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Notes on the foraging behaviour of Eurasian Oystercatchers Haematopus ostralegus feeding on bread

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Abstract

I report the first documented records of free-living Eurasian Oystercatchers feeding on bread. The observations were made in the city of Groningen and at other localities in The Netherlands. They include instances of adult oystercatchers picking up bread and feeding it to well-grown chicks. Most observations relate to urban habitats. Further studies are needed to evaluate the costs and benefits for oystercatchers of eating bread.
Notes on the foraging behaviour of Eurasian Oystercatchers
Haematopus ostralegus feeding on bread
Klaas van Dijk
Ornithological Society Avifauna Groningen, c/o Vermeerstraat 48, 9718 SN Groningen, The Netherlands.
klaas.vdijk@hetnet.nl
Dijk, K. van. 2014. Notes on the foraging behaviour of Eurasian Oystercatchers Haematopus ostralegus
feeding on bread. Wader Study Group Bull. 121(1): 15–17.
Keywords: Eurasian Oystercatcher, Haematopus ostralegus, diet, food, feeding behaviour, eating bread
I report the first documented records of free-living Eurasian Oystercatchers feeding on bread. The observations
were made in the city of Groningen and at other localities in The Netherlands. They include instances of adult
oystercatchers picking up bread and feeding it to well-grown chicks. Most observations relate to urban
habitats. Further studies are needed to evaluate the costs and benefits for oystercatchers of eating bread.
INTRODUCTION
Records of Eurasian Oystercatchers Haematopus ostralegus
breeding in urban habitats in The Netherlands go back to the
1930s (Hulscher 1976). Nowadays, breeding in urban areas
takes place all over the country (Ens et al. 2011). Almost all
records concern birds nesting on the roofs of buildings. A
census of the entire built-up area of the city of Groningen
(38.6 km2; 53°13’N, 06°34’E) revealed 70 breeding pairs in
2003 (1.8 pairs/km2, Oosterhuis 2004). Dijkstra & Dillerop
(2012) report an increase from 35 pairs in 2008 (8 pairs/km2)
to 49 pairs in 2012 (11 pairs/km2) in a study plot of 4.4 km2
in the city of Assen (53°00’N, 06°34’E). Casual observations
show that these birds forage on earthworms Lumbricidae
and on leatherjackets, the larvae of the cranefly Tipula
paludosa, on lawns, roadside verges, playgrounds and other
places with short vegetation, all being located within a short
distance from the nest (Dijkstra & Dillerop 2012, Oosterhuis
2004, own observations).
Dierschke et al. (2011) depict an adult Eurasian Oyster-
catcher eating food out of a person’s hand. The picture was
taken on the beach at Düne (Helgoland, Germany) on 21
April 2004. Details on the type of food are not provided, but
it is noted that some birds at Düne were specialized in
begging for food and in snatching food from tents and
restaurants. The behaviour of free-living Eurasian Oyster-
catchers deliberately taking food from people is not
mentioned in handbooks or other literature (e.g. Blomert et
al. 1996, Briggs 1980, Cramp & Simmons 1983, Duncan et
al. 2001, Gittings et al. 2012, Glutz von Blotzheim et al.
1984, Goss-Custard 1996, Lynch 1997). Moreover, these
sources do not mention that free-living Eurasian Oyster-
catchers can forage on bread, a source of food made from
Common Wheat Triticum aestivum.
Here I report several cases of Eurasian Oystercatchers
eating bread, together with notes on their behaviour when
taking this type of food. The observations were made in
urban habitats in The Netherlands, unless stated otherwise.
Urban Eurasian Oystercatchers are often tame and used to
people. Therefore, no special effort is needed to observe
them. Records in the city of Groningen are based on my own
observations. Additional records from other parts of The
Netherlands were compiled through an online request for
information and by sending requests to local ornithologists.
RESULTS
Records of Eurasian Oystercatchers eating bread
in the city of Groningen
On 3 June 2011, I assisted Rob Voesten with ringing Black-
headed Gulls Chroicocephalus ridibundus in city parks in
Groningen. These gulls are captured by encouraging them
to walk into a ca. 50-cm noose at the end of a thin 5-m rope
lying on the ground. The ringer holds the other end of the
rope. He throws food, bread or a mixture of tiny pieces of
bread and cheese, to lure the gulls and he pulls the rope to
capture a gull when one is standing in the noose.
The location, Mispelflat, was visited in the evening of
that day. Suddenly an adult Eurasian Oystercatcher landed
nearby. It started walking towards us and started to eat some
of the pieces of bread. The noose was prepared and the
oystercatcher was captured within a few minutes. It had no
obvious brood patch, no actively moulting primaries,
secondaries or tail feathers and it was released with a
stainless steel ring, Arnhem 5.283.649, on its right tibia.
Despite several visits to this site and to the surrounding area
in the next few weeks of that year, the bird was not seen
again. During the breeding season of 2012 I visited
Mispelflat and its surroundings at least weekly, but the
ringed Eurasian Oystercatcher was observed only once, on
6 May 2012, when I saw it at Orionvijver, a location visited
almost daily, and 1.1 km southwest of Mispelflat. For over
half an hour I watched the bird foraging on earthworms on
a grassy verge beside a busy road.
In 2013, I made more observations of oystercatchers
feeding on bread. An unringed adult was seen at Mispelflat
for the first time on 1 June. Probably the same bird was also
seen there several times during 8–10 June. On 9 June, it flew
away with a piece of bread in its bill. On 10 June, it walked
towards me while I was feeding bread to gulls and ducks. It
Wader Study Group Bulletin 121(1) 2014: 15
Wader Study Group Bulletin 121(1) 2014
16
took some bread and flew away with it in its bill. At 13:00
on 11 June, the bird with Arnhem 5.283.649 was present,
together with two chicks and an unringed mate. Both chicks
were almost able to fly. The ringed adult picked up pieces
of bread offered by me and fed the chicks with small pieces.
By 18:45, the ringed adult and a chick had moved to a
nearby lawn. The lawn was between rows of houses. The
adult was searching for earthworms and all were given to
the chick. The adult stopped foraging in this way as soon as
I threw some small pieces of bread in its direction. It walked
straight towards me, picked up some pieces of bread which
it ate. The same behaviour was noted on 12 June when at
20:00 the ringed adult was seen probing in the grass with a
chick waiting nearby. Once again, as soon as I threw small
pieces of bread in its direction, the adult walked towards me
and started to eat them. The bird also gave bread to the chick.
Within about five minutes, I threw seven pieces of bread
towards the adult. Invariably, the adult walked towards me
to take a new piece of bread. I was unable to find the birds
on 13, 14, 15 and 17 June. The last encounter was at 18:15
on 18 June when both adults were accompanied by one chick
which was just able to fly. The whole family flew away very
quickly. Soon afterwards, I found the unringed adult on a
nearby lawn. Once again, it immediately walked towards me
when I threw bread towards it. The bird picked up bread and
started eating it, but was disturbed by a flock of Lesser
Black-backed Gulls Larus fuscus.
Over the next few weeks, I conducted some investigations
to get an idea about the frequency of this behaviour. I
assessed the behaviour of the adults of nine breeding pairs
in Groningen. All of them foraged on lawns and roadside
verges, and all were used to the proximity of people. I found
the birds while cycling and the birds’ locations were spread
over the city. Each time I found a bird or a pair, I approached
slowly, threw small pieces of bread towards them and noted
their reaction. Six of the nine pairs did not take the bread or
react in any way (only one adult was present in three cases;
both adults were present in the other three cases).
On 27 June 2013, 4.2 km south of Mispelflat, I located
the adults of a roof-nesting pair with two chicks that were
already able to fly. As soon as I threw some pieces of bread
in their direction one of the adults started walking towards
me. I did not see it pick up any bread (but not much time
was spent watching to see if this would happen). The other
adult did not react.
I recorded two more cases of adult oystercatchers taking
bread on 4 July 2013. The first concerned a roof-nesting pair
in an industrial area, 3.1 km southeast of Mispelflat, with at
least one chick which was already able to fly. At first, one
of the adults did not react when I threw bread in its direction,
but later it ate some small pieces. Its mate did not react.
Later, 400 m NNE of the first pair, I located an adult from
another breeding pair foraging on a roadside verge. The bird
approached me when I threw bread in its direction and it ate
some. The bird’s mate was not present. All birds ignored
crusts and other hard parts and only ate soft bread.
Records from elsewhere in The Netherlands of
Eurasian Oystercatchers eating bread
In response to my online request for information, Gerrie
Evers reported that, in the 1980s, Eurasian Oystercatchers
breeding in an industrial area at Vianen (51°59’N, 05°05’E)
would regularly eat small crumbs of bread left over after a
lunchbreak. Martin van de Reep reported an encounter at
Voorburg (52°04’N, 04°23’E) on 2 February 2012 during a
period of severe cold weather. He provided supplementary
food to a mixed flock of birds, mainly gulls and ducks, and
noted an Eurasian Oystercatcher approaching him. The bird
was unable to compete with the large number of hungry gulls
and ducks. Martin directed some of the food towards the
oystercatcher and was able to feed it small pieces of bread
(only the soft parts). Leo Snellink encountered at least four
different pairs in The Hague (52°04’N, 04°17’E) in 2013 of
which the adults ate bread and also fed bread to their chicks
(Fig. 1). On one occasion on 28 June 2013, an adult captured
prey, probably an earthworm, just after Leo had thrown some
bread in its direction. A chick was waiting nearby, but the
adult started to walk in Leo’s direction, with the prey still in
its bill. The adult dropped the prey, picked up some bread
and fed it to the chick. Another adult, with a chick waiting at
Fig. 1. A roof-nesting Eurasian Oystercatcher and its chick at The
Hague, The Netherlands, on 19 June 2013: (a) the adult picks up
bread thrown towards it by the observer, (b) offers the bread to the
chick, (c) which takes and eats it (photo: Leo Snellink).
(a)
(b)
(c)
van Dijk: Notes on the foraging behaviour of Eurasian Oystercatchers feeding on bread 17
a distance of 50 m, attacked a Lesser Black-backed Gull in
order to obtain pieces of bread provided by Leo.
There are also records of oystercatchers eating bread in
non-urban habitats. René Oosterhuis reported that a breeding
pair would eat bread on the island of Griend (53°15’N,
05°15’E), an uninhabited nature reserve in the Dutch
Wadden Sea. In 2000–2001, bread was used to lure Black-
headed Gulls to a clap-net situated close to the wardens’
house (van Dijk & Oosterhuis 2008). Some decades ago,
captive Eurasian Oystercatchers on the island of Schiermon-
nikoog (53°29’N, 06°12’E, Dutch Wadden Sea) also ate
bread (Jan Hulscher, pers. comm.). The birds had been
captured on the nest and were used for various experimental
studies on food intake and feeding behaviour (Hulscher
1974, 1982). When not used for experiments they were fed
with pieces of flesh of Cockles Cerastoderma edule or
Mussels Mytilus edulis. Pieces of bread were also swallowed
on the few occasions when they were offered to them.
DISCUSSION
These observations are, to the best of my knowledge, the first
documented records of free-living Eurasian Oystercatchers
eating bread, and the first to show that they eat vegetarian
food. However, more observations are needed before firm
conclusions can be drawn about the frequency of this
behaviour or how widespread it occurs geographically.
Some of the adult oystercatchers that were searching for
food for their chicks showed an immediate switch from
invertebrates to bread when bread was offered. This suggests
that bread might be a more profitable type of food to feed to
the chicks than the available invertebrates (Zwarts et al.
1996a, 1996b). Further studies are needed to determine
possible differences in digestibility of bread and of animal
food (Kersten & Visser 1996).
ACKNOWLEDGEMENTS
I thank Bert Dijkstra, Rinus Dillerop, Gerrie Evers, Jan
Hulscher, René Oosterhuis, Martin van de Reep, Jan Allex
de Roos, Leo Snellink, Rob Voesten and Henri Zomer for
their help and assistance. I am also grateful to Humphrey
Sitters for his helpful comments and to Bruno Ens for his
review of this paper.
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