es the nest an unkempt appearance, which, 
nificantly, resembles the debris left hanging in trees 
er a flood. The structure of the Acadian’s nest may 
is be a kind of mimicry, related to the regular spring 
oding of Illinois streams, and may also account for the 
ular location of nests within the floodplain. 
The time requirement for nest construction is not 
urately known. One nest in southern Illinois was 
gely completed in 6 days. 
Mumford (1964), who worked with a_ banded 
pulation of Acadians in Michigan, found that both 
t building and incubation were carried out by the 
1ale alone. 
The egg-laying season extends from May 20 or earlier 
entral and southern Illinois and May 28 in the north 
at least July 12-15 in all regions of the state (Fig. 30). 
nsidering the laying dates for 62 eggs, we judge that 
peak of egg production in southern Illinois comes 
ween May 28 and June 7. The few laying records 
ilable for central and northern Illinois indicate a peak 
‘ing the period of June 1-15. 
During incubation some female Acadians are very 
acious to the nest, and will snap their bills at human 
ervers, often refusing to move even when touched. 
The most frequent clutch size for the Acadian 
atcher in Illinois is 3 eggs. Twenty-seven clutches 
n nonparasitized nests in all regions of the state 
wed the following distribution: 5 eggs — 1 (about 4 
cent), 4 eggs — 4 (15 percent), 3 eggs — 21 (78 
cent), 2 eggs — 1 (4 percent). We suspect that 2-egg 
ches are actually more frequent, and 5-egg clutches 
frequent, than these figures indicate. The 5-egg set 
collected by P. W. Smith, Jr. in Bond County in 
5;we have never found a clutch this large. On the 
er hand, we have seen a number of nests with 2 eggs, 
none which we observed from the onset of laying. 
H. M. Holland (in Bent 1942) determined the 
ibation period at one central Illinois nest to be 13 
s. In Michigan Mumford (1964) and Walkinshaw 
}1) recorded incubation periods for the Acadian 
atcher of 13-15 days, most frequently 14. 
Nestling life lasts at least 13 days. At a nest in 
thern Illinois, two 13-day-old nestlings which we 
lvertently frightened from the nest could not sustain 
it and merely fluttered to the ground. Thus for a 
‘ies that often nests over water, 13 days would seem an 
lequate nestling period. In Michigan Walkinshaw 
)1) determined 14 days to be the most frequent 
ling period. 
Considering the observations above, we estimate that 
nesting cycle, from the onset of nest building to the 
ging of three young, requires about 36 days. 
We have laying histories for only 12 Acadian nests, all 
ope County. The incidence of cowbird parasitism in 
sample was high — 50 percent. Cowbird parasitism 
cadians has been recorded in all regions of the state, 
there are too few nests with known histories to 
uate the effects of the cowbird on a poplation basis. 
Data on one of the Pope County nests indicates that host 
young do not survive in a successfully parasitized nest. In 
this nest two Acadians and one cowbird hatched on the 
same day, but only the cowbird survived to fledge. 
Mumford (1964) witnessed much the same thing at a nest 
in which a cowbird hatched more than a day ahead of 
three Acadian young. The Acadian nestlings died, 
appearently from neglect, because the cowbird usurped 
the food supply. Though Acadians raise some cowbirds, 
they also apparently resist parasitism to some degree. 
Bendire (in Friedmann 1963) described an Acadian nest 
in which a second floor had been built to cover a cowbird 
egg. An Acadian nest in Piatt County was deserted with 
four cowbird eggs and one host egg (Allison 1947). 
There are no adequate data on nesting success for any 
Illinois population of Acadian flycatchers. In our small 
sample of Pope County nests, only 25 percent fledged 
flycatchers and 10 percent fledged cowbirds. The causes 
of nest failure are also largely unknown. 
A stub-tailed juvenile Acadian collected in southern 
Illinois August 11 (U.S. National Museum 60892) is 
probably indicative of the end of the nesting season. 
Fawver (1947a) last saw an adult male on territory in 
east-central Illinois on August 7. In southern Illinois we 
have seen singing males still on territory at least as late as 
September 25. 
Fall Migration 
The fall migration of Acadian flycatchers may begin 
as early as late July and early August (Fawks 19685). As 
discussed earlier, identification problems make the study 
of fall migration of Empzdonax very difficult. Based on 
the relatively small numbers of Empzdonax identified, 
the peak in fall numbers of Acadians came between 
August 20 and September 20 (Fig. 30), but the actual 
pattern of the Acadian’s fall migration is essentially 
unknown and better techniques of study, such as netting 
operations, are needed. 
The last dates Acadians have been reported are 
October 3 in northern Illinois (Gault, unpublished notes 
1888), October 12 in central Illinois, and October 2 in 
the south (George 1968). 
Though there are a few reports of Acadian flycatchers 
being killed at television towers (Parmalee & Parmalee 
1959, Parmalee & Thompson 1963), the identity of the 
birds is in question. All tower-killed specimens that we 
have examined to date have proved to be either leasts, 
yellow-bellies, or Traill’s. Gastman (1886) writes of an 
Acadian killed on an electric light tower in Decatur on 
September 29, but it has not been possible to verify the 
identity of this specimen. 
Food Habits 
Five stomachs of Acadian flycatchers examined by 
Forbes (1878) all contained insects, Coleoptera being the 
principal item. Obviously more complete studies are 
required. 
tf) 
