Breeding system of Temminck's Stint Calidris

temminckii

OLAVI HILDENHILDEN, O. [Zool. Dept . Univ . of Helsinki, SF-00100 Helsinki 10, Finland]1975 . - Breeding system of Temminck's Stint Calidris temminckii . Ornis
Fenn . 52 :117-146 .
An isolated, colour-ringed population was studied for 10 years on thewest coast of Finland . The breeding strategy is a double-clutch system associated with successive bigamy . Every female pairs in rapid succession withtwo males on different territories and lays one clutch on each. Every malealso pairs successively on the same territory with two females and fertilizes
one clutch of each . The first clutch is incubated by the male, the secondby the female, and both take sole responsibility for their brood. Exceptions
to the normal schedule occur fairly often, chiefly due to the polygynous
tendency in males . They court every female that enters their territory, so
two females occasionally lay their first clutches on the same territory.
Replacement nests are very rare . Roughly one-third of the females shift
their breeding grounds from year to year and also lay their two clutches indifferent areas during a single breeding season .
Besides in Temminck's Stint, variations of the rapid multi-clutch systemhave been revealed so far in seven other wader species (Calidris alba, Cba-

radrius montanus, Tringa macularia, Phalaropus lobatus, Eudromias morinellus, Rostratula benghalensis, Jacana americana), in some of them as aregular strategy, in others occasionally . Evolution of the multi-clutch systemfrom the ancestral monogamous system with its persistent pair bonds andshared parental responsibilities could have proceeded along two main lines :either the female lays one clutch attended by a male and a second which
she incubates herself (as in Temminck's Stint), or she lays clutches that are
incubated by more than one male (polyandry) . The selective advantage ofmultiple clutches is the potentially increased number of offspring, but thisis counteracted by the loosening of pair bonds, increased losses of eggs andyoung because only one bird can carry out parental duties, and increased
demands on the female by laying more than one clutch. The availability offood during the laying period is thought to be the decisive factor : only
those species or populations living in very productive habitats with abundantfood supplies have been able to evolve the rapid multi-clutch system . Highpredation rates have intensified selection for production of multiple clutches .
On the other hand, the strong pair bond may have prevented the evolutionof multi-clutch system in species having potentially good qualifications forthis breeding strategy .
There is no general adaptation towards reduced clutch size in species exhibiting rapid multi-clutch systems, nor do they show any clear trend towards
prolonged laying intervals between clutches, or delayed sexual maturity . In
four species the eggs are slightly, and in two greatly reduced in size, whereas
in two species there is no reduction. A characteristic adaptation in Temminck's Stint is the delay of the male's incubation for several days, during
which he continues to display and is able to fertilize a second clutch.

ÖRNIS FENNICA Vol. 52, 1975

Introduction
Recently the biology of several wader
species have received intensive study .
Some 10-15 years ago, information
about wader breeding biology and behaviour was derived chiefly fromscattered observations made during
faunistic surveys, but now comprehensive population studies have been
published on many species. For the
sandpipers (genus Calidris), these include the Pectoral Sandpiper Calidris
melanotos (PITELKA 1959, HOLMES 1966,
NORTON 1972), Curlew Sandpiper C.
ferruginea (PORTENKO 1959, HOLMES &PITELKA 1964), Baird's Sandpiper C.
bairdii (DRURY 1961, NORTON 1972),
White-rumped Sandpiper C. fuscicollis(DRURY 1961, PARMELEE, GREINER &GRAUL 1968), Western Sandpiper C.
mauri (BROWN 1962, HOLMES 1971a,
1972, 1973), Red-backed Sandpiper or
Dunlin C. alpina (HELDT 1966, HOLMES
1966, 1970, 1971b, SOIKKELI 1967,
1970a, 1970b, NORTON 1972), Purple
Sandpiper C. maritima (BENGTSON1970), Sanderling C. alba (PARMELEE
1970, PARMELEE & PAYNE 1973), Semipalmated Sandpiper C. pusilla (NORTON
1972), Stilt Sandpiper C. himantopus(JEHL 1973), and Knot C. canutus(NETTLESHIP 1974).
Special attention has been paid inrecent years to the mating systems andtheir evolution in waders, i.e. the pairrelationship and participation of matesin parental duties (HOGAN-WARBURG
1966, LACK 1968, HAYS 1972, JENNI &COLLIER 1972, ORING & KNUDSON 1972,
GRAUL 1973, JENNI 1974, PITELKA,
HOLMES & MACLEAN 1974) . A wide
variety of different patterns or strategies
has been found, some species being monogamous, ohers polyandrous, polygynous or promiscuous . A special breeding system is shown by some waders inwhich females lay more than one clutch

in rapid succession. So far, the existenceof such a system has been demonstrated
convincingly in Temminck's Stint Calidris temminckii (HILDEN 1965, KoCHANOW 1973), Sanderling (PARMELEE &PAYNE 1973), Spotted Sandpiper Tringa
macularia (HAYS 1972, ORING & KNUDSON 1972), Mountain Plover Charadrius
montanus (GRAUL 1973), Painted Snipe
Rostratula benghalensis (LOWE 1963, ALI& RIPLEY 1969, JACKSON 19'70), andAmerican Jacana Jacana spinosa (JENNI& COLLIER 1972, JENNI 1974) ; to someextent it is known to occur also in the
Red-necked Phalarope Phalaropus lobatus (HILDEN & VUOLANTO 1972, RANER
1972) and Dotterel Eudromias morinelluS (PULLIAINEN
1971, NETHERSOLETHOMPSON 1973). However, there areconsiderable differences between these
species as to the mating system and theparticipation of both sexes in parental
duties . This diversity raises a number offascinating problems : how have all thesesystems evolved, what is the survival
value of the different adaptations, andwhy has evolution diverged in so many
directions even in closely related species?
In 1963, I started a population studyof Temminck's Stints on the west coastof Finland at the southern border of thespecies' range. The study continued forten breeding seasons, up to and including 1972. Until now, only two preliminary reports (HILDEN 1965, 1972) andan analysis of the variation in egg dimensions (VÄISÄNEN et al. 1972) havebeen published . This paper presents mydata on the breeding system of the species. Information on breeding biology,
behaviour, dispersion pattern, site tenacity and population dynamics has been
given only when appropriate ; these
topics will be reported in detail later.
The distribution of Temminck's Stint
extends throughout the tundra zone ofEurasia, from Scandinavia in the west
to Bering's Sound in the east. In Fenno-

Olavi Hilden : Breeding system of Temminck's Stint Calidris temminckii

119

The eight study areas (A-H) on Harrbåda (the western cape) and Rumme1ö (the easterncape) . Solid lines = woods, broken lines = meadows, dotted areas = sand with sparse vegetation . Shore areas within the dotted line are mudflats exposed during low water . The breeding
range of Temminck's Stint in NW Europe according to HAFTORN (1971) and the geographical location of the study area are shown on the inset.
FIG . 1 .

12'0

ORNIS FENNICA Vol. 52, 1975

TABLE 1.

Numbers of Temminck's Stint nests found during egg-laying or after clutch completion at
Kokkola in 1963-72.

Year

1 egg

Found incompleted
2 eggs3 eggs

Total

Found completed

Total

1963
1964
1965
1966
1967
1968
1969
1970
1971
1972

1
9
8
15
12
8
1
2
8
3

3
2
1
4
2
3
0
2
0
0

3
1
1
2
5
1
2
0
0
0

7
12
10
21
19
12
3
4
8
3

17
13
13
10
13
16
16
10
6
9

24
25
23
31
32
28
19
14
14
12

Total

67
30 .2

17
7.7

15
6.8

99
44.6

123
55 .4

222
100

scandia, the species breeds on the coast
The Harrbåda cape is of sand, covered with aof the Gulf of Bothnia, almost isolated sparse vegetation of grasses, herbs and moss ;the dominant plants include Elymus arenarius,
from the main breeding areas farther Deschampsia
flexuosa, Chrysanthemum vulgare,north and east (Fig. 1). Although Tem- Honkenya peploides and Silene inflata . In manyminck's Stint is one of the commonest places the sand is bare, and there are several
and most widely distributed Eurasian pits in the ridge, particularly favoured as nestingsites by Temminck's Stints . More luxuriant
sandpipers, with a total population esti- meadowsare found on the eastern sidethemated at more than 10 million indi- cape . Except for scattered willow bushesof andviduals (USPENSKI 1969), its biology some small planted alders and rowans, trees are
was poorly known at the time I started absent . The shores are lined by a thick growth
Phalaris arundinacea, with belts or patches
my study. In addition to the general ofof Scirpus tabernaemontanii, Eleocharis unigluinformation in handbooks and faunistic mis and Phragmites communis extending into
surveys, only two reports dealing spe- the water in places . The whole shore vegetationcifically with the breeding biology of has expanded and grown more luxuriant inyears due to pollution of the waters .
the species were available (HAVILAND recent
When the water-level is low, the cape is sur1916, SOUTHERN & LEWIS 1938). Quite
rounded by extensive mudflats .
recently a Russian study on the ecology
There are some summer cottages with surof Temminck's Stint on the Murman rounding outhouses, fences, poles etc. on the. These are of great significance for TemCoast was published (KOCHANOW 1973). capeminck's Stints, first because males use all kinds
Study area and methods
1 . Study area. The field studies were carriedout at Kokkola (63°52'N, 23°05'E) . The study
area consists of the narrow cape of Harrbåda,about 600 m long and 50 to 200 m wide, and theadjacent meadows of Rummelö on the opposite
side of a shallow bay (Fig . 1) . To facilitate description of the field work, Harrbåda was divided into six and Rummelö into two part areasusing conspicuous land marks (buildings, bushesetc.) . These areas are shown in Fig. 1.

of elevated sites when giving their territorial
songs and second because the even, sparsely vegetated house yards conform well to the species'
habitat requirements . Similarly, large boulders
lying scattered on the cape are important as song
posts of males .
The Rummelö area is flat meadow with several
shallow ponds and scattered boulders . Temminck's Stints are attracted only to those partsof the meadow where the vegetation is very low
or replaced by bare sand ; here also the yards ofsummer cottages are particularly favoured .
In addition to Temminck's Stints, several otherwader species inhabit the study area : the Ringed

Olavi Hilden: Breeding system of Temminck's Stint Calidris temminckii
Plover Charadrius hiaticula, Little Ringed Plover
Ch. dubius and Oystercatcher Haematopus ostralegus favour the sandy parts, the Ruff Philomachus pugnax, Redshank Tringa totanus, Dunlin Calidris alpina schinzii and Lapwing Vanellus
vanellus occur in the meadow areas . Altogether,
13 wader species have been observed breeding in
the area (CASEN 1960).
Kokkola is the southernmost permanent breeding locality of Temminck's Stint in Finland.
During my ten years of study, the population
increased slowly at first from about 27 adults
present in 1963 to 33-36 in 1966-69 but thendeclined rather abruptly to only 15 birds in1972 . In addition, 1-2 pairs have nested almost
annually in the nearby control area of Morsiussaari, located 2.5 km east of Harrbåda . The population at Kokkola is very isolated, the nearest
breeding grounds being some 50 km to the north,in the delta of River Kalajoki . This latter area,
inhabited by some 15-20 pairs, has been checked carefully only in 1971-72 to search for birds
ringed at Kokkola. North of Kalajoki, Temminck's Stints are found breeding in many places
along the coast.
2. Methods . Field work commenced each year
in late May, soon after arrival of the firstTemminck's Stints . Work was continued untillate July when all young were fledged. In 1963
-65, I carried out most of the field work myself
but in later years I usually stayed at Kokkola
only during the early phase of the breeding
season (to 6-12 June) and thereafter left thechecking of nests and ringing of young to one or
two assistants . In 1969 and 1970, all field work
was conducted by my assistant Mr. Harri
Hongell.
Temminck's Stint is in many respects a good
species for a population study. First, it lives inopen terrain, which makes the observation andrecording of colour ringed birds relatively easy .
Second, it occurs at high densities in suitable
habitats . Third, Temminck's Stints are rather
tame. Usually one can watch birds without
disturbing them from 15-20 m, and some fearless parents may tend their young almost at theobserver's feet . Fourth, the species very rarely
deserts its nest due to human interference, evenwhen the female is captured during laying .
TABLE 2.

121

Most nests are found in the same areas year
after year . These areas were searched before theonset of egg-laying to find nest scrapes of males,
which were then checked daily. This allowed
observations to start right after laying of the first
egg. Table 1 shows that almost half the nests
were found during egg-laying and nearly one
third at the 1-egg stage.
Adult birds were marked with both coloured
and numbered rings. They were captured at thenest by a simple automatic trap . In total, 85
adult birds (31 males, 51 females, 3 of unknownsex) were colour-ringed in the course of thestudy. This represents about 80 % of the total
population of the area during the study. The
birds were numbered according to the trappingorder, and these numbers are used as individual
symbols in this paper (M = male, F = female) .
Of the few birds without colour-rings that were
present annually in the population (mostly nonbreeding individuals or birds which had losttheir nests), about half had been marked as nestlings with aluminium rings only . In most cases,
numbers on the rings could be read by a 40 X
telescope. A total of 323 young were ringed in
the course of this study.
As will be shown later, most females lay two
clutches in the area and leave the first to be
incubated by the male . To solve which females
laid the clutches subsequently incubated bymales, it was necessary to capture birds whenlaying eggs . This required checking the trap at
frequent intervals. Attempts to capture egg-laying
females were made at 56 nests, 46 (82 %) of
which were successful ; 29 birds laid an egg whilestill in the trap and 15 later, usually soon after
being released, and only 2 females deserted theirnests following trapping . Ten attempts to trap
egg-laying females failed mainly because the trap
had been released either by wind or the malebefore the female had come to the nest . Sometimes it was possible to identify the female
which had laid a certain clutch by the specificform, colour and/or measurements of the eggs .
3. Separation of the sexes. The sexes ofTemminck's Stint are very much alike and noteasy to distinguish in the field. On average, thefemale is slightly larger and has more brownish
pattern on her back than the male . Usually theseWeights and wing and bill lengths of Temminck's Stints at Kokkola in 1963-72. If thesame individual was weighed more than once, a mean weight has been used .

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ORNIS FENNICA Vol. 52, 1975

FIG. 2.

Frequency distribution of weights of male (horizontal hatching) and female (vertical hatching) Temminck's Stints at Kokkola. Repeat weighings of the same individuals are included as separate
observations .
small differences in appearance are observable
when the birds are seen together but do notenable certain sexing of solitary birds. In manycases, however, it is possible to tell the sexes
apart by differences in behaviour (voice, postures, movements, etc.) . Gravid females about tolay eggs are easy to recognize by their thick,hanging cloacal region .
In the hand, most Temminck's Stint can besexed by weight : birds weighing less than 26 g
are usually males, those weighing more than 26
g are females (Table 2) . The values given in thetable are means for each bird (18 were weighed
2 to 5 times) . The weight of an individual bird
can vary considerably : M 6, for instance, weighed
24 .5 g on 6 June 1963, 27 .5 g on 26 June 1963
and 22 .0 g on 4 June 1965 thus showing both
extreme values for males! Fig. 2 presents allweights of Temminck's Stints taken at Kokkola
showing the slight overlap of the sexes around26 g. Females trapped at the nest during egglaying are not included ; they weigh up to 38 g.
In wing and bill length there are no significant
differences between the sexes (Table 2) .

Breeding system
1. Summary of the breeding schedule.
The breeding system of Temminck's
Stint is peculiar in many respects . Eachfemale normally lays two clutches, thefirst one subsequently incubated by themale, the second one by herself. She firstpairs with one male and lays a clutch
on his territory . As soon as this is completed, she leaves her mate, seeks a newmale intent on pairing and, 2-4 days
later, lays a second clutch on this new
territory . Usually these nests are situatedmore than 100 m apart. The femalecommences steady incubation immediately after completion of the second
clutch, whereas the male delays the onset
of incubation for several days. DuringOlavi Hilden : Breeding system of Temminck's Stint Calidris temminckii

this period he still courts females appearing on his territory and often mates witha new bird . Usually this is a female
which has already been paired with one
male and is seeking a new mate for her
second clutch . Consequently, most males
have two clutches laid on their territories by different females. Each maleand female takes sole responsibility for
its nest and brood.
Fig. 3 illustrates a simplified case inwhich the population comprises only
two males and two females. In this case,both males pair in turn with both females and thereby exchange their mates.
The situation is much more complicatedin larger populations (see p. 126) .
2. Pair bonds. The pair bonds in
Temminck's Stint are complex comparedto those in most other waders . During
the first few years of my study I was
unable to get a clear picture of the mating system. Most cases suggested successive bigamy connected with the double
brood system described above. In bothmatings the pair bond lasts only about
one week, i .e. as long as is needed forthe formation and laying of one clutchof eggs . It is also rather loose: the male123

and the female are seen more often separately than together. Observations on
colour-ringed birds indicated, however,
persistent pair bonds during this shortperiod, since most pairs seen on successive days when feeding, courting or copulating were formed by the same individuals. Some case histories:
M 26 and F 3711966: On 26 May the pair
was feeding sometimes together, sometimes separately, and copulated on the territory of the male .
On 30 May a copulation ; on 31 May a failed
copulation, later both birds visited in turn thesame nest scrape where the first egg was found .
On 1 and 2 June they were feeding together .
Later the male started to incubate the completed
clutch.
M 51 and F 4711967: On 25 May the pair wasseen together steadily, and a failed copulation
was recorded . On 28 May they copulated, on 30
May the female was trapped on the nest whenlaying her third egg. Later the male incubatedthis clutch .
M 52 and F 4811967: On 26 May three copulation attempts, on 29 May a successful copulation was observed . On 1 June the female wascaptured on the nest when laying her third egg .
Later the male started to incubate this clutch.

Besides these observations on definite
pairs, I also recorded cases indicating
simultaneous polygyny, polyandry or

FIG. 3 . Schematic representation of the breeding system of Temminck's Stint in a population comprising only two males and two females . 1-3- : each female enters the territory (circle) of one male,pairs with him, lays a clutch and then leaves the territory ; 4-5 : each female seeks a new male, pairs
with him and lays a second clutch ; 6: the males start to incubate the first and the females the second
clutches .

12 4

promiscuous mating systems. . On several
occasions one male was seen courting
two females, either at the same time orat short intervals. The following examples may illustrate such cases :M 911965 : On 26 May within an hour, themale was seen courting F 11 and an unringed
bird, both just as exitedly . On 3 and 4 June he
was feeding together with F 11, later he incubated the clutch laid by this female .
M 3011965: On 4 June the male followed F 22
and made repeated copulation attempts, but thefemale rejected him. A little while later on thesame day he copulated with F 31, the clutch ofwhich he then started to incubate.
M 5111968: On 30 May the male at first fed
closely together with an unringed female, thenabout six hours later he copulated with F 12 .
On 31 May he copulated successively with F 68
and the unringed bird, in the evening he wasseen courting simultaneously F 12 and F 68,
which fought together like two males.

In addition, I recorded some occasions
on which one female was courted by
two males, either simultaneously or on
successive days. Three examples :F 2511964: On 13 June when the female waslaying her second egg, M 15 was trilling exitedly
all the time close to the nest, sometimes "hanging" in the air above it, sometimes runningaround it . Also M 24 tried repeatedly to cometo the nest but was chased away by M 15 (several fights); in the evening M 24 was captured ina trap placed on the nest . Later the clutch was
incubated by F 25 (her third clutch, cf . p. 128) .
F 2211965 : On 4 June M 30 tried to copulate
repeatedly with this female but she rejected him;
after half an hour she copulated on the same
spot with M 1 . This male started to incubate thefirst clutch of F 22 .
F 2311965: On 10 June the female was seen
together with M 26 who courted her lively andmade copulation attempts but was rejected ; attimes small conflicts occurred between the birds.
On 11 June she was courted eagerly by M 6
on the adjacent territory; in the evening, as wellas on 13 June, both birds were seen close together . The female laid her second clutch on thisterritory (first egg on 13 June) and incubatedit herself.

As puzzling as the mating system of
Temminck's Stint may appear on thebasis of individual observations, myoverall notes reveal a fairly clear pattern

ORNIS FENNICA Vol. 52, 1975

to the pair-relationship. Each male occupies a territory and announces his presence through display, which serves torepel other males and attract females.
Once a female appears on the territory,
the male courts her, performs nest-scraping and tries to copulate. Since the females are sedentary, each one staying
most of the time before and during egglaying along the same small length ofshore, the male normally pairs with only
one female at a time . This result is also
promoted by the intolerance of females
towards each other (see the aggressive
combats between F 12 and F 68, mentioned above), which tends to spacethem over the whole area .
However, if another female, e.g. abird late to arrive, enters the territory,
the male courts even her in the sameway, and on several occasions one malehas been seen copulating or trying tocopulate with 2-3 females on the same
day or on successive days . Similarly, a
female keeping near the boundary between two territories attracts both males,
which compete with each other for theopportunity to mate with her. Accordingly, the males are potentially polygynous, even though in practice mostmales pair with only one female at atime. Owing to this polygynous tendency in males, every female appearing
on the territory attracts them, regardlessof her attitude ; also totally passive oreven aggressively defending females arecourted exitedly .
A good example is provided by the behaviourof an one-year-old male, which appeared in thearea on 11 June 1965 and remained unpaired .
At this advanced date two females, F 11 andF 12, were already incubating their clutches inthe very area that was occupied as a territory by
this late arriving male . As soon as either ofthese females left her nest to feed, she wasfollowed by the courting male who performed
display flight above her, circled exitedly trillingaround her and tried to invite her to a nest
scrape . By that date the females had lost theirsexual potency and showed no interest in the
courtship of the male .

Olavi Hilden: Breeding system of Temminck's Stint Calidris temminckii
The inclination of females to simultaneous polyandry, if it exists at all, isclearly weaker than that of the males .
Some instances of one female with two
courting males have been recorded, it istrue, but the formation of these trios is
attributable to simultaneous mating attempts by two neighbouring males, andnot to any active seeking for two malesby the female . On the contrary, in allcases I recorded, the female has rejected
the copulation attempts of one male .
There is also no evidence that a female
copulated with two males during thelaying of one set of eggs . Not until thefemale has completed her first clutch
does she leave her mate and pair witha new one .
3 . Mate-faithfulness . Theoretically,a female laying two clutches during one
breeding season, either may form a persistent pair bond with one male, or may
pair successively with two different
males . In the former case both clutches
would be located close to each other,
within the territory of the same male ;in the latter case they would lie farther
apart .
As stated before, the latter alternative
represents the normal case in Temminck's Stint . Each year I have recorded in the field cases in which an individually-known female at first associated with one male and then, after completing the first clutch, formed pairbonds with another . That this is the normal system is also documented by thelocations of the first and second nestsof the same females, which usually lie
far apart . The tabulation below shows
the distances between the successive
clutches in all 40 cases recorded (range
4 to 950 m, average 247 m) :Only in 13 cases were the first andsecond nest less than 100 m apart, buteven then the female was known to havepaired with two different males in atleast 6 cases . On the remaining 7 oc-

Distances (m)

N

%

0- 50
51-100101-200
201-300
301-500
501-700
701-900
901 G

7
6
11
7
2
3
2
2

17 .5
15 .0
27 .5
17 .5
5.0
7.5
5.0
5.0

casions mate-faithfulness during bothclutches could not be proven definitely .
The most probable instance refers to F
37 in 1966, which laid her both clutches
only 4 m apart on the territory of M 26 .
However, the first egg of the second
clutch was laid in the morning of 11
June, by which date M 26 was alreadyincubating the first clutch steadily . So
it is possible that the second set of eggsof F 37 was fertilized by one of theneighbouring males, which in this partof the area were concentrated close toeach other . To conclude, if mate-faithfulness during the same breeding season
does occur in Temminck's Stint, it isexceptional .
The first pair bond is broken immediately after completion of the firstclutch . Already on the same or thefollowing day I have recorded females
associating with a new male far fromthe first nest site . Two examples :F 2311965: The fourth egg of the first clutch,
situated in area H, was laid on 9 June at 09 .30
hrs. On 10 June at the same time the female wasfound in area C, about 800 m from her first
nest site, engaged in courtship display with theterritory holding M 26 . Next morning she wasseen in courtship activities with M 6 about 70 mfrom the above place; the second clutch waslaid on the territory of this male.
F 7911971 : The first clutch was situated inarea H and completed on 6 June at about 11 .00
hrs. At 17 .30 hrs the same day the female wasfound in area A, almost 1 km from the first nest
site, together with M 73 that was courting herexitedly . Later the second clutch was found on
the territory of this male .

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ORNIs FENNICA Vol . 52, 1975

All the facts described above show mate of a certain individual the sameconvincingly that PARMELEE & PAYNE in two consecutive seasons . However.
(1973) have totally misunderstood the since only 15 of the previous matesmating system of Temminck's Stint had returned, these figures mean thatwhen they discuss my earlier paper of birds still alive about every third(HILDEN 1965). According to them, "the rejoined its mate of the previous year.
male consorts with the female for several Although mate-faithfulness is muchdays after the first clutch is laid, appa- weaker than in the Dunlin and Western
rently competing with other males for Sandpiper, the frequency of remating
the opportunity to mate with her and nevertheless is significantly higher thanto fertilise a second set of eggs" . Suchwould be expected if matings were
instances have never been observed, nor random (see Appendix) . This tendency
did I suggest this in my paper. The to remating is without doubt attributableauthors also state incorrectly that "rare- to the strong site tenacity of the species :ly are both male and female Temminck's the males almost invariably occupy the
Stints taken with a single brood" . With- same territories year after year, and also
out a single exeption there was always half the females return to the same part
only one incubating bird on each nest, of the area (HILDEN, unpubl .) . For thiseither a male or a female.
reason, the chances for a certain indiviI also doubt the validity of KOCHA- dual to rejoin its former mate, if still
Now's (1973) conclusion, that on the alive, are considerable . For second pairMurman Coast male and female Tem- ing, my few observations indicate thatminck's Stint maintain their pair bonds mate-faithfulness is probably of thethroughout the breeding season and that same order as that during the firstboth clutches are laid within the same pairing.
territory . According to him, this is in4. Other breeding schedules . Excepdicated by the location of nests in pairs tions to the normal mating system of
5-45 m apart, with 30-200 m between Temminck's Stint occur fairly often .
adjacent pairs of nest. But these facts Such special cases include the following .
alone do not allow such a conclusion ;Males with two females, both laythe same distribution of nests also fol- ing their first clutch . As mentioned
lows if each male pairs successively with earlier (p. 124), on several occasions one
two females on his territory . As the per- male has been seen courting two females,
sistence of pair bonds was not showneither at the same time or at short interdirectly by means of ringed bird's, pos- vals. If both females are going to lay
sible geographical differences in the their first clutch, the male will have twomating behaviour remain unproven .
clutches to take care of. Six such inThose calidridine species which have stances have been revealed in the course
strong monogamous pair bonds, like the of the study, concerning four different
Dunlin (SOIKKELI 1967, 1970a) and the males.
Western Sandpiper (HOLMES 1971a),
M 911964: The nests, both with 4 eggs, were
have been found to show a high degree
25 m apart. The first nest was found onof mate-faithfulness from one year to situated
14, the second one on 15 June, and M 9 was
the next . In Temminck's Stint, with incubating on both when found! On later conshort and loose pair bonds formed each trols, he was always incubating on the first nest
year with two successive mates, one and thus had deserted the other one. The young
on 6 July .
would hardly expect high mate fidelity. hatched
M 6 : This male, a real "Don Juan", attracted
In 5 cases out of 25 was the first in three successive years two females to lay their

01avi Hilden: Breeding system of Temminck's Stint Calidris temminckii

127

first clutch on his territory. In 1965, one clutch
was laid between 31 May and 3 June . The malewas seen to visit this nest on 4 and 8 June, yet
he did not commence a steady incubation andsoon abandoned the nest . Instead he was foundon 14 June incubating another nest, situated 39
m from the first one, and continued the incubation until the nest was destroyed on 21 June .
In 1966, the first nest (with F 36) was completed on 27 May, and the second one (with anunringed female), 44 m apart, was laid on 3-7
June . The male was not recorded one single timeon the first nest, but on 9 June he started toincubate the second one. The young hatched on
29 June .
In 1967, the first nest (with F 43) was completed on 1 June, the second one was found ascompleted on 12 June from 20 m away . Eggs in
the first nest were cold at each check on 2-6June, but on 7 June M 6 was flushed twice fromthe nest ; the following day the nest was destroyed. On the second nest, M 6 was alreadyincubating when found; the young hatched on
3--4 July.
M 4111967: Both clutches (with F 49 andF 50) were laid between 31 May and 3 June andwere situated about 120 m apart. On 7 June themale started to incubate one of the clutches ; thefollowing day this nest was destroyed but thebird continued incubation on the other nest .
The young hatched on 29 June .
M 5111968: The male courted simultaneously
F 12 and F 68 (see p. 124) . The latter female laid
her clutch between 31 May and 4 June, but thenest of F 12 was not found until completed on
8 June . The distance between both nests was 33
m. On 9 June the male started to incubate theclutch laid by F 68 and left the other one unattented .

recorded fairly often (cf. p.124). Second,
if a male is found incubating one nest,
any unattended additional nest on his
territory is very likely to be overlooked
if not found during egg-laying. Third,in addition to the six definite double
nests mentioned above, I found four
completed clutches that remained unincubated, probably because they were"excess nests" of males.

These observations show that the male
may at first try to incubate both clutches but soon desert one . In two cases,
after the nest on which incubation hadcommenced was destroyed, the bird
shifted to incubate the other one. Onlyin these cases was it advantageous for amale to have two first clutches on his
territory, the other one as a "reservenest" ; otherwise, one of the clutches isalways doomed to go to waste .
Three facts suggest that laying of two
first clutches on the territory of one
male occurs more frequently than the six
cases recorded. First, males simultaneously courting two females have been

A male with no nest paired witha female going to lay her second clutch .

Two females laying in the samenest cup. In 1968, two females (F 54 andF 57) paired simultaneously with thesame male (M 30) and laid by turns inthe same nest cup. The nest was completed on 6 June and consisted of 7 eggs.
This was the first clutch of F 57 and thesecond one of F 54, which consequently
started to incubate the shared nest. The
incubating bird probably prevented F 57
from laying her last egg in the nest, forwhich reason she laid it in a new nestcup 38 m away. This last egg of the firstclutch was also the first one of thesecond clutch : after an interval of threedays, F 57 laid again in the same nest
but laid only two additional eggs.
BOTTOMLEY &BOTTOMLEY (1973)
have reported a similar case from Swedish Lapland : a Temminck's Stint nest
containing 7 eggs, clearly laid by two females and incubated by one bird.
At times there must be situations inwhich a male either has no clutch to incubate or has lost it before he pairs witha female about to lay her second clutch .
The question is, which bird subsequently
incubates the nest.
Unfortunately, my data are few because the male which has fertilized thesecond clutch often remains unknown .
Of the few identified males only three
have been known for certain to be without a first clutch at the date of thesecond pairing. In all these cases, thefemale started to incubate and the male128

was not once seen to share in incubation .
The most probable explanation is thatthe immediate start of incubation by thefemale at her second nest prevents thedevelopment of an incubation drive inthe male . As mentioned before, the malenormally delays the onset of incubation
for some days, during which he continues to display. Evidently the gradualchange from display to incubation behaviour is released by the uncovered
clutch . If the female is sitting on theeggs most of the time, the male's incubation drive will be inhibited.
A female laying three successive
clutches. Two instances have been re-corded in which the same female laid
three clutches in rapid succession . The
first two she left to males and incubated
the third one herself.
F 2511964 : The female completed her firstclutch the night between 3 and 4 June . The firstegg of her second clutch was laid on 6 June at
10 .30 hrs and the fourth one in the evening of
9 June . Laying of the third clutch began on 12
June at 20 .00 hrs, and the female commenced
steady incubation immediately after clutch completion on 16 June . The second clutch remained
unattended because the male (an unringed bird)
disappeared soon after pairing.
F 1211968: The first and second clutch were
found as completed on 30 May and 8 June, respectively . Although the female was not trappedon the nest when laying, both clutches belonged
certainly to F 12 judging from (1) the typicalsize and form of the eggs, (2) the staying of thisfemale near both nest sites during egg-laying,and (3) her copulation with M 51, the ownerof the territory on which the second clutch waslaid . Also the third clutch was completed whenfound on 16 June, and it was incubated by thefemale . The second clutch was deserted because
M 51 started to incubate a nearby clutch laid byanother female (see p. 127) .

Some triple clutches may have been
overlooked, because confirmation requires either that the female is captured
during egg-laying at the first two nests,
or that the eggs are recognizable by theirpeculiar appearance. Anyway, triple
clutches must be rare, since in nearly

ORNIs FENNICA Vol . 52, 1975

40 cases it was proven that a certain
female laid only two successive clutches .
The reasons which may force a female
to lay three clutches in a season are notknown . F 12, for example, laid two
clutches in four consecutive seasons,from 1964 to 1967, but in 1968 she laid
three. The reason cannot be a special
behaviour of the second male, which
would reveal that he will take care of
the incubation and thus would give thefemale a chance to lay and additional
third clutch, because in both cases I recorded the second clutch remained unattended .
Replacement nests. Because in Temminck's Stint each sex incubates its
own clutch, males and females are indifferent places if a nest should fail . If amale loses his nest, his chance of gettinga replacement clutch is dependent upon
finding a new mate who has not yet laid
her first clutch . A female, on the other
hand, has only to find a male intent on
pairing to fertilize the new set of eggs .
Hence, it must be more difficult for amale than a female to obtain a replacement clutch . By mid-June most females
are incubating, and even if a male succeeds in attracting a new female into his
territory, in most cases she is about tolay her second clutch . In the course of
the study, 32 nests incubated by males
were destroyed by 25 June, and only oneof these males was found later incubating a substitute clutch . This was M 1 in
1964 : his nest was robbed on 7 June, inthe early stage of incubation, and thereplacement nest was found on 24 June
14 m away from the first one. Thus, all
the other males failed to get a new
clutch, although display normally recommenced one or two days after thenest failure.
For a female which has lost her nest,'
finding a new mate is no problem if theseason is not advanced . Until late June,
there are always some males in the popu-

Olavi Hilden : Breeding system of Temminck's Stint Calidris temminckii

129

Numbers of completed first, second and third Temminck's Stint clutches foundat Kokkola in 1963-72 . X-clutches refer to nests of unknown position in the laying sequence.
TABLE 3 .

Year

First clutches

Second clutches

Third clutches

X-clutches

1963
1964
1965
1966
1967
1968
1969
1970
1971
1972

13
13
14
17
16
12
10
6
7
4

9
10
6
9
13
13
7
3
6
5

0
1
1
0
1
1
0
0
0
0

1
1
0
1
0
1
2
6
0
2

Total

112
53

81
38

4
2

13
7

%

lation who maintain their sexual activity (unpaired birds or males that havelost their nests) . Nevertheless, of 13 nests
incubated by females and destroyed by
25 June, only two were replaced :F 2311965: The second clutch was completed
on 16 June and incubated steadily by the female
until it was destroyed on 21 June. The bird wasfound incubating a new clutch on 30 June, at a
distance of 19'0 m from the second nest .
F 1211967: The female commenced incubationof the second clutch on 7 June, the day it wascompleted, but on the following day the nest
was flooded by high water and deserted . On 15
June she was found incubating a replacement
clutch 75 m away from the second nest .

In both these cases, the intervals between nest failure and the onset of laying a replacement clutch were at most
5 days. That other females failed to lay
a substitute clutch might indicate lowered hormonal activity after laying of
two clutches, i.e. they may be physiologically incapable of producing an additional third clutch .
S.

Do all females lay two clutches?

The total numbers of first and second
clutches found are presented in Table 3 .
In addition to nests whose sequence was
known from the females, all nests inctibated by males were classified as firstclutches, and those inc ubated by females

as second clutches. Eight nests which
remained unattended were also included
as first clutches, because females always
commence steady incubation of second
clutches immediately after completion.
The few nests in the category of "Xclutches" refer to cases in which (1) thenest was destroyed before the incubating
bird was identified (8 cases), (2) thecolour-rings of the incubating bird could
not be determined (3 cases), or (3) thesex of the incubating bird remained obscure (2 cases).
If all females laid two clutches, one
would expect about equal ratios of firstand second clutches among the nests
found . However, clearly more first thansecond clutches have been found (112against 81) ; the difference is significant(x2 = 4 .98, P < 0.05) . This cannot be
due to any methodological error, e.g.
that first clutches would be easier tofind. Although first clutches are there
to be found for a few days longer thansecond clutches (because of the delay inthe start of their incubation), most nests
are found either during egg-laying, by
daily checks of the nest scrapes, or during incubation when the bird flies off
the nest. On the other hand, first clutches are more often destroyed than second

ORNIs FENNICA Vol. 52, 19%5

13 0
TABLE 4.

Numbers of "vagrant" and "faithful" female Temminck's Stints (see text) caught whenlaying their first clutch, and the percentages of those birds found incubating a second clutch in thesame season.

"Vagrant" females"Faithful" females

Controlled when laying
the first clutch

Found in the same season
incubating a second clutch

13
40

4=31%
34 = 85 %ones (hatching successes of 52 % and 61 classified as vagrant, included some po°/o, respectively), and nest failure may, tentially faithful birds, which did notof course, happen before the nest is return simply because they died duringfound. This higher destruction rate of the winter . Since the mean annual
first clutches, and the fact that some mortality of adult females is c. 29 0/0"excess nests" of males probably have (HILDEN, unpubl .), their number can bebeen overlooked (see p. 127), suggests estimated to be about nine . The samethat the difference between the numbers ratio of potentially faithful birds mostof first and second clutches laid should probably is included also in the 13 febe slightly greater than recorded . As the males in Table 4. In that case, all four
second nests include 9 clutches of new birds which laid a second clutch in thebirds, not present in the population at area actually belonged to faithful fethe date when first clutches were laid males. The conclusion is that vagrant fe(see p. 131), the actual proportion of fe- males, which shift their breeding
males laying only one clutch in the area grounds from year to year, lay only one
is, according to the number of "missing" clutch in the area, while faithful females
second nests, roughly one third.
usually lay two. (The missing 15 '°/o of
About one third of the females do not second clutches of the 40 faithful fereturn to the study area in the year after males in Table 4 may have been deringing but breed elsewhere (HILDEN, stroyed before found.)unpubl .). This raises the possibility of a
A further question is, do the vagrant
connection between these two groups . females really lay only one clutch, or do
To test this, I have separated all 51 fe- they shift during a single breeding season
males colour-ringed in the course of the to another area and incubate theirstudy into two categories : those which second clutch there? This problem
bewere not recovered in the area in the answered only indirectly . If, aftercanlayyear after ringing (27), and those which ing their first clutch, they did not lay abred in the area in at least two years second one, they probably either re(24) . Of the former 27 "vagrant" fe- mained in the area forsome time ormales, 13 were trapped at their first migrated south immediately. In fact notnest during egg-laying . Later in the one of the 9 birds involved
season, 4 of them were found when in- was seen after completion of (Table 4)
firstcubating their second clutches, while the clutch, even though I searchedthe
for allremaining 9 where not recovered. The females regularly. This suggests thatsituation in the second group, females vagrant females actually leave the area
showing faithfulness to their breeding as soon as they have completed theground, is very different (Table 4).
clutch in early June. Southward migratIt should be noted that the 27 females,
ing Temminck's Stints have not been re-Olavi Hilden: Breeding system of Temminck's Stint Calidris temminckii

corded in Finland until one month later(HILDEN 1961), so birds which disappeared must have moved to anotherarea . Such behaviour would scarcely
have been evolved without any biological value, so it must be assumed that they
lay their second clutch in the new area ;if they did not, they would produce
only half the number of offspring of the
double-nesting females. Any such genetic trait would soon be eliminated .
If the conclusions reached above arevalid, then the emigration of vagrantfemales in June should be balanced by acorresponding immigration of other females that have laid their first clutcheselsewhere. But it seems not to be so,since second clutches are clearly fewer
in numbers than first ones (Table 3) .
The most probable explanation is that,in the southernmost parts of the breeding range, the movements of vagrant females between two breeding areas are
directed mostly to the north, away from
Kokkola. Such migration cannot be
verified in the field, because it overlaps
with the normal spring passage, which
continues until about 10 June .
However, a few new females do arrive at Kokkola in June . This can be
deduced from the high number of second
clutches laid by the 27 females not recovered after the year of ringing. As
many as 18 were found incubating asecond clutch, 14 of them new, unringed
birds (4 were ringed when laying theirfirst clutch) . Since 9 females were supposed to be faithful, half the incubating females were vagrant. As these
lay their successive clutches in two different areas, they must have come to
Kokkola from elsewhere. As further
evidence, the eggs of some of these females had a size, form or colouring that
did not fit any known first clutch in thearea . Because nearly all second clutches
were found and the incubating females
captured, the 9 vagrant females detailed

13 1

above must be very close to the actual
number of late immigrants which appeared at Kokkola to lay their second
clutches during the years of study. This
amounts to not more than 20-25 °/o ofthe number of emigrants present in the
population .
Proof of the suggestions could bemade in two ways: (1) examination of
the ovaries under a dissecting microscope, to show that all females lay two
clutches (Cf. PARMELEE & PAYNE 1973),
and (2) recovery of a female, ringed
when laying her first clutch, in anotherarea incubating her second clutch . The
first method was not used since it would
have involved killing several birds,
which would have reduced the population under study. The second alternative would require checking vast areas
along the coasts in order to find themissing females, which in practice is
impossible. The nearest breeding area
(in Kalajoki) was examined in 1971 and
1972, but without any success in thisrespect.
Discussion

1. Multiple clutches in other wader
species. GRAUL (1973) has introduced
the term "rapid multi-clutch system"
for strategies in which females lay morethan one clutch in rapid succession .
Temminck's Stint was the first wader
species in which such a mechanism was
documented
convincingly(HILDEN
1965) . Later similar systems have been
revealed in other species, e.g. the Sanderling . PARMELEE (1970) and PARMELEE &PAYNE (1973) have shown that onlya single bird, either male or female,incubates the eggs and attends the
young. Although they were not able
to prove by means of ringed birds thatfemales may lay multiple clutches in
rapid succession, an examination of the132
ovaries of two females taken as thebirds began incubation showed that they
had laid two clutches of four eggs each
within 8-10 days . This fits well withthe observation that at both nests subsequently incubated by males, the females disappeared after laying the last
egg and were not seen again . On a third
nest, attended by a female, she started
to incubate immediately after clutch
completion .
The onset of incubation by the Sanderling male was different at the twonests under observation : one male commenced steady incubation almost immediately after clutch completion, theother delayed the start of incubation fornearly six days . During this period hecould not be found on his territory, andthe authors believed that the pair was
attempting another nesting on anothersite . If this conclusion, based on a single
observation, is valid, then the Sanderling
differs from Temminck's Stint in which
the male normally pairs with two females on the same territory . However,
the maintenance of the pair bond during the laying of both clutches in the
Sanderling is only a hypothesis ; the male
could have associated with a new female
during his absence from the first nestsite . So far the data are too few to determine the precise mating system of theSanderling.
In other Calidris species this kind of
breeding system has not been observed
so far . It may occur in the Little Stint
C. minuta, judging from an observation
by KISTCHINSKI & FLINT (1973) of two
nests, located about 7 m apart, one incubated by a male, the other by a female.
The identical colouring of the eggs inboth clutches suggested that they had
been laid by the same bird . A sharednest containing 8 eggs., reported by REYNOLDS (1972), gives some indications ofpolygyny in the Little Stint (cf . p . 127) .
The breeding system of the M6untain

ORNIS FENNICA Vol . 52, 1975
Plover has much in common with thatof Temminck's Stint but shows also
certain differences (GRAUL 1973) . As in
Temminck's Stint, the female lays two
clutches in rapid succession, leaves thefirst one to the male and incubates thesecond herself . Another similarity is thelooseness of pair bonds : the mates of apair are commonly seen alone, and evenwhen together they generally maintainan individual distance of 6 to 15 metres .
Furthermore, Mountain Plover males
seem to court each female that enterstheir territories, and the females may
switch their mates prior to laying thesecond clutch, as in Temminck's Stint .
The most important difference is thatthe female may remain with her originalmate while she lays her second clutch,
and even if remated with a new maleshe nevertheless places her second clutch
within the original territory . The female
Temminck's Stint, on the contrary, always forms successive pair bonds withtwo males and places her clutches on
two territories some distance apart . The
way in which males of the two species
maintain their sexual activity after completion of the first clutch is also different . While Temminck's Stint males delay the onset of incubation for several
days, Mountain Plover males commence
incubation immediately ; however, they
do not attend the clutch steadily but
continue to court and copulate with
their mates or other females . Finally,
the interval between the two clutches is
9 to 13 days in the Mountain Plover,against only 2 to 4 days in Temminck's
Stint .
The Spotted Sandpiper also shows
serial polygamy connected with multiple
clutches, but the system differs in many
respects from that found in Temminck's
Stint (HAYS 1972, ORING &. KNUDSON
1972) . First, the roles of the sexes arereversed, the female being larger andmore aggressive but less active in parent-

Olavi Hilden : Breeding system of Temminck's Stint Calidris temminckii

al duties ; therefore, she is polyandrous
but each male is paired with only one
female . Second, both mates may incubate on the same nest and take careof the same brood. There is much variability in pairing behaviour 'between females. Some nest with only one maleand share the incubation with him, thus
exhibiting a normal monogamous mating
system . Others pair successively with
two, three, or even four males and do
not incubate until the final clutch ; theprevious males tend the eggs and young
without the female's help.
In the Red-necked Phalarope, serial
polyandry occur if excess males are present in the population (HILDEN & VUOLANTO 1972, RANER 1972) . The second
clutch can be started only 5-6 days
after completion of the first one. However, most females lay a single clutch .
The reversal of sexual roles is very pronounced in phalaropes, the male incubating and taking care of the young
alone .
The situation seems to be fairly similar in the Dotterel (PULLIAINEN 1970,
1971,

NETHERSOLE-THOMPSON1973) .

Most females lay only one clutch which
they leave to the males, but some arepolyandrous and lay a second clutch . In
one well documented case described by
PULLIAINEN (1971), laying of the second
clutch commenced 4 .7 days after completion of the first, and the distance between the two nests was 600 m. Contrary to the phalaropes, the female may
share the incubation of the second clutchwith the male (see also HILDEN 1966) .
In other species of the suborder Cbaradrii, multiple clutches have been demonstrated in the families Jacanidae(HOFFMANN 1949, JENNI & COLLIER
1972, JENNI 1974) and Rostratulidae(e.g. LOWE 1963, ALI & RIPLEY 1969,
JACKSON 1970), in both connected withpolyandrous social organization and concomitant reversal of sex roles. The best133

documented case refers to the American
Jacana (JENNI & COLLIER 1972, JENNI
1974) . This species inhabits small tropical ponds, and most females are polyandrous, simultaneously paired with 2
to 4 males. Eeach breeding male defends
a small territory within the female's
larger territory, and the female helps
her mates repulse territorial intruders .
The female may copulate with all her
males on the same day and lays one
clutch for each at intervals of 7 to 10
days, but does not share in incubationor care of the young . If a clutch is lost,a new one is laid within a few days.
The basic difference between this systemand those discussed above is the simultaneous mating of the female with two
or more males; in all polyandrous species of the family Charadridae, the pairbonds are formed serially.
Outside the suborder Charadrii, polyandrous systems are very rare and havebeen demonstrated so far in only a few
species of the orders Rheiformes, Tinamiformes, Gruiformes and (exceptionally) Passeriformes ; however, in most ofthese species, the reports were based onindirect or circumstantial evidence (JENNI 1974) . In addition, double-clutch production, not connected with polyandry,
is known to occur in the order Galliformes : hens of the Red-legged Partridge
Alectoris rufa may lay two clutches, one
incubated by herself and the other by
her mate (GOODWIN 1953, JENKINS
1957), just as in Temminck's Stint .
2. Evolution of the rapid multiclutch system . The suborder Charadrii ischaracterized by tremendous variation
in social systems . The monogamous system with persistent pair bonds andshared parental responsibility is the mostcommon and probably the ancestralpattern of social organization in waders(cf. JENNI 1974, PITELKA, HOLMES &MACLEAN 1974) . All other systems have

13 4

been evolved from this through natural
selection, partly in response to highlyvariable environmental forces (availability of food, predation pressure, interspecific competition, diversity of habitat, climatic factors, etc.), but partly
also in relation to other physiological or
ecological adaptations of the species to
its environment (feeding habits, breeding
season, share of parental duties between
the mates, timing of departure, sexual
dimorphism, delayed sexual maturity,etc.). The present systems are compromises to these various selective forces,
making the wide variety in strategies
understandable . In the following section,
I consider some important factors which
probably have played a part in the evolution of the rapid multi-clutch system,
an extreme form of 'breeding strategy .
Evolution of this system has proceeded along two main lines: either the female lays one clutch attended by a maleand a second clutch which she incubates
herself, or she lays clutches that are incubated by more than one male (polyandry) . The Mountain Plover, Sanderling and Temminck's Stint represent theformer evolutionary line, the Spotted
Sandpiper, Red-necked Phalarope, Dotterel, Painted Snipe and American Jacana the latter one (Fig. 4). Two mainquestions arise : what are the advantages
and disadvantages of the multi-clutch
system, and why has evolution not led
to the same strategy in other wader species?
Most waders lay a single clutch eachseason . A genetically determined capability of laying more clutches could beof definite selective value as he number
of offspring can be increased. On theother hand, there are certain disadvantages compared with the original monogamous single-clutch system . First, incubation and care of the young by one
parent instead of two may increase lossesof eggs and young by exposing them

ORNIS FENNICA Vol. 52, 1975

more severely to weather and predators.
Second, the rapid multi-clutch system
is usually associated with loosening ofpair bonds, which probably leads to decreased mate-faithfulness ; this, in turn,may reduce the breeding success. Third,
laying more than one clutch involves increased demands on the female . If thesenegative forces outweigh the selective
advantage of multiple clutches, then theevolution of the multi-clutch system will
be restrained. Let us examine closer
these disadvantages .
NORTON (1972) has observed at Barrow, Alaska, that overall nest attendance after clutch completion amounted
to 97 .5 and 96 .5 'o/o in the Dunlin andBaii d's Sandpiper, respectively, in which
species both parents share in incubation,
but to only 85 .0 % in the Pectoral
Sandpiper in which only the female
tends the nest . The clutch is exposed toenemies and adverse weather when left
unattended, so a lower rate of attendance may lead to a somewhat reduced
hatching success and young viability.
The average difference in breeding success between two-sex and single-sex incubating species is likely to be accentuated under severe conditions, especially inthe arctic . According to NORTON (1972),
time spent on the nest by the Pectoral
Sandpiper decreases on colder days because of the increased energy costs ofincubation and greater difficulty in securing insect prey. This can lead tosevere egg chilling. In the Dunlin and
Baird's Sandpiper, on the contrary, nest
attendance increases at low temperatures . Also, two adults are probably better
able to brood and protect their young
than a single bird. In addition, if thissingle parent is killed during the incubation or brood period, the nest or
young are doomed to destruction; but inthe case of two attending adults, thedeath of either is not necessarily fatal
as the other may manage the parental

Olavi Hilden : Breeding system of Temminck's Stint Calidris temminckii

135

Summary of the probable evolution of rapid multi-clutch systems in waders from the ancestral system, detailed at the bottom of the diagram. Evolution has proceeded along two main lines,
but the breeding systems now exhibited by different species need not show phylogenetic relationships,
FIG . 4.

duties alone. However, the total effectof this factor can hardly be of decisive
importance, because in several wader
species, even in arctic regions, only one
parent bird incubates and in manyothers either one of the mates abandons
the brood soon after hatching .
The widespread occurrence of matefaithfulness among birds shows that itrrust have some definite selective advantage. COULSON (1966, 1972) has beenable to prove this convincingly in the
Kittiwke Rissa tridactyla : birds which

retain their mate nest earlier, lay larger
clutches, have a better breeding successand produce more offspring, on average,
than "divorced" birds . SOIKKELI (1967)
has also emphasized the biological importance of mate-faithfulness in the
Dunlin . Hence, a reduced mate fidelity
may somewhat decrease the breeding
success, but in no case can this disadvantage be so great that it could obstruct
the evolution of the rapid multi-clutch
system.
There remains the third disadvantage,ORNIs FENNICA Vol. 52, 1975136

the increased demands on the female bylaying more than one clutch, a heavyenergetic expense during a short period.
In Temminck's Stint, for instance, eachfemale produces in about 10 days 8 eggs,
the total weight of which corresponds
to almost twice the 'bird's own weight!
Whether or not a bird is capable of laying multiple clutches must depend decisively on the availability of food during
a critical period . Consequently, only
those species or local populations living
in very productive habitats with abundant food supply have been able toevolve the rapid multi-clutch system .
For species living in less productive
habitats or specialized on a scarce foodsupply, production of two clutches in
rapid succession would probably weaken
the females so much that they would
be unable to take care of the second
clutch . The heavy expence of egg production could also lower the mean lifespan of females so that they would leave
less offspring, in total, than females laying a single clutch .
What do we know about the foodsupply in species laying multiple clutches? In my study area at Kokkola, themain laying period of Temminck's Stints
in the last days of May and early June
coincides with the mass emergence ofchironomids . At the same time of year
the sea level is usually low and extensive
mudflats are exposed along the shores .
Hence, feeding conditions are very favourable for the laying females . Similarly, the timing of egg-laying in Rednecked Phalaropes at Norrskär, on thewest coast of Finland, is adapted to themass emergence of chironomids, whichmake second clutches possible (HILDEN& VUOLANTO 1972) . Hence, in theseboth species there is clear evidence of therole of high food availability in the production of two clutches .
The same idea applies to the Spotted
Sandpiper. According to ORING&,KNUD-

the evolution of multiple
clutches in this species is a consequenceof its colonization of the south temperate parts of North America. In these
new areas, longer periods of high foodsupply have enabled the females to lay
multiple clutches . Also the short interval, 5 .3 days on average, between two
successive clutches or between loss of thenest and initiation of the replacement
clutch suggests availability of abundantfood for laying females.
As regards the Mountain Plover andSanderling, their multi-clutch systems
seem to be adapted to the extreme fluctuations in food levels that occur inthe habitats where they live (GRAUL
1973, PARMELEE & PAYNE 1973) . The
Mountain Plover inhabits the shortgrassprairie where sharp changes in insect
food occur due to fluctuations in precipitation . The Sanderling lives in thehigh arctic where climatic conditions
are often extremely variable from year
to year with concomitant fluctuations
in food supply. The authors suggest thatfemales of these species adjust their reproductive efforts to food conditions bylaying more than one clutch in goodyears but only one or perhaps none at
all in poor years.
The same opportunistic strategy islikely to explain the cases of multiple
clutches recorded in the Dotterel. I havestudied this species in Finnish Laplandand I know how abrupt are the changes
in food conditions on its breeding
grounds : on warm, sunny days the insectabundance on fjell heaths is high, butduring spells of cold weather, withstrong winds and even heavy snowfalls,
hardly any insects are to be found (cf.
also RITTINGHAUS 1962, NETHERSOLETHOMPSON 1973) . Second clutches probably occur only under favourable foodconditions .
Finally, as regards the American Jacana, its breeding habitat in small, shalSON (1972),

Olavi Hildén : Breeding system of Temminck's Stint Calidris temminckii

low ponds with diverse and abundantaquatic flora represents a very richtropical environment with high fooddensity . Although the suitable space
available for breeding territories is limited, and thus the food supply probably
critical during the brood period, thisdoes not restrict the availability of foodfor laying females because these also
feed outside their territories on the surCOLLIER
rounding lawns (,JENNI &1972) . In the protracted season of thetropics with constantly rich food resources, the females are able to aquireenough energy to produce multiple
clutches in rapid succession. The same islikely to apply also to the Painted Snipe,
living in tropical marshes or swamps
with thick vegetation, shallow ponds
and muddy patches, but very little is
known about the biology of this species .
There are also more general observations that support ,the significance of highfood supply in the evolution of therapid multi-clutch system . First, formany species it is known that the frequency of renesting is affected by thefood supply at the time of nest failure(e.g. SOUTHERN 1959, LACK 1966, SoIKKELI 1967) . In arctic areas most waders
fail to lay replacement clutches. According to HOLMES (1966), the Dunlin is the
only wader species at Barrow, Alaska,
to lay again . This is more likely due tophysiological restrictions on egg production under the severe arctic conditions than to the short breeding season,
because replacement of a nest lost at an
early stage of incubation would not leadto a severe delay in nesting . Without theability to renest, laying of multiple
clutches is impossible. In temperate regions, however, lack of multiple clutches cannot be explained so simply as mostwaders do lay replacement clutches incase of nest failure .
Second, it is generally accepted thatthe species-specific clutch sizes are ulti-

137

mately adapted to average level of thefood supply, either through the averagecapacity of the parent birds to feed their
young or the average amount of foodavailable for the laying female (e.g.
LACK 1966, 1968, KLOMP 1970) . Furthermore, many birds are known to laylarger clutches when food at the time oflaying is plentiful, and vice versa (seealso BENGTSON 1971) . In principle, there
is no difference if a bird lays, say, 8 eggs
in one clutch or 4+
4 eggs in two
clutches in rapid succession . Hence,
abundant food is to be expected to promote, and scarce food to restrain, theevolution of the rapid multi-clutch
system .
Third, the amount of food available
may be important not only at the timeof laying but also during incubation. In
all species laying multiple clutches, atleast the first nest is attended by a single
bird, and, as pointed out already by
PITELKA, HOLMES & MACLEAN (1974),

the one-adult incubation system can be
successful only when food density ishigh. If food is scarce more time is needed for foraging, and prolonged absencesfrom the nest could make the incubation
insufficient .
The significance of high food supply
for the evolution of a rapid multi-clutch
system has been stressed above. However, low food supply may also lead tothe same strategy. As pointed out bymany authors (SELANDER 1972, GRAUL1973,

NETHERSOLE-THOMPSON1973),

low food supply may promote a reduction in female participation in parental duties, partly because an early
departure by the female reduces competition for food, and partly because thefemale may lack the energy reserves
needed to share in parental responsibilities after egg production . Although thisis potentially an important step towards
a rapid multi-clutch system, evolution
can hardly proceed further as long as

138

the availability of food for the laying
female is low, but the situation willchange if the species colonizes new regions or habitats with richer food resources. Now the females., freed fromparental duties, are able to lay additional clutches and the multi-clutch system
can evolve . But a prerequisite is, ofcourse, that one adult is able to raise
the brood unaided, and this is not so iffood is too scarce in the original area .
Of environmental factors other thanfood which may have played a role in
the evolution of wader social systems,
predation pressure is probably the mostimportant. In wader populations where
predation rates are high, there must be
intensified selection for production ofmultiple clutches . ORING & KNUDSON(1972), GRAUL (1973) and JENNI (1974)
have all emphasized the significance of
this factor in the evolution of rapid
multi-clutch systems. Other possible
factors (interspecific competition, diversity of habitat, climatical conditions,etc.) are mainly indirect, influencing
habitat selection and so the availabilityof food and predation pressure.
On the other hand, some adaptationsin the breeding behaviour may have retarded the development of multiple
clutches . Laying of more than one clutch
is not possible without preceding weakening of pair bonds. But in the ancestralmonogamous single-clutch system, there
has been an opposite selective pressure
towards the persistent pair bond becauseof its general advantages (Cf. PITELKA,
HOLMES & MACLEAN 1974) . Once thepair bond has developed beyond acertain: strength, the evolutionary way
towards multiple clutches is blocked
because the necessary "intermediatestages", i.e. females with looser pairbonds and weaker incubation drive, are
not favoured by natural selection. Thismay be the explanation of the paradoxthat even species having potentially

ORNis FENNICA Vol. 52, 1975

good qualifications for laying multiple
clutches (high food supply, long breeding season, capability of renesting) haverarely evolved this system .

To conclude, the evolution of rapid
multi-clutch systems has not followeda standard pathway in all species. Manydifferent factors, both promoting andrestraining, have been involved, and the
combined effect of these counteracting
selective forces has determined the direction of the evolution. It is significant
that in none of the known species laying
multiple clutches, except perhaps theAmerican Jacana, have the mating systems reached the final stage of theevolution. In Temminck's Stint, forexample, various exceptions to thenormal schedule are common, and wide
individual variation in breeding behaviour has been stressed also by HAYS
(1972), ORING & KNUDSON (1972) andGRAUL (1973) with respect to the Spotted Sandpiper and Mountain Plover .

This suggests that the rapid multiclutch system is a rather new breeding
strategy and is not sufficiently advantageous to all species to become prevalent . It also may imply the existenceof geographical differences in breeding
strategies within the same species. Environmental conditions are often highlyvariable within a species' range, andwhat may be advantageous in one area
may be disadvantageous in another. In
Temminck's Stint, for instance, mystudies have been carried out at thesouthern border of its range and concern
an almost isolated population breedingon the coast of the Gulf of Bothnia. It
is quite possible that future investigations on the arctic breeding grounds ofthe species, with a shorter breeding
season and very different climatic andecological conditions, will reveal a different mating system . Such a comparative
study would be highly desirable.

Olavi Hilden : Breeding system of Temminck's Stint Calidris temminckii

13 9

TABLE 5.

Clutch size and relation of egg weight to female body weight in wader species laying
multiple clutches .

Calidris temminckri
Calidris alba
Tringa macularia
Charadrius montanus
Eudromias morinellus
Phalaropus lobatus
Jacana spinosa
Rostratula benghalensis
1 Egg weight as a percentage of female body weight .

s Clutch weight as a percentage of female body weight.
$ Average of both male and female weights.
a Data on egg weight .
a Data on female body weight.
3. Adaptations related to the rapid
multi-clutch system . Theoretically, there

are many possible ways of reducing thedemands on the female caused by laying
more than one clutch .
Reduced egg or clutch size . Production of smaller or fewer eggs consumes
less energy, and one might expect reduced egg or clutch size in species exhibiting a rapid multi-clutch system, as
claimed by LACK (1968), ORING &KNUDSON (1972), GRAUL (1973), PARMELEE & PAYNE (1973) and JENNI (1974) .
This has been tested in Table 5 . Tem-minck's Stint and Sanderling do notshow any reduction in egg size whencompared to other species of the same
genus, contrary to what has been stated:"the very small egg of Erolia temminckii . . ." (LACK 1968, p. 219), "bothTemminck's Stints and Sanderlings haveunusually small eggs in relation to bodysize . . ." (PARMELEE &. PAYNE 1973) .
Ten other Calidris species, on which

SCHÖNWETTER (1960-66) and GLUTZ
et al. (1975) give the necessary in-formation, have relative egg weightsof the same order, ranging from 13 to
28 '°/o and averaging 21 .2 °/o . On
the other hand, the Spotted Sandpiper
has considerably smaller eggs than thethree small European Tringa species,
the Common Sandpiper T. hypoleucos,
Wood Sandpiper T. glareola and Green
Sandpiper T. ochropus, which have relative egg weights of 26 .0, 22 .5 and 19 .4°/o, respectively (SCHÖNWETTER 196066) . The Mountain Plover and the Dotterel also have somewhat smaller relative egg weight than the other plover
species listed by GRAUL (1973) ; the latter average 19 .8 °/o . Likewise the eggs of
the Red-necked Phalarope are rather
small in relation to the body size, as inall phalaropes, but only the American
Jacana and Painted Snipe show much
reduced egg size.
,,__As to clutch size, all but two of these

140

species lay the ancestral Charadrii clutchof 4 eggs. The Dotterel and Mountain
Plover lay only 3 eggs, but a great
number of other plover species which
do not lay multiple clutches also have
reduced clutches of 3 or 2 eggs (MACLEAN 1972). Hence, reduction of clutch
size cannot be considered a generaladaptation in species with rapid multiclutch systems.
It seems clear why most wader species
show little or no reduction in egg size.
The smaller the relative size of the egg,
the less food reserve it contains for the
newly hatched young. For most species
treated here the climatic conditions on
the breeding grounds are very unpredictable, with frequent spells of adverse
weather and concomitant shortage offood, so it would be a great risk for precocial young to hatch without sufficient
food reserve. This risk does not affectthe American Jacana and Painted Snipe,
which live in a rich tropical environment with stable climatic and food conditions, and consequently these two species are the only ones with much reduced egg size.
That most wader species laying multiple clutches do not show a reduced
clutch size is also easy to understand. If,
on average, production of two clutchesof normal size in rapid succession is tooheavy a demand on the female, then areduction in clutch size is a prerequisite
for the evolution of a rapid multi-clutch
system . By itself, however, a smaller
clutch is merely a disadvantage, if thespecies is capable of producing the original clutch of 4 eggs, and so evolution
cannot proceed along this line. Where reduced clutches occur in waders, they
have not evolved to permit productionof multiple clutches but in response tocertain environmental factors, probably
most often to the availability of food.
Prolonged laying interval between the
clutches. One way to reduce the demand

ORNIS FENNICA Vol. 52, 1975

on females caused by successive clutches
could be to lengthen the interval between them. Temminck- s Stint has theshortest interval, only 2 to 4 days ; about
5 days is involved in the Spotted Sandpiper, Red-necked Phalarope and Dotterel, 7 to 10 days in the American Jacana and 9 to 13 days in the Mountain
Plover. In most of these species, theinterval between the two clutches isabout as short as is needed for eggformation in waders in general (cf.
HILDEN & VUOLANTO 1972, p. 73).
Hence, evolution has not led to a prolonged interval between clutches to facilitate the production of multiple clutches. The probable reason is that breeding
season available for wader species innorthern regions is very short, so that adelayed second nesting would be disadvantageous . The two species with thelongest intervals are those with thesouthernmost breeding ranges and thus
the longest seasons for breeding. In the
Mountain Plover, the relatively longclutch-interval is also likely to be dueto the poorer feeding conditions : its habitat, the shortgrass prairie, is less productive, on average, than those of theother species.
Delayed sexual maturity. Many bird
species do not breed until two or three
years old, probably because breeding at
a younger age would be too heavy astrain for unexperienced birds (LACK
1966, 1968) . As the laying of multiple
clutches is a particularly strenuous
breeding system, one would expect adelay in the age at which females firstbreed in species with this type of strategy.
In Temminck's Stint, however, females commonly breed when only one
year old. One of these birds (F 25/1964,
see p. 128) laid three successive clutches(12 eggs) within 16 days! So this species
does not show deferred maturity . On thecontrary, it starts breeding earlier thanOlavi Hilden : Breeding system of Temminck's Stint Calidris temminckii

the single-clutched Dunlin, for instance,
which usually breeds first when two
years old (SOIKKELI 1970'b).
As to the other species showing multiclutch systems, information on their age
at sexual maturity is scanty . ORING &KNUDSON (1972) assume that advanced
age at first breeding would be an adaptation to minimize strain on the female
in these species, but they give no data insupport. The unbalanced sexual ratio,with males predominating, shown toexist in populations of the Spotted Sandpiper (HAYS 1972, ORING & KNUDSON
1972) and the American Jacana (JENNI& COLLIER 1972, JENNI 1974), suggeststhat at least in these two species females
start breeding older, on average, thanmales. This, in turn, makes the polyandrous system possible, more males
than females being available. On thewhole, however, waders that lay multiple clutches seem to breed for the firsttime at about the same age as singleclutched wader species.
Delayed onset of the male's incubation. A characteristic breeding adapta-

tion of Temminck's Stint is the delay ofthe male's incubation for some days,
during which he continues to display.
Also at one Sanderling's nest, the maledelayed the start of incubation for nearly six days (PARMELEE & PAYNE 1973) .
The significance of this adaptation iseasy to understand . If the males commence incubating immediately after
clutch completion, they have no chance
to increase the number of their offspringby fertilizing additional clutches . Also
females would have difficulties to findsecond mates, with only those late toarrive or excess males available. Thissituation would lead to the type of polyandry found in the Spotted Sandpiper,
Red-necked Phalarope and Dotterel .
Hence, without the delayed start of incubation the whole breeding mechanism,of Temminck's Stint would not be poss-141

ible. Consequently, natural selection has
favoured those males which have delayed the onset of incubation and thereby
succeeded in fertilizing another set of
eggs. Another possibility, found in the
Mountain Plover (GRAUL 1973), is thatthe male maintains his sexual activity
during the first days of incubation andtends the nest only sporadically .
A further possible advantage of thedelay in the male's incubation is that thebrood period is synchronized . For, as aresult, the young in the nests incubatedby the male and the female hatch almost simultaneously. The somewhat increased egg losses due to the prolonged
incubation period apparently do not
outweigh the selective advantages of thehabit.
Acknowledgements
Messrs . Harri Hongell, Lasse Laine and Eugen
Söderström assisted in the field work, for which
I wish to express my sincere gratitude. I am
especially grateful to Dir. Ruben Casen for his
helpfulness and for many practical arrangements
during all the summers at Kokkola . Further, I
am greatly indebted to Dr . Peter Evans forchecking and improving the English of my manuscript and for his valuable comments on the
text . I also thank Dr . Richard T. Holmes, who
critically read parts of the manuscript . Dr. Urs N.
Glutz von Blotzheim kindly sent me a Germantranslation of KoCHANow's Russian paper, andDr . Lewis W. Oring allowed me access to unpublished data on the female body weight and
egg weight of the Spotted Sandpiper.
The work was supported financially by the
National Research Council for Sciences (Valtion
luonnontieteellinen toimikunta) and the Emil
Aaltonen Foundation .

S e 1 o s t u s : Lapinsirrin Calidris temminckii pesimäsysteemi
1. Tutkimus on suoritettu 1963-72 Harrbådan
-Rummelön alueella Kokkolassa, missä pesu
Suomen eteläisin pysyvä lapinsirrikanta (vuosittain 15-36 yks.) . Pääosa pesistä on löydetty,
lähes puolet jo munintavaiheessa (taul. 1) . Aikuisista linnuista n. 80 % on värirengastettu

ORNIs FENNICA VOI. 52, 1975

142
(yht . 85 yks.), poikasista lähes kaikki tavallisin
renkain (yht . 323 yks.) . Sukupuolet voi maastossa erottaa varmasti vain käyttäytymisestä, kädessä useimmiten painosta (taul. 2, kuva 2) .
2. Kukin ? pariutuu peräkkäin 2 d Ö :nkanssa ja munii pesyeen kummankin reviiriin .
Pesyeiden aikaväli on vain 2--4 vrk. Vastaavasti
kukin a pariutuu peräkkäin 2 Y Y : n kanssa ja
hedelmöittää pesyeen kummallekin . Ensimmäistä
pesyettä rupeaa hautomaan a, toista Y . Molemmat huolehtivat myös poikueestaan yksin. Poikkeukset normaalista pesimäsysteemistä ovat mel
ko tavallisia . Useimmat johtuvat a J :n taipumuksesta moniavioisuuteen . Ne kosiskelevat jokaista reviiriinsä tullutta ~:ta, ja monesti on
saman a : n nähty yrittävän parittelua 2-3 Y Y : nkanssa lyhyessä ajassa. Tämän seurauksena välistä
2 yy munii 1 . pesyeensä samaan reviiriin, jolloin toinen aina jää hautomatta . Kerran 2 YY
muni samaan pesään yht. 7 munaa. Kahdesti on?:n todettu munivan 3 peräkkäistä pesyettä . Uusintapesyeet tuhoutuneen tilalle ovat hyvin harvinaisia.
3. Naaraita on kahta tyyppiä: pesimäpaikalle
uskollisia, jotka palaavat vuosittain samalle
alueelle ja munivat sinne molemmat pesyeensa, ja
kierteleviä, jotka vaihtavat pesimäaluettaan sekämolempien pesyeidensä välillä että vuodesta toiseen . Jälkimmäisiä on n. kolmannes gY :sta .
Koska tutkimusalue sijaitsee lajin pesimäalueen
eteläreunalla, sieltä lähtee kierteleviä ~~ :ta pois
ennen 2. pesyeensä munintaa paljon enemmän
kuin uusia saapuu tilalle; tästä syystä alueella on
1. pesyeitä selvästi enemmän kuin toisia (taul. 3) .
4 . Samantapainen pesimäsysteemi (kaksoispesintä), jossa Y munii kaksi tai useampia pesyeitä
lyhyin välein, on todettu toistaiseksi 7 muulla
kahlaajalajilla (Calidris alba, Charadrius monta-

nus, Tringa macularia, Phalaropus lobatus, Eudromias morinellus, Rostratula benghalensis, Jacana
americana), toisilla niistä säännöllisesti, toisillatilapäisesti . Yksityiskohdissa näiden lajien pesimäsysteemeissä on kuitenkin paljon eroja.
5 . Kahlaajien alkuperäisin pesimäsysteemi on
yksiavioisuus, jossa parisiteet ovat kiinteät jamolemmat sukupuolet osallistuvat pesimistoimiin .
Lukuisat muut systeemit ovat erilaistuneet tästä
perustyypistä luonnonvalinnan kautta, sopeutumina erilaisin ympäristöoloihin ja lajien erilaisiin
elintapoihin . Kaksoispesinnän kehitys on edennyt
kahta päälinjaa: joko a ja ? hautovat omia pesyeitään tai 9 munii pesyeensä 2 Ö a :lie eikä
itse osallistu jälkeläisten huoltoon (kuva 4) .
6. Kaksoispesinnän valintaetuna on jälkeläismäärän kasvaminen . Haittoina ovat haudonnan
ja poikashoidon jääminen yhdelle emolle, parisiteiden heikentyminen ja lisääntynyt rasitus:lie, jotka kaikki joko huonontuneen pesimätuloksen tai Y : n lyhentyneen eliniän kautta voivat pienentää jälkeläisten määrää . Kaksoispesin

nän kehittyminen tai estyminen riippuu näiden
vastakkaisten valintatekijöiden keskinäisestä voimakkuudesta .
7. Kirjoittajan käsityksen mukaan kaksoispesintä on voinut kehittyä vain oloissa, missä ravintoa on runsaasti tarjolla muninta-aikana .
Useimmista tämän pesimäsysteemin omaksuneista
lajeista käytettävissä olevat tiedot osoittavatkin
näin olevan . Muista kaksoispesinnän kehittymiseen myötävaikuttaneista ympäristötekijöistä suuret pesä- ja poikastappiot ovat ilmeisesti tärkeimmät. Parisiteiden lujittuminen taas on voinut estää kaksoispesinnän kehittymisen sellaisillakinlajeilla, joilla olisi ollut tähän riittävät edellytykset.
8. Lopuksi tarkastellaan kaksoispesintään liittyviä muita sopeutumia . Munan koko on pienentynyt jonkin verran neljällä ja huomattavasti kahdella lajilla, kun taas kahden lajin munan koossa
ei ole eroa saman suvun muihin lajeihin verrattuna (taul. 5) . Pesyekoko ei ole yleensä pienentynyt, vaikka tämä vähentäisikin q :n rasitusta .
Myöskään pesyeiden aikaväli ei ole kehittynyt
juuri pitemmäksi kuin munien muodostaminen
vaatii . Kaksoispesintään sopeutuneiden lajien
eivät näytä saavuttavan sukukypsyyttä myöhemmin kuin yhden pesyeen munivien lajien Yg .
Selvä sopeutuma kaksoispesintään on sitä vastoin
lapinsirrillä todettu a :n tapa viivyttää haudonnan alkamista muutamia päiviä, jona aikana sesäilyttää soidinvireensä ja pystyy hedelmöittämään toisen Y :n pesyeen.

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