2010 NORTHEASTERN NATURALIST 17(1):155–160
Parasite Transmission Stages in Feces of Common Eiders
Flushed from their Nests
Jenelle D. King1 and Dave Shutler1,*
Abstract - Several species of ducks defecate when flushed from their nests, but it is
unclear why. Possibly, this behavior reflects manipulation by parasites to facilitate
transmission. We analyzed feces of 32 incubating Somateria mollissima (Common
Eider) for evidence of parasite transmission stages. We found a total of only 11 parasite
transmission stages (identified as digenean and nematode eggs) in feces of 3 different
hens, suggesting that defecation around the nest has a low probability of leading to
parasite transmission. Other hypotheses for defecation behavior in this and other duck
species (repulsion of egg predators, weight loss to increase hen maneuverability to escape
predators) appear insufficient to explain its persistence.
Introduction
Females of several duck species defecate on their eggs and nests when
flushed (Forbes et al. 1994). The primary hypothesis for this behavior is that
defecation deters predators (McDougall and Milne 1978, Swennen 1968).
Fecal odors may be offensive to predators, and adaptive because it reduces
their attraction to eggs where they may acquire parasites (including viral and
bacterial). However, some evidence suggests that feces attract both avian
and mammalian predators (Clark and Wobeser 1997, Olson and Rohwer
1998), and furthermore may transmit pathogens to developing embryos (Cox
et al. 2000, 2002). Thus, the primary hypothesis is not well-supported. Another
hypothesis is that defecation is a form of manipulation of host behavior
(Moore 2001) that provides transmission opportunities for parasites to egg
predators, intermediate hosts occupying the nest vicinity, or conspecifics in
high-density nesting areas.
Somateria mollissima L. (Common Eiders) commonly carry intestinal
parasites with fecal transmission stages, including coccidians, trematodes,
cestodes, nematodes, and acanthocephalans (Boorgsteede et al. 2005, Goudie
et al. 2000, Hollmén et al. 1999, Thieltges et al. 2006). We collected feces
from Common Eiders flushed from their nests and looked for parasite stages
therein to determine potential for parasite transmission around the nest.
Study Area and Methods
In May and June 2002, we searched for Common Eider nests on Bon
Portage Island (Outer Island on some maps; 43.5ºN, 65.8ºW), 3 km off the
southwest coast of Nova Scotia, Canada. Open coastal areas with inland areas
of coniferous forest, and small areas of freshwater marsh, characterize the
1Department of Biology, Acadia University, Wolfville, NS, B4P 2R6, Canada. *Corresponding
author - dave.shutler@acadiau.ca.
156 Northeastern Naturalist Vol. 17, No. 1
island. The outer 100 m (at most) above the high-tide line were opportunistically
ground-searched by two to four observers. In >10 yr of various research
activities on the island (D. Shutler, unpubl. data), no nests have been found
beyond this distance. Nests were located when a hen flushed, or when a hen
was detected sitting on her nest. When we approached sitting females, they
too would flush and defecate. Feces that we syringed, scraped, or washed off
eggs, nests, and surrounding vegetation were stored in watertight containers
until we returned to the lab. To minimize detectability to predators, down from
nests was used to re-cover eggs after we left (Götmark 1992).
Fecal samples were processed within hours of collection to prevent degradation
of parasite transmission stages. For most samples, we used fecal
flotation (Georgi and Georgi 1990) to find evidence of transmission stages.
Samples contained enough water from our collection procedures so that they
were immediately ready to be stirred and then poured through a tea strainer;
strained fluid was collected in a beaker. Using a plastic pipette, the fluid
fraction was distributed into two 1.5-ml centrifuge tubes. Extra fluid fraction
was discarded. Tubes were centrifuged at 380 g for 3 min. The top half
of the sample in each tube was then discarded, and a saturated sugar solution
(45.4 g of sugar dissolved in 35.5 ml of hot water, then cooled to room
temperature) was used to top up each tube. Tubes were stirred briefly before
they were again centrifuged at 380 g for 5 min. The tubes were allowed to
sit for 10–15 min before a bulb pipette was used to collect a sample from
the top of the liquid in the tube, where some parasite transmission stages
rise to (Georgi and Georgi 1990). One drop was deposited on a microscope
slide and covered with a cover slip. Because flotation is effective at extracting
only some intestinal parasites, and because few positives were obtained
with early samples, we also made some direct smears from unprocessed fecal
samples (Table 1). In these cases, a sample of feces was spread directly on a
microscope slide.
The area under the cover slip was examined with a light microscope
at 100x magnification. Approximately 20 min was spent on each slide.
We took digital images of objects we identified as parasite transmission
stages, based on Foreyt (1990) and Roberts and Janovy (2000). Digital
images were supplied to D. Duszynski (University of New Mexico), R.
Evans (Acadia University), and J.D. McLaughlin (Concordia University)
to confirm identifications.
Results
Ninety-nine smears were made from 43 fecal samples that came from 32
different female Common Eiders (Table 1). Direct smears were made from
9 samples; of these, 6 were from ducks that were sampled on two different
days. Of the remaining 90 smears, we made 2 for each of 15 ducks, 3 for each
of 6 ducks, 4 for each of 8 ducks (each sampled on two different days), and 5
from each of 2 ducks (also each sampled on two different days) (Table 1).
In total, 11 parasite transmission stages were isolated from 3 different
ducks; no transmission stages were found in direct smears. None of the
2010 J.D. King and D. Shutler 157
females sampled twice provided positive samples. Six nematode eggs (possibly
Capillaria; Fig. 1a) were found; a sample from 1 duck had 1 and a sample
from 1 duck had 5 (Table 1). Five digenean eggs were found (Fig. 1b); a sample
from 1 duck had 1 (a sample from this same duck had 5 nematode eggs),
Table 1. Distribution of sampling effort in collection of Common Eider feces. A sample represents
the feces of 1 duck on 1 day; these samples were usually converted into 2 smears, but
occasionally were converted into 3, and in the last 3 days we also made direct smears from each
of the samples. The number of positive samples is also indicated.
Samples positive for
Date Ducks sampled Flotation smears Direct smears Digeneans Nematodes
21 May 1 3
22 May 7 16
23 May 7 15
24 May 4 8
27 May 4 8
29 May 2 4
30 May 2 4
31 May 3 6
5 Jun 4 8
12 Jun 3 6 3 2 1
13 Jun 2 4 2 1
19 Jun 4 8 4
Figure 1. Representative eggs
found in feces of Common Eider
hens flushed from their nests:
a. Nematode egg. b. Digenean egg.
158 Northeastern Naturalist Vol. 17, No. 1
and a sample from 1 duck had 4 (Table 1). Thus, in only 3 of 32 ducks did we
detect parasite transmission stages in feces, and numbers per sample were low
in these ducks (c.f. Hall and Holland 2000, Moss et al. 1990).
Discussion
Parasitism is reportedly common in Common Eiders, and the low numbers
of transmission stages we found in feces of incubating Common Eiders
have several potential explanations. First, because Common Eiders fast
during incubation (Goudie et al. 2000), parasite transmission opportunities
may be low, so that parasites have been selected to stay dormant at this
time. Second, parasites may not survive fasting, and may only be reacquired
when eiders resume eating. Third, if transmission opportunities occur only
at drinking and/or bathing sites but not nesting sites, parasites may be less
likely to shed transmission stages when their host is flushed than when
their host leaves the nest of its own volition; this selectivity would require
extreme sensitivity by parasites, but this is not unheard of (Moore 2001).
Fourth, parasite populations exhibit significant temporal and spatial variation
in densities (e.g., Forbes et al. 1999; Shutler et al. 1995, 1999), and our
single-season of data may have coincided with low populations for each of
the parasites in which we were interested.
There are several hypotheses for defecation behavior in ducks. The most
frequently tested, the protection hypothesis, proposes that feces repel predators;
this hypothesis has been supported in two studies on Common Eiders
(McDougall and Milne 1978, Swennen 1968). Moreover, several species of
birds direct feces at predators that approach their nests (e.g., Sterna hirundo
L. [Common Tern]; Nisbet 2002), possibly to damage insulatory properties of
predators’ feathers or fur. In contrast, two studies (Clark and Wobeser 1997,
Olson and Rohwer 1998) found that duck feces attracted predators (neither
study identified predator species), and additional studies (Hammond and
Forward 1956, Keith 1961, Livezey 1980, Townsend 1966) found no effect of
feces on rates of predation. Thus, the nest-protection hypothesis has limited
support; in fact, feces appear in some circumstances to actually attract predators.
In addition, defecation on eggs and nests may spread pathogenic bacteria
to developing embryos or young that hatch (e.g., Cox et al. 2000, 2002). Accordingly,
many species of birds actually make significant investments to
transport feces away from their nests (Lang et al. 2002, Weatherhead 1984),
and the principal proposed reasons for this behavior are that it reduces the likelihood
of attracting predators and reduces the spread of disease to and among
offspring. Because predators and disease are costly to ducks and their progeny,
benefits that outweigh these costs of defecation on eggs need to be identified.
Perhaps feces divert a predator from a flushed, and potentially vulnerable, hen
to her nest. The loss of one season of reproductive investment may be a small
price to pay for a long-lived bird. Alternatively, defecation lightens an individual
so that it may more readily escape predators. However, adult Common
Eiders weigh between 1300 and 2600 g (Goudie et al. 2000), and even if a fecal
mass was 20 g, this would only be approximately 1% of a hen’s mass.
2010 J.D. King and D. Shutler 159
In sum, we found few transmission stages in feces of incubating Common
Eiders, so we have little evidence that defecation behavior, at least
around the nest, could lead to parasite transmission. A clear explanation for
defecation behavior remains elusive. In the case of Common Eiders, it may
be instructive to sample drinking and bathing areas for evidence of parasite
transmission stages.
Acknowledgments
For various kinds of help, we thank Paul O’Connell, the Department of Natural
Resources 2002 Eider Crew (Randy Milton, Mike O’Brien, Mike Boudreau, Glen
Parsons, George Boyd, Angela Bond, Laurence Benjamin, Ian Dunbar, Nick Ng-
A-Fook, and Laurie-Anne Croll, as well as Timber, Mocha, Myra, and Leah), Matt
Black, Lauren Barbieri, Lee and Carlene Adams, Brian Wilson, Rodger Evans, and
Andrea Dernisky. We thank Dan McLaughlin for discussing flotation with us, and
Rodger Evans, Donald W. Duszynski, and Dan McLaughlin for taking the time to
look at and identify items we photographed. We thank Mark Mallory and several
anonymous reviewers for extensive and constructive comments that improved the
manuscript. This manuscript is based on B.Sc. Honours Thesis research by J.D. King.
Funding was provided via NSERC to D. Shutler.
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