Table 6.6. Nest loss rates and predators of bird nests at Monteverde.
Species^3 Predation rate (%)b
Resplendent Quetzal (1)
Emerald Toucanet (2)
Long-tailed Manakin (3, 4)
Brown Jays (5)
Isolated trees
Nonisolated trees
Rufous-and-white Wren (6)
Plain Wren (6)
House Wren (6)
House Wren (7)
Gray-breasted Wood-Wren (6)
Slate-throated Redstart (8)
Collared Redstart (8)
Yellow-throated Euphonia (9)67-78%
20
834
100
28
40
12
27.2
50
66
81
66N (nests)
9
10
1225
5
11
5
38
318
6
41
26
41Identified Predators
Long-tailed weasel
White-faced Capuchin
Emerald Toucanet, Red Squirrel
UnknownUnknown
Unknown
Unknown
Mouse Opossum, Coati
Unknown
Unknown
Unknown
Unknown
^Source: (1) Wheelwright 1983; (2) Riley 1986; (3) D. McDonald 1993b; (4) D. McDonald unpubl. data; (5) Lawton and Lawton
1980; (6) Winnett-Murray 1986; (7) Young 1994a; (8) Shopland 1985; (9) Sargent 1993.
bPredation rate calculated by dividing the number of nests lost to predators by the total number of nests found or, in the case of
House Wrens and Yellow-throated Euphonias, from Mayfield (1975) daily survivorship estimators.gated Squirrels, White-faced Capuchins, and domes-
tic cats, which may explain the low rate of nest pre-
dation in this species (Lawton and Lawton 1980).
The study of tropical bird parasitology is in its
infancy, but Monteverde is the site of initial work in
this field. Parasites are often invisible to human ob-
servers but can cause significant levels of mortality
in adult and nestling birds (Brown and Brown 1986,
M011er 1990, Toft 1991). In Monteverde, 11% of 479
individuals sampled (representing 60 species) showed
evidence of blood parasite infections (Young et al.
1993). Among the parasites, Haemoproteus sp. was
responsible for 88% of all infections. Plasmodium sp.,
Leucocytozoon sp., Trypanosoma sp., and microfi-
larial worms caused the remaining infections. Most
birds were free of parasites, with the exception of
Emerald Toucanets, tanagers (especially Common
Bush-Tanagers), and emberizid finches (especially the
brush-finches, White-eared Ground-Sparrows, and
Rufous-collared Sparrows). Samples taken during the
period when most juveniles were fledging and dis-
persing (May—November) were 54% more likely to
show infections than samples taken during interven-
ing months. This pattern suggests that parasites may
time their occurrence in the blood stream to coincide
with the time when more susceptible individuals are
available in the host population (Young et al. 1993).
In a study on the effects of botfly larvae (Philornis
carinatus) on nestling House Wrens (botflies live just
beneath the skin), 8% of nests in Monteverde had at
least one nestling infected by botflies but mortality
was not higher in these nests (Young 1993a). Rates of
infection were much higher in House Wren popula-
tions in San Luis (31%; Zone 1) and in La Lucha (27%)
in the Caribbean lowlands below Zone 6. Botfly lar-
vae infestations in Rufous-and-white Wren nestlings
did not affect survivorship or fledging weight (Winnett-
Murray 1986). Further study of intestinal parasites
and the effects of ecto- and endoparasites on host
survivorship is needed.
The physical environment can also cause mortal-
ity in birds. Long periods of cold wind and rain are
conditions in which many insects do not fly and be-
come difficult for insectivores to find. This weather,
typical of December through March in Zones 3 and
4, can also increase the metabolic needs of birds. With
greater energy needs and fewer resources, some birds,
especially insectivores, may die of starvation. Wind
also influences bird fitness in Monteverde. During an
unusually strong 4-day storm in April, 1978,10 of 12
Brown Jay nests were destroyed; chicks, eggs, and
entire nests were blown out of trees (Lawton and
Lawton 1980). Similarly, wind blew a Rufous-and-
white Wren nest out of a tree; continuous heavy rain
led to chick mortality in other nests of this species
(Winnett-Murray 1986). Rain has caused floods that
washed out House Wren nests built in road banks
(Winnett-Murray 1986) and American Dipper nests
along the Penas Blancas River (F. G. Stiles, unpubl.
data).
Human activity in Monteverde also causes mortal-
ity in birds. Habitat destruction is the most obvious
cause (see Chap. 12, Conservation Biology). Glass
windows on houses built in forested areas are respon-
sible for hundreds of window-kills per year. Most of
the dozens of specimens from Monteverde in museum
collections were prepared from Monteverde birds that
died by flying into a pane of glass. Domestic cats197 Birds