To cite or not to cite?

Which of the following sentences need a citation? Click on the sentences in the below box that you would add a citation to.

Flight feather molt is a time-demanding activity in the avian annual cycle. Yet, annual or alternate-year replacement of flight feathers is essential, because physical abrasion and ultraviolet light rapidly degrade even the most sturdy wing quills after two years of use. Because flight performance declines during molt as new feathers are growing, most birds do not overlap molt and breeding, and those that do overlap these activities replace few flight feathers at a time, presumably to minimize the energetic and flight-performance costs of molting on reproduction.

Citation is sometimes necessary: This would be common knowledge to avian specialists, but probably not to the lay public. It will depend on the audience!

Correct, this sentence needs a citation, as this is not common knowledge.

Correct, this sentences requires citation, as this is not common information and refers to a specific hypothesis.

-Rohwer, Sievert, et al. “Allometry of the Duration of Flight Feather Molt in Birds.” PLoS Biology June 2009.