Summary
Previous work suggests that early learning plays a role in auditory preferences of female songbirds. We explored whether early experience shapes preferences for local geographic song in female song sparrows (Melospiza melodia), a species that prefers local geographic song in adulthood. We hand‐reared females from two locations 450 km apart and controlled song exposure early in life. To examine the effects of experience and inherited factors on geographic song preferences, we used a counterbalanced design. Females from each location were tutored with either natal song (recorded from their location of capture) or non‐natal song (recorded from the other location) and their preferences for tutor vs. non‐tutor song assessed in adulthood. We also examined song preferences in isolate females reared with no song experience. We found that tutored females preferred their tutor song over non‐tutor song, regardless of their capture location. Furthermore, birds not exposed to song (isolates) had no geographic song preferences. Thus, song exposure early in life clearly plays an important role in adult female preferences for local song in this species.
Methodology
Animals
Thirty‐six female song sparrow (Melospiza melodia melodia) nestlings, taken directly from nests prior to flight at ages 2–8 d post‐hatch (mean age 4 d) were hand‐reared for this study. All birds were captured in Ontario, Canada (under Environment Canada Permit CA0065). Thirty‐seven male and female nestlings were removed from 13 nests in a meadow adjacent to the University of Western Ontario in London, Ontario, Canada (42N59, 81W14), from 3 Jun. to 8 Aug. 2004. Forty male and female nestlings were removed from 14 nests at the Queen’s University Biological Station in a meadow near Newboro, Ontario, Canada (44N39, 76W19), from 21 May to 12 Jun. 2004. Nestlings were hand‐reared in the laboratory to control their song exposure early in life. Based on their age of capture, it is unlikely that song was learned prior to collection (Marler & Peters 1987). Upon self‐feeding, fledglings from the two capture sites were randomly placed into one of three acoustically isolated tutoring rooms: London Song Room, Newboro Song Room or Isolate (no song) Room (see Fig. 1 for experimental design). The sex of subjects was determined through PCR amplification of genes located on the sex chromosomes using primers P2 and P8 (Griffiths et al. 1998) around the time of fledging. Males were used for a parallel study (results presented elsewhere). The final sample size tested for this study was 33 females because of the death of two individuals and failure of molecular sexing of another. The three tutoring rooms consisted of the following distribution of birds: London Song Room (n = 11; five females captured in Newboro and six captured in London), Newboro Song Room (n = 13; six females captured in Newboro and seven captured in London) or Isolate (no song) Room (n = 9; four female captured in Newboro and five captured in London). The three tutoring rooms were of similar dimensions and were maintained on the same light cycle and temperature. Birds were housed in individual cages within a room of same tutoring group conspecifics. This group exposure was necessary because of evidence suggesting that isolate rearing, in the absence of same age conspecifics, may impede auditory perception (Sturdy et al. 2001).
Nestlings were syringe‐fed a mashed diet of ground Mazuri Small Bird Maintenance, wheat germ and hard boiled egg, mixed with water. Birds were housed in their original nest groups within cages (30 × 36 × 25 cm) prior to fledging (approx. 12 d old), then moved to individual cages (46 × 76 × 46 cm), maintained on a diet of Mazuri Small Bird Maintenance, millet, grit and water ad libitum, and periodically supplemented with spinach and blueberries. Birds were placed on a short day photoperiod (8 h light, 16 h dark) at the end of Oct. and maintained on short days until testing. Song preference tests were conducted from 16 Feb. 2004 to 28 May 2005, when birds were 255–315 d old. At the time of testing, females were moved into individual testing chambers and placed onto a breeding season‐like long day photoperiod (14 h light, 10 h dark). While order in which individuals were tested was assigned randomly, females captured later in the season were tested later to minimize variation among birds in their age at testing.
Song Tutoring
Fledglings were assigned to tutoring rooms from 29 to 45 d old (x̄ = 30 d). Peak song production learning in song sparrow males is from 22 to 62 d old, with evidence of acquisition up to 200 d post‐hatch in laboratory experiments (Marler & Peters 1987). Birds in the London Song and Newboro Song rooms were exposed to song from 07:00 to 12:30 h each morning. In addition, because of evidence suggesting that song learning may be enhanced by the presence of live song tutors (see Beecher & Burt 2004 for further discussion), three adult males were captured from each location, using mist nets and song playback, to serve as live tutors in the London and Newboro tutor rooms. Live tutors were housed in individual cages within the tutoring rooms; while singing behavior was not quantified, these birds were not heard to sing. Hand‐reared birds assigned to the isolate room, which contained no live tutors, were not exposed to song. All birds were housed in individual cages throughout the tutoring regimes. Birds remained in tutoring rooms until 107–125 d old (x̄ = 110 d), after 78–80 d of tutoring, and then all females were placed into one room and maintained on a winter‐like short day photoperiod until testing (see Fig. 1 for timeline of experiment).