Antipredator Behavior and Breeding Success in Greater Golden-Plover and Eurasian Dotterel’

The Condor89:40-47 0 The Cooper Ornithological Society 1987

ANTIPREDATOR BEHAVIOR AND BREEDING SUCCESS IN GREATER GOLDEN-PLOVER AND EURASIAN DOTTEREL’

INGVAR BYRKTEDAL Museum of Zoology, Universityof Bergen,N-5000 Bergen,Norway

Abstract. Breeding successand antipredator behavior of Greater Golden-Plovers (Plu- vialis apricaria) and Eurasian Dotterels (Charadrius morinellus) were studied in Norway over seven summers in an area 1,200 to 1,350 m altitude. Behavior was recorded in a standardizedmanner on nest inspections,on approachingparent birds with chicks, and by observing reactions to overflying predators on scheduled observation bouts. Red foxes (Vulpes v&es), Common Ravens (Corvuscorax), and Mew Gulls (Larus canus) were the most important nest and chick predators in the area. Nest predation was calculated from exposure time. During incubation both species either sneaked away from the nest when approached by a human (golden-plovers at a much larger distance than dotterels) or sat tightly and flushed at a short distancegiving distraction display. “Sneaking” had a positive effect on nest survival, and ground distraction displays had a better effect on nest survival than flight distraction displays. After hatching, golden-plover parents exposed themselves to an approachinghuman at several hundred meters distance by loud alarm calls and by encounteringthe intruder, whereasdotterels kept unobtrusive until approachedto about 40 m, and upon further approach finally gave distraction displays on the ground. Avian predators at a longer distance (~300 m) from nest or chicks at most arousedalertness, while at close quarters (~50 m) they induced golden-plovers to squat flat, while dotterels exposed themselves by “tail-flagging.” Nest loss was greater for golden-plovers (78%) than for dotterels (47%), while chick loss was greater for dotterels (65%) than for golden-plovers(28%). The difference in nesting successand antipredator behaviors is discussedin terms of greater detectability in golden-plovers than dotterels, and of biparental (golden-plover) versus uniparental (dotterel) care. Key words: Distraction displays;detectability; nest and chick losses;plovers: Norway.

INTRODUCTION with the resultant behaviors often boldly conspicuous. By contrast, uniparental systems should The nests and chicks of ground-nesting birds are involve selection of less bold and more cryptic particularly vulnerable to predation (Armstrong behavior. 1954, Lack 1968). Through selection, such birds I studied antipredator behaviors and the im- have evolved adaptations favoring concealment pacts of predation on the nests and chicks of and/or certain behavioral responses to the pred- biparental Greater Golden-Plovers (Pluvialis ator. The nature of the latter (whether a bird upricuriu) and uniparental Eurasian Dotterels hunting visually or a mammal hunting by scent) (Charadrius morinellus) breeding sympatrically often elicits very different antipredator strategies. on a mountain plateau in southern Norway. As Many shorebirds nesting in vegetative cover, e.g., both specieswere studiedcontemporaneously and snipes, sit tightly, while e.g., plovers nesting on in the same area, they were exposedto the same open ground often leave their nest early in the predation pressure.I primarily discussto which presence of a predator (Gochfeld 1984), implying degree their antipredator responses are influ- that decision rules for response distances and enced (1) by detectability, and (2) by their bi- types of reactions strongly depend on detectabili- parental and uniparental breeding systems. ty. In biparental breeding systems, certain anti- STUDY AREA AND METHODS predator adaptions (like standing guard or driv- ing off predators by mobbing) are enhanced The study site was on Hardangervidda, Norway through the cooperative efforts of both parents, (60”23’N, 07”38’E) in the middle alpine zone at about 1,200 to 1,350 m above sea level. Work was conducted during the summers of 1977 to ’ ’ Received 13 November 1985. Final acceptance 1 1981, 1984, and 1985. For additional details July 1986. concerning the site, see K&las and Byrkjedal

[401 PREDATOR AVOIDANCE 4 1

DOTTEREL (17 nests, 31 approaches)

* * * *

n GOLDEN-PLOVER (20 nests, LSapproaches)

123656 BEHAVIOR FIGURE 2. Frequenciesof distractiondisplays (see Fig. 1) given in responseto the observer.Asterisks indicatesignificant differences (*P < 0.01, **P < 0.001) 6 betweenthe species(x*-tests). FIGURE 1. Classificationof distractiondisplays given by birds flushedfrom the nest. 1, weaklyimpeded events and to use Mayfield’s (1975) original flight;2, stronglyimpeded flight; 3, rodentrun; 4, mo- method for testing differencesbetween nest sur- bile injury feigning;5, stationaryinjury feigning;6, vival rates. aggressivedistraction display. Motor patternsof 1, 2, and 3 were highly stereotypic,while 4 and 5 showed After leaving the nestgolden-plover chickswere somevariation (cf. illustrationsin Simmons1955). far more difficult to relocate than dotterel chicks. Thus, data on complete brood size in golden- (1984). The most important predatorsin the area ploverswere only obtained around fledging,while were the Common Raven (Corvus corax), Mew several unfledged dotterel broods were inspected Gull (Larus canus), and Red Fox (Vulpes vulpes) more than once. (Byrkjedal 1980). When flushing birds from nests or encounter- Portions of the study area were searchedsys- ing parents with broods, I considered myself as tematically (almost every day, and usually by two a simulation of a ground predator, and recorded persons) for nests or chicks. Usually nests were all antipredator behavior (flushing distancesand found by flushing the incubating bird, or by ob- types of reactions). Distraction displays (Fig. 1) serving a bird returning to its nest. In 198 1, a were recorded over defined sequences:either up trained pointing dog was used to locate some of to the moment the bird disappeared or stood the nests. quietly at 100 to 200 m distance, or, (for some I inspected nests at intervals to follow nesting dotterels)until the first “reentrapment” occurred success.Nests showing clear signs of predation (term used by Gochfeld [ 19841 for caseswhere (eggshells,etc.) and nests that became empty at a displaying bird returns and starts distracting times when hatching was not expected were once more if not followed by the predator on the counted as robbed. I excluded a few nests for first distraction attempt). In 1985 I placed a which it was uncertain whether the eggs had stuffed fox 10 m from five golden-plover nests, hatched or been robbed. Since only a few nests three dotterel nests and near five golden-plover were monitored from egg laying, I calculated broods, and studied the behavior of the birds nesting successfrom exposure time (Mayfield from a long distance for 15 min. The birds re- 1975). As there is a marked diurnal rhythm in acted in the same way as they did in the presence the feeding time of the predators(birds are active of a human. Behavioral responsesto avian pred- during the day and foxes at night) I considered ators overhead were recordedduring observation it justifiable to regard “nest days” as discrete bouts, both for birds on nests and with broods. 42 INGVAR BYRKJEDAL

TABLE 1. Responsesto human approachingnest.

Flushingdistance (m) O-5 6-10 1l-15 16-20 21-50 51-100 >I00

Golden-plover (46 nests, 111 approaches) Distraction display given 39 23 4 2 2 - 4 Sneakingaway, no distraction ------37 Dotterel (37 nests, 90 approaches) Distraction display given 41 ------Sneakingaway, no distraction - 5 4 9 18 5 8

Since I could not obtain all types of infor- nificantly more of the golden-plover nests than mation from all nests, sample sizes vary in dif- dotterel nests,while significantly more ofthe dot- ferent calculations. terels performed “Mobile Injury Feigning” and “Stationary Injury Feigning” than did golden- RESULTS plovers (Fig. 2). When approachedby a human, sneaking away RESPONSES TO GROUND PREDATORS (MAN) from the nest was seen at least once in 37% of Golden-plovers sneaked away from their nests 46 golden-plover nests and 54% of 37 dotterel significantly more often than dotterels when ap- nests. Such nests survived significantly better in proached by an observer further than 100 m from both species,compared to nests where sneaking the nest (x2 = 58.657, P -c 0.001) while dotterels never was observed (Table 2). Nest survival and let the observer approach closer than 5 m before distraction intensity were positively related in flushing significantly more often than golden- both species,as nestswhere ground displays were plovers (x2 = 27.876, P < 0.001, Table 1). All given survived better than nests at which only dotterels that flushed from the nest at short dis- flight displays were recorded. However, for dot- tances (0 to 5 m) performed distraction displays, terels but not for golden-plovers, survival was while none of those leaving the nest at longer significantly better in nests where stationary dis- distances did so (Table 1). All golden-plovers plays were given than in nests with only mobile performed distraction displayswhen flushedfrom displays (Table 2). the nest from up to 50 m distance, and some did After the eggshad hatched, adult golden-plo- even when the observer was still 2 100 m away. vers were very conspicuous.They started to give “Strongly Impeded Flight” was recorded at sig- loud alarm calls on generally more than 200 m

TABLE 2. Nest survival in relation to manner of leaving nest when approachedby human.

Estimatednest survival (%) X’ P n Golden-plover Sitting1Sneaking away ’ 20.729.9 5.923 CO.02 27 Plight distraction 26.6 Ground distraction* 53.6 5.026 CO.005 20 Mobile distraction 32.5 Stationary distraction 54.1 1.509 n.s. 20

Dotterel Sneakingaway ’ 79.3 Sitting’ 51.1 8.234

PlightGround distraction* distraction” 88.32.4 121.49

’ “Sneaking” includesall nestswhere this behaviorwas observed at leastonce; in the category“sitting” sneakingwas never observed and the birds alwaysgave distractiondisplays when Rushedfrom nest. z Including all the “sitters” and someof the “sneakers.”Flight distraction= 1and 2, Fig. 2; grounddistraction = 3-6; mobile distraction= 14, stationarydistraction = 5-6. PREDATOR AVOIDANCE 43

TABLE 3. Responsesto approachinghuman after hatching.

Golden-plover Singlemales Males in pairs Femalesin pairs Dotterel males (n = 6) (n = 19) (n = 21) (n= II) First response Loud alarm call 6 19 21 - Approaching’ - - - Retreating2 - - - :, Distraction display - - - 4 Reaction distance, meters (52,&SD) 288 f 128 343 ? 162 236 ? 138 40 + 32 Final response Taking flight 6 18 20 - Distraction display - 1 1 11 Reaction distance, meters (3, +SD)3 41 + 9 38? 11 54 + 4 16 * 9 Sitting alert on stone or tussockwhen approached 2 19 13 2 I Golden-plover: After giving alarm call, 8 of the pared males, I of the singlemales, and 5 of the femalesapproached the observer. 2Golden-plover: A+ giving alarm al& 1 of the pairedmales, 4 of the singlemales, and 8 of the femalesretreated from the approachingobserver. 3Golden-plover: Distance for taking Right;distraction display was releasedat 4 m (both matessimultaneously). distance, often encountered the observer, stood some hundred meters from nest or chicks (Table well exposed on top of stones or tussocks,and 4). When aerial predators passednests or chicks finally retreated by taking flight when on average lessthan 50 m away, golden-plovers squatted flat 38 to 45 m from the observer (Table 3). In con- (in the caseof ravens) or showedalertness (in the trast, dotterels remained silent (to the observer’s caseof gulls), whereasdotterels performed “tail- ear) and did not react until the observer was on flagging”(Fig. 3) a distancefrom the nest or chicks average 40 m away, by retreating, approaching, (for both ravens and gulls). In this display, the or performing distraction displays. When stand- attending bird quickly ran 10 to 15 m from the ing, they were partly hidden by stones or tus- nest or chicks and then stopped abruptly with socks.All dotterels ended up in distraction dis- breast on the ground and the white undertail play at close range (types 3 to 7, Fig. l), while coverts exposed. I was able to study the preda- for golden-plovers this occurred once (both tor’s reaction to tail-flagging only twice; in both members of a pair) in 25 approaches. casesthe predator (gull) took no notice, and in Golden-plover males and females showed neither of the observed casesof tail-flagging did slightly different reactions (Table 3). Females the predator alight or start a search. started calling at shorter distances than their In one observed case of nest predation by a mates (t = 2.100, P < 0.025), took flight at longer raven, a golden-plover crouchedon the nest until distances(t = 1.985, P < O.OOS),and more often almost hit by the swooping raven. When squat- ran away upon the observer’s appearance (x2 = ting flat by overflying ravens in the posthatching 7.134, P < 0.001). In 17 of 18 casesthe male period golden-plovers were not covering the was the first to give an alarm call, the female in chicks, which were dispersed nearby, crouching only one case (Fisher’s Test, P -K 0.0001). Fe- motionless. males sat exposed on stones and tussocksless BREEDING SUCCESS often than their mates (Fisher’s Test, P = 0.0050). The average reaction distance of six single gold- The estimated total nest predation was 47.4% for en-plover males with chicks was intermediate dotterels over the average 25-day incubation pe- between those of males and females in pairs. riod (16 of 53 nestsrobbed over 630.5 nest days), and 78.2% in golden-plovers (27-day incubation RESPONSES TO AVIAN PREDATORS period, 27 of 5 1 nestsrobbed over 492 nest days). Both golden-plovers and dotterels showed only The difference is statistically significant (x2 = alertnessor no responseat all to a flying predator 44.595, P < 0.001). (Common Raven, Mew Gull) at a distance of Golden-plovers sitting on the nest were more 44 INGVAR BYRKJEDAL

TABLE 5. Estimated minimum brood loss from observed clutch sizes around fledging.

Numbers of chicks estimated hatched Ob- from % Numberof served these Chicks chicks broods broods’ lost

Golden-plover 19 8 26.2 27.5 Dotterel 9 7 25.8 65.1

LTaking into account predation rate on single eggs and hatchability.

predation on single eggs,and hatchability, a min- FIGURE 3. Tail-flagging by dotterel when the nest imum chick loss of 27.5% for golden-plovers and is overflown by an aerial predator. 65.1% for dotterels can be estimated (Table 5) from brood sizes at the age of fledging (30 days easily found by scent than dotterels, as the point- for golden-plovers, 26 days for dotterels, pers. ing dog used in 198 1 found significantly more of observ.). The amount of chick loss caused by the former (7 of 12 available golden-plover nests predation is unknown, but chicks of both species vs. 1 of 10 dotterel nests,Fisher ’s Test, P = 0.038). were found in Mew Gull pellets in the area (Byrk- (The dog responded and pointed only to nests jedal et al. 1986). with a bird.) Mean clutch sizes were 3.87 for the golden- Predators usually took whole clutches. The plover (55 c/4, 8 c/3), and 2.98 for the dotterel daily disappearancerates of single eggswere only (50 c/3, 1 c/2). From mean clutch sizes, hatch- 0.05% in the dotterel(1 of 159 eggs, 1,86 1.5 egg abilities and losses, 100 nests are estimated to days), and 0.46% in golden-plovers (8 of 187 produce about 50 fledged chicks in both species eggs, 1,859 eggdays). These rates are not statis- (Table 6). tically different (x2 = 0.3935). In golden-plovers 2 of 67 eggs(17 nests) were DISCUSSION infertile, as were 2 of 77 dotterel eggs(26 nests), The behaviors recorded during the incubation implying a hatchability of 97.0% and 97.4%, re- period concern males. Dotterel males usually in- spectively. Relocation of 16 dotterel broods in cubate alone (Kalas and Byrkjedal 1984) and their first and second week gave a daily disap- golden-plover males sit on the nest during day- pearance rate of 12% according to the Mayfield time for about 12 hr while their off-duty females (1975) method (21 chicks disappeared during are far away from the territory (Byrkjedal 1985). 175.7 chick days), clearly too high a figure for Thus, both speciesincubate in the absence of a the whole season as chick loss is likely to be warning mate, and should therefore be expected highest soon after hatching (Nethersole-Thomp- to have similar antipredator responsesin the in- son 1973). Taking into account mean clutch sizes, cubation period, assuming a similar detectability

TABLE 4. Responsesto overflying Mew Gulls and Common Ravens.

Predator 300 to 1,000 m away Predator

Incubation Golden-plover 4 1 - 5’ - 553 2 Dotterel 1 3 - - 8 526 4 Posthatching Golden-plover - 7 32 31 - 4,654 5 Dotterel - 1 - - 1 152 5

’ Common Ravens. 2 Mew Gulls. PREDATOR AVOIDANCE 45

d‘ D” Dl

PREDATORS’ DISTANCE (D) FROM NEST FIGURE 4. Suggestedrelationship between nest predationprobability and the predator’sdistance from the nest,based on detectabilitycurves for: a bird in the act of leavingthe nest without giving distractiondisplay (P,), a bird sittingon the nest (P,), an unattendednest (P.), and the reciprocalprobability (PJ for deflectinga predatorby displaywhen a bird is flushedfrom the nest.Further explanation: see Discussion.

for the two species.In the presenceof a ground a displaying bird, which should be negatively predator both specieseither leave the nest early, related to the distance to the bird. The proba- or they sit tightly and display when flushed from bility (Pd) for nest predation during distraction a short distance, but the reaction distances and display is (1 - P,). display intensities are different. They also differ Provided P, < P,, early departure from the in their reactions to avian predators. nest should pay before the predator has ap- Detectability is presumably a monotonically proached the distance D, from the nest. If the decreasing function of the distance from the predator is discovered at CD,, the bird should predator to the nest, as suggestedin Figure 4 (see remain tightly on the nest and not start perform- Burnham et al. 1980 for likely shape of detect- ing distraction displays until the predator ap- ability curves). The decision to leave the nest proaches D,. This explains the “bipolarity” in early or sit tightly should depend on the differ- the nest departure distance, commonly observed encesbetween detectability (and hence, the prob- in birds (Gochfeld 1984), and recorded in the ability (P) for nest predation) of a bird in the act present study. As the gundog did not find un- of leaving the nest (P,), of a bird sitting on the attended nests, the scent stimulus from the nest nest (PJ, and of an unattended nest (P,), and also is apparently chiefly from the sitting bird itself. on the probability (P,) that a predator will chase As early departure was found to be a more efficient responsethan merely sitting tightly, there TABLE 6. Estimatedreproductive success in 100 should be a strong selection for early departure. golden-plover and dotterel nests. However, egg chilling and a possible high P, to avian predators should select for sitting. D, Golden- pIOVer Dotterel should, therefore, be the optimal point for early departure. Number of eggslaid 387 298 Low detectability expectedly skewsthe curves Number of eggsafter nest predation 84.4 156.7 in Figure 4 to the left. This is supported by the Number of eggsafter partial present study, as the dotterel (lower detectability predation 75.1 154.6 to the gundog and lower recorded nest predation Number of eggshatching 72.8 150.5 than for golden-plover) had the shortestground- Number of fledglings 52.9 52.5 predator reaction distances of the two species, 46 INGVAR BYRKJEDAL both in early departure and when sitting tightly. ders the birds more conspicuous to avian nest For early departure to be a good option, the in- predators than merely early surreptitious depar- cubating bird must discover the predator at a ture, this strategyshould incur a risk if the birds sufficiently long distance, presumably enhanced are not able to distract or actively drive away by a flat topography. Ratcliffe (1976) noticed that avian predators. Such a strategy has been re- in Britain there were differencesbetween golden- ported for Black-bellied Plovers (Pluvialis squat- plover populations in their tendency to leave the arolu), which effectively “dive-bombs” avian nest early. predators (Parmelee et al. 1967, Flint and Kon- When a bird performs distraction display the dratjew 1977, Portenko 198 1). Neither ofthe two impression of its physical incapability varies with speciesin the present study were seen to drive the types of displays given. The present study away aerial nest predators. In the study area a indicates that displays along the ground (high number of Mew Gulls were almost constantly on degree of incapability) are more efficient than the wing and ravens were frequent. displays performed while flying away from the However, after hatching, the golden-plover nest. Provided the birds are able to meet the risk doespractice a highly conspicuous‘approach and to themselves from high incapability displays by scold’ behavior, while the dotterel still acts cryp- hyperalertness(Gochfeld 1984), the selection for tically in the presenceof humans (displaying only such displays should increase with decreasing at close range). Such behavior may be less risky flushing distance, especially as the difference be- after hatching as chicks are dispersed,unlike the tween P, and P, may decrease.This is supported eggs,that are confined to a fixed location all the by the present study, as the dotterel, which has time. The difference between the species’ behav- the shortestflushing distance of the two species, ior after hatching may reflect the differencesbe- also showedthe highest frequency of ground dis- tween biparental and uniparental care. Cooper- plays. Such displays seemedto have greatereffect ation between the mates is apparently important on nest survival for the dotterel than for the gold- in the active antipredator behaviors of the Black- en-plover. bellied Plovers (Flint and Kondratjew 1977). Ad- The detectability to visually oriented (avian) mittedly, single golden-plover males with chicks predators is obviously different from detectabil- did not respond fundamentally differently from ity to predatorshunting by scent. In caseof aerial golden-plover pairs, and Purple Sandpipers (Cul- predators either P, is skewed far to the right rel- idris maritima) breeding in the same area utilize ative to that for ground predators, or P, 2 P,, the approach and scold behavior after hatching since early departure is not practiced by the stud- in spite of having uniparental chick care (pers. ied speciesin the presence of avian predators. observ.). However, both these speciesenjoy fe- For dotterelsP, for avian predatorsmay be higher male participation in incubating, which enables than for golden-plovers, as dotterels leave the extensive feeding during the incubation period. nest and tail-flag when a predator flies overhead, Golden-plover males improve their body con- while golden-plovers squat flat. A reaction to dition during incubation, probably enabling them flying predators similar to the tail-flagging of the to absorb high energetic costs during chick care dotterel, has been seen in incubating Ringed (for effect on vigilance, see Byrkjedal 1985), Plover (Charudrius hiaticulu) (Vaughan 1980), whereas dotterel males lose weight (Kfllas and which breeds in very open habitat, while squat- Byrkjedal 1984). Thus, constraints from unipa- ting flat on the nest is considered the most com- rental incubation cannot be ruled out as a factor mon responseto avian predators by shorebirds favoring cryptic chick-tending behavior. Also the that do not attack (Gochfeld 1984). Both species high estimated chick loss for dotterels suggestsa showed the same response to avian predators cost of being uniparental. after hatching as they did before hatching. To sum up, evidence suggeststhat the birds’ Several shorebirds approach a ground preda- reaction distances and display patterns in the tor after early departure and perform distraction, presence of a predator depend on detectability. scolding, or mobbing (Gochfeld 1984). In doing Those display types which signal high physical so they may display at the optimal display dis- incapability are the most efficient ones. Early sur- tance (P, independent of the predator’s distance reptitious departure is apparently a more efficient from the nest), when the predator is still beyond reaction to ground predators than merely sitting the distance D,. However, as such behavior ren- tightly, but may involve the cost of increased PREDATOR AVOIDANCE 47 detectability to visual predators.Uniparental care FLR*TT,V. E., AND A. J. KONDRATJEW.1977. Mate- may favor cryptic behavior. rialien zur Bioloaie des Kiebitzreaenofeifers U’lu- vialis squatarola-L.).Beitr. Vogelkd.*23:265-277. ACKNOWLEDGMENTS GOCHFELD,M. 1984. Antipredator behavior: Ag- gressiveand distraction displays of shorebirds,p. The nest-searchingwas mostly done jointly with _I.A. 289-377. In J. Burgerand B. Olla [eds.],Behavior K&l&s. I thank him for pleasant field companionship of marine animals, Vol. 5. Shorebirds: breeding and for information on antipredatorbehavior observed behavior and populations. Plenum Press, New while he studied incubation rhythms in dotterels. I am York. very grateful to M. Trebbi for allowing me use of his m, J. A., ANDI. BYRKJEDAL.1984. Breedingchro- Brittany Spaniel in 1981. I would also like to thank E. nologyand mating systemof the EurasianDotterel Pierce and two anonymous reviewers for useful com- (Charadrius morinellus).Auk 101:838-847. ments on the manuscript. The study was financially LACK, D. 1968. Ecological adaptations for breeding supportedby L. Meltzers Hoyskolefond. in birds. Methuen, London. MAYL~ELD,H. 1975. Suggestionsfor calculatingnest LITERATURE CITED success.Wilson Bull. 87~456-466. NETHERSOLE-THOMPSON,D. 1973. The Dotterel. Col- ARMSTRONG,E. A. 1954. The ecology of distraction lins, London. display. Anim. Behav. 2: 121-135. PARMELEE,D. F., H. A. STEPHENS,AND R. H. SCHMIDT. BURNHAM,K. P., D. R. ANDERSON,AND J. L. LAAKE. 1967. The birds of southeasternVictoria Island 1980. Estimation of density from line transect and adjacent small islands. Nat. Mus. Can. Bull. sampling of biological populations. Wildl. Mono- 222. gr. 72. PORTENKO,L. A. 1981. Birds of the Chukchi Pen- BYRKJEDAL,I. 1980. Nest predation in relation to insula and Wrangel Island. Vol. 1. Amerind Publ. snow-cover-a possiblefactor influencing the start Co., New Delhi. of breeding in shorebirds. Ornis Stand. 11:249- RATCLI~, D. A. 1976. Observationson the breeding 252. of the Golden Plover in Great Britain. Bird Study BYRKJEDAL,I. 1985. Time-activity budget for breed- 23:63-l 16. ing Greater Golden-Plovers in Norwegian moun- SIMMONS,K.E.L. 1955. The nature of the predator- tains. Wilson Bull. 97:486-501. reactionsof waders towards humans; with special BYRKTEDAL,I., J. A. KAtis, AND A. H&AND. 1986. reference to the role of the aggressive-,escape-, Summer food of a mountain population of Com- and brooding-drives. Behaviour 8: 130-113. mon Gull Larus canus. Fauna Norv.. Ser. C. Cin- VAUGHAN,R. 1980. Plovers. T. Dalton, Lavenham. clus 9: 17-24.