Why does the Wryneck Jynx torquilla bringstrange items to the nest?
Juhani Terhivuo

Terhivuo, J . 1983 : Why does the Wryneck Jynx torquilla bring strange items
to the nest? - Ornis Fennica 60 :51-57 .

Analyses were made of the contents of 121 Wryneck nests, collected after the
breeding season in different parts of Finland in 1976-79. The numbers of strange
items (stones, pieces of glass, porcelain, metal, putty, paint, plastic, egg-shelland bone fragments, and whole or broken bivalve and gastropod shells, etc.)
indicate that the tendency to bring such objects to the nest should be regarded
as the rule rather than the exception among Finnish Wrynecks . The mean numberof items in a nest was 37 .4, and only 9 (7 .4 %) nests lacked such objects.
Some Wryneck pairs had brought more than 200 objects to the nest .
The annual mean numbers of strange objects were fairly constant and no
significant differences could be detected between different parts of the country.
Some variation in the nature of the objects was detected between the years .
The nesting locality affected the nature but not the quantity of the items. Of
the 64 dead nestlings dissected, 7 (11 %) had died from eating strange objects.
The numbers of items in the nests showed no significant correlation with thenumbers of fledglings, which indicates that they had no great effect on the nesting
success .
Experiments with test objects revealed that the tendency to bring strange items
to the nest is most pronounced at the end of the nestling period, when theparents are busiest feeding the young . The stimuli from strange items together
with the inner motivation, or drive, of the parent bird to starch for food for
its young release the picking up reaction . Some of the test objects also elicited
picking up activity in parents inside the nest, but in this situtition the objects
were thrown or carried out of the nest .
The tendency to bring strange items to the nest should not be regarded as
adaptative behaviour supplementing the diet of the nestlings, but as the consequence of an error or mistake in the release of the picking up pattern in theparent bird . Learning seems to be involved in the adoption of strange objects
and, in sonic cases, this seemed to have facilitated the utilization of novel fooditems.
Juhani Terhivuo, Zoological Museum, University of Helsinki, P. 2autatiekrrlu
13, SF-00100, Helsinki 10, Finland

Introduction

The Wryneck is a myrmecophagous bird, which
also feeds the nestlings with ants and ant cocoons .
Occasionally, other types of food are utilized and'strange' items may be brought to the nest . Mostof the latter objects are not consumed by thenestlings and remain at the bottom of the nest
after the breeding season (Dekhuyzen-Maasland
et al . 1962, Klaver 1964, Dornbusch 1968, Heuer& Krägenow 1973). Many of the strange items
have no nutritional value and, in some cases atleast, they have caused the death of one or more
nestlings (Christensen 1975) . In Finland the nestling mortality due to such objects seems to below (Terhivuo 1977) .
Klaver (1964) and Löhrl (1978) suggested thatsome of the items are important for the nestlings .
For instance, small stones may facilitate digestion
by grinding the chitinous parts of the ants con-sumed by the nestlings, and the egg shell fragments possibly compensate for a deficiency of Ca
and P in the diet . Thus, they consider the tendency a behavioural adaptation of the parents .
Terhivuo (1977) suggested that the stimuli fromthe strange objects are usually inferior to thosefrom food items, and that a temporary scarcity
of food may induce the parent bird to pick up
strange objects and bring them to the nest .
The present paper reports on the contents of
121 Wryneck nests analysed in 1976-79 in Finland . Attention has been paid to the annual andregional variation in the quantity and nature of
the objects and to the nesting success of the
Wryneck pairs. The frequency with which objects
are brought to the nest in different phases of thenesting period was studied by laying out groupsof test objects in the vicinity of the nests .

52

ORNIS FENNICA Vol . 60, 1983

The test objects were 9x9 mm pieces of cream white
embossing tape (Dymo, clear 5238), each marked witha letter and a number . The thin film at the back of
the tape was not removed.
Prior to the experiments the contributors were asked
to check the onset of egg-laying of the Wrynecks . Whenthe clutch was completed, test objects marked with thesign A were set out in the vicinity of the nests in places
where the birds were observed to search for food . Objects marked Al were laid under the nesting tree, andobjects with higher serial numbers at increasing distancesfrom the tree, as follows : A2 20-30 m, A3 50-60 m,
A4 100-150 m and A5 200-300 m. Sets of 10 objects,
in some cases fever, were laid out in each site .
When the nestlings hatched, the objects with sign A
were replaced with objects marked B, and when the
nestlings were 10-12 days old these were exchanged
for series C, which was used up to the end of the nesting
period . The same sites were used for the groups of objects throughout the experiment .
In addition, in 1979 (3 pairs) and 1981 (2) the colour
preferences of the Wryneck parents were studied withtape of different colours: cream white, red, yellow, blue,
green and black . These experiments resembled those described above, with the exception that 6 different objects
were now included in each group .
Results

Fig . 1 . The localities sampled in 1976-79 . The broken
line indicates the northern limit of the regular breeding
range of the Wryneck in Finland (v . Haartman et al .
1963-72) .

Material and methods
Nest contents . The 121 nests of the Wryneck were collected by Finnish ornithologists in different parts of thecountry after four breeding seasons (1976 21, 1977 48,
1978 27 and 1979 25 nests) . The samples were taken
irrespective of the nesting success, most of them fromnest-boxes emptied annually . Data on the habitats of
the nests and the nesting success of most pairs werealso received . The locations sampled are indicated inFig. l . For the grid system adopted, see Heikinheimo& Raatikainen (1971) .
Fxperintents with test objects. Groups of test objects
were placed on the ground in the vicinity of the nest .
The objects were set out in the evening when the birds
had ceased searching for food and were counted thenext evening at the same time . Objects that were removed were replaced with new objects marked with thesame symbols. The procedure was repeated once or several times. When the breeding season was over thenumbers of objects in the nests were counted. Theseexperiments involved 8 Wryneck pairs and were carriedout in 1978-79 .

Annual and regional variation in the numbers of
strange objects. The number of objects recordedin the 121 Wryneck nests totalled 4528 . Only 9
nests (7 .4 %) lacked other objects than the droppings of the nestlings. Fig. 2 shows the numbersof objects found in the nests. This negative binomial frequency distribution shows that in about
half of the nests the numbers of objects wererather low (0-20) . The mean number of objects
in a nest was 37 .4 (Table 1) . Table 1 shows theannual variation in the mean numbers of items.
The Kruskal-Wallis test revealed no significant differences between the years (H*=1 .59, df=3).
The regional variation in the numbers of objects
was studied by calculating the mean numbers forthe pairs in three regional zones, viz. 660-680,
680-700 and 700-750 (see the grid in Fig. 1) .
The means (±SE) were 36 .2±5 .4 (N=57),
35 .0±8 .0 (N=42) and 46 .7±13 .5 (N=22), respectively . The Kruskal-Wallis test indicated no statistically significant differences between the zones(H*=1 .24, df=2). Nor was there any significant
difference between pairs nesting in habitats withconstant human influence (mean 38 .4±6 .3, N=66)
and pairs nesting in sites with very weak or no
human influence (mean 30 .9±6 .4, N=35) (H*=0 .05, df=1) . Thus, the geographical location andnesting habitat do not seem to affect the frequency of strange objects in the nest . Moreover,the number of the objects varied greatly evenwhen nesting took place in successive years in thesame nest-box .
The nature of the strange objects. Table 2 shows
the percentages of the different kinds of objects
recorded in the nests. The first five categories

J. Terhivuo : Strange items in Wryneck nests

comprise items without any potential nutritive
value . These total 54 .1 % of all the items. The
other four categories involve objects which might
have contributed to the diet if consumed by thenestlings .
Since the objects indicated in Table 2 were
found at the bottom of the nests, the parents had
not fed them to the ncstlings, or they had been
rejected by the ncstlings . The objects include
small stones, pieces of cement, putty, porcelain,glass, plastic, paint, wax, metal, fragments of eggshells (those belonging to the Wryneck were
excluded), pieces of exotic bivalves used in feeding hens, the whole or parts of gastropod andbivalve shells of Finnish species, bones and scales
or fragments of them (most probably picked up
from trash heaps close to human settlements) andheavily chitinized invertebrates or parts of them(e .g . diplopods, coleopterans, isopods, insect cocoons) . Plant material was scarce . The locationof the nest affects the nature of the objects, sincedifferent kinds of waste material (glass, porcelain,putty, etc.) were more abundant in the nests close
to human settlements than in those far from them .
Near Raurna, on the other hand the Wrynecks
had brought 81 fish scales and bones to the nest
(pair of the Osprey Pandion haliaetus nesting in
the vicinity) and in Eckerö, Signilskär, 79 isopods
were caught . Both locations were far from humansettlements .
The annual variation in the nature of the objects was examined by dividing the material into
two groups : (1) objects composed of inorganic material- without any potential nutritive value (thefirst 5 categories in Table 2), and (2) objects
which might have contributed to the diet of thencstlings (the last 4 categories) . The percentages
for the first group in the four years (1976-1979)
are : 49 .9, 63 .9, 32 .6 and 58 .9 . The differences between the four years are highly significant(X''-=250.9" . ., df=3) . Accordingly, although themean numbers of the objects in the nests did notvary much annually (Table 1), the nature of theobjects did . This is discussed in more detail later.
I also inspected many of the droppings left in
the nests and they mostly consisted of chitinousparts of ants . Very small stones measuring <2 mm
were fairly often present, and sometimes tiny shellfragments and spruce needles were found, too . It
is worth noting that the shell fragments were notmuch affected by the digestion process (see also
Heuer & Krägenow 1973) .
Number and nature of objects in relation to nesting
success . The data on the nesting success of thepairs include records of nests in which all the
young died and nests in which some fledged. The
broods of the former group total 12, or 9.9 %of all the broods . I dissected 25 nestlings from53

Number ofobjects
0- - 21-41-61-'81-'101=121=
1st-201: _ 281200 220
300
20 49 60 80 100 120 140
Fig. 2. Numbers of objects in 121 Wryneck nests collected in 1976-79 after the breeding season .
six broods in this group. In 14 the stomachs were
empty; in the other 11 they contained chitinousparts of ants, Hymenoptera cocoons, some plantmaterial, tiny stones and some spruce needles. In
one of them the stomach was almost full of plant
lice (Homoptera) . None of these nestlings had
been killed by eating a strange object . I also dissected 39 dead nestlings from 24 nests with atleast one young fledged . In 7 of them (18 %)death was caused by object(s) stuck in somepart(s) of the alimentary canal . These items were
(1) a piece of glass and a piece of porcelain in
the stomach, (2) an air-gun bullet and two piecesof blue plastic in the stomach, (3) a very big fragTable l . Annual variation in the nuan numbers of objects recorded in the 121 Wryneck nests studied in
1976-79 . The Kruskal-Wallis test applied to the actual
numbers of objects indicates no statistically significant
differences between the four years. (H`=1 .59, n.s .) . The
nesting success of the pairs is not considered .
Year

No . ofnests
NNo . of objects
Mean±SE

Range

1976
1977
1978
1979

21
48
27
25

42 .5 ±10 .9
40 .1 + 8.3
32 .6± 8.0
33 .2 ± 7 .8

3-212
0-297
0-188
0-136

Total

121

37 .4 ± 4.5

0-297

54

ORNIS FENNICA Vol . 60, 1983

Table 2 . Classification of the objects in the Wryneck nests in 1976-79 . The first five categories comprise objects
without any possible nutritional value to the nestlings, the other four those which might have contributed tothe diet, if consumed by the nestlings .
Objects

1976

1977

1978

1979

Total

Stones (0 2-10 min)Cement, putty
Glass, porcelain
Plastic, paint, wax
Metal
Fragments of eggs,
gastropod and bivalve shells
Bones, scales, fragmentsof vertebrate bones
Chitinous invertebrates
or their parts
Seeds, berries

23 .6
10 .5
11 .8
3 .2
0 .8

22 .8
3 .1
31 .3
5 .0
1 .7

6 .4
1 .1
9 .9
14 .2
1 .0

25 .7
0 .4
15 .7
17 .0
0 .1

20 .3
3 .7
20 .4
8 .6
1 .1

39 .9

27 .4

38 .8

25 .6

31 .7

8 .5

2 .0

24 .6

11 .4

9 .4

1 .7
-

6 .5
0 .2

3 .9
0 .1

4 .2
-

4 .6
0 .1

Total number of objects
Total number of nests

893
21

1927
48

879
27

829
25

4528
121

ment of bivalve shell in the stomach, (4) 4 piecesof plastic (the test objects) and 1 white stone in
the stomach, (5) two big pieces of bone in thestomach, (6) one very big fragment of the shellof Bradybaena fruticum (gastropod) stuck in thethroat and (7) six stones and one piece of eggshell in the stomach . In the other nestlings studied
the stomachs were either empty or contained someplant material, chitinous parts of ants and/or tinystones . Of all the nestlings dissected, about IIseem to have died from eating strange objects .
No statistically significant correlation was foundbetween the numbers of the objects and thefledglings within the years or in the total material .
Nor was there any significant difference between
the mean number of fledglings in nests with 3100
items (N=10, mean 6 .6±0 .62, range 3-9) and innests with only ;20 items (N=31, mean 6 .4±0 .39,
range 2-10) .
The following procedure was used to study boththe number and nature of the objects in relation
to the nesting success of the Wrynecks . All thenests with at least one fledgling were divided medianly into two categories : those with 25 or fewer
items and those with more than 25 . Bothcategories were further divided medianly into twogroups (A, B and C, D, respectively) according
to the percentages of the objects with possible
nutritive values for the nestlings . In A and B,
the mean percentages of such items were 25 .1±7 .0(SE ; N=17) and 93 .1±2 .5 % (N=17), respectively, and in C and D 11 .0±1 .9 % (N=18) and
79 .5±4 .1 % (N=17) . Factor analysis of varianceapplied to the numbers of fledglings in groups AD indicated no statistically significant differences
between the four groups (F=0 .886, df i =3,
df2 =65) .

Experiments with test objects . The data given in
the previous sections leave many questions unanswered . Do the Wrynecks pick up strange objects with equal frequency in all phases of thenestling period? How far from the nest were theobjects found? Do local weather conditions enhance the tendency, and do the parent birds show
any colour preference? It was in order to obtainsome answers to these questions that the test objects were set out for the parent birds during different phases of the nesting period .
Table 3 shows that the frequency with which
the objects were brought to the nests varies greatly between the different phases of the nesting
period . Only 5 objects were removed from thegroups during the incubation period and there isno clear evidence that they were taken by the
Wrynecks . The percentage of the total number ofobjects available found in the nests (c/a) differs
highly significantly between the first and the second half of the nestling period (x2=136 .6""",df=1) . Since the parents feed their young more
often during the second half (e .g . Bussmann 1941,
Ruge 1971), the tendency to pick up such objects
seems to be related to the feeding frequency .
Only about 55 % of the objects removed were
found later . Since the percentages of the objects
removed (b/a, Table 3) were also highest at theend of the nesting period, it is very likely thatthey were carried somewhere by the Wrynecks .
This is also suggested by the fact that some ofthem were found under the nest-box, having evidently been thrown out of the nest . The tendency
to take the test objects differed among the pairs
studied and other types of strange objects were
present in the nests, too . Some of the birds possibly used to visit sites where the test objects wereJ . Terhivuo : Strange items in Wryneck nests

Table 3. Data from the field experiments with cream white test objects of plastics laid out in groups of about 10
in the vicinity of the Wryneck nests during different phases of the breeding period . The sites of the groups werealways the same . Each object was available for one 24-h period . Symbols: 1 = the group laid out 0-2 m from thenest, 2 = 2()-30 m, 3 = 5()--60 m, 4 = 100-150 m and 5 = 200-300 m from it . See also the text .
Incubation period
1
No . of objects
available(a)No . of objects
removed(b)
No . of objects foundin the nests(c)b/a (%r)c/a (%
No . of
Wryneck pairs

2

3

4

Nestlings I-10 days old51

220 220 220 216 220 1096
-

3

1

1 -

5

- - - - - - 1 .4 0 .5 0 .5 - 0.5- - - - - 8

3

4

5

E

3211 320 320 313 3211 1593
42

44

20

56

12

174

17 17
3 15 - 52
13 .1 13 .8 6 .3 17 .9 3.8 10 .9
5 .3 5.3 0 .9 4.8 - 3.3

not available, but, since the objects under thenesting tree were not taken by all the pairs, thepairs evidently "accepted" the test objects unequally, too. The process of learning to "utilize"
the groups of test objects may have been important in this respect.
The majority of the objects found originatedfrom groups lying less than 200 m from the nests.
In general, the farther the group was, the fewer
were the objects from it found inside the nest .
The data obtained on the colour preferences ofthe Wrynecks were meagre ; only two of the test
objects were found inside the nests and both werewhite. Of the 22 test objects removed from thegroups, the majority were white (27.3 %) andblack (22.7 %) .
Discussion

2

Nestlings more than
10 days old

Bringing strange objects to the nest should undoubtedly be regarded more as the rule than the
exception among nesting Wrynecks in Finland.
What can be the reason for this tendency? Thesuggestion that it is adaptive behaviour, which
supplements the diet of the nestlings with Ca and
P and improves the efficiency of digestion (Klaver
1964, L6hrl 1978) is open to criticism . True, verysmall stones were found in the stomachs of thenestlings, but these stones seem to have been
picked up with the ants, as were, no doubt, also
the spruce needles found together with them inthe stomachs . Small fragments of egg-shells, gastropods _ and other lime-rich items may improve
the nestlings' diet to some extent, but it is questionable whether this is the ultimate reason for
the tendency .
Sutter (1941) showed that 10-12-days old nestlings have already gained about 2/3 of the total
weight of the adult, and that at about the same

7

1

2

3

4

No . of
other
items
5

E

327 343 337 340 3411 1687

-

3 422

-

147 10774

91

95 70 52 63 - 280
45 .11 31 .2 22 .0 26 .8 0.9 25 .0
29 .1 20 .4 15 .4 18 .5 - 16 .6
7

444
-

time the growth rate of many of their bones considerably decreases. Since objects are picked up
most frequently at the end of the nesting period(Table 3), it is not easy to understand how thistendency can have any great improvement to the
Ca and P contents of nestlings' diet . In general,
there seems to be no reason to assume that thediet of the nestlings is inadequate or that the ants
are not efficiently digested .
As regards the experiments with test objects,
some facts should be stressed . Like the otherstrange objects, these do not seem to be seen by
the parent birds solely as food items, since someof the objects brought to the nest were later
picked up and thrown out. As the parents carryor throw many of the droppings of the nestlings
outside the nest (e .g . Klaver 1964), it is very likelythat once inside the nest, the test objects wereregarded as droppings . Accordingly, the objects
can be differently treated, depending upon the
inner motivation of the parent bird . The behaviour released by the test objects is picking up
activity, but the subsequent behavioural pattern,i .e . what the Wryneck does with the objects,
seems to depend on the inner motivation of thebird . Thus, the tendency to bring strange items
to the nest should be regarded as the consequenceof a kind of error or mistake in the release of
the picking up pattern of the Wryneck parent .
At the end of the nestling period the motivationof the parent to search for food for the nestlings
is at its highest, as is indicated by the numbersof feeding visits made by the parents (e .g . Ruge
1971). Consequently, during this time strange objects may more easily elicit the picking up patternin parent birds.

Terhivuo (1977) reported that the feature common to the strange objects in the nests and the

56normal food items, i .e . ants and ant cocoons, istheir more or less shiny surface . In addition, themajority of the strange objects are whitish ortransparent in colour . This is also supported by
the few data received front the experiments withcoloured test objects . When food is abundant, thestimuli from it seem to be superior to those fromother objects, e .g . the pieces of tape . In general,
if the stimuli from the strange objects weresuperior or even equal to those from the ants andant cocoons, the nesting success and even the existence of the species would be endangered . In thisconnection, a letter from Mr . A . Suoranta deserves mention . He described how a Wryneck insearch of food for its young in Tammela pickedup ants very close to an ant heap lying within
30 cm of a group of test objects . No test objects
were accepted by the parents, even later in theseason, though 65 other "strange" items were
found inside their nest after the breeding period .
On the other hand, scarcity of food, although
merely momentary, together with the stimuli fromstrange objects may elicit picking up behaviour
in a Wryneck parent with a high motivation tofind food for the nestlings .
In some cases at least, the adoption of "unusual" items may result in utilization of novel foodsources . This is indicated by the great number offragments of terrestrial gastropods undoubtedly
broken up by parent birds, and by the large
amount of plant lice found in one of the deadnestlings . Probably learning also plays a role inthis adoption . The tendency may thus have some
adaptive value for the species, especially whenfood is scarce .
Table 3 shows that Wryneck parents searched
for food for the nestling, fairly close to the nest,
and the nature of the strange objects found inside
the nest indicates that the Wrynecks had visitedrather "unusual" places such as heaps of trash,dirtroads, shores etc . What made the Wrynecks
visit them'? One may hypothesize that althoughfood may be scarce in such places parent birds
can learn to visit them if there are items able
to release the picking up pattern, so that the bird
has something to bring to the nest . The physiognomical features of these sites may also deserve
consideration . For instance, heaps of trash andmanure are usually conical in shape and well demarcated from the surroundings, to the Wrynecks
they may well resemble a huge ant-heap .
There was great annual variation in the natureof the objects found inside the nests . Since thenesting habitat had an impact upon the natureof the objects, it may be that different types ofhabitats arc not evenly represented in the samplesof the nests taken in 1976-79 . Moreover, in
1978-79 the temperature conditions during thenestling period (latter half of June - first half

ORNIS FENNICA Vol . 60, 1983of July) were more favourable than in 1976-77(Ilmatieteen laitos 1976, 1977, 1978, 1979) . Since
there was no significant annual variation in themean numbers of objects in the nests, we cannot
conclude that they were afffected by the overall
weather conditions . However, the effect of thelocal weather conditions during the nesting periodon the tendency to pick up strange objects should
be studied in more detail .
The Wryneck picks up ants and ant cocoons
with its long, mucous tongue but does it takeother than food items that way, or does it pickup the latter with its bill, is not known . Someof the gastropod shells were broken up by the
Wryneck with its bill . Moreover, does the
Wryneck prefer ants and ant cocoons to strange
items because of their appearance and/or flavour?
Acknowledgements . In

1976-79 and 1981, 60 Finnish
ornithologists supported this study by collecting nests of
the Wryneck after the breeding season and carrying out
experiments with test objects . Without their co-operation, this study could not have been made . 1 am also
greatly indebted to Dr . Jaakko Syrjämäki and Dr . Olavi
Hilden, who read the manuscript and made many valuable comments on it .
Selostus : Miksi käenpiika tuo pesäänsä vieraita esineitä?
Kirjoittaja tutki eri puolilta Suomea vuosina 197079
tallennetut 121 käenpiian pcsää (kuva 1) . Näytteissä oli
mm . pieniä kiviä, lasin-, posliinin-, ikkunakitin-, sementin-, metallin-, muovin-, maalin- ja vahanpalasia,
kotiloiden, simpukoiden ja kananmunan kuoria sekä
luiden kappaleita, kalan luita ja suomuja ja kitiinipintaisia sclkärangattomia (mm . kaksoisjalkaisia ja siiroja) .
Pesissä oli keskimäärin 37 .4±4 .5 (SE) esinettä . Vain 9(7 .4 %") pesästä niitä ei ollut . Tapa tuoda vieraita
esineitä pesään ei siis ole poikkeus vaan sääntö
Suomessa pesivillä käenpiioilla .
Vieraiden esineiden lukumäärät eivät vuosittain vailidelleet tilastollisesti merkitsevästi (taulukko I), mutta
laatu kylläkin (taulukko 2) . Pesimäympäristölla ei ollut
vaikutusta esineiden määrään . Lentopoikasten ja vieraiden esineiden lukumäärien välillä ei ole merkitsevää
korrelaatiota . Kirjoittaja tutki 25 kuollutta poikasta 6
pesyeestä, joista ei tullut lentopoikasia, mutta yhdenkään poikasen kuolemaa eivät vieraat esineet olleet
aiheuttaneet . Lisäksi tutkittiin 39 poikasta 24 sellaisesta
poikueesta . joista tuli vähintään yksi lentopoikanen .
Näistä 7 poikasta oli kuollut koska niiden ruoansulatuskanavaan oli tarttunut teräväreunaisia, sulamattomia
esineitä .
Atrappikokeissa asetettiin eri etäisyyksille pesistä
muovinpalasia, joiden häviämistä seurattiin vuorokauden
mittaisissa
jaksoissa
pesimäkauden
erivaiheissa(taulukko 3) . Taulukossa 3 a-rivit osoittavat tarjottujen,
b-rivit poisvietyjen ja c-rivit pesästä löytyneiden atrappien lukumäärät . Atrappien määrät eri pesissä vaihtelivat suuresti, ja emot toivat pesiin myös muita
esineitä . Tuonti oli vilkkainta pesäpoikasajan lopussa .
Kirjallisuudessa esitetään, että tapa kantaa esineitä pesään on emolintujen ravinnonhakukäyttäytymiseen liittyvä sopeutuma (adaptaatio), jotta poikaset saisivat
enemmän kalsiumia ja fosforia, jota muurahaisravinnossa on vähän . Pienet kivet puolestaan saattaisivat
tehostaa mm . muurahaisten hienontumista ruoansulatuskanavassa . Tutkimus osoitti, että pesäpoikasten ja

J . Terhivuo : Strange items in Wryneck nests

kalkkipitoisten esineiden määrien välillä ei ole korrelaatiota . Koska lisäksi pesäpoikasten luiden kasvu
hidastuu ja painokin on jo 2/3 aikuisen painosta kun
poikanen on vasta 10-13 vrk:n ikäinen, on vaikeaa ymmärtää, että tapa olisi poikasten kasvua edistävä adaptaatio, sillä esincitähän tuodaan pesään runsainunin vasta
pesäpoikasajan lopussa .
Ärsykkeet vieraista esineistä ovat heikompia (suboptimaalisia) kuin normaalista ravinnosta tulevat, muutoin
lajin jälkeläistuotto kärsisi tuntuvasti . Ennenkuin esine
viedään pesään, tarvitaan ärsyke, joka saa emon poimimaan esineen nokkaansa. Sisäisen viretilansa mukaisestiemo, ollessaan etsimässä poikasillc ravintoa, vie esineenedelleen pesään . Mutta emo voi poimia esineitä myös
pesästä, esim . poikasen valkean, kiiltäväpintaiscn ulostepallon . Viretilan ollessa nyt toinen, se vie tai heittää
ulosteen pois pesästä - näin eräät emot menettelivät
myös atrappien kanssa . Viretilasta riippuen emot siis
menettelevät esineiden kanssa eri tavoin, mutta
yhteisenä piirteenä on, että näitä toimintoja edeltää ärsyke, joka saa emon poimimaan esineen nokkaansa. On
ymmärrettävää, että pesäpoikasajan lopulla emojen viretila (poikasten ruokkiminen) on voimakkaimmillaan ja
siksi luuri silloin tuodaan vieraita esineitä pesään runsaimmin. Ehkä ravinnon hetkcllinen niukkuus "epätavallisilla paikoilla" (tunkiot, kanatarhat vm .), joissa emot
ovat vierailleet. on ollut suboptimaalisten ärsykkeiden
vaikutusta lisäävä tekijä .
Tapa tuoda esineitä pesään on siis seuraus eikä syy
emojen ravinnonhakukäyttäytymistii ajatellen . Koska
käcnpiiat olivat käyttäneet poikastensa ravinnoksi nun .
kotilojen pehmeitä kudoksia ja kun erään poikasenmahasta löytyi runsaasti kirvoja, on selvää, että emot
ovat ajoittain hyödyntäneet uusia ravintokohteita . Virhetoiminnan laukeamincn saattaa johtaa, ehkä oppimisen kautta, uusien ravintokohteiden hyödyntämiseen .
Tällöin ilmiöllä saattaisi olla lajille adaptiivistakin merkitystä .
Aineisto ei paljon kerro oppimisen merkityksestä emojen ravinnonliakukäyttäytymisessii . Eräät parit kuitenkin
toivat atrappeja pesään runsaasti . toiset taasen eivät
niihin reagoineet, mutta toivat muita esineitä pesään
sitäkin enemmän . Ehkä emot oppivat jo ennen pesinnän

57
alkua hakemaan ravintoa paikoista, joissa käyvät myös
pesäpoikasten aikana .

References

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Received March 1981