Many of the nests that were in use in 1961 appeared to be relics from earlier years, as the material was darkened and disintegrating, but probably a new layer of sticks had been added on the top. Bent (_op. cit._:65) mentioned this kite's habit of frequently using the same nest in successive years. On one occasion as I drove over a little-used road in the Park and passed a cottonwood grove where kites were nesting, one of the birds swooped down and struck the top of the automobile. In a subsequent conversation, Harry Smith asked me if this had happened, and said that this particular kite had struck his truck frequently when he drove past its nest. This had occurred at the same place in three successive years, and Smith was convinced that the same kite had used the nest each year, although the bird was not recognizable except by its unusually aggressive behavior. On dozens of occasions in the course of my observations kites swooped at me when I was near their nests, but, except for this one individual, they always veered away at a distance of several feet or several yards. At the time of my visit to the Park in early June, kites were relatively silent and secretive in their behavior. Approximately half of those that were incubating flushed when a person walked near the tree, but others continued to sit on their eggs until a person had climbed to within a few feet of the nest. Upon being flushed, such a kite, in 50 per cent of observed instances, swooped at least once at the intruder, but some of the kites would soar overhead, watching without making any active defense. At the time of my next visit, July 18 to 21, when the kites were feeding well grown nestlings, behavior at the nest was much different. As soon as a nest was located the parents began scolding and swooping. At the first nest observed, a group of eight kites had congregated within two minutes to scold and harass the intruders. Even kites whose nests were kept under observation frequently, never became fully reconciled to the intrusion but there was much difference between individuals in this respect. Some were reluctant to deliver food and, having secured prey, would fly about in the vicinity without coming to the nest. Mortality Factors and Defense