Estimation of Female Home-range Size During the Nestling Period of Dark-eyed Juncos

—Studies of spatial activity of songbirds during the nesting cycle have largely focused on male activity and neglected female space use, patiicularly outside the fertile period. We estimated the home-range size of seven female Dai'k-eyed Juncos (Jutico hyemalis) 3 days after their nestlings had hatched. We used radiotelemetry to track female movements for 2 hrs on the afternoon of day 3 of nestling life, and 2 hrs on both the morning and afternooti of days 4 and 5. Female location and behavior were recorded every 10 min for the duration of tracking. Females exhibited a mean homerange size of 0.833 ha (range = 0.156-2.450 ha). Our estimate of home-range size during the nestling period was significantly smaller than a previous estimate of female home-range size during the fertile period in the same junco population. Home-range size varied greatly between individuals, and the observed differences may be attributable to variation in resource availability. Received 2 November 2011. Accepted 25 February 2012. ' Department of Biology and Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington, IN 47405, USA. " Corresponding author; e-mail: [email protected] The home-range size of temperate songbirds (Passeriformes) during the breeding season can have profound effects on access to resources and SHORT COMMUNICATIONS 615 reproductive success of both males and females (Zack and Stutchbury 1992, Both and Visser 2000, Rolando 2002). Males defend territories with song and active monitoring, presumably to protect resources for their offspring and to guard against extra-pair fertilizations (EPFs), while also moving outside of their defended territory to potentially seek their own EPFs or other resources (M0ller 1987, 1991). Males of most socially monogamous species also contribute to care of young, but females often perform a larger portion of parental care including incubation, brooding, and provisioning (Trivers 1972, Bennett and Owens 2002). Male spatial activity and homerange size, despite differing in territorial and parental behavior from females, have received much more attention than female home-range size, particularly during incubation and nestling provisioning (Whitaker and Warkentin 2010). Female songbirds encounter a variety of challenges during the nesting cycle. Females are not limited in use of space by incubation or nestling care during their fertile period and should have their largest home ranges at that time (M0ller 1987, 1990). Eemales of many species are known to undertake 'forays' outside of their mate's territory in addition to foraging and nest building during the fertile period, potentially resulting in EPFs as well as female home ranges that are much larger than teiTitories defended by their social mates (Neudorf et al. 1997, Pedersen et al. 2006, Stapleton and Robertson 2006, Evans et al. 2008; but see Akçay étal. 2011). Female home-range size is predicted to decrease as incubation begins as females no longer seek copulations and make shorter movements off the nest to forage and engage in nest defense. However, the abundance and proximity of resources to the nest can affect home-range size, and females may maintain larger home ranges depending on food availability (M0ller 1990). The subsequent transition from eggs to nestlings marks a period of increased effort as females begin to forage for nestlings in addition to themselves and may continue to devote a large amount of time to brooding. This increase in time spent foraging during the early nestling period predicts an increase in female activity but presents contrasting predictions about home-range size. Females may forage close to the nest and maintain smaller home ranges than during the fertile period to minimize energy expenditure and maximize time spent regulating nest temperature through brooding, which can impact nestling fitness (Dawson et al. 2005, Butler et al. 2009). Conversely, females may increase their home-range size to use a variety of foraging locations or to gather higher quality food items (Zach and Falls 1979, Grundel 1992, Garcia-Navas and Sanz 2010). We quantified female home-range size during the nestling period for Dark-eyed Juncos {Junco hyemalis) to examine if female home-range size declines between the fertile and nestling periods. We compared our home-range estimate to previously published data from Neudorf et al. (2002), collected from the same junco population, which estimated female home-range size during the fertile period.