Eastern Screech-owl Hatches Wood Duck Eggs

Abstract

I describe an Eastern Screech-owl (Megascops asio) hatching three Wood Duck (Aix sponsa) eggs in a suburban nest box. Wood Duck(s) removed all five eggs of a completed screech-owl clutch, the earliest of which had already been incubated for at least 19 days, and laid three eggs in their place. The female screech-owl hatched the Wood Duck eggs, preened the ducklings, and attempted to feed them until they exited the nest box within 48 hrs of hatching.

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THE WILSON JOURNAL OF ORNITHOLOGY
•
Vol. 119, No. 1, March 2007
The Wilson Journal of Ornithology 119(1):110–112, 2007
Eastern Screech-owl Hatches Wood Duck Eggs
Christian Artuso
1
ABSTRACT.—I describe an Eastern Screech-owl
(Megascops asio) hatching three Wood Duck (Aix
sponsa) eggs in a suburban nest box. Wood Duck(s)
removed all five eggs of a completed screech-owl
clutch, the earliest of which had already been incubat-
ed for at least 19 days, and laid three eggs in their
place. The female screech-owl hatched the Wood Duck
eggs, preened the ducklings, and attempted to feed
them until they exited the nest box within 48 hrs of
hatching. Received 22 December 2005. Accepted 27
July 2006.
Wood Ducks (Aix sponsa) are well known
to lay parasitically with conspecifics (Hartman
1972, Semel and Sherman 1986) and other
cavity-nesting ducks (Bouvier 1974, Eadie et
al. 1998). Wood Ducks occasionally remove
conspecific eggs; however, such records usu-
ally involve damaged eggs (Semel and Sher-
man 1986). Wood Ducks are reported to
‘‘evict’’ other bird species including screech-
owls from nest boxes (Bellrose and Holm
1994). However, Semel and Sherman (2001)
report that when returning female Wood
Ducks found boxes in which they had previ-
ously nested occupied by heterospecifics, in-
cluding Eastern Screech-owls (Megascops
asio), they switched to another box (n
⫽
10).
Here I record Wood Duck(s) removing an en-
tire clutch and laying in a nest of Eastern
Screech-owls.
OBSERVATIONS
While studying the reproductive ecology of
Eastern Screech-owls in suburban Winnipeg,
Manitoba, I installed a miniature video camera
in May 2004 inside a nest box in which a pair
had successfully reared broods in two previ-
ous years. Five chicks fledged from this box
in 2004. A female began laying on 3 April
2005 and by 10 April was incubating a clutch
of five eggs. There was no sign of any unusual
1
Department of Environment and Geography, Uni-
versity of Manitoba, Winnipeg, MB R3T 2N2, Canada;
e-mail: chartuso@gmail.com
activity at the nest until 22 April, when ob-
servers noted there were only three screech-
owl eggs and one much larger egg. On 23
April, there was a second large egg and the
three remaining owl eggs (Fig. 1A). On 24
April no change was noted; however, on the
morning of 25 April, two more owl eggs had
been removed and a third larger egg was pre-
sent (Fig. 1B). Video recordings were made
on a nightly basis but, unfortunately, did not
extend sufficiently into the morning to record
the removal of eggs. I monitored the nest box
from 0600 to 0730 hrs CST for the next 3
days and, on each morning, a pair of Wood
Ducks landed close to the box. The female
Wood Duck then flew to the roof of the box
and stepped repeatedly and heavily on it be-
fore making a short circular flight and landing
on the entrance hole. On each occasion I ob-
served this behavior, the incubating owl
jumped up to prevent the duck’s entrance. On
27 April, a female Wood Duck was recorded
gaining entrance to the nest box at 0638 hrs
but was expelled by the owl which tried to
bite the intruder on the back of the neck. On
the morning of 2 May, the remaining owl egg
was removed, although no new Wood Duck
eggs were added. Unfortunately egg removal
was not recorded due to a technical difficulty.
I concluded the larger eggs in the box were
Wood Duck eggs (confirmed upon hatching;
Helgeson Nelson 1993). There was no evi-
dence of any damaged eggs in the box and no
eggs had been buried in the nesting material.
The edge of the Red River was only a few
meters from the base of the nest tree and, be-
cause there were no eggs or shells below the
box, the removed eggs may have been
dropped over water or consumed (Semel and
Sherman 1986).
Despite the absence of her own eggs, the
female owl incubated the three Wood Duck
eggs. The first egg hatched at 2240 hrs on 25
May, the other two hatched later that evening.
Shortly after hatching, the owl preened the

111
SHORT COMMUNICATIONS
FIG. 1. (A) Three Eastern Screech-owl eggs and two Wood Duck eggs on 24 April 2005; (B) One Eastern
Screech-owl egg and three Wood Duck eggs on 25 April 2005, Winnipeg, Manitoba. The wing and tail of the
female screech-owl sitting at the box entrance are visible in the lower left corner in both images.
ducklings and ate pieces of eggshell. She also
brooded and attempted to feed the chicks.
When the ducklings attempted to exit the box,
the female owl gave whinny calls, which are
‘‘elicited particularly by dispersing juveniles’’
(Gehlbach 1995:7). The first chick exited the
box just before 2200 hrs on 26 May and the
second shortly afterwards. The third chick de-
parted the box at 0730 hrs on 27 May. The
property owner took one duckling to a local
nature reserve, but the other two were not lo-
cated. Wood Duck chicks are highly precocial
and brood merging has been recorded (Kirby
1990), but it is not known whether the chicks
in question survived.
DISCUSSION
Raptorial birds occasionally incubate water-
fowl eggs. Dawson and Bortolotti (1997) re-
ported an American Kestrel (Falco sparverius)
incubating a Bufflehead (Bucephala albeola)
egg and four kestrel eggs (the Bufflehead and
two kestrel chicks fledged). Fannin (1894) re-
ported a mixed clutch of Canada Goose (Bran-
ta canadensis) and Osprey (Pandion haliae-
tus). The Black-headed Duck (Heteronetta atri-
capilla), an obligate brood parasite, at times
parasitizes diurnal raptors (Weller 1968, Ho¨hn
1975). Wood Duck eggs have occasionally
been found in nests of Western Screech-owls
(Megascops kennicottii) (J. M. Eadie, pers.
comm.). In Winnipeg, Manitoba there are sev-
eral records from volunteers of the Fort Whyte
Nature Centre of joint use of nest boxes by
Eastern Screech-owls and Wood Ducks (e.g.,
on 11 April 1997, 1 Eastern Screech-owl egg,
5 Wood Duck eggs, and 7 membranes were
found in one box). This does not imply syn-
chrony of use because some may have been
from the previous year or sequential nesting,
and it is possible that dumping or usurpation
may have occurred. Eastern Screech-owls have
been recorded incubating the eggs of other spe-
cies (Breen and Parrish 1996). Manlove (1998)
reported an Eastern Screech-owl apparently
evicting a nesting Wood Duck, laying on top
of the covered duck eggs, and subsequently
hatching at least one owlet and one duckling.
The average incubation periods for both
Eastern Screech-owl and Wood Duck are ap-
proximately 30 days (Gehlbach 1995, Hepp
and Bellrose 1995). In this case, the female
owl sat on the Wood Duck eggs for 31–34
days, within the normal range of incubation
for Wood Ducks (25–37 days) (Hepp and
Bellrose 1995). However, because the owl ini-
tiated egg laying much earlier than the Wood
Duck(s), her eggs would have hatched ap-
proximately 3 weeks before any of the duck’s
had they not been removed. By accepting the
Wood Duck eggs, the female owl’s total in-
cubation period was extended to 55 days.
Eastern Screech-owls have been recorded in-
cubating infertile eggs for as long as 78 days
(Gehlbach 1995).
Incidental egg dumping has been recorded in
many avian species (e.g., Sealy 1989). However,
the removal of host eggs over a 10-day period
suggests this was not a case of egg dumping. A
failed attempt at nest usurpation, however, can-
not be dismissed. Unusual interspecific interac-
tions of this nature have been attributed to com-
petition for nest sites (Eadie et al. 1988), but

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several studies suggest that nest parasitism in
Wood Ducks is not related to a lack of cavities
(Semel and Sherman 1986). Dawson and Bor-
tolotti (1997) argued that certain desirable qual-
ities of the nest site might be a factor. In this
case, there was a vacant nest box in the same
yard with no discernable structural differences
in which Wood Ducks had previously reared
several broods. Semel et al. (1988) demonstrat-
ed that conspicuous placement of nest boxes in-
creased intraspecific nest parasitism rates in
Wood Ducks and the box in question was highly
visible. This serves as a reminder, perhaps, of
the caution required when artificial nesting
structures are used as management tools (Eadie
et al. 1998).
ACKNOWLEDGMENTS
I am grateful to David and Sigrid Warrenchuk for
assisting in the video recording and permitting obser-
vation on their property. S. E. Cascino and Barry Pom-
eroy produced the photographs. This manuscript was
greatly improved by the thoughtful comments of R. P.
Berger, J. R. Duncan, J. M. Eadie, F. R. Gehlbach, R.
W. Nero, S. G. Sealy, M. W. Shoesmith, and an anon-
ymous reviewer. Funding was provided by small grants
from the Special Conservation Fund of Manitoba Con-
servation, Manitoba Hydro, and the Gray Owl Fund
administered by R. W. Nero.
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