THE list of birds for which helpers at the nest commonly occur has grown rapidly since Skutch's (1961) compilation, and now about 80 spe-cies in 32 different families are known to exhibit such cooperative breed-ing (Harrison 1969, Fry 1972). Widespread as the phenomenon may be, few studies have continued long enough to provide much information on the effect hdpers have on reproduction or the ... [Show full abstract] possible filial relationships of the helpers to the breeders. In the absence of such facts arian co-operative breeding provides little information of use in the current con-troversy about group or kin selection versus individual selection (Ham-ilton 1964). This preliminary report on the helper system of the Florida Scrub Jay, Aphelocoma c. coerulescens, is based on 5 years of study, 1969-73, at the Archbold Biological Station in Highlands County, Florida. A recent paper (Woolfenden 1973), which provides information on some aspects of breeding and survival, characterizes Florida Scrub Jays as long-lived, permanently territorial, permanently monogamous, and single brooded with a short, highly synchronized breeding season. The overall stability of the population is indicated by the fact that during the last 3 years of study only about five territories have disappeared and six new ones come into existence in a sample of some 27 territories that occupy a study tract of about 400 ha.