Further observations on foster-feeding by Purple Martins

TitleFurther observations on foster-feeding by Purple Martins
Publication TypeJournal Article
Year of Publication1968
AuthorsSouthern WEdward
JournalThe Wilson Bulletin

In an earlier paper (1959. Wilson Bull., 71:96) I reported a single instance of foster-feeding by Purple Martins (Progne subis). Since then similar types of behavior have been observed repeatedly during studies associated with the homing ability of this species. The following observations were made at a colony of about 80 pairs located near Indian River (Chebogyan County), Michigan. Between 9 and 17 July 1962, 31 Purple Martins (15 females, 4 subadult males, and 12 juveniles) were removed from the colony by me or an assistant. During the absence of one member of a pair, and occasionally even after its return, I noticed unmarked martins serving as "helpers' at 10 different nests. In some instances a "helper" was observed to make several trips to a particular nest. Details regarding these examples of foster-feeding are presented in Table 1. The significance of this behavior cannot be determined at this time. Speculation regarding the selective value of this arrangement in a colonial species is possible but as yet premature. Since all foster-feeding observations for Purple Martins have been associated with colonies used in homing trials, there is need for a careful comparative study of marked individuals in an "undisturbed" population and one where particular individuals can be removed for varying lengths of time. It is possible that foster-feeding normally occurs if a member of a pair is killed during the feeding stage of the nesting cycle. This behavior was only observed when the colony was near full capacity, i.e., most of the available nest compartments were full. A factor which may have stimulated particular instances of foster-feeding during the later stages of the nesting cycle is that fully feathered young occasionally changed nest compartments along the same tier. In these instances, the adults may find their own compartment void of young and, as a result, move to another nest and feed those young. On one occasion, I observed a color-marked martin (No. 22) feeding young in a compartment on the opposite side of the house. I did not know whether or not her young had left the compartment.