Summary
Male songbirds typically mate-guard by closely following the female during her fertile period. At dawn, males may sing near the nest or roost to direct their chorus at mates. Recent evidence suggests males may also be involved in singing interactions with neighbours during the dawn chorus. We used a 16-channel acoustic location system to examine the movement behaviour of 37 male black-capped chickadees, Poecile atricapillus, during the dawn chorus to determine if male proximity to the nest is a function of breeding stage. Males with fertile females covered a significantly smaller area within their territory, made fewer long-distance movements and sang at a lower song rate compared to males with nonfertile females. Males with fertile mates remained significantly closer to their nest cavity than males with incubating mates. Males with nonfertile mates spent more time near their neighbours with fertile mates than near their neighbours with nonfertile mates. Neither social rank nor age had a significant effect on movement behaviour or song rate. Our results clearly show that female fertility influences dawn chorusing behaviour in male black-capped chickadees. Males may remain near their nest to minimize the risk of cuckoldry, but when their partner is not fertile males may increase movement behaviour to interact with neighbours and/or to advertise to potential extrapair mates
Methodology
Study Area, Population and Recording Methods
We studied a banded population of black-capped chickadees at Queen's University Biology Station, near Kingston, Ontario, Canada (44°34′N, 76°19′W) from January to July of 2005–2007. We captured adult birds (N = 149 birds in 2005, N = 236 in 2006, N = 61 in 2007) in winter using treadle-traps baited with sunflower seeds and banded with a unique combination of three coloured bands and a numbered aluminium Canadian Wildlife Service band. We determined the dominance status of males in winter flocks by observing pairwise interactions at feeding stations (N = 2811 interactions in 2005, N = 8423 in 2006, N = 1100 in 2007). Behaviours of dominant birds included supplanting or chasing subordinates, whereas behaviours of subordinate birds included waiting to feed and displaying submissive postures (details provided in Ratcliffe et al. 2007). Following Mennill et al. (2004), we classified males into three rank categories: (1) high-ranking males were the top two males in flocks of four or five males and the top male in flocks of two or three males; (2) midranking males were the middle male in flocks of three or five males; (3) low-ranking males were the bottom two males in flocks of four or five males and the bottom male in flocks of two and three males.From 27 April to 15 May of 2005–2007, we recorded neighbourhoods encompassing 6–10 (average 7.2 ± 0.3 males, N = 15) black-capped chickadee territories using a 16-microphone ALS. A neighbourhood consisted of a cluster of breeding territories with males who were familiar with each other from their winter flocks and males from nearby flocks. Average territory size of males was 18 393 ± 990 m2 (range 4637–28 957 m2, N = 37 males). We recorded in 15 different neighbourhoods of up to 160 000 m2, five neighbourhoods in each of 2005, 2006, and 2007. The ALS consisted of 16 omnidirectional microphones housed in PVC tube rain covers and mounted on 3-m-long wooden poles that were elevated and attached to small trees using bungee cords. In each array, the average between-microphone distance was 206.8 ± 2.2 m (calculated pairwise for all microphones in each array, N = 1800), minimum distance was 75.3 ± 1.2 m (N = 240) and maximum distance was 350.2 ± 4.1 m (N = 240). We placed microphones as evenly as possible throughout the neighbourhood, to the extent permitted by vegetation and topography. Microphones were connected to a central computer using 2200 m of cable. Input from all microphones was digitized using a multichannel data acquisition card (National Instruments DAQ-6260) and recorded as 16-channel AIFF files using Chickadee version 1.9 recording software (J. Burt, Seattle, Washington, U.S.A.). This set-up was an extension of the eight-microphone system described by Mennill et al. (2006). We recorded from 0425 to 1130 hours Eastern Standard Time (EST) on 2 to 4 consecutive days in each neighbourhood. During recording sessions, three or four observers transcribed the activities of individual birds within the recording area, including details of male singing locations and identities.
As winter flocks began to break up and breeding pairs began to defend territories (late March to early April), we visited each pair every 1–3 days. We recorded movements and territorial interactions of each pair on a detailed map using both landscape features and grid flags as landmarks to map breeding territories using the method of Bibby et al. (1992). We also recorded all pair locations during the array recordings, when we intensively followed the 6–10 pairs in the neighbourhood over a period of 2 to 4 days. A pair's territory was defined as the maximum extent of space exclusively occupied by the pair following the period of winter flock breakup but before the female's fertile period (Mennill et al. 2004). We calculated the area of the territory by plotting the boundaries from our field maps on the GPS map of the detailed landscape features using software (J. Burt) written in MatLab (Mathworks, Inc., Natick, Massachusetts, U.S.A.).