Can chemical cues from a predator change the nest-selection of birds?

The nest-selection process of many birds can be affected by traces of potential predators. However, it remains debatable if birds are capable of recognizing and responding to chemical cues of predators when selecting their nest sites. To investigate this, I installed a pair of nest boxes at 12 sites in 2013 and 2014 and 24 sites in 2015 and 2016, each with nest conditions that differed for two variables, that is, height (high or low), hole depth (deep or shallow). Under these experimental conditions, tree swallows displayed a strong preference for high nests over low ones and deep hole nests over shallow holes. In a consecutive experiment, we applied chemical cues (i.e. urine, feces) of domestic cats to the preferred nests to determine if this would alter the nests selected; the chemical cues led to a stepwise alteration in the nests selected. The birds changed their nest selection by chemical cues of a predator when one variable (nest height or hole depth) was applied. Interestingly, however, when provided with a choice between the most preferred nest combination (high and with a deep hole) and the least preferred nest combination (low and with a shallow hole), tree swallows selected the most preferred nest even in the presence of the chemical cues.