MALE PARENTAL CARE AND EXTRAPAIR COPULATIONS IN THE INDIGO BUNTING DAVID F. WESTNEAT 1 Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27514USA AI•STRACT.--Levels of parental care by male Indigo Buntings(Passerina cyanea) were pre- dicted to be lower and the tendency to pursue extrapair matings greater when (1) the op- portunity of additional matings (extrapair copulations) was high, (2) the male was cuckolded, and (3) the clutch or brood size was small. Observations of male carerevealed that approx- imately 10% of all males fed nestlings at leastonce, whereas more than 30%fed fledglings. Males in their first breeding season were never seenfeeding young. Males made more trips off their territorieswhen females were fertilizable on nearby territories,but other measures of parental care (feeding young and time spent within 10 m of nest) were not affected. Cuckoldedmales(known through geneticanalyses of parentsand offspring)tended to feed young less often, but forayed off their territories significantlylessthan apparentlyuncuck- olded males. Finally, males with small clutches or broods gave slightly, but not significantly, less carethan maleswith large clutches or broods.These resultssuggest that the relationship between mating effort and parental effort is complicated by the presence of extrapair copu- lationsasa type of mating effort, and that factors not includedin current theory on parental caremight influence a male's parentalcare. Received 18June 1987, accepted 19 October 1987. WHEN an individual spends time and energy to help raise its offspring, it potentially sacri- ficesopportunitiesto pursueadditional repro- duction (Trivers 1972,Maynard Smith 1977).In other words, reproductiveeffort can be divided into two components, mating effort and paren- tal effort (Low 1978).Because energy spenton one componentoften reduces the energy avail- able to spendon the other component, parent- ing behavior can be thought of as a reproduc- tive strategy in competition with other strategies. Maynard Smith (1977) quantified the trade- off between the gain in reproductionfrom ad- ditional matings and the gainfrom parental care. In this model, deserting a matewith youngwill be favored if pV2 > (V2 - V•), where p is the probability of mating with a sec- ond female, V• is the numberof youngsurviv- ing with single-parent care, and V2 is the num- ber surviving with two parents helping with care.Thus, the payoffs to an individual for de- serting depend on the chances of finding a new • Present address: Section of Genetics and Devel- opment, Emerson Hall, Cornell University, Ithaca, New York 14853 USA. 149 mate as well as the effect of desertion on the survival of presentyoung. Total desertion is not the only alternativeto parental care.Males of some species canattempt to attract additional females to their territories and still provide some care to the offspring (Wittenberger 1981). Effort spent on the attrac- tion of females cannot be spenton parentalcare, however. Studies of polygynous species bear this out; males that attract more than one female to their territories often reduce the amount of parental effort to one or more of their broods (Verner and Willson 1969, Patterson et al. 1980, Muldal et al. 1986). The relationship between parental invest- ment and polygyny has been the focusof nu- merous studies (e.g. Willson 1966; Martin 1974; Patterson 1979; Searcy1979; Weatherhead 1979, 1984; Orians 1980; Smith et al. 1982; Witten- berger 1982; Yasukawa and Searcy 1982).Males could pursue other strategies besides polygyny, however, as an alternative to parental care that maximizes reproductive success. Detailed ob- servations of the mating behavior of many mo- nogamous birds have revealedthat copulations between individuals paired to another are quitefrequent (Ford1983, McKinneyet al. 1984, Birkhead et al. 1985, Frederick 1987a, Westneat 1987a), Extrapair copulations (EPCs) generally are pursuedby males that are already paired The Auk 105: 149-160. January 1988 Downloaded from https://academic.oup.com/auk/article/105/1/149/5192767 by guest on 23 February 2024