SHORT COMMUNICATION

The asynchronous timing of antler casting of Reeves’muntjac (Muntiacus reevesi)

Norma G. Chapman & Luděk Bartoš

Received: 7 November 2013 /Revised: 4 March 2014 /Accepted: 14 March 2014 /Published online: 4 April 2014# Springer-Verlag Berlin Heidelberg 2014

Abstract From 1973 until the present time, captive Reeves’muntjac (Muntiacus reevesi) have been observed in England.The dates of casting of both antlers have been recorded for 25bucks, totalling 121 antler cycles. All casting dates were be-tween 1 May and 17 July (63.64 % of the cycles occurred inMay, 34.71 % in June, and only 1.65 % in July). Only 13.2 %of the antler cycles were synchronous. In 45.71 % of cases, theleft antler was cast 1 day or more before the right one, whereasin 54.29 % of cases, the reverse was true. For 57.14 % of cases,the time between castings of the first and second antlers was upto 3 days, and for 32.38 % of the cases, the interval was 4 to8 days, and in 10.48 %, the difference was 9 to 13 days. Allbucks cast their antlers asynchronously at least in some of theantler cycles. No external factor, which would be responsiblefor this, was detected. Significant variation across season hasbeen shown with no apparent trend. Although records onsubsequent seasons were available for most of the bucks, therewas a zero repeatability of the process.

Keywords Muntjac . Cervid . Antler . Asynchrony .

Muntiacus reevesi

Introduction

Various authors have stated that both antlers are often cast onthe same day (e.g. Goss 1983), but the species of deer and the

number of antler cycles over which observations were maderarely have been reported.

A colony of captive Reeves’muntjac provided the opportu-nity to test whether this generalisation is applied to this prim-itive non-herding, aseasonally breeding cervid native to Chinaand Taiwan but introduced to England where, now, it is widelydistributed and abundant (Chapman et al. 1994; Ward 2005).

Methods

From 1973 until the present time, muntjac has been observedin England (at latitude 52° 20′) within three enclosures (eachat least 1,000 m2, with trees, shrubs, grass and other vegeta-tion) situated adjacent to the house of one author. The deerwere fed on herbage, root crops and fruits. The dates of castingof both antlers have been recorded for 25 bucks, totalling 121antler cycles. The maturity of the bucks ranged from first headof antlers to 15th head. Casting was defined as synchronouswhen both antlers were cast on the same day; an interval of1 day or more was asynchronous.

All data were analysed with the aid of SAS System version9.3 (SAS Institute, Inc.). The analysis was made in three steps.First, we tested the probability of asynchronous casting by themuntjac bucks and the association between this and otherfactors, using a general linear mixed model (GLMM; PROCGLIMMIX for binary distribution). To account for the use ofrepeated measures on the same individuals, analysis wasperformed using mixed model analysis with ID of the bucksas a random factor. Fixed effects were classes ‘month’ (May,June, July), ‘season’ (38 levels; 1974, 1976 to 2007 and 2009to 2013), ‘sharing the enclosure with other males’ (yes/no),‘sharing the enclosure with females’ (yes/no), ‘enclosure’(H, A, P) and a continuous variable ‘age’ (416 to 1,420 days),‘number of males sharing the enclosure’ (1 to 5), ‘number offemales sharing the enclosure’ (0 to 4) and ‘dominant index’

Communicated by C. Gortázar

N. G. Chapman (*)29 The Street, Barton Mills, Suffolk IP28 6AA, UKe-mail: ngchapman@btopenworld.com

L. BartošDepartment of Ethology, Institute of Animal Science,Přátelství 815, 104 00 Praha Uhříněves, Czech Republice-mail: bartos.ludek@vuzv.cz

Eur J Wildl Res (2014) 60:563–565DOI 10.1007/s10344-014-0815-2

(ranging between 0 and 1, the rank of a buck within a givenenclosure, where the alpha buck=1, etc., was divided by thenumber of bucks in the paddock; after Bartoš and Perner 1985).

Second, we focused on the asynchronous casting data onlyand tested associations between the dependent variable, thetime between castings of the first and second antlers (days),and the same random and fixed effects as previously, usingPROC MIXED for GLMM.

Third, finally, we used data on those bucks for whom wehad records on at least two consecutive antler cycles andassessed the repeatability of the time between castings of thefirst and second antlers by computing an intraclass correlationcoefficient (ICC) (Sokal and Rohlf 1981), using the estimatesof within- and between-subject variability obtained from aone-way analysis of variance model (Lessells and Boag1987). The ICC is an overall index of repeatability rangingbetween 0 and 1. The ICCwas derived from a GLMM (PROCMIXED) accounted for factors affecting the time betweencastings of the first and second antlers. In the PROCMIXED, the ICC estimate = compound symmetry estimate/(compound symmetry estimate + residual variance estimate).In the GLMMmodel, the tested fixed effect was the season inthe REPEATED statement.

In all cases, we constructed the GLMMby entering first theexpected factor and/or factors and then checking the modelwith addition of the factors, which could also affect the result.The significance of each fixed effect in the mixed GLMMwasassessed by the F test. If not specifically explained, nonsig-nificant factors (P>0.05) were dropped from the model and

will not be mentioned any further. Where appropriate, wetested interaction terms. Association between the dependentvariable and fixed effect was estimated by fitting a randomcoefficient model using PROC MIXED as described by Taoet al. (2002). We calculated predicted values of the dependentvariable and plotted them against the fixed effect with predict-ed regression lines for month.

Results

Only 13.2 % of the 121 antler cycles were synchronous. In45.71 % of cases, the left antler was cast 1 day or more beforethe right one, whereas in 54.29 % of cases, the reverse wastrue. For 57.14 % of cases, the time between castings of thefirst and second antlers was up to 3 days, and for 32.38 % ofthe cases, the interval was 4 to 8 days, and in 10.48 %, thedifference was 9 to 13 days.

All bucks cast their antlers asynchronously at least in someof the antler cycles. The greatest number of paired castingdates for an individual buck was 13 (n=4). These bucks castsynchronously only once out of 14 antler cycles, once out of7 cycles, and never in 2 and 4 cycles, respectively.

All casting dates were between 1 May and 17 July(63.64 % of the cycles occurred in May, 34.71 % in June,and only 1.65% in July). For first heads (n=21), the range (10May to 25 June) was almost as wide as for older bucks (1Mayto 17 July). The median date for all castings of left and rightantlers was 26 May.

Fig. 1 Time between castings ofthe left and right antlers across theseasons (days, mean±S.E.) withthe number of muntjac malesinvolved above bars

564 Eur J Wildl Res (2014) 60:563–565

The GLMM has detected none of the analysed fixedeffects to affect significantly whether the buck would castasynchronously. Even age did not play any role (GLMM,F(1, 92)=0.12, NS). In the model focused on asynchronouscycles only (n=105), just the time between castings of thefirst and second antlers appeared variable across the sea-sons (F(37, 81.4)=1.96, P=0.006, Fig. 1). Of the 25 bucks,for 19 of them, we had two and more records on subsequentantler cycles. These 19 bucks showed very poor repeatabil-ity in the number of days, which elapsed between castingsof the first and second antlers (0.0397).

Discussion

For all castings of left and right antlers, the median date 26May corresponded with an earlier report on a small subset ofthe present data that had reported 27 May for the left and 26May for the right (Chapman and Chapman 1982). Althoughthe incidence of synchronous casting was only 13.2 %, morethan half the pairs of antlers were cast within 3 days. However,no external factor, which would be responsible for this, wasdetected. Significant variation across season has been shownwith no apparent trend (Fig. 1). Although records on subse-quent seasons had been available for most of the bucks, therewas a zero repeatability of the process.

For comparison with other species, the most comprehen-sive data are those for a park herd of red deer (Cervus elaphus)where 146 casting dates for 25 stags showed that synchronyoccurred in 60.3 % (Bartoš and Perner 1991). The range ofintervals between castings of left and right antlers was notgiven. In muntjac, we could not confirm their result that theasynchronously casting males were on the average older andhigher ranking than those casting synchronously.

For sambar (Cervus unicolor), data had been published for67 antler cycles of an unspecified number of stags in a park inIndia (Acharjyo 1982). Synchronous casting occurred on44.8 % of occasions and 86.6 % of castings of both antlersoccurred within 3 days. The maximum interval between cast-ing left and right antlers was 6 days. For hog deer (Axisporcinus), a delay of several days was sometimes observedin a park in Australia (Mayze and Moore 1990), and for roedeer (Capreolus capreolus), up to 2 days has been reported(von Raesfeld 1970).

Bilateral synchrony, or at least close succession, in loss ofantlers is to be expected because the process occurs in re-sponse to a fall in testosterone levels (Bubenik 1982), even inthe special case of muntjac (Pei et al. 2009) in which the malesremain fertile during the growth of the next pair of antlers

(Chapman et al. 1997). Sheng (1991) reported two examplesof casting by captive Reeves’ muntjac in China as 14 and 16June and 6 and 8 May respectively.

The examples cited show that asynchronous castings arenot unusual and were frequent in the studied population ofReeves’ muntjac, but an interval of up to 13 days seems to besurprising long. Comparative information from a greater rangeof species would be of interest.

Acknowledgments Study was partly supported by the Ministry ofAgriculture of the Czech Republic (MZeMZERO074).

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