Green Matters! Growing Vegetation Stimulates Breeding under Short-Day Conditions in Wild Canaries (Serinus canaria)

JOURNAL OF BIOLOGICAL RHYTHMS, Vol. 22 No. 6, December 2007 554-557 DOI: 10.1177/0748730407306928 © 2007 Sage Publications Many organisms measure changes in day length as a cue to detect changes of the season and to regulate seasonal behavior patterns. In birds, the reproductive period is determined by endogenous rhythms and the response to environmental factors (e.g., Gwinner, 1986; Wingfield and Farner, 1993). Birds breeding at higher latitudes encounter favorable conditions for breeding mostly during an increasing photoperiod in spring, inducing gonadal growth and rising levels of reproductive hormones (Dawson et al., 2001). Photoperiod as long-term predictive information is usually integrated with supplementary cues (i.e., temperature, rainfall, food availability) and synchronizing information (i.e., behavioral interactions) to time breeding (Hahn et al., 1997). Integration of environmental cues other than photoperiod is known from several opportunistic breeders (e.g., Zann, 1996; Hahn, 1998; MacDougall-Shackleton et al., 2006; Perfito et al., 2007). Occasionally, also strictly seasonal breeders demonstrate temporal flexibility by initiating or extending breeding activities outside their normal breeding season (e.g., Ligon, 1974; Schoech et al., 2004). Therefore, integrating environmental cues may represent an adaptive strategy for both opportunistically and seasonally breeding species and may have the capacity to release seasonal breeders from strict photoperiodic control. Early breeding has been observed in seasonally breeding island canaries (Serinus canaria) on Ilhéu Chão, Madeira (32°35’N, 16°32’W). Due to large amounts of rain in October and November and subsequent early growth of feeding plants, birds started breeding in December in 1999 and 2001, 6 weeks earlier than the usual onset of breeding (Leitner et al., 2003). We aimed to experimentally test whether nonphotic environmental cues are sufficient to stimulate breeding in seasonally breeding island canaries. During 2 consecutive years in November-December, when photoperiod was still decreasing, we simulated either rainfall or green vegetation to see whether one of these cues alone is sufficient to induce breeding. When we simulated rainfall (November-December 2004), females were not interested in nesting material and did not nest. Breeding started in March 2005, just as during the previous years (Fig. 1), and ended in mid-August. In December 2005, about 3 weeks after introduction of green plants, all birds came into breeding condition (Fig. 1). This was confirmed by observing nest building and copulations. First nest structures were recognizable on December 19, and 2 females started egg-laying by December 27 and 28, respectively. However, these 1st eggs did not develop. By mid-January 2006, all females had finished egg-laying, and the 1st young hatched at the beginning of February. Breeding ended on June 30. Finally, in November 2006, when no experimental manipulations had been performed, females were not interested in nesting material and consequently the 1st complete nest was noticed at the end of February 2007. In summary, the onset of nest-building significantly differed LETTERS