Wilson Bull, 115(2), 2003, pp. 176-185 DIURNAL AND NOCTURNAL BEHAVIOR OF BREEDING AMERICAN AVOCETS MATTHEW JOHNSON,’ 2.4 jON P. BECKMANN,’^ AND LEWIS W. ORING’ — ABSTRACT. We studiednocturnalanddiurnalbehaviorofbreedingAmericanAvocets(Recurvirostraamer- icana) at the Jay Dow, Sr. Wetlands in the northwestern Great Basin, USA. Seven-day observationperiods were centered on two full moons when ambient light was maximal and auxiliary lighting unnecessary. We recorded avocet density, habitat use, interbird distances, and behavior three times daily (beginning at 07:00, 15:00, 23: 00 PST) for 14 days. We calculated the mean proportion ofindividuals within flocks engaged in four behavior classes (foraging, copulating, agonistic, other). Foraging birds were further subdivided by technique (pecking, dunking, scything). Avocetscopulatedwithsimilarfrequenciesduringthemorning,afternoon,andnight.Avocets were more aggressive and closely spaced at night than during day. The full repertoire ofbehaviors seen during daylight also occurred at night, though frequencies ofparticularbehaviors, flock location, and interbirddistances varied among morning, afternoon, and nighttime observations. The role of nocturnal reproductive behavior should be assessed in species generally perceived as being diurnal. Received 12 January 2003, accepted 20 March 2003. Nocturnal foraging throughout the annual ically and physiologically adapted to noctur- cycle is common among coastal shorebirds in nal activity as their eyes contain a higher pro- North and South America, Africa, and Europe portion of rods in the retina compared to di- (Goss-Custard 1969, McNeil and Robert urnal species, and retinal sensitivity is higher 1988, Zwarts et al. 1990, McNeil 1991, Evans among birds that forage visually at night com- and Harris 1994, Staine and Burger 1994), yet pared to those that use tactile techniques (Tan- there is relatively little understanding of the sley and Erichsen 1985; Rojas De Azuaje et latitudinal and seasonal variation in nocturnal al. 1993; Rojas et al. 1999a, 1999b; McNeil behavior within and among shorebird species. et al. 1999). Researchers have proposed that tactile forag- Although several studies have examined ers should be relatively less affected by dark- nocturnal foraging at coastal locations, there ness than visual foragers (Vader 1964, Goss- are few studies of shorebird nocturnal behav- Custard 1969, Evans 1976, Dugan 1981), yet ior on the breeding grounds and at inland lo- plovers (Charadriidae) are primarily visual cations. During the breeding season, Red-wat- foragers that commonly forage at night (Pien- tled Lapwings {Vanellus indicus) and Stone- kowski 1983). The relatively large eye in re- curlews (Biirhinus oedicnemus) are vocal pri- lation to head size of plovers may enhance marily at night (Bannerman 1959), and some visual detection ofprey (Evans 1976), yet sev- species display or call from dusk into the eral smaller-eyed sandpipers (Scolopacidae) night (Scolopax spp.: Sheldon 1961, Krohn also forage visually at night, including Com- 1971, Stribling and Doerr 1985; Gallinago mon Redshanks {Tringa totcinus\ Goss-Cus- spp.: Lemnell 1978). Breeding Common tard 1969), Semipalmated Sandpipers (Cali- Ringed Plovers {Charadrius hiaticula), and dris pusillcv, Evans 1979), and Whimbrels Piping Plovers (C. melodus) forage at night {Nitmenius phaeopiis\ McNeil and Rompre (Pienkowski 1983, Staine and Burger 1994), 1995). Nocturnal bird species are morpholog- and the role each sex plays in nocturnal in- cubation also has been examined for several ' Dept, of Environmental and Resource Sciences, species (Laven 1940, Mundahl 1982, Warriner Univ. of Nevada, Reno, NV 89512, USA. et al. 1986, Staine and Burger 1994, Thibault 2Current address: Dept, of Biology, Virginia Poly- and McNeil 1995a, Warnock and Oring 1996). technic Inst, and State Univ., Blacksburg, VA 24061, American (Recurxirostra americana) and Pied USA. avocets {R. avosetta) forage diurnally and ^Current address: Eastern Idaho Eield Office, Wild- nocturnally throughout the annual cycle life Conservation Society, Rigby, ID 83442, USA. Corresponding author; e-mail: (Evans and Harris 1994, Dodd and Colwell [email protected] 1996, Hotker 1999, Johnson et al. 2002), and 176 Johnson et al. • AMERICAN AVOCET BEHAVIOR 177 TABLE I. Akaike Information Criteria (AIC) for candidate model.s used to examine variation in American Avocet behavior during the daily cycle at Jay Dow, Sr. Wetlands, Las.sen County, California, 2001 Numberof Model^ parameters AAIC^’ AICweighC Overall behavior {T, L, D, W, L X D} 5 0.0 0.865 {T, L, D, W, T X L, T X D, L X D} 7 3.7 0.135 {T, ES, L, D, EL, W, S, I, dist, inter} 23 35.1 <0.001 Habitat use {T, L, ES, A, T X L) 5 0.0 0.932 {T, ES, L, E, A, T X FS, T X L} 8 5.9 0.050 {T, FS, L, F, A, 5, T X FS, T X L, FS X L) 9 7.8 0.019 Interbird distance {T, FS, L, D, EL, T X L, L X D) 7 0.0 0.999 {T, FS, L, D, EL, inter) 15 15.2 0.001 {T, FS, L, D, EL, M, A, C, F, W, S, I, inter} 22 29.0 <0.001 Foraging technique {T, FS, L, D, EL, W, 1, T X EL, L X D} 9 0.0 0.873 {T, FS, L, D, EL, W, 1, T X EL, L X D, T X D, FS X L} 11 3.9 0.127 {T, FS, L, D, EL, W, 1, inter} 17 15.5 <0.001 for^agTin=g,trMeat=menptro(pmorotrinoinngse=lf0m7a:i0n0t,eanfatnecren,ooCn== 1p3r:o0p0o,rtniiognhtco=pu2l3a:t0i0n)g,,FAS==fplroocpkorstiizeo,nLag=onilsotciact,ioWn,D==prdoaptoer,tEioLn=ineoarpleyn/lawtaetesre,asSon,=Fp=ropporrotpioorntioonn s5,ho6r-e,10I,=11p-r2o0p,or>t2io0nmo)n,iisnltaenrds=, a1ll=twporo-pwoarytiionnteorfacbtiirodnss.<1 mapart,5 = proportionofbirds 1-5 mapart,dist = allinterbirddistanceclasses(<1, 1- AAICistherankofeachmodelbyrescalingthemodelwithaminimumAICvaluetozero(AAIC = AlCj - AlCmin). AICweightsarethelikelihoodofthemodelgiventhedata(Akaikeweights). several shorebird species, including the Amer- JDW is a 540-ha constructed wetland contain- ican Avocet, copulate at night (Johnson et al. ing 16 bodies of water at the southern end of 2002). Honey Lake, Lassen County, California. JDW Knowledge of nocturnal behavior is essen- includes a seep draining to Honey Lake, a nat- tial for understanding both ecology and ener- ural playa lake, and 14 constructed ponds. getics, yet current understanding of shorebird With the exception of the seep, water was nocturnal behavior is limited. Shorebird hab- maintained at a constant level from March to itat use and foraging technique varies during July. Honey Lake Basin (23,000 ha) is char- the daily cycle (Rompre and McNeil 1995, acterized by agricultural production and by Robert et al. 1989). Nocturnality also appears Great Basin desert scrub vegetation on gently to affect energy balance (Pienkowski 1983) sloping to nearly level alluvial fans, flood- and, potentially, reproductive strategy (John- plain, and basin floor. Common vegetation at son et al. 2002). Recent technological advanc- JDW included sagebrush {Artemisia tridenta- es in night vision equipment facilitate the ta), saltbrush (Atriplex spinosa), greasewood study ofnocturnal behavior, permitting a more {Sarcobatus vermiculatus), rabbitbrush {Chry- thorough approach to behavioral ecology and sothamnus spp.), saltgrass {Distichlis spicata), allowing more accurate assessment of energy rush {Juncus spp.), and cattail (Typha latifol- budgets, space use, and social interactions. ia). Avocets arrive at JDW during late March The aim of this study was to describe the ex- and initiate clutches from the end of April tent of nocturnality among American Avocets through the beginning of June (Robinson and breeding at an inland location. Oring 1997). — Observations. During 2001, we centered METHODS 7-day observation periods on two full moons — Study area. We studied American Avocet (3-10 May and 2-8 June) when ambient light behavior at the Jay Dow, Sr. Wetlands (JDW; was maximal and auxiliary lighting unneces- 40° 07' N, 120° 14' W, elevation 1,220 m). sary. We used a hand-held generation III night 1 178 THE WILSON BULLETIN • Vol 115, No. 2, June 2003 TABLE 2. Multivariate analysis of variance for time ofday (07:00, 13:00, 23:00) and covariate effects on American Avocet behavior at Jay Dow, Sr. Wetlands, Lassen County, California, 2001. Degreesoffreedom Wilk’s Factor Numerator Denominator lambda F p Overall behavior Time ofday 8 210.00 0.278 23.52 <0.001 Date 4 105.00 0.679 12.40 <0.001 Location 28 380.01 0.434 3.54 <0.001 Proportion birds in open water 4 105.00 0.770 7.84 <0.001 Date X location 24 367.51 0.663 1.92 0.007 Habitat use Time ofday 6 200.00 0.691 6.77 <0.001 Location 21 287.70 0.199 10.37 <0.001 Flock size 3 100.00 0.934 1.62 0.189 Proportion birds agonistic 3 100.00 0.954 1.61 0.192 Time ofday X location 36 296.19 0.568 1.73 0.008 Interbird distance Time ofday 10 182.00 0.328 13.59 <0.001 Date 5 91.00 0.719 7.12 <0.001 Month 5 91.00 0.744 6.25 <0.001 Location 35 385.23 0.630 1.28 0.139 Flock size 5 91.00 0.728 6.79 <0.001 Location X time ofday 60 429.90 0.644 0.70 0.952 Location X date 30 366.00 0.570 1.84 0.005 Foraging technique Time ofday 6 202.00 0.749 5.24 <0.001 Date 3 101.00 0.799 8.47 <0.001 Month 3 101.00 0.789 8.98 <0.001 Location 21 290.57 0.430 4.73 <0.001 Flock size 3 101.00 0.891 4.14 0.008 Proportion birds in open water 3 101.00 0.645 18.54 <0.001 Proportion birds <1 m apart 3 101.00 0.892 4.10 0.009 Time ofday X month 6 202.00 0.865 2.54 0.022 Location X date 18 286.16 0.717 1.98 0.01 vision scope with a 100-mm zoom lens to intraspecific encounters, and behavior class (NiteMate NAV-3, Litton) to observe avocet “other” included selfmaintenance, nestbuild- behavior at night. We established 43 obser- ing, and incubation. We further subdivided vation points that enabled total coverage of foraging birds by technique (pecking, dunk- JDW during diurnal and nocturnal surveys. ing, scything). Foraging classes corresponded We recorded avocet density, habitat use, and to the visual (pecking) and tactile (dabbling behavior three times daily (morning, after- scythe and multiple scythe) foraging tech- noon, and night: 07:00, 15:00, and 23:00 PST, niques described by Hamilton (1975). After respectively) for 14 days at each observation we completed each survey of JDW (approxi- point. We recorded avocet density for each mately 1 h), we returned to the three locations pond and the entire study site. We recorded containing the largest avocet flocks and the distance from each individual to the near- scanned flocks, recording each bird’s behavior. est next individual as one offive interbird dis- We scanned each flock five times with >3 min tance classes (<1 m, 1-5 m, 6-10 m, 11-20 between successive samples. Time required m, >20 m), and we categorized occupied hab- per scan sample (1-3 min) varied with flock itats as shoreline, open water, or island. We size. The five scans represented subsamples of categorized behavior as foraging, copulating, each flock, which we used as ourexperimental agonistic, or other. Agonistic behavior refers unit (mean proportion of total number of av- Johnson et al. • AMERICAN AVOCET BEHAVIOR 179 ocets present at JDW for which individual be- tributed. When we performed Huber’s itera- havior was recorded after each census was tive robust ANOVA to reduce the impact of 0.74 ± 0.07 SD, n = 42 censuses, n = 126 highly influential observations, the data as- flocks). sumed a normal distribution (D’Agostino- — Analysis. From each set of scans, we cal- Pearson Omnibus P = 0.62; Huber 1981). We culated the mean proportion of individuals used Tukey’s test for comparison ofall means, within each flock engaged in the fourbehavior and we report nontransformed values. classes, as well as the proportion of foraging birds utilizing each foraging technique. We RESULTS also calculated the proportion ofbirds in each Avocet behavior varied within the daily cy- habitat, and the proportion of birds in each of cle, and among days, locations, and months. five interbird distance classes. These methods The mean number of avocets was similar at produced four multidimensional response vec- all times of day (morning: 148 ± 14 SE, af- tors for the behavior of each flock. The re- ternoon: 145 ± 12 SE, night: 157 ± 8 SE; P sponse vectors (behavior, foraging technique, = 0.92), but more avocets were present early habitat use, interbird distance) served as in- i3n) the breeding season than later (May: 170 ± dependent data points for analysis. Because 6 SE, June: 130 ± 10 SE; P = 0.015). — percentages within vectors summed to 100 Behavior. Behavior (foraging, copulating, and were thus correlated, it was necessary to agonistic, other) varied as a function of time use multivariate analysis techniques. We arc- ofday, date, proportion ofbirds in open water sine transformed data and set alpha = 0.05 a habitat, and location (Tables 1, 2). There also priori, then tested for behavioral variation was a significant interaction between date and during the daily cycle using a multivariate location (Tables 1, 2). We found no significant analysis of covariance model (MANCOVA) difference in the proportion of avocets copu- for each response vector, with time of day lating or foraging throughout the day (Table (morning, afternoon, night) as the main effect However, birds were five times more ag- . and month (May, June), date (day one through onistic at night compared to morning and af- seven during May and June sampling periods), ternoon (Table 3), and birds engaged in other location (pond), and flock size as covariates behavior less at night than during morning (Seber 1984, Johnson and Wichem 1988). Be- and afternoon (Table 3).— havioral responses not modeled by the re- 4)Foraging technique. Eoraging technique sponse vector also were included as covariates varied as a function oftime ofday, flock size, in each model. We compared potential models location, date, month (Table 4), open water for each behavioral response beginning with habitat, and proportion of birds < Im from the saturated two-way interactive model using another avocet (Tables 1, 2). There also was information-theoretic methods to direct model an interaction between time ofday and month selection (Burnham and Anderson 1998). For and between location and date (Tables 1,2). each model we calculated Akaike information Avocets foraged by pecking more in the criteria (AIC), which were used to compare morning compared to afternoon and night (Ta- candidate models to achieve the most parsi- ble 3). The proportion of birds dunking in- monious model that accurately represented the creased from morning to afternoon and again data (Burnham and Anderson 1998, Anderson from afternoon to night (Table 3), and higher et al. 2000). proportions of avocets foraged by dunking We used three-way ANOVA to examine av- early in the breeding season compared to later ocet density at ponds during the daily cycle (Table 4). Avocets scythed less at night than (morning, afternoon, night) and throughout during day (Table 3), and lower proportions the study (May, June). We used SAS macro of avocets used the scythe technique to forage FXQLQLQL (Fernandez 1999) to check nor- early in the breeding season than later (Table mality and equal variance assumptions ofAN- OVA . — and examined student residuals for the Habitat use. Habitat use by avocets varied presence of significant outliers and influential as a function of time of day and location, and observations. Data differed significantly from there was a significant interaction between normality and variances were not equally dis- these two variables (Tables 1, 2). Avocets fre- 180 THE WILSON BULLETIN • Vol. 115, No. 2, June 2003 TABLE 3. Mean (± SE) proportion ofAmerican Avocets conducting various behaviors in differenthabitats during three daily sampling periods (morning = 07:00, afternoon = 13:00, night = 23:00) in early (May; n = 21 flocks) and late (June; n = 21 flocks) breeding season and combined (May-June; n = 42) at Jay Dow, Sr. Wetlands, Lassen County, California, 2001. Different superscripts within a row denotes statistically different means (Tukey’s test, P < 0.05). Morning Afternoon May June May-June May June Behavior Agonistic 0.019 -1- 0.007 0.026 H- 0.009 0.023 -1- 0.006^ 0.040 -F 0.009 0.033 ± 0.008 Copulate 0.017 ± 0.005 0.005 H- 0.002 0.011 ± 0.003^ 0.027 -F 0.005 0.002 -h 0.001 Other 0.449 ± 0.060 0.350 -h 0.033 0.400 -h 0.035^ 0.421 -F 0.042 0.425 -F 0.035 Foraging 0.515 -1- 0.057 0.620 -h 0.034 0.567 -h 0.034^ 0.512 -F 0.038 0.540 -F 0.033 Dunking 0.591 ± 0.075 0.466 -h 0.063 0.529 -+- O.O49A 0.777 -F 0.056 0.446 -F 0.068 Pecking 0.395 -H 0.077 0.213 -h 0.047 0.304 -h 0.047A 0.186 -F 0.053 0.231 -F 0.040 Scything 0.014 ± 0.005 0.321 -h 0.058 0.168 ± 0.037^ 0.037 -F 0.027 0.323 ± 0.063 Habitat Water 0.510 ± 0.081 0.847 -h 0.038 0.679 -1- 0.05U 0.705 -F 0.054 0.733 -F 0.038 Island 0.261 ± 0.073 0.042 0.020 0.151 ± 0.04U 0.130 -F 0.050 0.039 -F 0.019 Shore 0.229 0.053 0.111 -h 0.028 0.170 -1- 0.03U 0.164 -F 0.027 0.227 -h 0.033 Interbird distance <1 m 0.160 0.032 0.062 -h 0.016 0.111 0.020^ 0.222 -F 0.032 0.113 -F 0.024 1-5 m 0.230 ± 0.029 0.180 -h 0.025 0.205 -+- 0.019A 0.280 -F 0.021 0.243 -h 0.027 6-10 m 0.209 ± 0.024 0.221 ± 0.024 0.215 ± 0.017^ 0.175 ± 0.025 0.184 -F 0.024 11-20 m 0.193 0.031 0.380 -1- 0.036 0.287 ± 0.028^ 0.144 -h 0.018 0.292 ± 0.045 >20 m 0.207 0.029 0.157 ± 0.025 0.182 ± 0.019^ 0.179 -F 0.016 0.169 -F 0.027 quented certain ponds at specific times of the an interaction between date and location (Ta- day and some ponds were used predominately bles 1, 2). Mean proportion of avocets < Im during either the early or late portion of the apart was higher at night than during day (Ta- breeding season (Fig. 1; ANOVA; = ble 3). Similarly, the proportion of birds 1-5 36.39, P < 0.0001; location F,o4,6 = 61.65, P m apart was higher in the afternoon compared < 0.0001; month = 13.44, P = 0.0003; to morning but greatest at night (Table 3). The time of day F24K, = 0.49, P = 0.61; time of proportion of birds in all larger interbird dis- day X location F20416 = 0.3.47, P < 0.0001; tance classes was least at night (Table 3). mmoonntthh XXlotciamtieonoFf|o,d4ai6y=F1274.K,84,=P9<.0,0.0P001=; hMiegahnerperaorployrtiinonthoefsaevaoscoent,sa<ndIamlaarpgaerrt pwraos- 0.0001). Island habitat use decreased from portion ofbirds were spaced farther apart later morning through night (Table 3), and a greater in the season (Table 4). proportion ofavocets used islands early in the DISCUSSION breeding season compared to later (Table 4). Mean proportion ofavocets utilizing open wa- All behaviors performed by breeding ter did not differ significantly among the three American Avocets during the day also oc- sampling periods (Table 3), but avocets used curred at night, though frequencies of partic- open water more often late in the breeding ular behaviors, flock location, and interbird season (Table 4). The proportion of avocets distances varied among morning, afternoon, utilizing shoreline habitat did not differ sig- and night. Nocturnal social behavior was suf- nificantly among the three daily sampling pe- ficiently frequent that further study of avocet riods (Table 3) or between early and late sea- behavior must eonsider nocturnal habits. son (Table 4). While observations in this study were limited — Interhird distance. Interbird distance var- to the week around the full moon, earlier ob- ied as a function of time of day, flock size, servations at the study site confirm that sev- date, and month (Tables 1, 2). There also was eral shorebird species are socially active at 8 Johnson et al. • AMERICAN AVOCET BEHAVIOR 181 TABLE 3. Extended. Afternoon Night May-June May June May-June 0.036 ± 0.006^ 0.186 ± 0.017 0.210 ± 0.021 0.198 ± 0.014« 0.014 ± 0.003^ 0.025 ± 0.008 0.008 ± 0.003 0.016 ± 0.004^ 0.423 ± 0.027^ 0.240 ± 0.028 0.160 ± 0.019 0.200 ± 001 » . 0.526 ± 0.025^ 0.549 ± 0.027 0.623 ± 0.026 0.586 ± 0.019^ 0.612 ± 0.051^ 0.816 ± 0.037 0.685 ± 0.055 0.750 ± 0.034c 0.209 ± 0.033« 0.142 ± 0.032 0.204 ± 0.045 0.173 ± 0.028^ 0.180 ± 0.041^ 0.042 ±0.017 0.111 ± 0.028 0.076 ± 0.017B 0.719 ± 0.033^ 0.776 ± 0.035 0.768 ± 0.027 0.772 ± 0.022^ 0.085 ± 0.027^* 0.053 ± 0.016 0.002 ± 0.001 0.027 ± 0.009c 0.196 ± 0.022^ 0.171 ± 0.029 0.231 ± 0.027 0.201 ± 0.020^ 0.167 ± 0.021^ 0.438 ± 0.024 0.305 ± 0.023 0.372 ± 0.019^' 0.261 ± 0.017'^ 0.312 ± 0.017 0.419 ± 0.016 0.365 ± 0.014c 0.179 ± 0.017A 0.063 ± 0.009 0.138 ± 0.010 0.101 ± 0.009^ 0.218 ± 0.027^ 0.086 ± 0.010 0.079 ± 0.015 0.082 ± 0.009c 0.174 ± 0.015^ 0.101 ± 0.012 0.059 ± 0.010 0.080 ± 0.008'" — night throughout the lunar cycle (Johnson et ior. Avocets were more aggressive and more al. 2002). Further, Pied Avocets are active at closely spaced at night than during the day, night, regardless oflunar illumination (Hotker and the mean proportion of agonistic birds 1999). was five times higher at night. Avocets ap- — Copulations. Nocturnal copulation rarely parently increased nocturnal agonistic behav- has been reported, but is not necessarily un- ior at the expense of self maintenance or in- common among shorebirds (Lemnell 1978, cubation, as the proportion of birds engaged Johnson et al. 2002). We found avocets cop- in other behaviors was 50% less at night. Av- ulating with similar frequency during morn- ocets and other shorebirds potentially are bet- ing, afternoon, and night, and previous obser- ter able to reduce incubation duties at night vation at JDW found several shorebird spe- when the risk of desiccation to uncovered cies, including avocets, copulating at night re- eggs due to overheating is minimal (Thibault gardless of lunar phase (Johnson et al. 2002). and McNeil 1995a). Shorebird eggs are robust Theory on mating strategy has failed to ad- to cool temperatures, but highly susceptible to dress the possibility of nocturnal reproductive extreme heat. Thus, avocets may be more tactics among most shorebirds (e.g., Oring prone to leave the nest at night when ambient 1982). Considering that Ring-billed Gull {La- temperature is low. Conversely, it is possible rus delawarensis) copulations are interrupted that we failed to detect incubating birds during less often at night (Hebert and McNeil 1999), nocturnal observations. However, this is not and ourobservation that nocturnal copulations likely as there was no significant difference in are likely to play substantial roles in avocet the number of birds observed on the entire reproduction, study of shorebird nocturnality wetland during morning, afternoon, and noc- is critical for accurate assessment of repro- turnal surveys. ductive tactics among temperate breeding Avocets also may be tightly spaced at night shorebirds. to reduce the threat of predation. However, Interbird distance and agonistic behav- nocturnal agonistic encounters generally were 182 THE WILSON BULLETIN • Vol. 115, No. 2, June 2003 TABLE 4. Mean (± SE) proportion of American Pond2 Pond3 Avocetsperformingvariousbehaviorsindifferenthab- itats early (May; n = 63 flocks) and late (June; n = 63 flocks) in the breeding season at Jay Dow, Sr. Wet- lands, Lassen County, California, 2001. Different su- perscripts within a row denotes statistically different means (Tukey’s test, P < 0.05). May June Behavior Agonistic 0.082 0.012^ 0.089 -+- 0.013^ Copulate 0.023 -E 0.004^ 0.005 0.001A Other 0.370 0.028^ 0.312 0.022^ Foraging 0.526 0.024^ 0.594 ± 0.018^ Time ofday Dunking 0.728 -+- 0.035^ 0.532 -1- 0.038« Pecking 0.241 ± 0.035^ 0.216 ± O.O25A PIG. 1. Variation in mean number of American Scything 0.031 0.011^ 0.252 ± 0.032^ Avocets at four locations at Jay Dow, Sr. Wetlands, Lassen County, California during morning (07:00), af- Habitat use ternoon (15:00), and night (23:00) observations, 2001. Water 0.664 ± 0.037^ 0.783 -E 0.02P White bars represent May observations (n = 7), black Island 0.148 ± 0.031^ 0.027 -E 0.009« bars represent June observations {n = 7), and error Shore 0.188 ± 0.022^ 0.190 ± 0.018^ bars provide standard error (ANOVA: all locations, n Inter<b1irdmdistance0.273 0.023^ 0.160 -E 0.018B 6=1.6151:, PE46<.4160.=000316;.3m9o,nPth<^,.04.,0^0=01;13l.o4c4a,tiPon=F0,o.040i603=; >210611---m51200mmm 0000....111246471394 ±±±- 0000....000011114443^^^^ 0000....211288251180 ±--EE 00O0....O00021115428«^^B ^ttl2ioi.ocm4na1et6Fio,o=f0n.49d1F.6a02y,0=.4P1E6127.=~.4186400,..=03P.0400<7.1,4)9.0,P.0P0<01=0;.00m0.o06n11t;;htmiXomnettihomfeXdoaflyodcaaXy- loud and created a commotion easily detected 1974, 1976; Evans 1976; McNeil and Robert by predators. Hawk and owl predation is a key 1988; Robert and McNeil 1989, McNeil and factor in shorebird mortality during the non- Rompe 1995, Rompre and McNeil 1995). Eye breeding season (Page and Whitacre 1975, morphology and physiology are correlated Townshend 1984, Whitfield 1985, Whitfield et with nocturnal foraging behavior in many bird al. 1988); however, the extent of diurnal ver- species (Rojas De Azuaje et al. 1993; Rojas sus nocturnal raptor predation on shorebirds, et al. 1999a, 1999b; McNeil et al. 1999). especially during the breeding season, has not Shorebirds that used tactile foraging tech- been thoroughly investigated (Townshend niques, including Short-billed Dowitchers 1984). (Limnodromus griseus), American Woodcocks — Foraging. The proportion of birds en- (Scolopa.x minor), and Willets exhibited lower gaged in foraging behavior varied from 0.50- retinal sensitivity and had lower rodicone ra- 0.60 throughout the daily cycle and the entire tios compared to those that used visual for- season; however, foraging technique was less aging techniques at night, such as Black- consistent. Change in prey visibility or avail- winged Stilts and Wilson’s Plovers (Charad- ability may account for daily and seasonal rius w'ilsonio', Rojas et al. 1999a, 1999b). Var- variation in foraging technique. A shift to tac- iation in foraging technique between day and tile foraging techniques at night may be more night also may be a consequence of variation efficient for avocets if prey is difficult to de- in prey behavior during the daily cycle, re- tect visually at lower light intensities. Eur- sulting in changes in prey availability. Similar asian Oystercatchers {Haematopus ostrale- or distinct prey communities may be available gus), yellowlegs {Tringa flavipes, T. melano- to shorebirds in common or discrete habitats leuca). Black-winged Stilts {Himantopus hi- between day and night (Thibault and McNeil mantopus), and Willets {Catoptrophoriis 1995b, Rompre and McNeil 1995). Overall, semipabnatus) showed less visual foraging shorebird prey were more abundant at night at and more tactile foraging at night (Hulscher a Venezuelan lagoon (McNeil et al. 1995), and Johnson et al. • AMERICAN AVOCET BEHAVIOR 183 two annelid prey species commonly taken by McNeil, B. Sandercock, J. Sedinger, L. Smith, and T. shorebirds in Europe {Nereis diversicolor, Sordahl for manuscript reviews. Lumbricus terrestris) also were most available LITERATURE CITED at night (MacLennon 1979, Dugan 1981). JDHWabiwtearte uussee.d—cAolnstihsotuengthlystohmreougphoonudtsthaet Andesrosno.n,20D0.0.R.,NuKl.lRhBypuortnhheasims, atensdtinWg.: Lp.rTobhloemmps-, prevalence, and an alternative. J. Wildl. Manage. daily cycle and the entire breeding season, av- 64:912-923. ocets frequented certain ponds at specific Bannerman, D. a. 1959. Thebirdsofthe British Isles, times of the day and some ponds were used vol. 2: Glareolidae, Otididae, Burhinidae, Grui- predominately during either the early or late dae, Laridae. Oliver and Lodge, London, United Kingdom. portion of the breeding season. Variation in prey community distribution and composition Burnham, K. P. and D. R. Anderson. 1998. Model selection and inference: a practical information- during both the daily and breeding cycle may theoretic approach. Springer-Verlag, New York. affect avocet distribution. Habitat use also Dodd, S. L. and M. A. Colwell. 1996. Seasonal var- varied within ponds at JDW as birds were iation in diurnal and nocturnal distributions of found less often on islands and more often in non-breeding shorebirds at North Humboldt Bay, open water late in the breeding season. Re- California. Condor 98:196-207. duced use ofislands may be a consequence of Dugaang,inPg. iJ.n 1sh9o8r1e.biTrhdse:iampcoorntsaenqcueenofcenoocftuirnncarleafsoerd- nest loss. Avocets commonly nest on islands invertebrate prey activity. Pp. 251-260 in Feeding at JDW, and if early season island nesters lost and survival strategies ofestuarine organisms (N. clutches and failed to renest, we would expect V.Jones andW.J. Wolf,Eds.). PlenumPress,New use to shift from islands (incubation) to either York. shore or open water. Evans, P. R. 1976. Energy balance and optimal for- aging strategies in shorebirds: some implications American Avocets, and potentially other for their distributions and movements in the non- waterbirds, do not fit the typical diurnal, noc- breeding season. Ardea 64:117-139. turnal, or crepuscular paradigm. Rather, avo- Evans, P. R. 1979. Adaptations shown by foraging cets practice a labile life history strategy shorebirds to cyclic variations in the activity and throughout the annual cycle (Evans and Harris availabilityoftheirintertidal prey. Pp. 357-366 in 1994, Dodd and Colwell 1996, Hotker 1999, C(Ey.clNicayplohrenaonmdenRa. iGn.mHaartinnoell,plaEndtss.).anPdearngiammaolns Johnson et al. 2002). Such behavioral plastic- Press, Oxford, United Kingdom. ity enables birds to profit in the dynamic en- Evans, T. J. and S. W. Harris. 1994. Status and hab- vironments they commonly inhabit. At coastal itat use by American Avocets wintering at Hum- locations, a labile foraging strategy indepen- boldt Bay, California. Condor 96:178-189. dent of solar cycle allows avocets to take ad- Ferntaincdaleza,nalGy.siCs.IIJ:.A1N99O9.VAQufiicxkedraesnudltmsifxreodmmostdaetilss- vantage oftidally induced changes in resource using SAS macros. Dept, of Applied Statistics, availability (Robert et al. 1989). Further, av- Univ. ofNevada, Reno, http://www.ag.unr.edu/gf, ocet energy acquisition appears independent MS 204. of day length, which also may be beneficial Goss-Custard, J. D. 1969. The wintering feeding to avocets breeding in arid environments. ecology of the Redshank (Tringa totanus). Ibis 111:338-356. Nocturnal sexual and agonistic behaviors in Hamilton, R. B. 1975. Comparative behavior of the avocets are sufficiently frequent that further American Avocet and the Black-necked Stilt {Re- study of avocet reproductive behavior must curvirostridae). Ornithol. Monogr. 17:1-98. consider nocturnal habits. The role of noctur- Hebert, P. N. andR. McNeil. 1999.Nocturnalactivity nal reproductive behavior should be assessed ofRing-billed Gulls at and away from thecolony. Waterbirds 22:445-451. in species generally perceived as being diur- Hotker, H. 1999. What determines the time-activity nal. budgets of avocets (Recurvirostra avosetta)? J. Ornithol. 140:57-71. ACKNOWLEDGMENTS Huber, P. 1981. Robust statistics. John Wiley and Sons, New York. We thank the Nevada Agricultural Experiment Sta- Hulscher, J. B. 1974. An experimental study of the tion, Univ. of Nevada, for financial support and for food intake ofthe Oystercatcher (Haematopusos- allowing us to conduct research at Jay Dow, Sr. Wet- tralegusL.) incaptivityduringsummer. Ardea62: lands. We also thank M. Colwell, A. Hartman, R. 155-171. 184 THE WILSON BULLETIN • Vol. 115, No. 2, June 2003 Hulscher, J. B. 1976. Localization of cockles {Car- Robert, M., R. McNeil, and A. Leduc. 1989. Con- dium edule L.) by the Oystercatcher{Haematopus ditions and significance ofnight feeding in shore- ostralegus L.) in darkness anddaylight. Ardea64: birds and other water birds in a tropical lagoon. 292-310. Auk 106:94-101. Johnson, M., J. P. Beckmann, andL. W. Oring. 2002. Robinson, J. A. and L. W. Oring. 1997. Natal and Temperate breeding shorebirds copulate at night. breedingdispersal inAmericanAvocets.Auk 114: Wader Study Group Bull. 97:45-46. 416-430. Johnson, R. A. and D. W. Wichern. 1988. Applied Rojas, L. M., R. McNeil, T. Cabana, and P. Lacha- multivariate statistical analysis. Prentice Hall, Up- PELLE. 1999a. Diurnal and nocturnal visual capa- per Saddle River, New Jersey. bilities in shorebirds as a function oftheirfeeding Krohn, W. B. 1971. Some patterns of woodcock ac- strategies. Brain Behav. Evol. 53:29-43. tivities on Maine summer fields. Wilson Bull. 83: Rojas, L. M., R. McNeil, T. Cabana, and P. Lacha- 396-407. PELLE. 1999b. Behavioral, morphological and Laven, H. 1940. Beitrage zurbiologie des Sandregen- physiological correlates of diurnal and nocturnal peifers (Charadrius hiaticula L.). J. Ornithol. 88: vision in selected wading bird species. Brain Be- 183-287. hav. Evol. 53:227-242. Lemnell, P. a. 1978. Social behavior of the Great Rojas De Azuaje, L. M., S. Tai, and R. McNeil. Snipe (Capella media) at the arena display. Ornis 1993. Comparison of rod/cone ratio in three spe- Scand. 9:146-163. cies of shorebirds having different nocturnal for- MacLennon, j. a. 1979. Formation and function of aging strategies. Auk 110:141-145. mixed species wader flocks in fields. Ph.D. diss., Rompre, G. and R. McNeil. 1995. Variability in day Univ. ofAberdeen, Aberdeen, United Kingdom. and night feeding habitat use in the Willet Catop- McNeil, R. 1991. Nocturnality in shorebirds. Pp. i1c0al98C-o1n1g0r4esisn(ABc.taD.XBXellI,ntEedr.n).atiNoenawlZOeranliatnhodlOorg-- ts8er2ao-sp8oh7no.riunsVseneemziupeallam.atWuasdedrurSitnugdythGernoounp-bBrulele.di8n1g: nithological Congress, Christchurch, New Zea- Seber, G. a. F. 1984. Multivariate observations. John land. Wiley and Sons, New York. McNeil, R., O. D. Diaz, A. I. Linero, and S. Rodri- Sheldon, W. G. 1961. Summer crepuscular flights of guez, Jr. 1995. Day- and nighttime prey avail- American Woodcocks in central Massachusetts. ability for waterbirds in a tropical lagoon. Can. J. Wilson Bull. 73:126-139. Zool. 73:869-878. McNeil, R. and M. Robert. 1988. Nocturnal feeding Staine, K. j. andj. Burger. 1994. Nocturnalforaging behavior of breeding Piping Plovers {Charadrius estnrvaitreogniemsenotf.sPopm.e2s3h2o8r-eb2i3r3d6sipneciAecstainXaIXtroIpnitcearl- melodus) in New Jersey. Auk 111:579-587. national Ornithological Congress (H. Ouellet, Stribling, H. L. and P. D. Doerr. 1985. Nocturnal Ed.). National Museum of Natural History, Otta- use of fields by American Woodcock. J. Wildl. Manage. 49:485-491. wa, Ontario, Canada. McNePiElL,LE.R.,19L9.9.M.ViRsoijoan, aT.ndCanboacntuar,naalndactPi.viLtaiecshai-n Tansl6e2y3,-6K2.9 ainndAj.diTc.tiEorniarcyhseonf.bi1r9d8s5.(B.ViCsiaomnp.bePlpl. wading birds and shorebirds. Pp. 2691-2710 in and E. Lack, Eds). Poyser, Calton, United King- dom. Acta XXll International Ornithological Congress (B. D. Bell, Ed.). New Zealand Ornithological Thibault, M. T. and R. McNeil. 1995a. Day- and Congress, Christchurch, New Zealand. night-time parental investment by incubating Wil- McNeil, R. andG. Rompre. 1995. Dayand nightfeed- son’s Plovers in a tropical environment. Can. J. ing territoriality in Willets Catoptrophorus semi- Zool. 73:879-886. palmatus and Whimbrel Niimeniusphaeopiis dur- Thibault, M. T. and R. McNeil. 1995b. Predator-prey ing the non-breeding season in the tropics. Ibis relationship between Wilson’s Plover and fiddler 137:169-176. crabsin northeasternVenezuela.WilsonBull. 107: Mundahl, j. T. 1982. Role specialization in the paren- 73-80. tal and territorial behavior ofthe Killdeer. Wilson Townshend, D. j. 1984. The effects ofpredators upon Bull. 94:515-530. shorebird population in the non-breeding season. Oring, L. W. 1982. Avian matingsystems. Avian Biol. Wader Study Group Bull. 40:51-54. 6:1-92. Vader, W. j. M. 1964. A preliminary investigation Page, G. and D. E Whitacre. 1975. Raptorpredation into the reactions of the infauna of the tidal flats on wintering shorebirds. Condor 77:73-83. to tidal fluctuations in water level. Neth. J. Sea PiENKOWSKi, M. W. 1983. Changes in the foragingpat- Res. 2:189-222. tern of plovers in relation to environmental fac- Warnock, N. and L. W. Oring. 1996. Nocturnal nest tors. Anim. Behav. 31:244-264. attendance of Killdeers: more than meets the eye. Robert, M. and R. McNeil. 1989. Comparative day Auk 113:502-504. and night feeding strategies of shorebird species Warriner, j. S., j. C. Warriner, G. W. Page, and E. in a tropical environment. Ibis 131:69-79. Stenzel. 1986. Mating system and reproductive Johnson et cil. • AMERICAN AVOCET BEHAVIOR 185 success of a small population of polygamous Ornithological Congress(H. Ouellet, Ed.). Nation- Snowy Plovers. Wilson Bull. 98:15-37. al Museum of Natural History, Ottawa, Ontario, Whitfield, D. P. 1985. Raptor predation on wintering Canada. waders in southeast Scotland. Ibis 127:544-558. ZwARTS, L., A. M. Blomert, and R. Hupkes. 1990. Whitfield, D. R, A. D. Evans, and P. A. Whitfield. Increase of feeding time in waders preparing for 1988. The impact ofraptorpredation on wintering spring migration from the Banc d’ Arguin, Mau- waders. Pp.674-687 in Acta XIX International ritania. Ardea 78:237-256.