seriously some household fly sprays contain permethrin, which does derive from flowers ,lavender etc , at this time of the year , i believe that flies are the major cause of disease [biss, called them flying hypodermic needles] red mite at this time here, can multiply to epidemic levels in days , which will feed on the blood of the pigeon [squeeze one , between your thumb nails ,,,,,pure blood] lift a week old yb look under its wing ,,,,,,,,,and hope you don't see them :-/the yb will be pale and lacking, the parents will be so bothered ,theil come off them, i beleive the odd lice [feather lice] are not a big problem , unless covered ,as in my opinion , this keeps the preening and oil gland in good working order ,,, i know a lot will disagree, but that is my opinion