheep for those of ewe that do not know. I say my study seems like an oxymoron because prior to investigating sheep behavior, I never considered this species to live in groups that consist of unique individuals. Although more approachable mouflon (Ovis musimon) are the wild counterparts thought to have been selectively bred for their outlying personalities into what we now refer to as domesticated sheep (Ovis aries), the species itself remains a bit clingy.
Turns out this herbivore still needs their predator-protecting, shelter-seeking, food-finding flock mates to survive, even after 7,000 years of human management. One might say sheep are the co-dependent type; an understanding reinforced by our childhood ideations and whimsical clay-mations (if you know, you know) depicting intense leader-follower tendencies within sheep. Despite these timeless narratives, more nuanced research has indicated that there are indeed individual temperaments that manifest within flocks [1], and these temperament differences can be assessed during or after a human interaction.
Thanks to my wonderful research collaborator, Dan Macon, the UCCE- Placer, Nevada, Sutter, and Yuba livestock and natural resources advisor, I am able to assess the unique responses of ~ 60 ewes towards unfamiliar humans, prior to and after being bred since this is around the time they receive handling. We started this work together after discussing issues related to his flock and other flocks across northern California at the UC Davis Sheep Innovators Conferences. Amongst other concerns like predation and grazing management, Dan brought up his observations about individual behavioral traits during lambing season. He told me that some ewes will steal, reject, and be aggressive towards lambs (not exactly the most maternal response). I did some further investigation afterwards and decided perhaps we can see if there is an association between maternal care and reactivity towards humans in sheep since this is a relatively unanswered question.
In order to assess ewes’ unique responses towards humans we have set up repeated behavioral trials that expose each ewe to a human interaction on a gradient (human presence, approach, and contact) within a restrained (alleyway) and open environments (experimental arena). Within the alleyway, five ewes are lined up single-file with only minimal opportunity for movement. This is a relatively common method used for administering treatment as it does not involve separation from the entire flock. Though other species of livestock (dairy and beef cattle, pigs, chickens, etc.) may be isolated from their social group when individual attention is required from the human manager, this situation is often circumvented on small and sometimes even large-scale sheep operations. The experience of social isolation in sheep can cause considerable distress [2] and induce a strong motivation to return to the flock. I learned this the hard way through unintentional mutton-busting, which is a rodeo except with sheep and 7-year-olds, at age 25. Minimizing stress is especially important at this time as these gals should be getting pregnant, or at least be thinking about it. Within the alleyway test, an unfamiliar human will approach and contact each ewe for 10 seconds, allowing them to respond to this type of interaction, and thereafter be released for the next stage of testing.
Based on previous literature, I decided to build a 36’ x 36’ experimental arena where we can observe the willingness of sheep to approach an unfamiliar human. By partitioning this arena out into 25 squares, indicated using the red paint marker, it is possible to quantify the average amount of time the ewe spends in close or distant proximity to a centrally positioned human. In addition to qualities of distance, I have been recording behaviors such as vocalizations, frequency and duration of walking/pacing, and duration of grazing or vigilance, as these are understood to be important for identifying individual behavioral types. My favorite sheep, number 17, likes to stand directly in the square with the stationary human in hopes to get some good head scratches. I might have accidently reinforced this behavior when testing is not on-going.
In addition to these behavioral tests in the alleyway and arena, I also wanted to get a better idea of how these individual behavioral types may influence how these ewes react to humans once they become moms. After about 5 months, it is the shepherds’ great hope that their ewes will be nice and plump with offspring. Once lambing season begins, a flurry of time-sensitive activity ensues; shepherds must keep track of lamb births so they can ‘tag’ lambs less than 24 hours after being born to ensure that the lamb(s) are healthy and marketable. This ‘tagging’ process may involve castration, tail docking, ear tagging, and/or vaccine injections.
Lamb tagging is the opportune time to capture a different kind of human animal interaction. While the shepherd is busy with the lambs, I am more concerned with what the ewe is up to since a human approaching and collecting the lamb (even briefly) could be considered quite challenging for her as a mother [3]. She is likely presented with a motivational conflict to flea in avoidance of the shepherd, who may be perceived as a predator, or she might stay near the shepherd in order to protect her offspring. Sheep number 17 takes the approach of trying to actively steer the shepherd back to where he had grabbed the lamb(s) and if that tactic doesn’t work she has been known to bite and growl (then becoming my not-so-favorite sheep).
Using video recordings during lamb tagging, we will observe the ewe’s response to her lamb(s) being handling for processing and quantify specific behaviors like vigilance, licking/sniffing and vocalizing, all considered indicators of strength of the ewe-lamb bond [4]. Not many studies have tracked individual sheep across multiple years and contexts during human interactions. By doing so we can 1) assess consistency of her individual responses in a longitudinal manner, 2) gather some secondary information about the ewe’s maternal capabilities and 3) investigate if these two aspects of ewe behavior are correlated. All this for the sole purpose that this area of inquiry will stop keeping you awake at night and you can get back to counting sheep.
Kaleiah Schiller is a 4th year PhD student in the Animal Biology Graduate Group and Animal Behavior and Cognition lab at the University of California, Davis. Kaleiah received her Bachelors of Science at the University of Wisconsin, River Falls, where she studied detection of febrile signs in piglets. Once entering UC Davis, Kaleiah met a wonderful shepherd named Dan Macon and they have been researching individual differences in ewes ever since.
References
[1] Plush, K.J., Hebart, M.L., Brien, F.D., and Hynd, P.I. 2011. The genetics of temperament in Merino sheep and relationships with lamb survival. Appl. Anim. Behav. Sci., 134, 130-135.
[2] Price, E.O., and Thos, J. 1980. Behavioral responses to short-term social isolation in sheep and goats. Appl. Anim. Etho., 6(4), 331-339.
[3] Napolitano, F., Rosa, G., and Sevi, A. 2008. Welfare implications of artificial rearing and early weaning in sheep. Appl. Anim. Behav. Sci., 110, 58-72.
[4] Dwyer, C.M. 2008. Individual variation in expression of maternal behavior: a review of the neuroendocrine mechanisms in the sheep. Jour. Of Neuroendocrin., 20, 526-534.
[Edited by Karli Chudeau and Maggie Creamer]
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