Ha, J.C., P.N. Lehner and S.D. Farley. 1990. Risk-prone foraging behavior in captive gray jays (Perisoreus canadensis). Anim. Behav. 39:91-96.

The question of how animals make decisions about how, where, and when to forage has been an active area of research in behavioral ecology in recent years. This paper addressed a particularly controversial series of findings by a single researcher in a novel way, by requiring the animal to make foraging decisions in order to obtain its entire caloric requirements rather than being provided ad–libitum food in its home cage for much of the day. This research was the one of the first to establish that the decision about where and when to forage in the face of predictable and unpredictable patches of food was not as simple and straightforward as originally suggested in earlier, theoretical work.

Weigl, P.D., L. Sherman-Jones, M.A. Steele, J.C. Ha and T. Sharpe. 1990. The ecology of the fox squirrel (Sciurus niger) in North Carolina: implications for survival in the southeast. Bull. Tall Timbers Res. Sta. 24:1-93.

This publication, a monograph summarizing many years of work by the first author, provided the documentation of, and the explanation for, the decline of the eastern fox squirrel to endangered status, and presented a scientifically-based management plan for the species’ recovery. My research provided the critical information, based on hundreds of hours of solo field work tracking radiocollared animals, that eastern fox squirrels required five times more home range area than the more common and closely related midwestern fox squirrel. Thus, we were able to demonstrate that management practices based on extensive research on the midwestern subspecies were inappropriate for the eastern subspecies.

Conrad, S., J.C. Ha, C. Lohr, and G. Sackett. 1995. Ultrasonic assessment of fetal growth in the pigtailed macaque (Macaca nemestrina). Amer. J. Primatology 36:15-35.

In this work, we established norms for fetal growth in pigtailed macaques (a research species in increasing demand), and demonstrated a systematic statistical procedure for establishing growth curves which are used in aging fetuses by ultrasound. This work is now being used in numerous research studies at our U.W. research facilities as well as others.

Ha, J.C., C.L. Kimpo and G.P. Sackett. 1997. Multiple-spell discrete-time survival analysis of developmental data: object concept in pigtailed macaques. Developmental Psychology 33:1054-1059.

This paper was the first to adapt a statistical method, survival analysis, to developmental data. The analysis is extremely appropriate for this type of data, and eliminates a number of constraints and assumptions of more traditional techniques. In addition, this paper presents the first in-depth, large-sample analysis of object concept development in any species of non-human animal.

Ha, J.C., C. Nosbisch, J.L. Abkowitz, S.H. Conrad, N.K. Mottet, G.C. Ruppenthal, R. Robinette, G.P. Sackett, and J.D. Unadkat. Toxicity of Zidovudine (Azidothymidine) in Macaca nemestrina. Journal of Acquired Immune Deficiency Syndrome and Human Retrovirology 18:27-38.

This contribution was the result of a three-year study of the effects of zidovudine, an anti-HIV drug, on the development of the fetus and infant following administration throughout pregnancy. It was the first study in a primate to administer zidovudine in the first trimester, when the fetus is most sensitive to environmental toxins, such as drugs administered to the mother. This was a comprehensive study involving the monitoring of fetal growth; hematology and blood chemistry of mother, fetus, and infant; and psychological, behavioral, and physical growth of the infant. The results indicated that zidovudine had no long-term deleterious effects on the developing infant and following the earlier publication of our preliminary results, the decision was made to recommend zidovudine treatment of HIV-infected pregnant women during the first trimester and throughout their pregnancy.

Ha, J.C., R.L. Robinette and G.P. Sackett. 1999.  Social housing and pregnancy outcome in captive pigtailed macaques. American Journal of Primatology 47:153-163.

This paper summarizes the effects of sire presence, the presence of other pregnant females, group size, and group stability on pregnancy outcome in over 2000 macaque monkeys over the past 30 years at the U.W. Regional Primate Research Center. It is the first in a series of publications based on the largest database of breeding, clinical, physical growth, hematology and blood chemistry information available on any primate species. Based on this unique set of records, we were able to show that the social environment has a dramatic effect on the progress and outcome of pregnancies, and that individual characteristics, like age and pregnancy history, play a less significant role than has been frequently assumed. The information in this contribution will be extremely valuable in breeding programs for endangered species of primates, and has implications for dealing with poor pregnancy outcomes in humans as well.


Ha, R.R. and J.C. Ha.  2003.  Effects of prey type, prey density and energy requirements on the use of alternative foraging tactics in crows.  Animal Behaviour 66: 309-316.

In this paper, we apply the concepts of producer-scrounger theory to the first field test of its predictions.  We test for the significant effects of a wide range of metabolic, predation, and food supply characteristics on the decision by tidal-beach-foraging Northwestern crows to produce (locate their own prey items) or scrounge (steal items from successful producers).  We conclude that, in this species, only opportunity drives this decision.  If producers locate a large food item, with measurable handling time, then they risk loss of the item, or at least the energy involved in defending their food item from scroungers.  On the other hand, these large items yield significantly more energy per unit time, and hence there is a balanced trade-off to the system.  We found that crows balance the use of the two tactics to achieve identical energy intakes over the course of a day.  This work produced several other papers which document the use of vigilance in this system, the use of high-cost and low-cost scrounging behavior towards kin and non-kin, and several papers on the basic natural history of the Northwestern crow.