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line between too little defense and too 
much. Whether a parent mobs a partic- 
ular predator depends on the danger to 
the adult if it does mob and the danger 
to the eggs or chicks if it does not. 
In their long-term study of the ecol- 
ogy of peregrine and prairie falcons in 
Utah, Richard Porter and Clayton 
White found that American avocets 
were by far the major prey species 
brought to aeries. Undoubtedly, this 
was mostly due to their abundance in 
the marshes and their misfortune in be- 
ing the ideal size for the falcons to carry 
back to the cliffs. Since neither of these 
large falcons hunted at the Barrens, I 
was curious about how avocets and 
stilts might react to them. So I enlisted 
the aid of a local falconer. On the two 
occasions he flew his prairie falcon at 
the Barrens, the bird, accustomed to 
hunting pheasants and pigeons but un- 
accustomed to the teeming bird life of a 
marsh, soared into the clouds and 
wasn’t recovered until the next day. 
The project had to be discontinued. I 
wish I could boast that the avocets and 
stilts had driven the falcon away, but 
they seemed to ignore him. Current 
programs for restocking peregrines in 
Utah hold promise for answering ques- 
tions about the behavior of breeding 
avocets and stilts toward them. 
How avocets and stilts obtain the in- 
formation about specific predators that 
allows them to employ their discrimi- 
natory powers, and on what basis they 
discriminate, is unknown. The fineness 
of discrimination and the large number 
of animals dealt with suggest that much 
of it is learned. For example, stilts in 
Utah ignore the mostly insectivorous 
Franklin’s gull, while in Florida they 
vigorously mob the similar-looking but 
egg-robbing laughing gull. How do 
they learn that a golden eagle is too 
dangerous to dive bomb, but ravens or 
marsh hawks can be chased at less risk? 
Since the penalty for making a mistake 
may be injury, breeding failure, or 
death, it seems doubtful that trial-and- 
error learning is the principal means of 
Flapping its wings and running 
awkwardly, this black-necked stilt is 
demonstrating another variety of 
distraction display. Such defensive 
behavior is only partially successful, as 
40 percent of all stilt and avocet eggs 
at one of the author's study sites were 
taken by predators. 
Tom Bledsoe 
48 
gaining knowledge about predators. I 
am tempted to speculate that chicks 
learn by observing their parents and 
neighbors during the twenty-eight days 
or so before they are able to fly. They 
should be especially attentive to their 
parents’ behavior then because their 
very lives depend on running or hiding 
at the first alarm. But acquiring knowl- 
edge about predators in this way would 
entail an outstanding memory. Volant 
birds without eggs or chicks react only 
to predators that prey on adults, and 
the response is to flee; hence, informa- 
tion about egg or chick predators 
would not be useful to avocets and stilts 
until they attempt to breed, probably at 
age two or older. It is perhaps more 
likely that young breeding birds learn 
about predators by observing more ex- 
perienced neighbors in the colony, 
whose reactions to predators cover for 
some of the young birds’ naive mis- 
takes. 
