Chen etal. • SEARCH BEHAVIOR OF MIGRATORY SONGBIRDS 
355 
Euclidean distance 
0 12 3 
FIG. 5. Dendrogram of cluster analysis of 31 arboreal insectivorous migrant species based on search rate, frequency of 
flight, and hop distance a. Gulf Coast stopover sites in spring, 1993-1995. Phylogenetically related spec.es are clustered in 
•he same group. Nomenclature for bird species codes is in Table 1. 
continuum from "widely foraging" to "sit-and- 
wait.” The Yellow-billed Cuckoo serves as a 
good example to illustrate a combination of the 
two extremes. Yellow-billed Cuckoos mainly 
forage on large caterpillars (C.-C. Chen, pers. 
nh U They usually scan the surrounding area 
from their perches, occasionally for several 
minutes. This strategy becomes efficient when 
Prey moves frequently. Their scanning radius was 
Probably large because cuckoos have been 
observed using "sally-pounce" or taking several 
quick hops to catch prey at distances > I m (C.-C. 
Chen, pers. obs.). Thus, it was efficient to detect 
large caterpillars from a stationary position. 
However, due to the relatively low abundance of 
large caterpillars, cuckoos must move to a new 
foraging patch from time to time to find another 
prey. Consequently, the search strategy of Yel¬ 
low-billed Cuckoos was characterized by a high 
frequency of flights, long movements, and low 
search rates; a combination of "sit-and-wait and 
"widely foraging." 
Factors Affecting Search Movements.— Vege¬ 
tation structure accounts for a set ol opportunities 
and constraints that influence how a bird moves 
during foraging (Robinson and Holmes 1982, 
