Birds that wake up earlier have more offspring, a study of the songbird Parus major claims. Moreover, the early birds have a habit of taking advantage of their snoozing counterparts, with late-rising males often raising young fathered by their up-and-atem counterparts.
Before we go any further, let's get the sniggering out of the way. Yes, the common name for these birds is “great tits”. Happy now? Let's get back to the science.
P. major is a pair-bonding bird, with males and females sharing the job of raising the young. However, DNA studies have shown that many such species are far from monogamous, with birds often “cheating” on their partners so that males end up raising another male's offspring. For P. major, these non-pair couplings usually occur early in the morning when one partner has not woken up, and the other sneaks off for a quickie with a neighbor.
North Dakota State University's Dr. Timothy Grieves is the first author of a paper in Functional Ecology reporting on the effects of giving melatonin to male birds to change their body clocks. The melatonin-enhanced birds showed confusion about when dawn was coming and rose later, but were not affected in their capacity to fertilize eggs, feed young or in any other behavior once they woke up.
"We found that birds that received the implants filled with melatonin woke up slightly later than birds that received an empty implant. Further, we found that males that received an implant filled with melatonin were more likely to be found raising young in their nest that had been sired by another male," said Dr. Timothy Greives. There were no signs of ill-effects for young that were fathered by birds given melatonin.
Questions remain about the applicability of this study to nature in general. For a start, the sample size was small, with just nine birds given melatonin and ten controls, although the trial was continued over two breeding seasons. Moreover, the effects may be different for those birds that naturally rise later.
The effects in this study occurred because females were up and about with time on their wings while their partners were still sleeping. Late risers that have bonded with those with similar sleeping patterns might have to cope with demanding offspring early in the morning, but are unlikely to find themselves at the same risk of cuckolding. A study earlier this year also found that P. major couples are more likely to stay together when their hormonal levels are aligned.
Grieves intends to extend his research to see what happens when males and females are naturally misaligned. If similar disadvantages have occurred, it will raise questions about how traits for late rising survive.