Study of incubation, chick rearing and breeding phenology of Red KnotsCalidris canutus rogersi in sub-Arctic Far Eastern Russia aided by geolocators

Egor Y. Loktionov1, Pavel S. Tomkovich2 & Ronald R. Porter3

1N.E. Bauman Moscow State Technical University, 2nd Baumanskaya Str., 5, Moscow, 105005, Russiaeloktionov@mail.ru2Zoological Museum, M.V. Lomonosov Moscow State University, Bolshaya Nikitskaya Str., 6, Moscow, 125009, Russia3800 Quinard Court, Ambler, PA 19002, USA

Loktionov E.Y., P.S.Tomkovich & R.R. Porter. 2015. Study of incubation, chick rearing and breeding phenology of Red Knots Calidris canutus rogersi in sub-Arctic Far Eastern Russia aided by geolocators. Wader Study 122(2):142–152.

INTRODUCTION

Despite the fact that the Red Knot Calidris canutus is oneof the best studied wader species in the world (e.g. Piersma2007, Piersma & Davidson 1992, Sitters & Tomkovich2010), knowledge about incubation and chick rearing ofthis species is limited because of their secretive behaviorduring incubation (e.g. Harrington 2001, Johnson &Brusseau 2012, Tomkovich et al. 1994, Tomkovich & Don-dua 2008, Tulp et al. 1998, Whitfield & Brade 1991).

We have been monitoring a small local breeding popula-tion (estimated at 10–12 breeding pairs) of subspecies C.c. rogersi in southern Chukotka Autonomous Region, FarEastern Russia since 2009. To learn about migration path-ways, staging areas and non-breeding grounds of birdsfrom this particular population we applied light-level ge-olocator (GL) tags (Tomkovich et al. 2013). As a byproductof the GL light data, we also obtained valuable information

about the incubation regimes and breeding phenology ofthe birds, which are unknown for the rogersi subspecies.Furthermore, we learned how to recognize the broodingof chicks in GL data.

Valuable information has recently been obtained on thebreeding behavior of several high-Arctic wader speciesusing GL data (Burger et al. 2012, Gosbell et al. 2012). Tothe best of our knowledge, behavior of waders based oninterpretations of GL data, have never been confirmedby direct field observations. Such observations are im-portant to correctly interpret breeding phenology and in-cubation behavior using GL light signals. This paper hastwo aims: (1) to match GL data with direct observationsof Red Knots, and (2) based on this, to present data onseveral breeding parameters for rogersi Red Knots.

research paper Wader Study 122(2): 142–152. doi: 10.18194/ws.00012

Keywords

Red Knot

Calidris canutus rogersi

breeding phenology

incubation

chick rearing

sub-Arctic

geolocator tags

This is the first study of the breeding biology of Red Knots of the subspeciesCalidris canutus rogersi in the Chukotka region, Far Eastern Russia. Direct behavioralobservations and geolocator data of two Red Knots were compared to study thebreeding phenology, incubation period and incubation bouts in sub-ArcticChukotka, a region with twilight around midnight. The incubation period was 23days after the second or third egg was laid, including about half a day in the nestwith the hatched chicks. This corresponds with 21–21.5 days of incubation esti-mated by the traditional way (interval for the last egg of a clutch from laying tohatching). We suggest that males incubate longer than females. Geolocator dataof brooding males after their chicks left the nest differed from those of femalesthat do not attend chicks. Geolocator data might thus indicate the sex of RedKnots. For both males, the lengths of their respective incubation bouts and off-duty periods did not significantly differ. Both bout lengths increased in the secondhalf of the incubation period. Brooding time of chicks seems to gradually decreaseduring the summer, but it was not possible to determine when brooding ceasedor when the chicks became independent. Birds started their southward migration28–28.5 days after families left their nests. This is longer than estimated by directlocal field observations and by another geolocator study of Red Knots.

METHODS

Study area

The study area in the vicinity of Meinypilgyno Village,Chukotka, Russia (62°32’ N, 177°03’ E) is briefly describedelsewhere (Tomkovich et al. 2013, Zöckler & O’Sullivan2005). In this part of the world, tundra landscape descendsto rather low latitudes along the coast due to the coolingeffect of the Bering Sea (e.g. Loughlin & Ohtani 1999).Red Knots breed near Meinypilgyno in a restricted areaof ca. 14 km2 of the coastal plain which is several metersabove sea level. Low ridges of sand and fine gravel on thecoastal plain were deposited by the Bering Sea in prehis-toric time and are overgrown by lichens, dwarf shrubsand a few herbs and have a variable amount of bare soilon the surface.

The study area is 445 km south of the Arctic Circle, theregion of continuous daylight in summer. During the RedKnot breeding season at this latitude lighting conditionsbetween astronomical sunset and sunrise are characterizedas civil twilight lasting for ca. 4 hours – from about 22:00to 02:00 hr.

Geolocation

Eight breeding male knots were fitted with light-level GLs:five in 2011 and three in 2013 (from now on referred toas GL males). Five GLs were retrieved the year followingdeployment but only two contained useful incubation in-formation. Hence, the study presented here is almost ex-clusively based on data from two individuals (from nowonwards referred to as GL 176 and GL 180). The datafrom two other GLs were additionally used to estimatedates of departure from the breeding grounds. Males werechosen for deployment because of their higher return rateto the breeding area in comparison with females(Tomkovich & Soloviev 1994, our unpubl. data) and be-cause only males stay with the chicks (Tomkovich et al.1994, Whitfield & Brade 1991, this study), increasing thechances of recapture and retrieval of GLs.

We used GLs of model MK10 from British Antarctic Sur-vey (BAS) weighing 1.1 g (1.4 g with plastic leg attachment;1.3% of the mean male weight, 1.5% of the lightest maleweight). These devices sampled the light level everyminute and recorded the maximum value every five min-utes (thus, each GL recorded 288 samples of light leveldaily). The MK10 sensors recorded a signal digitized to ascale of 0 to 64 with the light level clipped at approximately100 lux (=64). We considered light levels less than 32 dur-ing daytime as low-light. We refer to low-light levels as‘nightshade’ if they occurred between sunset and sunrise.Depending on weather and date (there are mountains of600–800 m high to the north of the study area), the lightdip started between 0 and 1 hr after sunset or before sun-rise. However, we used time of astronomical sunrise/sun-set as a firm cut-off for the nightshade. The software Bas-trak from BAS was used to retrieve and analyse the data.Various GL data were obtained from different birds indifferent seasons, for the breeding periods which are pre-sented in Table 1 (see page 5).

Many breeding Red Knots in the local population havebeen individually color-marked since 2009. We deter-mined the sex of most individuals by observations of ter-ritorial and mating behavior of marked individuals ortheir partners in spring. Some birds were sexed as femalesduring the period of egg-laying, based on the shape oftheir abdomen, clearly indicating that they were carryingeggs in their body (Tomkovich et al. 2013). All individualsunder consideration in this study were color-marked andsexed in years prior to deployment of the GLs. Their sexwas confirmed a number of times.

The geographical positions determined by the GLs indi-cated when birds arrived to or departed from the breedinggrounds (Tomkovich et al. 2013). After arrival to thebreeding area the GL signal fluctuated close to maximumlevel most of the day; approximately two weeks after ar-rival, the GL data contained prolonged periods of inter-mittent readings of darkness and light, which in otherstudies have been interpreted as incubation and brooding(Burger et al. 2012, Eichhorn et al. 2006, Gosbell et al.2012). We identified incubation and post-hatching activ-ities from GL data (Burger et al. 2012, Gosbell et al. 2012)by considering the long-lasting periods (several hours)of predominant darkness in the GL data to be incubationbouts, whereas the intermittent periods of light to be off-duty times. Because of the 4-hour civil twilight in oursub-Arctic study area, the GLs typically register full dark-ness for several hours, depending on weather-related shad-ing (e.g. clouds) and their sensitivity settings. We discussthis below.

Incubation bouts of Red Knots that were not interruptedby nightshade always lasted longer than 5.7 hr (see Re-sults). Therefore, we assumed that a bird incubated duringthe 4-hour nightshade period continuously, if it was in-cubating both just before and after the nightshade dip.We included incubation bouts that contained nightshadeperiods in our analysis, but not those that only started orfinished during nightshade. The same approach was usedfor off-duty periods. If nightshade so interrupted the boutthat start or stop times were unclear, the bout was ex-cluded. With these criteria we were able to recognize 56days of incubation recorded by GLs, but identified onlyten incubation bouts and one off-duty period without in-terruption by nightshade (Table 2, page 7). We identifiedmore off-duty than on-duty bouts, because the GL signalpattern was more clear when a bird was not incubating.In total, 66.9% of recording time (including nightshade)during the incubation days could be assigned to one ofthe two types of bout.

Observations

Whenever possible, we observed the behaviour of RedKnots which were deployed with GLs to confirm whetherthe interpretation of the light signal (incubation or off-duty) was correct. We undertook daily searches for RedKnots in late May and the first days of June every year;occasional surveys were undertaken during most of June,and once in two or three days in late June and through

Loktionov et al. l Incubation, chick rearing and breeding phenology of Red Knots in sub-Arctic Far Eastern Russia--143

Wader Study 122(2) 2015144

most of July. During the breeding season, we recordedthe status (solitary, paired, nesting, chick-rearing) andbehavior (displaying, feeding, loafing, incubating, guidingchicks) of Red Knots that were deployed with GLs. Thesewere compared with the light signal of the GLs at thattime to find out whether visual observations matchedwith GL data (low-light during incubation or brooding).

Several visits, especially close to expected hatch, werepaid to the single known nest of GL 180 in the year ofdeployment to observe whether the clutch was beingincubated, and if so, whether the male or female was onduty (see page 6).

During this study only two nests of Red Knots werefound with incomplete clutches. One of them was depre-dated by a Raven Corvus corax soon after, while the maleon another nest was caught and fitted with GL 180 on the

twelfth day of incubation of the complete clutch and tendays before hatching of chicks (Table 1). Direct observationson another nest (GL 176) were limited because the deploy-ment took place when two of four chicks had alreadyhatched in the nest (Table 1). Both males were recapturedin July of the following year for retrieval of GLs whenthey were accompanying their broods.

Our attempts to record the activity of knots attendingchicks failed most times because birds tried to lead chicksaway from us. We believe that this caused unnatural brood-ing behavior. We were able to observe vigilant, alarmingmales deployed with GLs that were guiding chicks. Suchobservations were used to compare with data from GLs(Table 1). At the first encounter of each brood we caughtand weighed the chicks. Repeated chick measurementswere obtained at occasional recaptures to document chickgrowth. Age of chicks was estimated using growth curves

Fig. 1. Geolocator output of three Red Knots in southern Chukotka, Far Eastern Russia during the breeding seasons of2011 and 2012: (a) day-time averaged light signal and (b) number of signal oscillations. The relative time scale indicatesthe number of days before (negative) or after (positive) chicks left the nest at day zero. The day the chicks left wasdetermined by direct observation of birds GL 176 and 180 in 2011 and estimated from the GL output in all other cases(see Table 1).

of body-mass, bill-length and length of the outermost pri-mary feather (Tulp et al. 1998, our unpubl. data).

RESULTS

During most of the year the GL light curve was near max-imum all day (median=64). Only during incubation wasthis maximum interrupted by sufficient shading to lowerthe median below 32. The signal’s daytime median alsohad sharper variation than the day-time average duringthis period (compare Figs. 1a & 2), and use of the medianhelps to identify the hatching day more clearly: the medianjumps to the maximum (64) on the observed or estimatedhatching day, and remains at that level afterwards (Fig.2). The mean, however, is slightly above 32 (Fig. 1a). Dis-tinctive bird behavior at hatching can be also seen fromthe light signal oscillation (Fig. 1b) caused by standingup to help chicks and sitting down to warm them. Sinceleaving the nest is an event that can be recorded both byobservations and by GL data, we chose this event as oc-curring on day zero, so the incubation period is negativedays and brooding the chicks is positive days (Fig. 1).

The GL light signal is fractured during incubation, withon-bouts constantly interrupted by spikes of full light(presumably when the bird stands or turns). To defineincubation on-bouts and off-bouts we analyzed thedistribution of the durations of shading episodes. Basedon this analysis, we decided to define an on-bout as aperiod of at least five hrs duration containing 80% lightsamples below level 32 (Fig. 3).

During six summers of our surveys in Meinypilgyno wefound six nests of Red Knots (0–3 per year). Nests werefound by coincidentally flushing a bird from the eggs orduring focused rope dragging. We did not find the nestsof males that were fitted with GLs in the preceding sum-mer. As a consequence, we had only limited possibilitiesfor direct observations at nests of knots fitted with GLs(Table 1, Fig. 4).

Signals from GL 180 during the incubation period in 2011showed clear successive periods of light and darkness(Fig. 4) identical to those suggested to be caused by incu-bation bouts in Canadian C. c. rufa Red Knots (Burger etal. 2012). Presence or absence of the male on the clutchcoincided well with the signals of the GL: dark when onthe nest, light when the female was on the nest (Fig. 4).During hatching of the chicks of GL 180 on 24 June thelight signal pattern of the GLs became quite different fromthe incubation signals: the number of light spikes was atleast doubled (Fig. 4). The last chick was hatched just be-fore our last visit to the nest on that date at 21:35 (thechick was wet). This period with many spikes lasted forabout 12 hrs, after which the GL recorded predominantlylight signals with regular spikes of darkness (from 05:50on 25 June; Fig. 4), which indicated the start of broodingconfirmed by absence of the family in the nest and closevicinity several hours later (at 09:30) on 25 June. The male#180 accompanying his brood was recorded later on 6, 11,14 and 17 July and without the brood on 23 July (Table 1).

GL 176 was deployed at noon on 1 July 2011 when two offour chicks had hatched and were warming up. At 22:30

Loktionov et al. l Incubation, chick rearing and breeding phenology of Red Knots in sub-Arctic Far Eastern Russia--145

Fig. 2. Daily median of the light signal from two Red Knot males (GL 176 and GL 180) in southern Chukotka, Far EasternRussia, in 2012. Periods of strong oscillations correspond to incubation periods.

Wader Study 122(2) 2015146

the same day, there were four chicks in the nest. Thefamily probably left the nest early the next morning (dur-ing nightshade). The male was observed only once later,while attending one of his fledglings, on 20 July. The lightsignal pattern recorded for this male changed similarly tothat of GL 180 when the family left the nest (not on Fig.4). Both families with GL males left their nests early inthe morning, after the last chicks had hatched the previousnight. In the third nest we recorded brood departure bydirect observations in the afternoon. During six summerswe were able to observe very few individually-marked fe-males after their chicks had hatched. Observations werelimited to 0–8 days (n=4) after hatching. None of thesefemales guided chicks, either with or without the male.In contrast, males were observed with chicks in 31 cases.

The median of the daily light signals from the MK10 GLswas a useful criterion for correctly identifying incubationperiods. Before start of incubation and after hatch, themedian of the daily light signal was almost constantlyclose to the daytime maximum illumination of 64. Duringincubation periods strong oscillations of the daily median(0 to 64) were recorded when the bird was on- and off-duty during the day (Fig. 2). Using this method, we deter-mined that incubation lasted for 23 days in 2012 in bothmales. Using field observations of GL 180 in 2011 duringperiodic visits to the nest, we roughly estimated the incu-bation period from clutch completion until hatching ofthe last chick to be about 21 days. Based on our estimatesof chick age in the two broods at capture and retrieval ofthe GLs, we estimated that hatch had taken place on 28–29 June and 3–4 July in 2012. This corresponds ratherwell with the hatch dates indicated by GL data (26 Juneand 3 July).

The length of incubation on-bouts and off-bouts varied

Fig. 3. Frequency distribution of low-light episodes of GLRed Knots 176 and 180 (combined) (1) during the entiretwo months that the birds were on the breeding groundsand (2) during incubation only (note the log-scale of thex-axis).Table 1. D

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121

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330

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from 5.70 to 23.75 hrs and changed in the course of theincubation period, and both were of similar duration(Table 2, Fig. 5). The GLs recorded two exceptionally longoff-duty periods of 30.3 and 31.2 hours. We consideredthem to be outliers (see Discussion) and did not includethem in regression analysis. For each day of incubation,the data from all the birds and all seasons was searched,and any well-defined bout that was found, on- or off-, wasassigned to the day of incubation on which it ended. Forexample, on day six there ended three well-defined off-bouts, and one well-defined on-duty bout. In Fig. 5, it canbe seen that incubation bouts in knots were shorter in thefirst days of the incubation period. We never recorded anest with a complete clutch being unattended during 46visits to six nests. By assuming that the male off-bouts arethe on-bouts of the female, we tested the relative boutlength. Analysis of covariance of bout length showed thatit did not depend on its type – on or off, that is the bird’ssex (Ft,l = 0.213, p = 0.648); therefore we calculated best fit

regression for a joint set of on- and off-duty bouts (Fig. 5).

After hatch, the daily average signal was higher thanduring incubation and had a trend of slight increase withdate (Fig. 1a). Day-to-day oscillations in average lightsignal were more pronounced than in the pre-incubationperiod (relative time <-26 days; Fig. 1a). There wereclearly more signal oscillations (caused by warming thechicks) at hatch and during about five days after hatching(Fig. 1b). The amount of total daily shaded time tendedto decrease with the chicks’ age (Fig. 6). The GL signalsdid not show a clear end of brooding.

Phenological events on the breeding grounds for the maleswith GLs are presented in Table 1. They are based both onGL readings and direct observations. One of the twomales was first observed one day, and the other five daysafter arrival to the breeding grounds (as indicated by theGL fixes). The birds started to incubate 13 and 17 daysafter arrival. Fledged young were last seen being accompanied

Loktionov et al. l Incubation, chick rearing and breeding phenology of Red Knots in sub-Arctic Far Eastern Russia--147

Fig. 4. Changes of light signal recorded by the geolocator output of male Red Knot GL 180 from the moment ofdeployment in the middle of incubation until its southward departure in 2011. The value is high when the GL is exposedto light, and lower when shaded. Observations during visits to nests are marked with vertical arrows: incubation bymale (M), by female (F), nest empty (N); male seen with a brood (B) or alone (A). Thick horizontal line shows on-duty(unbroken line) and off-duty (dashed line) periods of the bird recognized from GL signal (see Methods). Vertical dashedlines separate daytime and twilight/night periods.

Wader Study 122(2) 2015148

by GL males when they were 19, 20 and 23 days old, butthe birds could have stayed together in a family group forlonger. According to the GL data, males #176 and #180remained in the study area 28–28.5 days after their chickshatched in 2011. GL 176 was last seen 19 days after hatch,and GL180 28.5 days after hatch. Comparison of dates oflast direct observation and actual departure from breedinggrounds of other males with GLs shows similar differences:0–16 days (10.3±7.3 SD, n=4).

DISCUSSION

With help of the GLs we obtained information aboutsome of the breeding characteristics of the ChukotkaRed Knot subspecies C. c. rogersi never previously observed.The incubation behaviour of Red Knots is poorly studied,which can be partly explained by the incubating birdssitting very tight on their nests when disturbed, makingit very challenging to find their clutches (e.g. Flint 1972,Hobson 1972, Tulp et al. 1998). It is already known thatincubation bouts in Red Knots last for many hours withmales and females exchanging duties only a few timesper day (Burger et al. 2012, Dorogoi 1982, Tulp et al.1998). Our data support the conclusions of earlier studies(Burger et al. 2012, Gosbell et al. 2012) that GLs providevaluable and reliable information about breeding parametersof waders in the Arctic. For the first time, direct observationsof Arctic shorebirds with GLs confirmed that the lightsignals of GLs indicate incubation and identify periodsof both chick presence in the nest and early stages ofbrooding accurately. However, because both parents maytake turns to incubate during hatching, and the first/lastshift may add one day, the GL signal does not allow exactcalculation of the number of hours from the start of

hatching to nest departure. Following earlier studies(Dorogoi 1982, Tomkovich & Dondua 2008, Tomkovich& Soloviev 1996, Tulp et al. 1998, Whitfield & Brade1991) we confirmed that female Red Knots do not staywith their chicks when the chicks leave the nest. Therefore,the pattern of GL signals should differ between the sexesas soon as the chicks hatch.

Incubation behavior

The start of egg-laying was not detected in the GL signalin males, possibly because incubation time was insufficientuntil more eggs were laid. The frequency distribution ofthe duration of shading episodes, which was about thesame for both GL 176 and GL 180, reveals two peaks at20 min and 6 hrs (Fig. 3). Short low-light episodes outsidethe incubation period could presumably be caused byshading of the GL during resting, feeding, wading, orchick-rearing activities, while long ones took place onlywithin the dates of daily-median signal oscillation, i.e.during incubation (an incubation bout could consist ofseveral shading episodes with short high-light spikes inbetween). The percentage of low-light samples in incu-bation bouts was 88.9% (±5.56 S.D., n=23).

Incubation bouts that were not interrupted by nightshadealways lasted longer than 5.7 hrs (Table 2) during the 11incubation periods on three nests recorded by two GLs.After adding incubation bouts that were interrupted by anightshade to the analysis and applying the same approachto off-duty bouts, we found that the length of incubationbouts and off-duty ones did not differ at the same stageof incubation (Table 2). Because females incubated duringoff-duty bouts of males (see above), this indicates that in-cubation bouts of both sexes were similarly long.

Table 2. Length of incubation bouts and off-duty periods (in hours) of two male Red Knots at three nests in southernChukotka, Far Eastern Russia, according to GL light signals uninterrupted and interrupted by nightshade.

n Range Mean ±SD

Incubation bouts not interrupted 10 6.5–20.2 12.80 ±4.36

Off-duty periods not interrupted 1 5.7 5.7

Incubation bouts interrupted 13 10.1–22.7 18.85 ±3.83

Off-duty periods interrupted 28 11.7–31.2 18.63 ±4.85

Total incubation bouts and off-duty periods, both notinterrupted 11 5.7–20.2 12.15 ±4.66

Total incubation bouts and off-duty periods, both interrupted 41 10.1–31.2 18.70 ±4.50

Grand total – interrupted and not interrupted incubationbouts and off-duty periods combined in one series 52 5.7–31.2 17.31 ±5.24

Loktionov et al. l Incubation, chick rearing and breeding phenology of Red Knots in sub-Arctic Far Eastern Russia--149

Based on prior studies where incubation bouts have beenestimated (see below) and the minimum bout length of5.7 hrs obtained in our study, we suggest that a cumulativeperiod of four hrs of low-light signal within a five-hr pe-riod is a sufficient criterion for identification of an incu-bation bout using GLs .

We do not know the reason or reasons for the two excep-tionally long off-duty periods of males recorded by theGLs (30.3 and 31.2 hr). These could arise because the GLwas somehow exposed to light even though the bird wassitting on the nest or perhaps the bird failed to return tothe nest, as suggested in other studies in which very longincubation periods have been recorded (Burger et al. 2012,Lislevant & Byrkjedal 2004). We assume that the one com-paratively short off-duty data point on the last day of in-cubation (Fig. 5, day 23) reflects the strong attraction ofthe male to the hatched chicks, and his reluctance to re-linquish care to the female.

During the incubation bouts of GL males there were fre-quent brief light signals (5–20 min long) which couldhave resulted from the behavior of birds, e.g. changingposition or turning the eggs and exposing the GL to light.It was found that neither the start nor the termination ofincubation bouts (i.e. the times that parents changed overincubation duties), occurred at any particular time of aday (e.g. Fig. 4).

An automatic camera placed near a Red Knot nest onWrangel Island (C. c. roselaari subspecies) indicated thatboth sexes incubate for similar periods and that theychange incubation duties 2–4 times per day. Each partner

incubated continuously for periods of 2–11 hrs and eggswere only left unattended for up to two hrs during veryearly incubation (Dorogoi 1982). Another study, in whichradio-tags were used to follow the movements of birds,also showed that males and females incubate for similarperiods, and that incubation bouts usually last for 15–20hrs. The incubation rhythm was ‘free-running’, making itimpossible to predict which partner would be incubatingat any one time of the day (Tulp et al. 1998). Incubationbouts of Canadian rufa Red Knots derived with GLs lasted6–20 hrs (Burger et al. 2012). The incubation patterns(by bout lengths) at the beginning of the incubation periodin our study (Fig. 5) are consistent with those recordedby Dorogoi (1982), but in the middle of the period aremore similar to those found by Tulp et al. (1998), and ingeneral are most similar to the patterns shown by GL datafor rufa Red Knots (RRP, unpubl.).

Instances of eggs being unattended for up to two hrs dur-ing very early incubation are mentioned by Dorogoi(1982). Unfortunately he did not determine whether theclutch had been completed, or whether the camera thatwas set up close to the nest had any influence on the bird’sbehavior. Dorogoi (1982) also mentioned that an incu-bating bird turned the eggs in the nest about four timesper hour. Our field observations indicate virtually constantincubation of complete clutches. This is consistent withdirect observations of incubating Red Knots by Whitfield& Brade (1991) who showed that Red Knots were presenton the nest for 99% of the time and only made 0.5 ±0.2SD shifts in position per hour. Therefore we assume thatthe off-duty periods of males must be equal or very close

Fig. 5. Length of incubation bouts and off-duty periods in Red Knot males on their southern Chukotka, Far EasternRussia, breeding grounds in 2011 and 2012 as shown by GLs plotted against incubation period (two off-duty periodsexceeding 30 hr were considered outliers and not used in the analysis). The off-duty periods are most likely the periodthat the females (without GL) were incubating (see text). The equation of the fitted curve for both types of boutscombined is: y = 7.9 + 1.35x - 0.037x2 (R2 = 0.495, p = 0.0021).

Wader Study 122(2) 2015150

to the incubation bouts of females on the same nests. Thisexplains why we found no difference in incubation boutsand off-duty periods (Fig. 5). This conclusion is in accor-dance with previous studies that found an equal role ofsexes in incubation (Burger et al. 2012, Dorogoi 1982,Tulp et al. 1998). Burger et al. (2012) assumed that “someincubation bouts that appeared to be as long as 20 hrs ina 24 hrs period … may result from compensation, whena mate failed to return”. Both incubation bouts and off-duty periods of about 20 hrs long were also common inour GL males, especially in the second half of the incuba-tion period (Fig. 5), as well in the study of Tulp et al.(1998). Apparently, Red Knots normally spend such longperiods on their nests, but this is uncommon among otherwader species (e.g. Bulla et al. 2013, Kondratyev 1977,Norton 1972).

The shape of the plot of temporal change in the length ofincubation bouts in Red Knots of both sexes is a skewedparabola (Fig. 5). A similar result has been shown for in-cubation bouts in Ruddy Turnstones Arenaria interpres(Gosbell et al. 2012). More data are needed to determinewhether this pattern is typical of incubation bouts inwaders generally.

Incubation period length

We found that the GL males in both nests incubated for atotal of 23 days in 2012. Red Knots pairs start virtuallycontinuous incubation from the laying of the third egg(PST & EYL unpubl. and PST unpubl. observations onTaimyr, Siberia), sometimes from the second (Alaska,James Johnson, pers. comm.), and chicks stay in the nestbeing brooded by a parent for about half a day after thehatching of the last chick (Nettleship 1974, our observations).

Possibly females start incubation later than males becausethey still need to feed actively to develop the last egg(s)and to replenish their body stores after egg-laying. Wewould thus predict that females incubate at least twodays less than males. The incubation period of the twoGL males in our study lasted ca. 21–21.5 days, if wesubtract the day that is taken by laying the last egg(s) andthe half day that chicks still stay in the nest from the total23 days of incubation as indicated by the GLs. The incu-bation period from clutch completion until the hatchingof the last chick was estimated by direct observation onone nest to be about 21 days. In other studies observed orinferred incubation periods were 21.5–22.4 days (onenest observed, Nettleship 1974) and 18–24 days (11 GLs,Burger et al. 2012) in Canada, 23 days on Wrangel Island,Russia (one nest observed, Dorogoi 1982) and 21.5 dayson Taimyr, Russia (four nests observed, Tomkovich et al.1994). Thus, our results are consistent with earlier studies.

We believe that the large variation in the estimated dura-tion of incubation found by Burger et al. (2012) can partlybe explained by the lengths of incubation periods of malesand females being different. The data collected by Burgeret al. (2012), which is more plentiful than ours, show twoseparate groups of data with different length of the incu-bation periods of 18–20 and 23–24 days, respectively. Weassume that the first group represents females with shorterincubation periods, and the second group representsmales. Similarly, the GL knots in the study by Burger etal. (2012) showed distinctly different post-incubation pe-riods: one group stayed 4–9 days and another group stayedmuch longer after hatch: 20–21 days. The post-hatch lightsignal pattern of the GLs of the birds in the second groupwas similar to ours in that period and characteristic chick-

Fig. 6.Aggregate time that GLs were shaded each day expressed as the percentage of total daylight hours (i.e. excludingnight hours) plotted against the age of the chicks. Data are for five chick-rearing periods of three male Red Knots insouthern Chukotka, Far Eastern Russia. The equation of the regression line is: y = 13.25 – 0.33x (R2 = 0.174, p = 0.113).

Loktionov et al. l Incubation, chick rearing and breeding phenology of Red Knots in sub-Arctic Far Eastern Russia--151

brooding (Burger et al. 2012). We believe that GL dataduring the breeding season of Red Knots can not only beused to collect relevant information about the reproductivecycle (and whether it was successful), but also, in suc-cessful nests, the duration of the incubation period and/orthe post-breeding period might also indicate the sex ofthe birds. This may be possible for other Arctic and sub-Arctic wader species with a strongly reduced role of fe-males in the post-hatching chick attendance, such as GreatKnots Calidris tenuirostris (Tomkovich 1995, 2001).

Post-hatch period

This study demonstrates that GLs can be helpful in iden-tifying some parameters of brooding behavior in (sub-)Arctic waders (Fig. 6). It is known that the proportion oftime that wader parents spend brooding their chicks isinversely related to ambient temperatures (e.g. Beintema& Visser 1989, Krijgsveld et al., 2003, Sullivan Blanken &Nol 1998). This may explain the large daily variation inbrooding time shown in the Figs. 1b & 6, since chicks ofthe same age hatched on different days, and may have ex-perienced different temperatures. Nevertheless, broodingtime gradually decreased with the progression of the sea-son, and our data suggest that chicks were highly depend-ent on parental brooding for thermoregulation duringthe first five days after they left the nest. Unfortunately, itwas not possible to determine when chicks became com-pletely independent of brooding or when they fledgedand families dispersed.

Breeding phenology

Unlike other studies based on GL data (Burger et al. 2012,Gosbell et al. 2012), we were unable to obtain informationabout the length of complete breeding seasons becausedeployment and retrieval of GLs took place during thisseason. Nevertheless, the GLs provided accurate infor-mation about dates of arrival to and departure from thebreeding grounds (Tomkovich et al. 2013), as well as aboutthe dates on which incubation started and the family de-parted from the nest.

For Red Knots of the Chukotka sub-Arctic population,the dates of arrival, start of incubation, and hatching areabout 1–2 weeks earlier than in high Arctic populations(e.g. Burger et al. 2012, Dorogoi 1982, Nettleship 1974,Tomkovich & Dondua 2008, Tomkovich et al. 1994, Tulpet al. 1998, Whitfield & Brade 1991). However, the numberof days that birds spent between arrival to the breedingarea and start of incubation in our study (13 and 17 days)falls within the range estimated for the Canadian high-Arctic (9–31, mean 16.5 ±1.6 days, Burger et al. 2012). Itis noteworthy that after nesting the two GL males in ourstudy stayed on their sub-Arctic Chukotka breedinggrounds significantly longer (28–28.5 days) than 17 un-sexed knots in the Canadian Arctic (1–21 days, mean 8.6±1.4, Burger et al. 2012) and longer also than males onthe Taimyr peninsula, N Russia (22–24 days, Tomkovichet al. 1994). This is possibly related to a milder climate inChukotka and/or lower food abundance for accumulationof body reserves for subsequent southward migration.

In conclusion, we show that the use of GLs can yield im-portant and relevant information that extends our knowl-edge about various aspects of the natural history of Arcticand sub-Arctic waders. As proposed earlier by Burger etal. (2012), the use of GLs on Arctic breeding grounds inparallel with direct observations provides many advan-tages in comparison with results obtained by other means.Although our results are based on few data, we hope thatour findings and conclusions will soon be confirmed bymultiple studies of various wader species in the circum-polar Arctic and sub-Arctic.

ACKNOWLEDGEMENTS

Studies in Meinypilgyno area, Chukotka, were undertakenwithin the framework of the International Arctic Expeditionof BirdsRussia organized by Evgeny E. Syroechkovskiyand funded from multiple sources. Nikolay N. Yakushev,Elena V. Golub, Elizabeth V. Tambovtseva, Simon Buckell,Phil Palmer and Elena G. Lappo helped in search for nestsand broods of Red Knots. Lawrence J. Niles and JoannaBurger provided the first set of GLs. Evgeny Syroechkovskiy,Gerrit Vyn and Roland Digby were helpful with logisticsto provide GLs for the study. Some valuable commentsand suggestions for the early version of manuscript weremade by Theunis Piersma and Humphrey Sitters, and themanuscript was fundamentally rewritten after commentsby Martin Bulla, Joanna Burger and Jeroen Reneerkens.Polina A. Volkova and Ivan G. Pokrovskiy providedstatistical advice. We are grateful to all these people. Workon this paper by PST has been done within the frameworkof the project No.  01200117416 ‘Taxonomic and bio-chorological analysis of Animalia as a framework forinvestigation and conservation of the structure of biologicaldiversity’ in Zoological Museum of Moscow State University.Statistics were performed using RFMEFI59014X0001 com-putational facilities, supported by the Russian Ministryfor Education and Science.

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