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Wild zebra finches form long-term monogamous pair-bonds that are actively maintained year-round, even when not in breeding condition. These desert finches are opportunistic breeders, and breeding is highly influenced by unpredictable rainfall. Their high levels of affiliation and complex breeding patterns make zebra finches an excellent model in which to study the endocrine regulation of affiliation. Here, we compared zebra finch pairs that were provided with water ad libitum (control) or water restricted. We examined (1) reproductive physiology, (2) pair-maintenance behaviors in several contexts, and (3) circulating and brain steroid levels. In females, water restriction profoundly reduced largest ovarian follicle size, ovary size, oviduct size, and egg laying. In males, water restriction had no effect on testes size but decreased systemic testosterone levels. However, in the hypothalamus, local testosterone and estradiol levels were unaffected by water restriction in both sexes. Systemic and local levels of the androgen precursor dehydroepiandrosterone (DHEA) were also unaffected by water restriction. Lastly, in three different behavioral paradigms, we examined a variety of pair-maintenance behaviors, and none were reduced by water restriction. Taken together, these correlational data are consistent with the hypothesis that local production of sex steroids in the brain promotes the expression of pair-maintenance behaviors in non-breeding zebra finches. (c) 2013 Elsevier Inc. All rights reserved.