BREEDING CHRONOLOGY AND MATING SYSTEM OF THE EURASIAN DOTTEREL ( CHARADRIUS MORINELLUS) JOHN ATLE KALAS AND INGVAR BYRKJEDAL Museum f Zlgy, University f Bergen, N-5000 Bergen, Nrway ABSTRACT.--We studied and clr-banded a ppulatin f Eurasian Dtterel n a middle alpine breeding grund in suthern Nrway ver 4 yr. Birds arrived paired in mid-may, dispersed nt nesting sites in late May t early June, when 75% f the grund was still cvered by snw, and began t lay eggs a few days later. The egg-laying seasn f the ppulatin was lng, up t 1 mnths. After cmpletin f the earliest clutches, females started t perfrm display flights, apparently t seek males. The female displaying perid lasted until the secnd week in July, when the females began t frm flcks and prebasic mlt was in prgress. The display perid thus cvered mst f the egg-laying perid f the ppulatin. Females had a lw site tenacity during the seasn, and evidence fr territriality was fund in neither f the sexes. We argue that sequential plyandry is cmmn in this dtterel ppulatin. Received 20 September 1983, accepted 4 March 1984. POLYANDRY is nt cmmn. Amng mammals, Eisenberg (1966) fund n gd case. Less than 1% f the species f birds studied t date are plyandrus (Jenni 1974), and all have preccial yung. Mst f the dcumented cases are fund in the rders Gruifrmes and Charadri- ifrmes (Jenni 1974). In Eurasian Dtterel (Charadrius mrinellus), cases f sequential plyandry have been dcumented (Franke 1953, Pulliainen 1971, Nethersle-Thmpsn 1973). Because f the reversal f sexual rles and the fact that the male alne cares fr the yung, the species hlds a great ptential fr the regular ccurrence f plyandry. We reprt here the breeding-seasn schedule f a dtterel ppulatin in suthern Nrway and discuss the patterns in relatin t the mating system. STUDY AREA AND METHODS The study area was a 6-km 2, nrth-facing, slping plt (1,170-1,350 m) in the middle alpine regin at Steinbuheii (60ø23'N, 07ø38'E), Hardangervidda, suthern Nrway. The vegetatin is a msaic f meadws and small bgs, the frmer characterized by grasses ( Anthxanthum dratum, Deschampsia fiexusa, Nardus stricta), Carex spp., [uncus trifidus, Empetrum hermaphrditum and lichens, and the latter by Eriphrum spp. The mnthly mean temperatures fr June and July are 4.7 and 8.0øC, respectively. Ttal Present address: Directrate fr Wildlife and Freshwater Fish, Sverresgt. 1, N-7000 Trndheim, Nrway. 838 snw-cver usually extends frm Octber until the beginning f June. Even in the middle f the summer, hwever, snw-fall is nt uncmmn, and cld spells with temperatures belw 0øC may last fr several days. In the middle f the summer there is nly a 3.5-h dark perid. [Fr mre infrmatin n climate, see Skartvit et al. (1975).] The mst cmmn mammalian and avian predatrs in the area are red fxes (Vulpes vulpes), Cmmn Ravens (Crvus crax), and Mew Gulls (Larus canus) (Byrkjedal 1980a), all ptential predatrs n dtterel adults, chicks, and eggs. The fieldwrk was carried ut frm mid-may t early August 1978-1981. Dtterel are abundant n Hardangervidda (K d/ts and Byrkjedal 1981), and each year 11-28 nests and/r brds were fund n the study plt (Fig. 1). The breeding seasn was divided int the fllwing perids: (1) Arrival--frm arrival n the breeding grund until the birds disperse frm the hill-tps t the area where the nests are placed; (2) Pre-laying--frm the time a pair is present n the nesting grund until the first egg is laid (als including new matings by males frm destryed nests); (3) Egg laying--frm the time the first egg is laid until the clutch is cmpleted; and (4) Incubatin--frm the time the clutch is cmpleted until the last chick is hatched. Censuses f all the dtterel in the study area were dne in May and early June, befre and just after dispersal dwnhill t the breeding sites in 1979 and 1980. During subsequent daily fieldwrk, hwever, all bservatins f dtterel were recrded and mapped. We fund nests by walking at randm and flushing birds frm their nests r by watching birds return t their nests. The entire area was searched many times each seasn. Snw-melting was mnitred by phtgraphing the area frm a fixed pint, usually nce a week. The Auk 101: 838-847. Octber 1984
Octber 1984] Dtterel Breeding System 839 We determined the dates f egg laying by exact bservatins, by back-dating frm hatching date (using a 25-day incubatin perid), r frm chick weights (y = 3.2 x + 10, where y = age in days, and x = chick weight in grams; based n 32 weighings f 14 chicks). Eggs that sank during a water test were regarded as newly laid. Captured birds were weighed and measured. Their physical cnditin was calculated by using the frmula: 1978. I Cnditin = [Bdy weight (g)/wing length (ram) x 100]. We als recrded the prebasic mlt f birds captured fr clr-banding. Only the primaries were cnsidered, and they were scred accrding t Snw (1967), i.e. each feather was given a scre frm 0 (ld) t 5 (new, fully grwn). In additin, newly mlted primaries fund in the study area were cllected. When estimating the mlt scre f the birds that had mlted these feathers, we identified the feather fund and gave it a scre f 1, the prximate primary next t this a scre f 3, and any ther prximate primaries a scre f 5 (cf. Blanken et al. 1981). Clr-banding started in 1979, and the adults were marked individually (70% f the males and 20% f the females each year), whereas chicks were given nly year cdes. Mst adults were captured n their nests; nly a few were mist-netted befre egg laying. In 1981, 3 males and 1 female were radi-marked and fllwed fr a ttal f 19, bird-days. The flight display f the females ("winnw-glide" display flight; Nethersle-Thmpsn 1973) is characterized by quick rhythmic sequences f the basic peep call. The frequency f female display flight was expressed as the number f females displaying per hur f bservatin, including any displaying female recrded, nt nly thse under bservatin during the activity-bservatin buts. Thus, the data cnsist f the number f flights perfrmed by an unknwn number f females. Only thse days with mre than 5 h f bservatins were included. The time spent feeding was calculated frm a cmbinatin f "fcal animal sampling" and "instantaneus sampling" (Altman 1974). The activities f a male and female were recrded simultaneusly nce each minute. Only sampling perids when the birds were watched cntinuusly fr mre than 30 min during the arrival perid and 60 min during the prelaying perids were used. Observatins were made at different times f the day and n different pairs. Sampling f feeding activity was never undertaken during rainy r fggy weather. NESTING CHRONOLOGY RESULTS Arrival.--The birds arrive in the study area in mid-may. In 1980, the birds were first b~ 1980. Z 1981. Fig. 1. Spacing f dtterel nests and different brds in fur breeding seasns at Hardangervidda study area. Height cnturs in 20-m intervals. (O = nest fund; O = chicks fund but nest site unknwn; dashed line = brder f study area.) served n 17 May; in 1981, the birds had arrived n 18 May but were nt present n 13 May. Data frm the pst-dispersal censuses in 1979 and 1980 (8 males/11 females and 4 males/ 5 females, respectively) indicate that initially there is n skewed sex-rati in favr f males. Dispersal nt nestin grunds and agnistic behavir.--when the birds arrive, the study area
840 KXL,S AND B¾1 KJED^L [Auk, Vl. 101 15 1979, A ) 10 30 5 15 1980 B) 15-1981 400 ß IO- 5O 20 25 MAY 10 JUNE Fig. 2. Dispersal f birds frm hill tps nt nesting grund in different years. (Open = bservatins n hill tps; shaded = bservatins n nesting grund.) Slid line illustrates snw cver; arrws indicate start f egg laying f the first nest in the study area. is nearly ttally cvered by snw. Frm the very first day f bservatin, the birds are paired and spend mst f the time feeding n snw- free patches n higher grund. As sn as snwfree areas emerge n the slpes, the pairs disperse dwnhill and start their pre-laying activities. Time spent n the hilltps depends n the prgressin f snw-melting (Fig. 2). When the snw-cver is abut 75%, all birds have dispersed nt their nesting grunds. The dtterel des nt defend any defined area during the pre-laying perid. During 75 h f scheduled bservatin f six different pairs, we never saw flight displays that culd be interpreted as territrial demarcatin. In 32 cases, ne pair encuntered ther pairs, which came as clse as abut 10 m befre aggressin was elicted. These encunters ccurred mre r less randmly, nt alng specific territry bundaries. During the pre-laying perid, the hme 0 200 400 600 m Fig. 3. Hme-range f pair 3/81 at different times f the seasn in 1981 (frm bservatins f the clrbanded male and the radi-tracked and clr-banded female). (Star = nest 3/81, dts = ther dtterel nests.) (A) Slid line = pre-laying hme range f male and female; dashed line = egg-laying hme range f male and female. (B) Slid line = hme range f the female during incubatin; dashed line = hme range f the male during incubatin. range f pair 3/81 was 0.22 km 2, and, as can be seen frm Fig. 3, at least tw ther nests were lcated in the pre-laying hme range f this pair after they had cmpleted their wn nests. Each f these nests was used by a different fe- male. The nest-spacing mechanismseem rather weak, as the distances between nests may be shrt (Fig. 1). Mst f these clse nests are knwn t be used by different females. During egg laying, the hme range (0.06 km 2) f pair 3/81 was smaller than during the pre-laying perid, and the birds usually stayed within a few hundred meters f the nest (Fig. 3). At this nest, the female tk part in incubatin, but she had a much larger hme range than the
Octber 1984] Dtterel Breeding System 841 1978 N'16 1979 N= 14 1960 N:22 1961 Fig. 4. Cmpleted clutches f dtterel (2-day intervals) in different years. male did during the incubatin perid (0.57 km 2 and 0.09 km 2, respectively; Fig. 3). Egg laying.--egg laying starts nly a few days after the birds have dispersed frm the hill tps prduced per female each year was btained. Dissectin f the varies f tw females (fllwing the prcedure given by Parmelee and Payne 1973) indicated that each had laid at least (Fig. 2). The length f the egg-laying seasn tw clutches. If the first nest is destryed, the varies frm year t year (Fig. 4) but usually male will accept a secnd ne. In tw cases, the starts the last week f May. The latest clutches distance between the first and the secnd clutch are finished in mid-july. During egg laying, the birds cntinue t cpulate. All but ne nest cntained three eggs (n = 52). The average interval recrded between the laying f individual eggs was 30.8 h + 2.1 (SD) (n = 7). f the same incubating male was 250 and 400 m. Clr-banded males sat n five ther nests, which were eventually rbbed thrugh predatin. The predatin tk place after mid-july, s new nestings culd nt be expected in these Little infrmatin n the number f nests cases, and the males were nt seen again. In
842 KALAs and BYR JED^L [Auk, Vl. 101 TABLE 1. Percentage f nests in which the male dtterel incubated alne and in which bth male and female incubated. Time f egg laying Befre After 15 15-30 30 June June June Number f nests 7 I0 10 Percentage f nests in which the male incubated alne I00 60 50 Percentage f nests in which bth male and female incubated 0 40 50 ne case a male accepted a new clutch f eggs after the lss f his 4-day-ld chicks. Incubatin.--The incubatin perid is 24.6 + 0.6 (SD) days (n = 6). The male starts incubating during egg laying. We bserved n sexual behavir n the part f incubating males after egg laying at their nests was finished. In early nests, the male is in sle charge f the incubatin, but, in nests started later than mid-june, the female frequently assists (Table 1). Females were never fund incubating alne. Female flight displays and excess female grups.- The ccurrence f flight displays in the study area varied frm day t day, but there was a distinct seasnal pattern (Fig. 5). We bserved sme birds displaying just after their arrival, but there was a drastic increase after cmpletin f the first nests. The frequency then fluctuated at a high level until it drpped in early July. Of 17 ccasins upn which the displaying bird was seen well enugh fr sexing, all were females. Display flights were lng, ften ver several kilmeters, and they seldm ended at the starting pint (Fig. 6). In fact, nne f the clr-banded females was seen in the study area after egg laying, except fur that were incubating late clutches (see belw). Presumably the display flights take the females ver large distances. Grups with excess females (mst ften 1 pair + 1-3 females) ccurred thrugh the egglaying seasn, especially in the latter part, and there was an increase in the relative number f single females tward the last week in June (Fig. 7). In 13 f the 16 bserved grups with excess females, aggressin between the grup members was seen. The six pairs held under systematic bservatin were jined by a female n seven ccasins, all f which resulted in aggressin frm bth pair members tward the newcmer. Female flcks.--the females start flcking at the beginning f July. At first, the flcks cn- 2.0, ß1980 1981 e ø ø 0.5' O 15 Fig. 5. MAY 23 31 8 JUNE 16 24 ß 10 JULY 18 Intensity f female flight-display during the breeding seasn.
Octber 1984] Dtterel Breeding System 843 Fig. 6. Flight paths (arrws) f displaying dtterels within and adjacent t the study area as far as the bird culd be fllwed with 8 x 30 binculars. (A) Start and finish f the flight seen; (B) start r finish nt seen (dtted end f arrw indicates which). sist f nly a few females, but, by mid-july, they may cntain 30-40 individuals. At the end f July, males and fledged yung als jin the flcks. Incubating males have never been bserved in these flcks, but all fur clr-banded incubating females were seen in the female flcks when they were ff the nest. Hatching and fiedging.--the time lapse in hatching between the first and the third chick was fund t be 24.3 h +_ 5.5 (SD) (n=11). Females were never bserved attending chicks. Yung frm tw clutches were bserved flying at the ages f 24 and 26 days, respectively. Mlt.--The mlt f primaries starts at the beginning f July (Fig. 8). There are n significant differences in the mlt prgressin between males attending chicks and incubating males. We have n data n the mlting f the utermst primaries, but Fig. 8 suggests that the mlt f primaries is finished befre the birds' departure frm the breeding grunds. ference in time spent feeding between the early pre-laying (I; early June) and late pre-laying (II; early July) perids. This des nt indicate a fd shrtage during the egg-laying seasn. =.5 - Single males (N=4} LO 0. Single females (N=21) Female excess grups (N=16) 6 10 11 14 5 2 4 5 2 Peir grups (N=59) FEEDINGACTIVITY During the first days after arrival, nearly 90% f the daylight time is spent feeding (Table 2). There is a significant decrease in the time spent feeding between the arrival and pre-laying perids (X 2 test, P < 0.001) but n significant dif- PERIODS Fig. 7. Seasnal distributin f single birds and grups in the study area in relatin t the number f bserved pair grups. "Pair grups" cnsisted f mre than ne pair in nly fur cases. Birds having nest r yung and pstbreeding female flcks are nt included.
844 K L.s AND BYRKJEDAL [Auk, Vl. 101 50 n' 30 0 e-males,-females --Sex unknwn - IO- I 5 I 0 I 5 20 25 Days Fig. 9. Variatin in the physical cnditin [(wing length/weight) x 100] f dtterel males during the incubatin perid. (Lines jin the same individuals.) JUNE t JULY I AUGUST Fig. 8. Mlt f primaries f dtterel. (Lines jin the same individuals.) The sexes did nt differ significantly in the prprtin f time spent feeding in any f the three perids. PHYSICAL CONDITION OF INCUBATING MALES There was a significant decrease in the rati f wing length t weight (a measure f physical cnditin) f incubating males during the incubatin perid (r =-0.50, P < 0.001), but the decrease was slight (Fig. 9). Frm the regressin, the average decrease during the whle incubatin perid was estimated t be 8.8%. Birds weighed bth early and late in the incubatin perid had a daily weight decrease f 0.39 g + 0.32 ($D) (n = 6), which means a ttal weight decrease f 6.9% thrugh the incubatin perid. Thus, incubatin des nt imply a serius physical taxatin upn the males. PREDATION Predatin n adult birds was never recrded. During incubatin, hwever, there was severe but highly variable predatin n eggs. Table 3 indicates that the predatin n nests (calculat- ed accrding t May field 1975) varied between 22% and 67% during the years 1979-1981, with an average f 48%. Predatin n chicks ccurs but culd nt be quantified. DISCUSSION The breeding schedule f the dtterel n Hardangervidda is schematically summarized TABLE 2. Percentage f daylight time (0400-2300) spent feeding by dtterel n Hardangervidda. X 2 test f Ttal Number f Number f hmgeneity sample Percentage sampling different between sampling size f time Perid Sex perids pairs perids (rain) feeding Arrival 20 5 X2 9 = 4.89 942 89.4 (17-20 May) 20 5 X2 9 = 5.67 942 88.4 Pre-laying (I) 9 4 X28 = 9.77 731 58.7 (29 May-6 June) 9 4 x 8 = 11.55 770 57.1 Pre-laying (II) 6 3 x 5 = 9.19 382 53.7 (2-6 July) 6 3 x = 1.61 363 54.5
Octber 1984] Dtterel Breeding System 845 TABLE 3. Predatin n dtterel nests in different years n Hardangervidda. Year 1979 1980 1981 Number f nests 7 12 19 Number destryed 2 8 3 Percentage predatin 29 67 16 Percentage predatin estimated accrding t Mayfield (1975) 56 67 22 in Fig. 10. The mst striking difference frm the ther shrebird species in the area [Greater Glden-Plver (Pluvialis apricaria), Dunlin (Calidris alpina), Purple Sandpiper (Calidris maritima), Temminck's Stint ( Calidris temminckii)] is that the egg-laying seasn is 30% lnger in dtterel (Byrkjedal 1978, Breiehagen pers. cmm., pets. bs.). Frm indirect evidence, we find this mst likely t be explained by a high incidence f plyandry in this dtterel ppulatin. Cases f plyandry have previusly been dcumented in ther dtterel ppulatins (Franke 1953, Pulliainen 1971, Nethersle-Thmpsn 1973), but the species was regarded as mngamus by Jenni (1974) and Wittenberger (1979). There are several aspects f dtterel that strngly favr plyandry. (1) The females are emancipated nce the eggs are laid, and the males take n all parental duties (the few cases f females sharing incubatin with males are cmmented upn belw). (2) Unaided incubatin seems t have a minr influence n the males' physical cnditin. (3) Fd [mainly larvae and adult Tipulidae, Cleptera, and Mi- tpus mri (Byrkjedal unpubl. data)] is available ver a large part f the the summer (Hfsvang 1974, Byrkjedal 1980b), thus facilitating a lng breeding seasn. (4) Males are available thrughut the seasn because f nest predatin, which may be severe (n average 48%). (5) Eggs are relatively small, and a full clutch cnsists f nly three eggs, s the cst f egg prductin shuld be relatively lw. The indicatins that plyandry des ccur frequently are summarized as fllws. (a) The females apparently seek new mates during a large part f the seasn by the display flights. These flights are nt cnsidered t be territrial flights, because they appear nt t be cnfined t specific areas. Rather, the females seem t make advertisement flights ver large areas, in a similar manner as the male Eurasian Wdcck (Sclpax rusticla) (Hirns 1980). The lack f subsequent sightings f clr-banded females als indicates a lw within-seasn site tenacity. Mrever, the flights start t appear in the ppulatin after the cmpletin f the first nests, nt in cnnectin with the earlier dispersal dwnhill t the nesting sites, as wuld be expected if the flights were territrial demarcatins. Observed encunters between dis- playing and ther birds have nly been seen at sme distance, but, instead f resulting in a chase, the encunters ended with bth birds sn alighting tgether. These cases lked mre like encunters between displaying females and unattached males than like thse be- tween territrial ppnents. Because the flight starts after the earliest clutches in the ppula- I I I... I / Female flight display sflcking. I MAY Fig. 10. latching i i I J u NE JULY AUGUST Summary f the breeding schedule f the dtterel at Hardangervidda.
846 KXLXS AND BYRKJEDAL [Auk, Vl. 101 tin have been cmpleted, it is likely that at least sme f the displaying females have already laid a clutch. Cnsidering the lw site tenacity and the high frequency f displays it is likely that many different females are invlved. (b) As female flcks d nt start t frm befre the end f the egg-laying seasn, it is likely that mst f the females are invlved in seeking mates and laying eggs ver mst f the egg-laying seasn. (c) That there is frequent aggressin between members f grups with excess females strngly indicates that cmpetitin between females fr males ccurs thrughut the seasn and seems, indeed, t increase tward the end f the seasn in accrdance with a decreasing number f available males [cf. Byrkjedal (1980a) n seasnality f nest predatin] and a pssible increase in the number f emancipated females. (d) We have shwn that females lay tw clutches in ne seasn and that males accept new clutches after nest predatin. These may, admittedly, be cases f replacement clutches (i.e. a secnd nesting by the same pair). As the emancipatin f females fllws immediately after clutch cmpletin, hwever, and as the emancipated females seem t ram far and wide, we find it unlikely that they cme int cntact with their frmer mates fr a secnd (replacement) clutch. The system utlined abve is in cntrast t that seen in Sctland. It seems that female advertisement flights are less frequent there than n Hardangervidda, and mngamy is cnsidered t be the rule (Nethersle-Thmpsn 1973). In Sctland the dtterel is als reprted t be territrial; nt nly are there pre-laying hstilities, but incubating males drive ff ther dtterels frm the vicinity arund the nest, and the nests are usually spaced at least 200-250 m apart (Nethersle-Thmpsn 1973). On Hardangervidda, we have never bserved such behavir by incubating dtterel males. In fact, n tw ccasins, we saw an incubating dtterel (tw different nests) squat flat in the presence f ther dtterels a few meters frm the nest. This was als seen by Wilkie (1981) at a nest n Hardangervidda. Prbably in accrdance with the lack f territries, spacing f nests n Hardangervidda seems t be less develped than in Sctland. The pre-laying fights seen n Hardangervidda are nt cnfined t specific territry bundaries, and they are elicited nly at shrt distances. Thus, we cnsider them as having t d with mate guarding rather than territrial defense. Female participatin in incubatin has als been reprted by Hild n (1966), Pulliainen (1970), and Nethersle-Thmpsn (1973). The ccurrence f this phenmenn nly in the late clutches indicates that, as the prspects fr fur- ther matings and successfully raising brds decrease late in the seasn, females may increase investments in late clutches by taking part in the incubatin instead f cntinuing t seek mates. Female participatin in brd rearing has been bserved nce, a case in which a male and a female were seen t divide a brd between them (D.B.A. and P.S. Thmpsn in Cramp and Simmns 1983). Several instances f females shwing up near males with chicks have been interpreted as the returning f females t their mates after the chicks have hatched (Franke 1953, Rittinghaus 1962, Pulliainen 1970, Nethersle-Thmpsn 1973). Such females were ften met with aggressin frm males (Cramp and Simmns 1983), and we rather assume they were strange females prspecting fr mates. Apparently the breeding system f the dtterel may differ between ppulatins. A cmparative study f its breeding eclgy in Nrway and Sctland, invlving large-scale clr banding, wuld hld great prmise. ACKNOWLEDGMENTS Financial supprt was received by J.A.K. frm the University f Bergen and by I.B. frm L. Meltzers Hysklefnd. We express sincere thanks t S.-A. Bengtsn fr his interest and advice during all stages f this study and t N. Davies, D. Thmpsn, S. T. Maxsn, and tw annymus reviewers fr useful cmments n the manuscript. We als kindly thank A. Henden, A. Hidand, and S. Kt lt s fr their assistance during parts f the fieldwrk. LITERATURE CITED ALTMAN, J. 1974. Observatinal study f behavir: sampling methds. Behaviur 49: 227-267. BLANKEN, G. DEN, G. C. BOERE, & E. NIEBOER. 1981. Primary mult f the Redshank Tringa ttanus in the Dutch Waddenzee studied by cllecting shed feathers, a test. Ardea 69: 115-124. BYRKJEDAL, I. 1978. Altitudal differences in breeding schedules f Glden Plvers Pluvialis apricaria in Suth Nrway. Sterna 17: 1-20.
Octber 1984] Dtterel Breeding System 847 ß 1980a. Nest predatin in relatin t snwcver--a pssible factr influencing the start f breeding in shrebirds. Ornis Scandin vica II: 249-252. ß 1980b. Summer fd f the Glden Plver Pluvialis apricaria at Hardangervidda, suthern Nrway. Hlarctic Ecl. 3: 40-49. CP mp, S., & K. E. L. SimmONS (Eds.). 1983. The birds f the Western Palearctic, vl. 3. Oxfrd, Oxfrd Univ. Press. EISENBERG, J. F. 1966. The scial rganizatins f mammals. Handbuch Zl. Berlin 8: 1-92. FKANKE, H. 1953. Zur Bilgie des Mrnellregenpfeifers. Phtg..r. Frschung 5: 200-206. HILI f N, O. 1966. Uber die Brutbeteiligung der Geschlechter beim Mrnellregenpfeifer, Charadrius mrinellus L. Ornis Fennica 43: 16-19. HIRON$, G. 1980. The significance f rding by Wdcck Sclpax rusticla: an alternative explanatin based n bservatins f marked birds. Ibis 122: 350-354. HOFSVANG, t. 1974. Tipulidae (Diptera) frm a high muntain area. Finse, suth Nrway. Nrwegian J. Entml. 21: I-4. JENNI, D. A. 1974. Evlutin f plyandry in birds. Amer. Zl. 14: 129-144. K. L.I S, J. A., & I. BYRKJEDAL. 1981. The status f breeding waders Charadrii in Nrway including Svalbard. Prc. 2nd Nrdic Cngr. Ornithl. 1979: 57-74. MAYFIELD, H. F. 1975. Suggestins fr calculating nest success. Wilsn Bull. 87: 456-466. NETHERSOLE-THMPSON, D. 1973ß TheDtterel. Lndn, Cllinsß PARMELEE, D. F., & g. B. PAYNEß 1973. On multiple brds and the breeding strategy f arctic Sanderlingsß Ibis 115: 218-226. PULLIAINEN, E. 1970. On the breeding bilgy f the Dtterel Charadrius mrinellus. Ornis Fennica 47: 69-73ß ß 1971. Breeding behavir f the Dtterel Charadrius mrinellus. V irri6 Subarctic Res. Sta. Rept. 24. RITTINGHAU$, H. 1962. Untersuchungen zur Bilgie des Mrnellregenpfeifers (Eudrmias mrinellus L.) in Schwedisch Lappland. Z. Tierpsychl. 19: 539-558ß SKARTVEIT, A., B. G. RYDt N, & L. K RENLAMPI. 1975. Climate and hydrlgy f sme Fennscandian tundra ecsystems. Pp. 41-53 in Fennscandian tundra ecsystems, Part I. Plant and micrrganisms (F. E. Wieglaski, Ed.). New Yrk, Springer- Verlagß SNOW, D.W. 1967. A guide t mult in British birdsß B.T.O. Field Guide 1 I. Tring, Lutn. WILKIE, A. O. M. 1981. Incubatin rhythm and behaviur f a Dtterel Charadrius mrinellus nesting in Nrway. Ornis Fennica 58:11-20. WITTENBERGER, J. F. 1979. The evlutin f mating systems in birds and mammalsß Pp. 271-349 in Handbk f behaviral neurbilgy, vl. 3: Scial behavir and cmmunicatin (P. Marler and J. G. Vandenbergh, Eds.). New Yrk, Plenum Pressß