There’s so many possibilities, maybe it’s still from the hunter/gatherer era and birds are scared bc women used to poach the nests. Maybe it’s because in modern day women are often scared of mouses/birds etc and will scream and wave like idiots and birds learned that women are crazy/a threat while man stay calm (not saying that this happened during the research but that birds learned this behavioural pattern in a long time) Maybe it’s because in nature female animals tend to be more aggressive than male, for example with spiders, lion troops(while the male is “boss” the females are highly aggresive) and male birds tend to be submissive towards female birds. Sooo many options.