Some experts think that birds may be chirping more at night because an increase in daytime noise, such as traffic, has forced them to change their singing time. After all, if a bird sings a mating song during the day and background noise prevents other birds from taking notice, our chirping bird has to pick a time when his message can be loud and clear!
Sources & links
Marcum, Diana. “Cause of Birds Singing at Night Probed.” Tulsa World. World Publishing Co., 24 Aug. 2008. Web. 24 May 2012. Peck, Kirsi. “How Much Sleep Does a Bird Need?” RSPB. The Royal Society for the Protection of Birds, 23 Mar. 2012. Web. 24 May 2012. "whippoorwill". Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc., 2012. Web. 24 May. 2012 “Who’s Making All That Racket After Dark? The Birds That Sing at Night.” eNature.com. 21 Jun. 2011. Web. 24 May 2012.