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American Dipper (Cinclus americanus)
By Holly
Middleton
The American
dipper is a songbird that has taken up the unusual habit of
swimming in fast-flowing mountain rivers and streams in
western North America. There are five species world wide and
all dippers spend their entire lifecycle in and along rivers
and streams. Dippers dive into cold, fast-flowing water in
search of aquatic prey such as caddisflies, stoneflies, and
mayflies as well as salmon eggs, alevin and fry. Some dippers
in southern British Columbia move between higher elevation
breeding streams and lower level main stem of rivers for the
winter. The best time to see large numbers of dippers is
between November and February when they aggregate on low
elevation rivers during winter. Why they dip is not known but
it is likely a means to make them more visible to other
dippers. American dipper populations are not at risk. However,
the dipper’s strictly aquatic lifestyle makes them an ideal
indicator of the health of rivers. Studies on Eurasian dippers
(Cinclus cinclus) show they are sensitive to changes in
stream water quality associated with human activities
including stream acidity (Ormerod et al 1991) and toxins and
silt in the water.
References
Kingery, H.
E. 1996. American Dipper (Cinclus mexicanus). In:
Poole,
A. and Gill, F. (eds) The Birds of North America, No. 229. The
Academy
of
Natural Sciences,
Philadelphia, PA., and The American Ornithologists’ Union,
Washington, D. C.
Middleton,
H. A., Morrissey, C. A. and D. J. Green 2006. Breeding
territory fidelity in a partial migrant, the American dipper
Cinclus mexicanus. Journal of Avian Biology 37:
169-178.
Middleton,
H. A. 2006. Post-fledging behaviour and dispersal of American
dippers. M.Sc. thesis,
Simon
Fraser University, Burnaby, BC
Morrissey,
C. A. 2002. The ecological and toxicological significance of
altitudinal migration by the American dipper (Cinclus
mexicanus). PhD. thesis,
Simon
Fraser University, Burnaby, BC
Ormerod, S.
J., O’Halloran, J., Gribbin,
D. D. and
S. J. Tyler 1991. The ecology of dippers (Cinclus cinclus
(L)) in relation to stream acidity in upland Wales: breeding
performance, calcium physiology and nestling growth. Journal
of Applied Ecology 28: 419-433.
Tyler, S.
J. and S. J. Ormerod 1994. The Dippers. T & A. D. Poyser,
London,
UK
American Dipper
Distribution & Migration
American
dippers are found on rivers and streams throughout western
North America from Alaska to Mexico, west of the Rocky
Mountains. American dippers are not long-distance migrants,
however some birds move between high and low elevation within
watersheds and some interior populations make short-distance
movements in winter.
American Dipper
Behaviour
Feeding and Foraging Behaviour
Dippers feed
on the aquatic larvae and emerged adults of many aquatic
invertebrates including caddisflies, stoneflies and mayflies
as well as the eggs, alevin and fry of salmon. Dippers reach
their aquatic prey by diving into the water and swimming by
beating their wings. They dive for an average of 5 seconds
often in raging rivers suited to adventure rafting. Their
anatomy and physiology is a good match to their aquatic
lifestyle. They have extra layers of feathers to keep them
warm and an enlarged oil gland that is applied to the feathers
to keep them dry, and a third eyelid, or nictitating membrane
that helps them to see while underwater. Dippers make use of
their grasping feet to hold onto underwater features to help
them stay submerged and move around in the powerful water.
Dippers also catch flying insects out of the air and pick prey
off the surfaces of rocks, stream banks and the water surface.
Flight Patterns
Dippers have a
fast, buzzing wingbeat and typically fly low to the water.
They often give out their rattling ‘jhe’ call as they are
flying.
Aggression and Territoriality
Dippers defend
an exclusive breeding territory against other dippers from
about March to July. The territory aggressiveness relaxes
during the winter months when large numbers of dippers share
popular river stretches. Territorial defense is performed by
both sexes. Intruding dippers often fly silently over a
territory at a high altitude to elude detection. Intruders are
quickly approached by territorial holders. One or both birds
will stretch into a long, high posture with their bills
pointed straight up in the air. The contest ends when one bird
submits by crouching low on the ground where it is jumped and
pecked. Territorial holders will pursue intruders in a long,
vocal chase and mid-air squabble. Disputes often end with one
bird forcing the other under the water.
Courtship and Breeding
Dippers mate
monogamously. They form pairs at the end of winter often with
the same mate and on the nesting territory occupied the
previous year (Middleton et al. 2006). Birds that breed on the
lower elevation river begin nest-building or renovations as
early as late-February. Birds that breed at higher elevations
begin breeding about 2 weeks later. The breeding season
extends from late-February until early-July. Dippers begin
breeding earlier than most songbirds likely to avoid nest loss
to high spring floods fed by melting snow off nearby
mountains.
Nesting
Dippers build
their nests on surfaces that overhang flowing water. They have
been found on a variety of structures including mid-stream
boulders, logs overhanging the water, river banks, cliff
edges, under bridges and culverts and other man-made
structures. The nest is formed out of moss plucked from the
banks of the river that is shaped like a soccer ball with a
lining of grass and leaves. The opening overlooks the water
below. The nest is constructed in about a week by both
parents. Once complete, the female lays a clutch of 4 or 5
eggs and incubates for 16-18 days. Young hatch within a day of
each other and are brooded for up to 10 days. They are
provisioned by both parents on a diet of aquatic insects and
fish. They depart the nest about 24-26 days after hatching - a
relatively long nestling period for a songbird. They continue
to be fed by both parents and depart from the parent’s
territory anywhere between 6-21 days after leaving the nest
(Middleton 2006). Pairs often initiate a second brood,
especially if the first one is depredated or destroyed by
spring floods. The male does not incubate or brood the young.
While females are incubating or brooding young in the nest,
the male will often stand sentry on a favourite rock or log in
the territory looking out for intruders. This is a good sign
that there is a nest nearby.
Vocalizations
Both male and
female dippers sing. The song is a long, wren-like, fluty set
of notes that can extend from 10 seconds to several minutes in
length. Their call is a repeated ‘jhe’ and they often give a
rattling call in flight. The female makes a soft ‘whump’ noise
in the presence of nestlings.
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