For an animal that lives and hunts socially like a wolf, is there a lower threshold to the size of prey items they will hunt? A pack wouldn't have much trouble with catching say a rabbit, but would the food provided be enough to actually make the hunt worthwhile? What is the limit in which a prey item becomes too small to be worth catching?
You should not post here until you've demonstrated your own research effort. Given this stipulation -- and the rich literature about this very topic -- I will keep my answer cursory so as to act as starting points for your search. A simple Google or google Scholar search on your part will reveal many more details/studies.
According to Becker et al 2018:
[Wolf] Prey selection is influenced by the absolute and relative abundances of prey types, the life history characteristics of predators and prey, and the attributes of the environment in which these interactions occur.
Smith et al. 2010 demonstrate that diets vary with season -- their focus being on winter diets.
- Huggard 1993 shows the impact of environmental variables such as snow.
Herd density plays a significant role:
Davis et al 2012 showed that lower density of secondary prey mattered more than heightened density of primary prey.
Huggard 1993 (Canadian Journal of Zoology) showed that density of herds (vs herd density) mattered more in Banff National Park in Canada. Herd size and habitat also mattered -- with wolves avoiding some habitats and seemingly choosing places that optimized preferred habitats and large herd size.
Wolf scat/diet studies showing smallest species in their diet:
Sin et al 2019: smallest for Sandanavian wolves = domestic dogs
Nowak et al 2011 showed the following small prey made up the stated percentages of wolve's diets in Poland:
brown hare Lepus europeus (2.5%) and Eurasian beaver Castor fiber (1.4%). Domestic animals, exclusively dogs and cats, made up 1.0% of food biomass.
Becker, M.S., Garrott, R.A., White, P.J., Gower, C.N., Bergman, E.J. and Jaffe, R., 2008. Wolf prey selection in an elk-bison system: choice or circumstance?. Terrestrial Ecology, 3, pp.305-337.
Cohen, J.E., Pimm, S.L., Yodzis, P. and Saldaña, J., 1993. Body sizes of animal predators and animal prey in food webs. Journal of animal ecology, pp.67-78.
Davis, M.L., Stephens, P.A., Willis, S.G., Bassi, E., Marcon, A., Donaggio, E., Capitani, C. and Apollonio, M., 2012. Prey selection by an apex predator: the importance of sampling uncertainty. PloS one, 7(10), p.e47894.
Henriques, J.F., Lacava, M., Guzmán, C., Gavín-Centol, M.P., Ruiz-Lupión, D., De Mas, E., Magalhães, S. and Moya-Laraño, J., 2021. The sources of variation for individual prey-to-predator size ratios. Heredity, 126(4), pp.684-694.
Huggard, D.J., 1993. Effect of snow depth on predation and scavenging by gray wolves. The Journal of wildlife management, pp.382-388.
Huggard, D.J., 1993. Prey selectivity of wolves in Banff National Park. I. Prey species. Canadian Journal of Zoology, 71(1), pp.130-139.
Nowak, S., Mysłajek, R.W., Kłosińska, A. and Gabryś, G., 2011. Diet and prey selection of wolves (Canis lupus) recolonising Western and Central Poland. Mammalian Biology, 76(6), pp.709-715.
Sand, H., Eklund, A., Zimmermann, B., Wikenros, C. and Wabakken, P., 2016. Prey selection of Scandinavian wolves: single large or several small?. PloS one, 11(12), p.e0168062.
Sin, T., Gazzola, A., Chiriac, S. and Rîșnoveanu, G., 2019. Wolf diet and prey selection in the South-Eastern Carpathian Mountains, Romania. PloS one, 14(11), p.e0225424.
Smith, D.W., Drummer, T.D., Murphy, K.M., Guernsey, D.S. and Evans, S.B., 2004. Winter prey selection and estimation of wolf kill rates in Yellowstone National Park, 1995–2000. The Journal of Wildlife Management, 68(1), pp.153-166.
Tsai, C.H., Hsieh, C.H. and Nakazawa, T., 2016. Predator–prey mass ratio revisited: does preference of relative prey body size depend on individual predator size?. Functional Ecology, 30(12), pp.1979-1987.
Vézina, A.F., 1985. Empirical relationships between predator and prey size among terrestrial vertebrate predators. Oecologia, 67(4), pp.555-565.