Recently I've been up late at night and have noticed something rather strange about the birds in my area: they will continuously sing from about 11pm until 3am, possibly even later. At this time of year (middle of January), it won't be fully bright until about 7 or 8, getting dark at 5 or 6 in the evening. What is their reason for doing this? I live relatively close to the centre of Dublin. Is light pollution an issue?

Stephen,

Dublin, Ireland