A noisy, chattering, social species, the Pygmy Nuthatch lives in long-needled pine forests—in the United States, principally ponderosa pines (Pinus ponderosa). Frenetic movements—head first, up tree, down tree, along branches, right-side up and upside down—accompanied by constant chatter, convey the busyness and nervous activity of this gregarious bird as it searches for food.

Because it uses cavities for roosting and for breeding, the Pygmy Nuthatch reaches its highest densities in mature pine forests little affected by logging, firewood collection, and snag removal. It feeds mainly on weevils and leaf and bark beetles (but also eats pine seeds), and is one of the few cooperatively breeding passerines in North America and one of only two cooperatively breeding nuthatch species worldwide. A third of the breeding pairs have 1–3 male helpers, usually progeny or other relatives. Helpers feed incubating females, nestlings, and fledglings and participate in defense of the nest site. Breeding units and their offspring form the nucleus of winter flocks. During the nonbreeding season, family groups flock with other Pygmy Nuthatch families that range over a foraging territory. They also join with other flocking birds of the conifer forests. Pygmy Nuthatches generally dominate these species in the social hierarchy and in volubility.

The Pygmy Nuthatch roosts in cavities, which it selects depending on season and weather. It picks roosts based on insulation and ventilation provided by roost cavities and relies on hypothermia to survive cold winter nights. Although a few other North American birds are capable of controlled hypothermia, only the Pygmy Nuthatch links hypothermia with protected roost sites and communalism. Pairs roost together; juveniles roost with parents, and collectives of several flocks roost together. Stacks of 6, 8, and 10 birds, and more, roost together in formations of squares, oblongs, triangles, diamonds, wedges, and tiers. Two articles report more than 150 individuals roosting in a single tree ( Knorr, O. A. (1957). Communal roosting of the Pygmy Nuthatch. Condor no. 59:398. Close Knorr 1957, Sydeman, W. J. and M. Güntert. (1983). Winter communal nesting in the Pygmy Nuthatch. Flagstaff: Snag Habitat Management Symposium. Northern Arizona Univ. Close Sydeman and Güntert 1983).

Robert A. Norris ( Norris, R. A. (1958b). Comparative biosystematics and life history of the nuthatches Sitta pygmaea and Sitta pusilla. Univ. Calif. Publ. Zool. no. 56:119-300. Close Norris 1958b) conducted the most extensive research on Pygmy Nuthatches. His thorough monograph covers all aspects of the biology of this species and compares it to its sister species, the Brown-headed Nuthatch (Sitta pusilla). Russ Balda and associates have addressed many aspects of Pygmy Nuthatch biology, such as cooperative breeding, roosting behavior, physiology, flocking behavior and hierarchy, feeding strategy, and habitat use ( Balda, R. P. (1967). Ecological relationships of the breeding-birds of the Chiricahua Mountains, Arizona. Ph.D. thesis, Univ. of Illinois, Urbana. Close Balda 1967, Balda, R. P. (1969). Foliage use by birds of the oak-juniper woodland and ponderosa pine forest in southeastern Arizona. Condor no. 71:399-412. Close Balda 1969, Balda, R. P. (1975). The relationship of secondary cavity-nesters to snag densities in western coniferous forests. Southwest Region Wildl. Habitat Tech. Bull. 1, Albuquerque: U.S. Dep. Agric. For. Serv. Close Balda 1975, Szaro, R. C. and R. P. Balda. (1979a). Bird community dynamics in a ponderosa pine forest. Stud. Avian Biol. no. 3. Close Szaro and Balda 1979a, Szaro, R. C. and R. P. Balda. (1982). Selection and monitoring of avian indicator species: an example from a ponderosa pine forest in the southwest. Fort Collins, CO: U.S. Dep. Agric. Close Szaro and Balda 1982, Balda, R. P., W. S. Gaud and J. D. Brawn. (1983). Predictive models for snag nesting birds. U.S. Dep. of Agric., For. Serv. Gen. Tech. Rep. Close Balda et al. 1983, Hay, D. B. (1983). Physiological and behavioral ecology of communally roosting Pygmy Nuthatch (Sitta pygmaea). Phd Thesis, Northern Arizona Univ., Flagstaff. Close Hay 1983, Brawn, J. D. (1985). Population biology, community structure, and habitat selection of birds in ponderosa pine habitat. Phd Thesis, Northern Arizona Univ., Flagstaff. Close Brawn 1985, Brawn, J. D. (1987). Density effects on reproduction of cavity-nesters in northern Arizona. Auk no. 104:783-787. Close Brawn 1987, Brawn, J. D. (1988). Selectivity and ecological consequences of cavity nesters using natural vs. artificial nest sites. Auk no. 105:789-791. Close Brawn 1988, Brawn, J. D. and R. P. Balda. (1988a). Population biology of cavity nesters in northern Arizona: do nest sites limit breeding densities? Condor no. 90:61-71. Close Brawn and Balda 1988a, Brawn, J. D. and R. P. Balda. (1988b). "The influence of silvicultural activity on ponderosa pine forest bird communities in the southwestern United States." In Bird conservation 3., edited by J. A. Jackson. Madison: Int. Council for Bird Preservation U.S. section. Univ. of Wisconsin Press. Close Brawn and Balda 1988b, Güntert, M., D. B. Hay and R. P. Balda. (1988). Communal roosting in Pygmy Nuthatches: a winter survival strategy. Proc. Int. Ornithol. Congr. no. 19:1964-1972. Close Güntert et al. 1988, Löhrl, H. (1988). Etho-ökologische untersuchungen an verschiedenen kleiberarten (Sittidae), eine vergleichende Zusammenstellung. Bonn: Bonner Zoologische Monographien Nr. 26. Zoologisches Forschungsinstitut und Museum Alexander Koenig. Close Löhrl 1988, Sydeman, W. J., M. Güntert and R. P. Balda. (1988). Annual reproductive yield in the cooperative Pygmy Nuthatch (Sitta pygmaea). Auk no. 105:70-77. Close Sydeman et al. 1988, Sydeman, W. J. (1989). The effects of helpers on nestling care and breeder survival in Pygmy Nuthatches. Condor no. 91:147-155. Close Sydeman 1989, Sydeman, W. J. (1991). Facultative helping by Pygmy Nuthatches. Auk no. 108:173-176. Close Sydeman 1991, Szaro, R. C., J. D. Brawn and R. P. Balda. (1990). Yearly variation in resource-use behavior by ponderosa pine forest birds. Stud. Avian Biol. no. 13:226-236. Close Szaro et al. 1990, Ghalambor, C. K. (1998). Ecological and evolutionary determinants of incubation strategies in three coexisting nuthatches (Sittidae). Phd Thesis, Univ. of Montana, Missoula. Close Ghalambor 1998, Martin, T. E. and C. K. Ghalambor. (1999). Males feeding females during incubation, I. Required by microclimate or constrained by nest predation? Am. Nat. no. 153:131-139. Close Martin and Ghalambor 1999).