Occurrence of strange objects in nests of
the Wryneck Jynx torquilla

JUHANI TERHIVUOTERHIVUO, J. 1977 : Occurrence of strange objects in nests of the Wryneck
Jynx torquilla . - Ornis Fennica 54 :66-72 .

A study was made of the contents of 41 nest-boxes of the Wryneck ; thesample localities cover the Finnish range of the species fairly well. The
samples included various objects brought to the nests by the Wrynecks, themajority with no nutritional value - pieces of glass, porcelain, plastic, bones,
metal, egg shell fragments, shells and fragments of bivalves and terrestrial
snails, stones, etc . It is concluded that to find many of them the birds had tovisit unusual feeding sites, and that in some cases they had shifted to novel
food items, possibly owing to a temporary food shortage . The only featurecommon to these objects and ants, the normal food of the Wryneck, seems tobe their shiny surface .
The presence of strange objects did not appear to affect the number ofnestlings per brood, but the frequency of broods with one or more dead nestlings was higher in the group of nests containing such objects . Fourteen deadnestlings were dissected, and four of them (29 %) had stones or a piece ofglass in their stomachs . Possible reasons for the occurrence of strange objects
in the nests are discussed .
Juhani Terhivuo, Zoological Museum, University of Helsinki, P. Rautatiekatu 13, SF-00100 Helsinki 10, Finland

Introduction
Throughout its range the Wryneck is
an extreme food specialist. Its diet consists mainly of ants and ant cocoons,but other insects, spiders and slugs,
and even Lupine seeds (Lupinus luteus)
may occasionally be taken (PUHLMANN
1914, BUSSMANN 1941, STEINFATT 1941,
DURANGO 1942, Szöcs 1942, DEMENTEV
et al. 1951, STEIL 1957, KÖNIG 1961,
V . HAARTMAN et al. 1963-72 and RUGE
1971) . In Norway (HAFTORN 1971 :486)
and in Finland (TERHIVUO 1976), Wry-necks have been reported to carry terrestrial snails to the nestlings. In Germany and Denmark pieces of glass andplastic fed to nestlings have increased
nestling mortality (CHRISTENSEN 1975) .

suggested that theseare parallel examples of the same tendency. To study this phenomenon
further in Finland, I asked ornithologists to save the material left in thenest-boxes of Wrynecks after the
breeding period .
TERHIVUO (1976)

Material and methods
Altogether 20 samples with notes on thebreeding result of the pairs were received and these were examined together with earlier data on the nesting
success and nest-box contents of 21
pairs studied by Mr. T. Leino (locality
11 below) . The 17 sample localities(Fig. 1) and the breeding schedules of

J. Terhivuo: Strange objects in the nests of the Wryneck67

the pairs studied are described below.
Data on nestling mortality is given
later in this paper .
1 . Valkeakoski, Kirsi (679 :34, Grid 27oE,
see HEIKINHEIMO & RAATIKAINEN 1971) ; a sparse,
dry, mixed forest . The nest-box was emptied inautumn 1975 . In spring 1976 it was first occupied
by Great Tits (no eggs), but by 29 May, 3 eggs
had been laid by the Wryneck. These were destroyed by man. On 19 June, 9' Wryneck eggs ;on 9 July, 6 nestlings .
2. Svartå, Andersro (667 :32) ; a yard . The
nest-box was emptied in spring 1976 .
3. Kyrdskoski (684 :29) ; vicinity of humansettlement. The nest-box was not emptied before
the nesting in 1975 .
4 . Riihilahti, Kalkkinen (680 :42) ; a yard . The
nest-box was set out in spring 1975, but evidently
not used until 1976 .
5 . Iitti, Siyhtee (676 :45) ; a dry coniferous
forest near a field. The nest-box, not emptied
earlier, was inhabited by the Wryneck in both1975 and 1976 . 7 nestlings were ringed on 2 July
1976 .
6. Tuustaipale, Saviniemi (682 :48) ; a yard .
The nest-box was inhabited by Great Tits in 1975,
but not emptied after that . The Wryneck nested
in 1976 and an unknown number of young fledgedon about 6-8 July .
7. Nilsiä, Eteli-Reittiö, Tarpinen (701 :54) ;vicinity of human settlement. The nest-box wasset out in spring 1976 . On 25 June, 9 nestlings,
which all fledged in July .
8. Harjunpää (683 :22) ; unknown habitat . The
nest-box was emptied in autumn 1975 . In spring
1976 it was occupied by Great Tits (no eggs), andlater by the Wryneck. 4 juveniles fledged on about
7 July .
9. Saarinen (700 :48) ; a garden surrounded byfields . No nesting in 1975 . In spring 1976 thenest-box was first inhabited by Great Tits (noeggs), and later by the Wryneck. On 21 June,
9 nestlings .
10 . Hietasilta, Pilkanmaa (675 :4'7) ; a yard .
The nest-box was set out in 1976 . An unknown
number of young fledged on about 9 July .
11 . Ylämaa, Leino (674 :55) . A. A sparse,
mixed forest near a garden . The nest-box was set
out in spring 1965 and emptied in spring 1966 .
By 9 July, 9 young fledged. B. A garden . The
box was set out in spring 1966 and emptied inspring 1967 . On 5 June 1967, 11 eggs ; by 10 July,
10 young fledged . The nest-box was emptied in
March 1968 . On 7 June 1968, 10 eggs ; by 10
June, 7 juveniles hatched, and by 10 July, 6 ofthem fledged. In 1973 the Wryneck nested again.
C. A hill with mixed forest, about 500 m fromhuman settlement . The box was emptied in winter

FIG . 1 . Sample localities . Black line = northern
limit of the regular breeding range of the Wryneck in Finland according to v. HAARTMAN et al .
(1963-72).

1968 . On 15 June 1968, 9 eggs ; by 26 July, an
unknown number of juveniles fledged. D. A hillwith mixed forest, about 500 m from humansettlement . The box was emptied in spring 1971 .
On 10 June 1971, 10 eggs ; on 23 June, 9 nestlings. E. Centre of a village, the nest tree surrounded by bushes . The nest-box was emptied inspring 1976 . On 12 June 1976, 8 eggs ; on 2
July, 3 nestlings . P. A hill slope near a field;
the nest in a cavity in a rowan stump.
12 . Korso, Nisbacka (669 :39) ; vicinity ofhuman settlement . The material was collectedfrom 1-3 nest-boxes of the Wryneck in 1969.
Other data lacking (see TERHIVUO 1976).
13 . Askainen, Lempisaari (672 :21) ; a sparseforest near human settlement. An unknown number of live nestlings .

68
14 . Vantaa, Silvola (668 :38) ; unknown habitat. The box was first inhabited by Pied Flycatchers . On 18 June 1976, 10 eggs of the Wryneck ; by 13 July, 8 young fledged.
15 . Liminka, Virkkula (719 :41) ; unknown
habitat. The box was emptied in 1975, 8 juveniles
fledged in July 1976 .
16 . Salla, Kursu (740 :5'5); unknown habitat .
On 24 June 1976, 10 nestlings and two unhatchedeggs . This record is north of the usual breeding
range of the species in Finland .
17 . Yläne, Vaskijärvi (675 :24) ; two nestboxes in a mixed forest, no nesting in 1975 . A.
On 6 June 1976, 7 eggs ; on 27 June, 5 nestlings .
B. On 2 July 1976, 10 eggs ; on 15 July, 8 live
and 1 dead nestlings .

Results and discussion
The excrements among the material
sampled consisted almost entirely of
the chitinous parts of ants (Formica,
Lasius spp.) mixed with dead plantmaterial and small stones (diameter <1 mm), which were evidently takenwith the ants . Only a few fragments ofColeoptera and Hemiptera were found,which indicates that the Wryneck is anextreme food specialist in Finland as
well .
The Wrynecks had also carried agreat number of strange objects to theirnests (Table 1). The wide range of thesample localities (Fig . 1) suggests that
this is not an unusual or local phenomenon in Finland, at least in 1976 .
Moreover, as far as is known, thematerial collected is unbiassed. The
pieces of glass, porcelain, metal, plastic,bones, fishbones and fish scales, aluminium foil and stones may have been
picked up from trash heaps, yards androadsides. Many objects probably comefrom poultry farms such as the fragments of exotic marine bivalves (mostly
Cardium spp. ; imports used in poultry
farming) and the fragments of egg
shells (distinctly thicker than those of
the Wryneck, most probably from thedomestic hen) . The shells and shell

ORNIs FENNICA VOI. 54, 1977

fragments of Finnish bivalves had been
picked up from shores . It can thus beconcluded that the birds have visitedunusual feeding sites. The shells of thebiggest terrestrial snails had beenbroken to extract the soft parts ; thisfood item had been particularly favoured at locality 13. Except for the snails,
the objects found were of no nutritional
value to the nestlings.
Most of the objects were found in
the loose material left in the nest-boxes,
not in the excrements . Thus in mostcases either the nestlings were not fed
with the objects or they had been rejected by them. In fact, many objects
were too big to be swallowed even byan adult bird.
Altogether 14 dead nestlings (fromlocalities 1, 8, 10, 13 and 17B) were dissected . One dead nestling from locality
8 had three stones (6X5, 6X5 and
5 X 3 mm) in its stomach and anotherhad a piece of brown glass (7 X 5 mm)
and one stone (6 X 4 mm). One of thefour dead nestlings from locality 10
had swallowed a stone (4X3 mm), andtwo stones (5 X 3 and 4 X 3 mm) were
found in the stomach of the smallest of
the three dead nestlings from locality
17B. Since the Wrynecks do not carryany nest material, the tendency to takeobjects to the nest seems to be related
to the feeding of nestlings.
It can be assumed that the parent
birds are driven to search for food by
their inner motivation (physiologicalstate) and stimuli from the hungry
nestlings, and that their subsequent behaviour is triggered by stimuli from thefood items, probably mostly visual .
FEARS (1967) reported that in times offrost Song Thrushes Turdus philomelos
feed on Dogwhelks Thais lapillus (Mollusca), on the shore, and according to
HARTLEY (1953) and GIBB (1954), during cold periods tits Parus spp. may
feed in other parts of the trees thanJ. Terhivuo: Strange objects in the nests of the Wryneck

69

TABLE 1 . The number of nestlings produced in relation to the objects found in the nests of the
Wryneck . Symbols : I = pieces of glass or porcelain, II = stones (max. diameter ~ 5 mm), III shells and shell fragments of terrestrial snails, IV = shells or shell fragments of bivalves, V = eggshell fragments (those of Wrynecks excluded), VI = fishbones and fishscales, VII = mammalianbones and bone fragments, VIII = pieces of metal, IX = pieces of aluminium foil, X = pieces ofplastic, XI = seed of a leguminous plant . Sample volume in dl .

Localityand year

Sample Nestlings
volume Alive Dead
(dl)

1
1976
2
1976
3
1975
4
1976
5 1975-76
6
1976
7
1976
8
1976
9
1976
10
1976
11A
1965
11B
1966
11B
1967
11B
1968
1113
1973
lic 1968
11D
1971
11E
1976
11F
1976
12
1976
13
1976
14
1976
15
1976
16
1976
17A
1976
17B
1976-

3 .0
0 .5
0 .1
0 .3'
1 .5
0 .8
2 .5'
0 .6
3 .0
3 .0
?
?
?
?
?
?
?
0.3
0 .3
0.1
3 .0
3.0
3 .0
0 .5
5 .00
17 .5°

0
-+-++
7
-+9
4
0
-I9
8
10
6
10
9
9
3
+
?
8
8
10
5
6

6
0
0
0
0
0
0
3
9
4
0
1
0
1
0
0
0
0
0
?
1
0
1
0
0
3

objects found
III

IV

V

VI

VII

VIII

IX

la
8a
le
-

lc
-

9b
lib
6b
20b
34b
lb

1
2
4
-

id
-

-

3
-

+
125
6
19
7
- 16i
- 122i3
665
336- 8+2f
-

27c
92c
5k
61
-

+b
28b
7b
2b
4b
-

-

1h

-

7
31n
-

3m
-

-

1

II

2
2
8
3
5
4
2+2f 16+2f
1
if
+g

2
-

X

XI

26
-

1

a = from Bradybaena fruticum (1 ex .), b = from eggs of the domestic hen, c = from exotic species, mostly Cardium,d = humerus of the Mole Talpa europaea, e = unbroken shell of Cochlicopa lubrica, f - found in the stomach(s) ofdead nestling(s), g = a great number of pieces, h = bullet of an airgun, i = from Bradybaena fruticum (1 ex.),
Tricbia bispida (6 exx .), Cocblicopa lubrica (2 exx .) and Nesovitrea bammonis (1 ex .), i = from B. fruticum (about
36 exx .), k = shells of Mytilus edulis (1 ex.) and Mya arenaria (3-4 exx.), 1 = from Finnish freshwater spp .
(Unio vel Anodonta), m = bullet of an airgun and two pieces of a paste tube, n = small pieces of big bones andright half of mandible of the Root Vole Microtus oeconomus, o = including moss and wadding put by man in thebottom .

usual . The Wryneck may also change
its diet if ants are scarce (v. HAARTMAN
et al . 1963-72), and the present material indicates that the birds had visitedplaces where ants are not usually observed . Accordingly, I suggest, as aworking hypothesis, that if food is
scarce during unfavourable periods e.g.
on cold and rainy days, the birds tend

to visit new feeding places and perhaps
use new food items.
The nestlings need a large daily
supply of food (see BusSMANN 1941,
RUGS 1971), and during periods ofpoor weather it may be especially difficult for a monophagous bird like the
Wryneck to find enough food. Only
one of the 14 nestlings dissected had a

ORNIs FENNICA VOI. 54, 1977

70
TABLE 2. Nesting success of the Wrynecks
studied. The nests are divided into two groups, A.
Nests without objects and B. Nests with objects .
Localityand year

Nestlings
Alive
Dead

Total

A. Nests without objects
11/19651111966
11/1967
11/1967
11/1968
11/1970
11/1971
11/1971
11/1971
11/1972
11/1972
11/1972
11/1973
11/1974
11/1974
11/1975
3/1975

7
8
8
5
7
9
7
12
9
9
6
5
10
9
10
10
-+

0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

7
9
8
5
7
9
7
12
9
9
6
5
10
9
10
10
?

9
10
6
9
9
7
0
+-

0
0
1
0
0
0
6
0
0
0
0
0
3
9
4
0
0
1
0
1
0
0
3

9
10
7
9
9
7
6
?
?
7
?
9
7
9
?
3
?
?
8
9
10
5
9

B. Nests with objects
11/1965
11/1967
11/1968
11/1968
11/1971
5/1975-76
1/1976
2/1976
4/1976
5/1976
6/1976
7/1976
8/1976
9/1976
10/1976
11/1976
11/1976
13/1976
14/1976
15/1976
16/1976
17/1976
17/1976

-+

7
9
4
0
-13
-+

8
8
10
5
6

full stomach (all three nestlings fromlocality 10 had empty stomachs) .
Most animals do not respond to
many characteristics of a situation but
only to a few essential sign stimuli, andonly to a few of them at a time (TINBERGEN 1951). What resemblance have
all these objects to ants, the normal
food of the Wryneck? The objects varyin colour : white (porcelain, bones,
stones), green (pieces of glass), yellow
and brown of different shades (piecesof glass, snails, stones), dark blue
(shells of Mytilus), silver (aluminiumfoil), lead grey ('bullets of an airgun)
transparent (pieces of glass) . The colourof ants also varies : red and brown(Formica), yellow and black (Lasius) .
The shape and the size of the objects
seem to lack importance ; there were
triangular, quadrangular, ± elongated,thin and thick pieces of glass, porcelain,etc., and e.g. the pieces of glass measured from 45 X 15 mm to 2-3 mm,
but most of the objects were bigger
than ants or ant cocoons. The only
character common to the objects andants seems to be the more or less shiny
surface.
In normal situations, the stimuli ofthe objects may not be strong enoughto have any effect, but if the innate
motivation of the bird is high enough,they may elicit some reaction, viz. picking up. DELIUS (1968) has pointed outthat hunger and thirst shift the colour
preference of pigeons. The possibility
that the objects always have more effective (supernormal) stimuli than normal food is not supported by the present material, but it cannot be completely ruled out without further study.
However, in habitats with permanenthuman influence there are so manysmall, shiny objects available that selection should operate effectively
against their continuous preference tonormal food .
Feeding is a complicated process, inwhich learning plays an important role,
not only affecting the development offeeding behaviour and the selection of
the sites where the bird searches for1. Terhivuo : Strange objects in the nests of the Wryneck
food, but also largely determining thenature of the effective stimuli (seeHINDE 1973 :506-8). The possible roleof learning in the present case is unknown .
CHRISTENSEN (1975) reported that the
Wrynecks carrying pieces of plastic,
glass, etc. to their nests suffered fromhigh nestling mortality. Table 2 gives
data on the presence of abnormal objects in the nests and the nesting success in the present material . In the nests
without such objects (group A), thenumber of nestlings per brood was 8 .25±0 .49 (S.E.), and in the nests with abnormal objects (group B), the number
was slightly lower, 7.82±0.46. However, the difference is not statisticallysignificant (t test, P = 0.53) . The number of nestlings fledged per brood wasapparently higher in A than in B, 8.19
±0 .48 vs. 6 .47±0.77 (t test, P<0.1).
The frequency of broods with deadnestlings is 1/17 in A and 8/23 in B,
the difference being statistically significant (Fisher's exact test, P = 0.04) .
Only 4 (29 0/o) of the 14 dead nestlings
dissected could have been killed directly by the objects found in their stomachs .
The tendency to carry strange objects to the nests should be studied
further in Finland and other countries.
Although this tendency seems to becommon in Finland (at least in 1976)
the rather comprehensive literature on
the breeding biology of the Wryneckin Central Europe hardly contains any
note of it. It is thus possible that thetendency is more common in peripheral
populations, or that it has arisen only
recently .
Acknowledgements . The author is grateful tothe following persons for the samples : H . Ahola,
L . v. Haartman, J . Hakala, J . Hirvelä, R. Hyvönen, A . Järvinen, P . Kreuger (t), E . Lassila, T .
Leino, K . Lundström, K. Mattila, J. Mustonen,
H . Pöysä, A. Riihelä, J . Taskinen, V . Vestala andV .-M . Vuormala . Without their co-operation this71

study could not have been carried out . Mrs Anna
Damström kindly checked the English of themanuscript .

Selostus : Käenpiian tavasta kantaa esineitä pesäänsä
Tutkituista käenpiian pesänäytteistä (taul . 1)
löytyi lukuisia erilaisia ravinnoksi kelpaamattomia
esineitä : lasin- ja posliininpalasia (sarake I), kiviä(II), simpukankuoria ja kuorirouhetta (IV), kananmunan kuoren kappaleita (V), kalojen luita ja
suomuja (VI), nisäkkäiden luunsiruja ja luita(VII), metailliesineitä kuten ilmakiväärin luoteja(VIII), alumiinipaperia (IX), muovikelmun palasia (X), hernekasvin siemeniä (XI) sekä maakotiloiden kuoria (III), joista pehmeät osat oli käytetty ravinnoksi . Löytöpaikkojen sijoittuminen eripuolille Suomea (kuva 1) osoittaa, että kyseessä eiole paikallinen ilmiö . Koska näytteet pyydettiin
lähettämään ilman minkäänlaista valintaa, ilmiö
oli ainakin v . 1976 tavallinen . Koska aikaisemmat
kirjallisuustiedot tavasta ovat niukat, vaikka lajin
pesimäbiologiaa on melkoisesti tutkittu, ilmiö voi
olla Suomessa tavallisempi kuin esim . KeskiEuroopassa .
Käenpiian ravintona ovat normaalisti lähes yksinomaan muurahaiset ja niiden kotelot ("muurahaisenmunat") . Ravintopulan sattuessa monet lintulajit hakeutuvat uusiin ympäristöihin jaltai siirtyvät uusien ravintokohteiden käyttöön . Ehkä hetkellinen ravinnon niukkuus (esiin . sadepäivinä) ja
toisaalta ravinnon jatkuva suuri tarve pesäpoikasten ruokkimiseksi on aiheuttanut muutoksia käenpiikaemojenkin ravinnonhaussa . Ilmeisesti ne ovat
löytäneet esineitä mm . kanatarhoista (simpukkarouhe, kananmunien kappaleet), rannoilta (kotimaisten simpukoiden kuoret), tunkioilta (luunsirut, kalojen luut ja suomut, lasinpalaset) ym, paikoista, joista ne eivät tavallisesti etsi ruokaansa .
Rikotut maakotilot, joista pehmeät osat oli syöty,
osoittavat lintujen osittain muuttaneen myös ravintokohdetta .
Yleensä linnut eivät reagoi kaikkiin ympäristönärsykkeisiin, vaan ainoastaan ns . avainärsykkeisiin .
Ainoa yhtäläisyys löydettyjen esineiden ja lajinnormaalin ravinnon välillä on näiden enemmän
tai vähemmän kiiltävä pinta . Käenpiiat eivät ehkä
normaalisti reagoi lainkaan tai vain harvoin ko .
esineiden aiheuttamiin ärsykkeisiin, ts . nämä ovat
suhoptimaalisia . Jos ravintoa on niukasti, saattaa
linnun viretilassa (motivaatiossa) tapahtua muutos,
jolloin se reagoi moniin kiiltäviin esineisiin . Vähemmän todennäköistä on, että kiiltävät esineet
aiheuttaisivat jatkuvasti voimakkaampia (supernormaaleja) ärsykkeitä kuin normaali ravinto . Esimerkiksi kulttuuriympäristössä, joista lähes kaikki
näytteet ovat, kiiltäviä lasin- ja posliininpalasia,
pikkukiviä ym . on yleensä niin runsaasti, että jos

72
emot suosivat niitä jatkuvasti normaaliravinnon
kustannuksella, laji häviäisi näiltä alueilta nopeasti kokonaan . Oppimisen mahdollista osuutta
tutkittuun ilmiöön ei ole voitu päätellä.
Taulukossa 2 on esitetty käenpiikojen pesimätulos (ryhmä A = pesissä ei esineitä, B = pesissä
oli esineitä) . Keskimääräinen kokonaispoikasmäärä paria kohden ei riipu merkitsevästi esineiden
esiintymisestä pelissä. Pesyeitä, joissa oli kuolleita
poikasia, oli tilastollisesti merkitsevästi useammin
ryhmän B emoilla. Näillä myös elävien pesäpoikasten määrä paria kohden oli, jonkin tilastollisesti vain suuntaa-antavasti, pienempi kuin ryhmässä A. Koska useimmat esineet löytyivät pesäainesten joukosta eivätkä ulosteista, emot eivät
aina olleet tarjonneet esineitä poikasilleen tai poikaset eivät olleet pystyneet niitä nielemään. Kuolleita pesäpoikasia voitiin tutkia 5 eri pesästä 14yksilöä ; neljällä (29 %) oli kiviä tai lasinpalanen
mahassaan. Muiden kuolema on ehkä aiheutunut
ravinnon niukkuudesta (mahat yhtä lukuunottamatta miltei tyhjät) .
Jatkotutkimuksia varten kirjoittaja pyytää pesänäytteitä (myös kuolleet poikaset mukaan) ja mahdollisimman yksityiskohtaisia pesimätietoja kesäkaudelta 1977 . Jotta ilmiön yleisyyttä voitaisiin
luotettavasti arvioida, jokainen käenpiian perä
sisällöstä riippumatta tulisi lähettää.
Lähetykset osoitetaan kirjoittajalle (Eläinmuseo,
yleinen osasto, Helsingin yliopisto, P. Rautatiekatu
13, 00100 Helsinki 10). Samalla kirjoittaja haluaa
esittää kiitoksensa tutkimuksessa jo avustaneille(ks. englanninkielinen Acknowledgements) .

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DELIUS, J. D. 1968 : Color preference shift inhungry and thirsty pigeons . - Psychos. Sci.
13 :273-274 .
DEMENTEV, G. P., N. A. GLADKOV, E. S. PTUS-

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Received November 1976, revised December 1976