We monitored two color-marked populations of the Brown-headed Nuthatch (Sitta pusilla) for Ն5 years and collected data on survival, dispersal, territoriality, and cooperative breeding. Adults (n ϭ 284) were sedentary, maintained long-term pair bonds, and had higher apparent annual survival (66-78%) than previously reported. Territories monitored (n ϭ 347) contained up to five adults; the percentage of territories containing Ͼ2 adults averaged ϳ20% but varied widely. Most groups with Ͼ2 adults

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... nsisted of a breeding pair and a male helper related to at least one breeding adult (n ϭ 8), but several exceptions were noted. The presence of helpers did not improve nest productivity. Apparent annual survival for females was lower than apparent survival for males in one population and may have influenced cooperative breeding. In the other population, apparent survival was similar between males and females. We suggest food resources and other environmental factors may have influenced cooperative breeding in this setting.