Early bird gets the free sex?

From: Nature - June 11, 2015

Lazy male birds pay a high price

Male songbirds that sleep late risk having their female partners mate with another male.

Mating outside of a monogamous pair in birds normally happens early in the morning. To find out if rising earlier or later would affect reproductive patterns of great tits (Parus major), Timothy Greives of North Dakota State University in Fargo and his co-workers captured male birds in Germany and implanted them with a device that releases melatonin. This hormone is generated mostly at night to set the circadian clock. Male tits that had night-time-like levels of melatonin around the clock began their daily activities on average 10 minutes later than the control group. Their nests also contained more offspring fathered by another male, suggesting that the late-rising males were less able to defend their mates.