Antipredator Behavior and Breeding Success in Greater Golden-Plover and Eurasian Dotterel’
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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 pred- ators 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 dot- terels (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 uni- parental (dotterel) care. Key words: Distraction displays;detectability; nest and chick losses;plovers: Norway. INTRODUCTION with the resultant behaviors often boldly con- spicuous. 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 giv- en 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 <O.OOl 26 PlightGround distraction* distraction” 88.32.4 121.49 <O.OOl 17 Mobile distraction* 58.2 Stationary distraction* 81.6 3.918 CO.05 17 ’ “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.