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Adult male RTHUs arrive on their breeding grounds in spring and quickly establish non-overlapping feeding territories from which they drive away intruders, especially rival males. If a bluffing charge attack does not dispel a trespasser, the resident male may engage him in a brief but intense physical battle. These seldom cause physical damage other than the loss of a few feathers.
An adult male also will repeatedly drive away any female until she mates with him, after which she typically gets "free passage" into his territory. This is a great benefit to her; when she is sitting on eggs or chicks, it is important that she not be off them too long searching for food, or her offspring may die.
A male RTHU is effectively able to defend a territory of approximately a quarter-acre or so (1,000 square meters or 0.1 hectares). If the territory contains prime resources such as patches of nectar plants and/or a well-maintained artificial feeder, the bird will not have to leave his area on foraging trips. Females are known to defend nesting territories young males will defend food resources, so it's best not to assume that a defensive bird is always an adult male. Female RTHUs will forage up to half a mile in any direction from a nest--inscribing a circle of up to a mile in diameter--but it would be impossible for her to defend this area.
Mating also occurs within a prime, well-defended territory, presumably because a female is attracted to a dominant male and/or his holdings. It is not well-documented whether a female always/sometimes/never builds her nest within the territory of a male with whom she mates.
After the breeding season is over, RTHUs of either sex and any age may attempt to monopolize a hummingbird feeder; however, because the feeder represents a super-rich, almost indefensible food source, several birds will probably "take turns" during the day dominating the feeder.
Although many folks who feed hummingbirds are irritated by the territoriality of a dominant bird that drives away all its conspecifics, the hummingbird is just doing what comes naturally. One solution to the conflict is to put up several additional feeders where they cannot be seen from each other.
Considerable work still needs to be done on territoriality in RTHUs, especially to determine how extensively they defend territories on their non-breeding grounds in Mexico and Central America. In fact, during his Operation RubyThroat mid-winter hummingbird expeditions to Guanacaste Province in northwestern Costa Rica, Dr. Bill Hilton Jr. observed adult male RTHUs defending territories just as they do within their breeding range in North America. This was the first documented evidence for such behavior.
Go back to Reproductive Behavior; forward to Foraging Behavior
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