Conservation & Science Staff Bios

Stephen Ross, Ph.D.

  Director
Lester E. Fisher Center for the Study and Conservation of Apes

Education

  • Ph.D. - Providing Opportunities for Naturalistic Behaviour and the Implications for Captive Nonhuman Primate Management, Behaviour and Welfare, University of Copenhagen
  • M.A. – Differential Rearing Effects on Chimpanzee Behavior, University of Chicago
  • B.S. – University of Guelph

Areas of Expertise

  • Chimpanzee behavior
  • Comparative ape cognition
  • Animal welfare

About Steve Ross:

Steve began his career in animal behavior studying alternative housing for domestic pigs as a research assistant at the Center for Food and Animal Research in Ottawa, Ontario, Canada. Following a year studying free-ranging rhesus monkeys in Puerto Rico, he continued to pursue his interest in the proximate and ultimate effects of captive environments on animal welfare as a researcher at facilities in Texas and Georgia. Here he helped conduct studies of the effects of human interaction, social introductions and computer-assisted enrichment on the behavior of chimpanzees.

In 2000, Steve was hired by Lincoln Park Zoo as a behavior specialist with a primary role in the design of what eventually became the award-winning Regenstein Center for African Apes. He conducted a wide breadth of ape and visitor studies that helped directly influence the design of the new ape facility and continues that line of research today in his applied behavioral research with both gorillas and chimpanzees.

Steve assumed the position of chair of the Chimpanzee Species Survival Plan® (SSP) in 2002. In this role, he leads the multi-institutional effort to manage the population of chimpanzees living in zoos accredited by the Association of Zoos and Aquariums (AZA). Steve has been instrumental in promoting the SSP as a global leader in the promotion of progressive chimpanzee management that optimizes chimpanzee welfare, both within and outside AZA zoos.

Though Steve has published papers on species as diverse as polar bears, otters, gorillas and zoo visitors, his primary focus is improving the welfare of chimpanzees in a wide scope of conditions. His research on how the inappropriate portrayal of chimpanzees in the popular media affects public conservation attitudes of this species is a unique contribution to these efforts. These interests culminated with the initiation of Lincoln Park Zoo's Project ChimpCARE in 2009. This innovative program seeks to assess the housing and management of chimpanzees living as pets, performers and in other private situations with the goal of facilitating policy change that will benefit this often-unseen population of chimpanzees in the United States.

With almost 15 years of experience studying animal behavior, Steve is enthusiastically supportive of Lincoln Park Zoo’s approach to scientific-based decision-making. Utilizing the unique research resources available at the Lester E. Fisher Center for the Study and Conservation of Apes, he focuses on using science to influence policy that will have positive effects for animal welfare. Studying ape behavior and cognition allows him a unique insight into how these fascinating animals interact with their environments and how to best transform these areas to support their complex needs.

Publications

E. R. Boeving, M. A. Shender, K. E. Wagner, S. R. Ross 2013. A behavioral evaluation of pregnant zoo-housed gorillas (Gorilla gorilla gorilla). American Journal of Primatology. 75(S1), 77.

Chelluri, G.I., Ross, S.R. and Wagner, K.E. 2013. Behavioral correlates and welfare implications of informal interactions between caretakers and zoo-housed chimpanzees and gorillas. Applied Animal Behaviour Science 147: 306-315.

S. E. Henley, M. A. Shender, K. E. Wagner, S. R. Ross 2013. Behavioral development in a new group of bachelor gorillas (Gorilla gorilla gorilla). American Journal of Primatology. 75(S1), 77.

Kurtycz, L.M., Shender, M.A., & Ross, S.R. 2013. Changes in western lowland gorilla (Gorilla gorilla gorilla) group cohesion following the birth of a baby. American Journal of Primatology. 75(S1), 89.

L. M. Kurtycz, M. A. Shender, S. R. Ross 2013. Changes in western lowland gorillas (Gorilla gorilla gorilla) group cohesion following the birth of a baby. American Journal of Primatology. 75(S1), 89.

K.E. Wagner, S. R. Ross 2013. Female sexual state influences the cognitive test performance of zoo-living chimpanzees (Pan troglodytes) but not gorillas (Gorilla gorilla gorilla). American Journal of Primatology. 75(S1), 44.

M. H. Brown, M. A. Shender, K. E. Wagner, S. R. Ross 2013. Potential factors associated with stereotyped ear-covering behavior in an adolescent male gorilla (Gorilla gorilla gorilla). American Journal of Primatology. 75 (S1), 49.

Ross, S.R. 2013. Preface to the Special Issue on the Welfare of Zoo Animals. Applied Animal Behaviour Science 147: 306-315.

Ross, S.R. 2013. Questioning the use of privately-owned apes in Anthropological Research. American Journal of Physical Anthropology, 152: 313-314.

Hopper, L.M., Bonnie, K.E., Kurtycz, L.M., & Ross, S.R. 2013. Testing for chimpanzee innovation and social learning in a zoo setting. American Journal of Primatology. 75(S1), 56.

L. M. Hopper, K. E. Bonnie, L. M. Kurtycz, S. R. Ross 2013. Testing for chimpanzee innovation and social learning in a zoo setting. American Journal of Primatology. 75(S1), 56.

M. A. Shender, S. R. Ross 2013. The effects of available space on a group of captive gorillas (Gorilla gorilla gorilla) and chimpanzees (Pan troglodytes) living in a naturalistic zoo-setting. American Journal of Primatology. 75(S1), 51.

H. D. Freeman, S. R. Ross 2013. The relationship between early human exposure and current behavior in former pet/performer chimpanzees (Pan troglodytes). American Journal of Primatology. 75(S1), 46.

B. I. Neier, D. Boyer, K. E. Lukas, S. R. Ross 2013. Wounding rates in bachelor and mixed-sex grouping of lowland gorillas (Gorilla gorilla gorilla). American Journal of Primatology. 75(S1), 61.

Wagner, K.E., and Ross, S.R. 2012. Association between cognitive test performance and disposition to arousal in chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla gorilla). American Journal of Primatology, 74 S1: 66.

Fitzpatrick, M.C., Wagner K.E., Ross S.R. 2012. Behavioral changes associated with sexual state in zoo-living chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla gorilla). American Journal of Primatology, 74 S1: 39.

Jean, S.M., Preuss, T., Stobert, E., Anderson, D., Sharma, P., Ross, S.R., Stroud, F.C. 2012. Case Report: Cerebrovascular Accident (Stroke) in Captive, Group-Housed, Female Chimpanzees. Comparative Medicine, 62 (4): 1-8.

Finestone, E.M., Bonnie, K.E., Vreeman, V.M., Ross, S.R., Lonsdorf, E.V. 2012. Chimpanzee (Pan troglodytes) food selections differ between solitary and social conditions. American Journal of Primatology, 74 S1: 61.

Ross, S.R., and Anderson, K.E. 2012. Estimating daily travel distances for captive apes. American Journal of Primatology, 74 S1: 35.

Bonnie, K, Ross, SR, and Lonsdorf, EV. 2012. Flexibility and persistence of chimpanzee (Pan troglodytes) foraging behavior in a captive environment. American Journal of Primatology, 74: 661-668.

Shender, M.S., Anderson, K.E., Ross, S.R. 2012. Group cohesion in captive gorillas (Gorilla gorilla gorilla) and chimpanzees (Pan troglodytes) living in a naturalistic zoo exhibit. American Journal of Primatology, 74 S1: 75.

Lonsdorf, EV and Ross, SR 2012. Socialization and Development of Behavior. In: Mitani J, Call J, Kappeler P, Palombit R, and Silk J (eds) The Evolution of Primate Societies. University of Chicago Press. pp.245-268.

Ségurel, L, EE Thompson, T Flutre, J Lovstad, A Venkat, SW Margulis, J Moyse, SR Ross, K Gamble, G Sella, C Ober, M Przeworski. 2012. The ABO blood group is a trans-species polymorphism in primates. Proceedings of the National Academy of Sciences, 109 (45) 18493-18498.

Ross, S.R., Melber, L., Gillespie, K.L., and Lukas, K.E. 2012. The impact of modern, naturalistic exhibit design on visitor behavior: A cross-facility comparison. Visitor Studies, 15(1): 3-15.

Heggs, L.E., Matheson, M., Ross, S.R., Mulcahy, J.B. 2012. The influence of a novel outdoor environment on the behavior of captive chimpanzees (Pan troglodytes) in a sanctuary setting. American Journal of Primatology, 74 S1: 36.

Kurtycz, LM, Wagner, KE, Ross, SR, Lonsdorf, EV. 2011. Behavioral effects of providing a choice for outdoor access to captive gorillas (Gorilla gorilla gorilla). American Journal of Primatology, 73(S1): 68.

Hopkins, WD, Phillips, KA, Bania, A, Calcutt, SE, Gardner, M, Russell, J, Schaeffer, J, Lonsdorf, EV, Ross, SR, and Schapiro, SJ. 2011. Hand Preferences for Coordinated Bimanual Actions in 777 Great Apes: Implications for the Evolution of Handedness in Hominids. Journal of Human Evolution, 60: 605-611.

Anderson, K.E., and Ross, S.R. 2011. Methods and preliminary results for the social space of captive chimpanzees. Annual meeting of the Midwestern Primate Interest Group, Cleveland, OH, September 2011.

Faust, LJ, Cress, D, Farmer, K, Ross, S.R., Beck, B. 2011. Predicting Capacity Demand on African Chimpanzee Sanctuaries. International Journal of Primatology, 32:849-864.

Ross, S. R., Calcutt, S. E., Schapiro, S. and Hau, J. 2011. Space use selectivity by chimpanzees and gorillas in an indoor-outdoor enclosure. American Journal of Primatology. 73: 197-208.

Ross, SR, Vreeman, VM, Lonsdorf, EV. 2011. Specific Image Characteristics Influence Attitudes about Chimpanzee Conservation and Use as Pets. PLoS ONE 6(7): e22050. doi:10.1371/journal.pone.0022050.

Ross, S.R., Wagner, K.E., Schapiro, S.J., Hau, J., and Lukas, K.E. 2011. Transfer and acclimatization effects on the behavior of two species of African great ape moved to a novel and naturalistic zoo environment. International Journal of Primatology, 32: 99-117.

Wagner, K.E. and Ross, S.R. 2010. Advances in the use of computerized technology in ape cognitive research. American Journal of Primatology, 72: S1: 67.

Ross, S.R., Wagner, K.E., Schapiro, S.J., and Hau, J. 2010. Ape behavior in two alternating environments: comparing exhibit and short-term holding areas. American Journal of Primatology. 71: 1-9.

Fenn, T.E., S.R. Ross, K. Wagner. 2010. Behavioral effects of female immigration on solitary and bachelor group male gorillas (Gorilla gorilla gorilla). American Journal of Primatology, 72: S1: 71.

Meguerditchian, A., Calcutt, S.E., Lonsdorf, E.V., Ross, S.R., and Hopkins, W.D. 2010. Captive gorillas are right-handed for bimanual feeding. American Journal of Physical Anthropology, 141: 638-645.

Ross, S.R. 2010. Chimpanzee (Pan troglodytes) Care Manual. Association of Zoos and Aquariums, Silver Spring, MD.

Truitt, A and Ross, SR. 2010. Current legislative challenges facing chimpanzee sanctuaries in the United States. American Journal of Primatology, 72 (S1): 49.

Ross, S.R., Wagner, K.E., Schapiro, S.J. and Hau, J. 2010. Differential ape behavior in two alternating environments: Comparing behavior in exhibit and short-term holding spaces. American Journal of Primatology, 72: 951-959.

Ross, S.R., Ross, M.R., and Clark, A.B. 2010. Ethosearch: A comprehensive repository of ethograms for use in animal behavior research. Proceedings of the 7th International Conference on Methods and Techniques in Behavioral Research, 369 (abstract).

Milstein, M.S., S. E. Calcutt, S. R. Ross, K. E. Bonnie, E. V. Lonsdorf. 2010. Food-sharing in a variable environment among a group of zoo-housed chimpanzees (Pan troglodytes). American Journal of Primatology, 72: S1: 70.

Ross, S.R. 2010. How cognitive studies help shape our obligation for the ethical care of chimpanzees. University of Chicago Press.

Ross, S.R., Milstein, M.S., Calcutt, S.E., Lonsdorf, E.V. 2010. Preliminary assessment of methods used to demonstrate nut cracking behavior to five captive chimpanzees (Pan troglodytes). Folia Primatologica, 81: 224-232.

Ross, S.R., and Vreeman, V.M. 2010. Project ChimpCARE: An assessment of privately-owned chimpanzees in the United States. American Journal of Primatology, 72: S1: 48.

Ross, S.R. 2010. Research, advocacy and conservation efforts on behalf of chimpanzees: How American zoos are strengthening their commitment to the species. Proceedings of the 15th Kyoto University International Symposium (COP10 Partnership Program): Biodiversity, Zoos and Aquariums: The Message from Animals, 28 (abstract).

Ross, S.R. 2010. The challenges facing chimpanzee sanctuaries. American Journal of Primatology, 72: S1: 48.

Lonsdorf, E.V., Ross, S.R. and Matsuzawa, T. (eds).  2010. The Mind of the Chimpanzee: Experimental and Ecological Perspectives. University of Chicago Press.

Calcutt, S., Milstein, M. Ross, S.R., Lonsdorf, E.V. 2009. Acquisition of nut-cracking behaviors in a group of zoo-living chimpanzees (Pan troglodytes). American Journal of Primatology, 71, Supplement 1: 49.

Lonsdorf, E.V., Ross, S.R., Linick, S.A., Milstein, M.S. and Melber, T.N. 2009. An experimental, comparative investigation of tool use in chimpanzees and gorillas. Animal Behaviour, 77: 1119-1126.

Milstein, M.S., Lonsdorf, E.V. Ross, S.R., Bonnie, K.E., and Calcutt, S. 2009. Extractive tool-use by a group of zoo-housed chimpanzees (Pan troglodytes) in an variable environment: preliminary evidence of persistent strategies. American Journal of Primatology, 71, Supplement 1: 82.

Ross, S.R. and Gillespie, K. 2009. Influences on visitor behavior at a modern immersive zoo exhibit. Zoo Biology 28(5): 462-472..

Ross, S.R., Lonsdorf, E.V., and Holmes, A.N. 2009. Interactions between indigenous wildlife and four species of zoo-housed apes in North America: Patterns of aggression and hunting. American Journal of Primatology, 71, Supplement 1: 34.

Ross, S.R., Lonsdorf, E.V., and Holmes, A.N. 2009. Interactions Between Zoo-Housed Great Apes and Local Wildlife. American Journal of Primatology, 71: 458-465.

Wagner, K.E. and S.R. Ross. 2009. Sequencing performance and error trends in gorillas (Gorilla gorilla gorilla) and chimpanzees (Pan troglodytes). American Journal of Primatology, 71, Supplement 1: 35.

Ross, S.R. 2009. Sequential list-learning by an adolescent lowland gorilla (Gorilla gorilla gorilla) using an infrared touchframe apparatus. Interaction Studies 10(2): 115-129.

Ross, S.R., Schapiro, S.J., Hau, J., and Lukas, K.E. 2009. Space use as an indicator of enclosure appropriateness: A novel measure of captive animal welfare. Applied Animal Behaviour Science, 121: 42-50.

Ross, S.R., Bloomsmith, M.A., Bettinger, T.M., and Wagner, K.E. 2009. Wounding patterns in adolescent male chimpanzees: management and welfare implications. Zoo Biology, 28: 623-634.

Milstein, MS, Lonsdorf, EV, Ross, SR and Linick SA. 2008. A comparison between chimpanzee (Pan troglodytes) and gorilla (Gorilla gorilla gorilla) social tolerance at an artificial termite mound. American Journal of Primatology, 70:58.

Wagner, K.E. and Ross, S.R. 2008. Association between self-directed behaviors and performance in a cognitive sequencing task in a female chimpanzee. American Journal of Primatology, 70:55.

Wagner, K. and Ross, S.R. 2008. Chimpanzee (Pan troglodytes) birth patterns and human presence in zoological settings. American Journal of Primatology, 70: 1-4.

Ross, S.R. and Wagner, K.E. 2008. Differential behavior patterns in zoo-housed apes between exhibits and holding: Effects on welfare assessment. American Journal of Primatology, 70:41.

Ross, S.R., Lukas, K.E., Lonsdorf, E.V., Stoinski, T.S., Hare, B., Shumaker, R. and Goodall, J. 2008. Inappropriate Use and Portrayal of Chimpanzees. Science, 319: 1487.

Foster, M.W., Linick, S.A., Milstein, M.S., Wagner, K.E., Margulis, S.W., Ross, S.R., and Lonsdorf, E.V.  2008. Motivating a new generation of primatologists: the Lincoln Park Zoo's Exploring Ape Behavior Program. American Journal of Primatology, 70:38.

Ross, S.R., Wagner, K.E., Lonsdorf, E.V. 2008. Preliminary evidence for sequential list-learning by a western lowland gorilla (Gorilla gorilla gorilla): Performance measures and analysis of errors. Primate Eye, 96.

Linick, S.A., Lonsdorf, E.V., Ross, S.R., and Milstein M.S. 2008. The development of termite-fishing skills in captive Western lowland gorilla infants (Gorilla gorilla gorilla). American Journal of Primatology, 70:58.

Ross, S.R., Lonsdorf, E.V. and T.S. Stoinski. 2007. Assessing the welfare implications of visitors in a zoo setting: A comment on Wells (2005). Applied Animal Behaviour Science, 102: 130-133.

Vreeman, V.M. and Ross, S.R. 2007. Do seasonal changes affect activity in captive chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla gorilla) living in a northern zoo?. American Journal of Primatology 69 (supplement 1): 89.

Halloran, A.R., Broadfield, D., Ross, S.R. and Marshall, A. 2007. Exploring diachronic change in the group specific vocalizations of chimpanzees (Pan troglodytes). American Journal of Physical Anthropology (Suppl 44): 123-124.

Melber, T.M., Lonsdorf, E.V. and Ross, S.R. 2007. Social learning of tool-use skills in captive chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla gorilla). American Journal of Primatology 69 (supplement 1): 100-101.

Lonsdorf, E.V., Ross, S.R. and Melber, T.N. 2006. An experimental, comparative approach to social learning of tool-use skills in chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla gorilla). International Journal of Primatology (supplement 1): 27.

Ross, S.R. and Lukas, K.E. 2006. Attitudes and knowledge of visitors towards African apes at a North American Zoo. International Journal of Primatology (supplement 1): 27.

Bloomsmith, M.A., Ross, S.R., Bettinger, T., Clay, A.W. and Anderson, U. 2006. Cross-sectional study of the behavioral development of young male chimpanzees in twenty zoos. American Journal of Primatology 68 (supplement 1): 48.

Ross, S.R. 2006. Issues of choice and control in a pair of captive polar bears (Ursus maritimus). Behavioural Processes, 73(1): 117-120.

Ross, S.R., Bettinger, T.M., and Bloomsmith, M.A. 2006. Patterns of wounding incidents in captive chimpanzee groups with adolescent males. International Journal of Primatology (supplement 1): 2.

Melber, T.N., Lonsdorf, E.V., and Ross, S.R. 2006. The Lester E. Lester E. Fisher Center for the Study and Conservation of Apes: A new center for the advancement of research, conservation and education. American Journal of Primatology 68 (supplement 1):121.

Ross, S.R. and Lukas, K.E. 2006. Use of space in a non-naturalistic environment by chimpanzees (Pan troglodytes) and lowland gorillas (Gorilla gorilla gorilla). Applied Animal Behaviour Science, 96: 143-152.

Bloomsmith, M.A., Baker, K.C., Ross, S.R. and Lambeth, S.P. 2005. Early rearing conditions and captive chimpanzee behavior: Some surprising findings. Nursery Rearing of Nonhuman Primates in the 21st Century. Kluver Academic Publishers, New York, New York, 289-312.

Ross, SR and Lukas, KE. 2005. Zoo Visitor Behavior at an African Ape Exhibit. Visitor Studies Today, 8(1): 4-12.

Lukas, K.E. and Ross, S.R. 2005. Zoo visitor knowledge and attitudes towards gorillas and chimpanzees.. Journal of Environmental Education, 36(4): 33-48.

Maestripieri, D. and Ross, S.R. 2004. Maternal influences on infant behavioral development in western lowland gorillas. Advances in Psychology Research, 27: 96-112.

Maestripieri, D. and Ross, S.R. 2004. Sex differences in play among western lowland gorilla (Gorilla gorilla gorilla) infants: Implications for adult behavior and social structure. American Journal of Physical Anthropology, 123 (1): 52-61.

Ross, S.R. 2003. A guide to caring for chimpanzees (book review). Zoo Biology, 22: 609-612.

Hopkins, W.D., Stoinski, T.S., Lukas, K.E., Ross, S.R. and Wesley, M.J. 2003. Comparative Assessment of handedness for a coordinated bimanual task in chimpanzees (Pan), gorillas (Gorilla), and orangutans (Pongo). Journal of Comparative Psychology, 117(3): 302-308.

Ross, S.R. 2003. North American regional studbook for the chimpanzee (Pan troglodytes). Lincoln Park Zoo, Chicago, Illinois.

Bloomsmith, M., Kuhar, C., Baker, K., Lambeth, S., Brent, L., Ross, S. and Fritz, J. 2003. Primiparous chimpanzee mothers and their infants: Behavior, interactions, and success. Applied Animal Behavior Science, 84: 235-250.

Maestripieri, D., Ross, S.K. and Megna, N.L. 2002. Mother-infant interactions in western lowland gorillas (Gorilla gorilla gorilla): Spatial relationships, communication, and opportunities for social learning. Journal of Comparative Psychology, 116(3): 219-227.

Platt, J., Brown-Palsgrove, M. and Ross, S.R. 2002. Otter enrichment and the benefits of keeper involvement in behavioral research. Animal Keeper's Forum, 29(11).

Ross, S.R. 2002. 2002. The effect of a simple feeding enrichment strategy on the behavior of two small-clawed Asian otters (Aonyx cinerea). Aquatic Mammals, 28 (2): 113-120.

Bloomsmith, M., Kuhar, C., Baker, K., Lambeth, S., Brent, L., Ross, S. and Fritz, J. 2001. Early interactions between primiparous chimpanzees and their infants. American Journal of Primatology, 54(1): 31.

Ross, S.K. and Lukas, K.E.  2001. Exhibit use by great apes as part of a post-occupancy evaluation. American Journal of Primatology, 54(1): 31.

Ross, S.K., Barger, N., Ganas, J., Lukas, K., Nichols, C., Megna, N., Stoinski, T. and Maestripieri, D. 2001. Maternal scaffolding of offspring behavior in western lowland gorillas. American Journal of Primatology, 54(1): 31.

Baker, K.C., Bloomsmith, M.A., Ross, S.K., Lambeth, S.P. and Noble, P.L. 2001. The behavioral effects of control vs. passive exposure to joystick-controlled computer tasks intended as enrichment for chimpanzees. American Journal of Primatology, 54(1): 64.

Ross, S.R., and Lukas, K.E. 2001. The care and management of captive chimpanzees workshop: Managing social behavior. Journal of Applied Animal Welfare Science, 4(4.

Bloomsmith, M.A., Ross, S.K. and Baker, K.C. 2000. Control over computer-assisted enrichment for socially housed chimpanzees. American Journal of Primatology, 51(1): 45.

Ross, S.K., Bloomsmith, M.A., Baker, K.C. and Hopkins, W.D. 2000. Initiating a computer-assisted enrichment system for captive chimpanzees. American Journal of Primatology, 51(1): 86-87.

Bloomsmith, M.A., Baker, K.C., Lambeth, S.P., Ross, S.K. and Shapiro, S.P.  2000. Is giving chimpanzees control over environmental enrichment a good idea?. Proceedings of The Apes: Challenges for the 21st Century Conference, Chicago, Illinois, 88-89.

Weary, D.M., Pajor, E.A., Bonenfant, M., Ross, S.K., Fraser, D. and Kramer, D.L. 1999. Alternative housing for sows and litters: Effects of a communal piglet area on pre- and post-weaning behaviour and performance. Applied Animal Behavior Science, 65: 123.

Bloomsmith, M.A., Baker, K.C., Ross, S.K. and Lambeth, S.P. 1999. Comparing animal training to non-training human interaction as environmental enrichment for chimpanzees. American Journal of Primatology, 49(1): 35.

Bloomsmith, M.A., Baker, K.C., Ross, S.K. and Lambeth, S.P. 1998. Enlarging chimpanzee social groups: The behavioral course of introductions. American Journal of Primatology, 45: 171.

Weary, D.M., Pajor, E.A., Bonenfant, M., Ross, S.K., Fraser, D. and Kramer, D.L. 1997. The effects of mixing litters during lactation and at weaning on piglet behaviour and performance. Proceedings of the 31st International Congress of the ISAE, Prague, Czech Republic.

Weary, D.M., Ross, S. and Fraser, D. 1997. Vocalizations by isolated piglets: A reliable indicator of piglet need directed towards the sow. Applied Animal Behaviour Science, 53: 249-257.