This hypothesis appears valid in birds tested so far. Individual recognition devices evolved to minimize this risk. Increased infanticide and cannibalism - killing chicks that wander from the nest site. Increased transmission of ectoparasites and disease. Most birds flock outside of the breeding season.
Flocks help ensure that all individuals find at least some food on a regular basis.
This is especially important in stressful winter conditions. Flocks may confuse predator when they can't isolate an individual to prey upon. This decreases the amount of time that an individual must spend watching for predators, so it increases the amount of time available for foraging. Disadvantages - The main disadvantage is increased competition for available food. This type of organization exists in many colonial or flocking birds.