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Spurting
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current news with links to colour ringing and to
'spurting' behaviour
Spurting
behaviour in wading birds
by Brian
Fellows, Emsworth
Paper
published in the Wader Study Group Bulletin Vol 120
(3) 2013 208-209
Keywords: Black-tailed
Godwit, Limosa limosa ssp islandica, Emsworth Harbour,
England, wading birds, feeding, spurting water.
Many wading birds,
including up to 150 Black-tailed Godwits Limosa limosa
ssp. islandica, feed regularly in winter in Emsworth
Harbour (50°50N, 0°57W), part of
the Chichester Harbour complex, a large tidal harbour
on the south coast of England. Emsworth is my home
town and I have been watching the godwits there for
many years, counting and logging the colour-ringed
birds and taking photos.
Looking through my
photos, and those of other local birdwatchers, it
appeared that, on occasions, the godwits would spurt
water from their bills when feeding in shallow water
(Figs. 1 & 2, overleaf). It was also apparent that
this behaviour was not restricted to Black-tailed
Godwits, as it was also recorded in other wading
birds, including Spotted Redshank Tringa erythropus,
Common Redshank T. totanus, Greenshank T. nebularia
and Eurasian Spoonbill Platalea leucorodia (Figs. 3, 4
& 5). This suggested that spurting may
be a general characteristic of wading birds feeding in
shallow water and not confined to Black-tailed
Godwits.
Several wader experts
have been shown the photographs, but none have
recognised the behaviour as something they have seen
themselves or been able to explain. In my experience
the behaviour is relatively common. Therefore it is
surprising that the expulsion of water by waders
during feeding has not previously been
acknowledged.
I describe spurting
behaviour as follows: the bird dips its bill into the
water for a couple of seconds, or sometimes a bit
longer, presumably to obtain food. It then withdraws
its bill and slightly pushes its head forward, usually
(though not always) with the bill lowered and then
ejects or spurts a stream of water, as if ridding
itself of surplus liquid taken in while feeding
underwater. The bill is then reinserted in the water
and the sequence is repeated.
All this happens very
quickly and is not easily seen with the naked eye,
though the behaviour shows up well in photographs,
such as those presented here. More reports of this
behaviour with photographs can be seen on my special
spurting web page
(www.emsworthwildlife.hampshire.org.uk/x-black-tailed-godwit-spurting.htm).
I have also put a short digiscoped video of some
Black-tailed Godwits feeding near the shore at Nore
Barn, Emsworth, in January 2012 on YouTube showing
examples of spurting (http://youtu.be/uHXSH9jzh94).
The only other published photograph of spurting I have
come across for the United Kingdom is by Matt Thomas
(2011) who has two images of Black-tailed Godwits in
August 2011 ejecting what appears to be muddy water
and pieces of worms. There is also a photograph on
PBase.com (2007) showing a Hudsonian Godwit L.
haemastica seemingly doing the same thing.
Although my
observations lead me to the opinion that water is
forcibly ejected, I do not discount the possibility
that water drains more passively from the bill and is
thrown out by the action of the bird in raising its
bill from the water. Thus, the bird feeds below the
surface of the water for a few seconds, then lifts its
head quickly throwing out the excess water from its
bill as it does so. A good-quality video, suitably
slowed down, would probably show just what was going
on more clearly. My explanation for spurting behaviour
is that water, and other material inadvertently taken
in along with prey during feeding, needs to be
expelled by the bird before it can continue feeding.
It is clear from the photographs that a good quantity
of water is ejected. Sometimes, small objects can be
seen in the stream of water (Fig. 6), but often the
water coming from the bill looks clear and
unsullied.
To explain why water
may be forcibly ejected, Ralph Hollins (pers. comm.)
has suggested that when a bird is hungry, it might try
to ensure that it gets any food content out of a bill
that is full of water by forcing the water out though
a minimal gap between the mandibles, thus retaining
tiny food items in the bill, much in the manner of
filterfeeding ducks, such as Northern Shoveler Anas
clypeata. A potential explanation for the evolution of
spurting behaviour (either being active spurting or
just the shape and design of bill that allows for the
expulsion of water and unwanted items) could be that
birds foraging in saline waters, and already having to
deal with salinity on their prey, would need to
excrete all other excess water (and sediment), thus
reducing the saline load acquired during foraging. It
is well known that dealing with salinity is costly to
birds and this could be a way in which this is reduced
(Gutiérrez et al. 2011, Hannam et al. 2003,
Peaker & Linzell 1975). Once this behaviour
evolved to deal with foraging in saline waters, then
it might also occur in freshwater habitats as the
medium is similar.
I thank Sid Davies,
Tony Wootton and Malcolm Phillips for allowing me to
use their photographs. I am grateful to José
Alves for his comments on a draft of this
note.
Gutiérrez,
J.S., Dietz, M.W., Masero, J.A., Gill Jr, R.E.,
Dekinga, A., Battley, P.F.,
Sánchez-Guzmán, J.M. & Piersma, T.
2012. Functional ecology of saltglands in shorebirds:
flexible responses to variable environmental
conditions. Functional Ecol. 26:
236244.
Hannam, K.A., Oring,
L.W. & Herzog, M.P. 2003. Impacts of salinity on
growth and behaviour of American avocets chicks.
Waterbirds 26: 119125.
Peaker M. &
Linzell J.L. 1975. Salt glands in birds and reptiles.
Cambridge University Press, Cambridge, UK.
PBase.com2007.
Shorebird feeding behaviour. www.pbase.com/mbb/prey_
transport_by_surface_tension_of_water
(accessed 1
February 2014).
Thomas, M. 2011.
Photos of Black-tailed Godwits feeding. 4 & 24 Aug
2011. http://deebirder.blogspot.com/2011_08_01_archive.html
(accessed 1 February 2014).
Figures
Fig 1 - Black-tailed
Godwit spurting. Thorney Island 17 Feb 2009. Sid
Davies
Fig 2 - Close up of
Black-tailed Godwit spurting. Nore Barn Emsworth
Harbour. 9 February 2012. Brian Fellows
Fig 3 - Spotted
Redshank spurting. Nore Barn Emsworth Harbour. 14
February 2012. Tony Wootton.
Fig 4 - Common
Redshank spurting. Nore Barn Emsworth Harbour. 15
March 2012. Malcolm Phillips.
Fig 5 - Spoonbill
spurting. Emsworth Harbour. 13 December 2002. Brian
Fellows
Fig 6 -
Black-tailed Godwit spurting objects. Nore Barn
Emsworth Harbour 5 December 2012. Brian Fellows
COMMENTS
OF REFEREE
This short
communication describes what I believe to be a novel
aspect of wader foraging behaviour. To the best of my
knowledge and after consulting experts on wader
foraging behaviour, "spurting" in these species has
never been described. I myself have never noticed it,
although I have noticed water splashes around the bill
when it is pulled out of the water, and the bird makes
a swallowing movement tilting the head and neck
forwards. I remain unconvinced that this is an active
expulsion of water (and sediment) under pressure from
the bill. In my view, this is mostly water draining
down the bill (both inside and outside) which together
with the swallowing movement done to ingest the prey
item gives the impression that water is being actively
expelled under pressure. But having said this, I
believe that based on observations of active birds it
won't be possible to test which process is underlying
the observer pattern. Therefore my recommendation is
that this communication is published and perhaps then
other experts can shed light on this matter.
José A. Alves