Reproductive characteristics of female Bengal tigers, in Ranthambhore Tiger Reserve, India

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  • ORIGINAL PAPER

    Reproductive characteristics of female Bengal tigers,in Ranthambhore Tiger Reserve, India

    Randeep Singh & Qamar Qureshi &Kalyanasundaram Sankar & Paul R. Krausman &Surendra Prakash Goyal

    Received: 25 March 2014 /Accepted: 15 April 2014# Springer-Verlag Berlin Heidelberg 2014

    Abstract Reproductive characteristics of tigers (Pantheratigris) are important to understand population viability. Westudied the reproductive parameters of female Bengal tigers(P. t. tigris) in a dry, tropical, deciduous habitat inRanthambhore Tiger Reserve (RTR), western India, fromApril 2005 to March 2010. We monitored tigers by directobservation and with cameras placed throughout their habitat.The potential breeding population included 13 adult females.The average age at first reproduction was 3.3 years; 34 cubswere born during the study period (6.20.82 per year). Sixty-six percent of the births occurred between October and De-cember. Mean litter size was 2.260.52 (n=13, range=13).The sex ratio of 32 cubs was 1.29 M:1.00 F. The survival rateof cubs (3 years old. Only 2 of the 13 femalesreproduced twice during the 5 years of the study. The birthinterval was 33.43.7 months (range 2465 months). Themean reproductive rate was 0.590.23 cubs/female/year.Our study indicates that tiger populations can grow rapidly ifthe habitat provides adequate protection, an adequate popula-tion of prey, and minimal to no poaching.

    Keywords Camera trap . Litter size . Mortality .Pantheratigris tigris . Sex ratio . Survival

    Introduction

    Reproductive success is a key to survival and continued exis-tence for any species, and understanding species reproductiveparameters (e.g., age at first reproduction, reproductive rate,liter size, interbirth interval, and breeding period) is critical todeveloping effective conservation strategies (Carter et al.1999). Reproductive parameters are important to determinepopulation turnover, potential growth rates, and are importantindicators to detect the lineage persistence in a population (i.e.,lineage loss, individual fitness, population viability [Kelly2001; Holt et al. 2003]), population viability (Kelly 2001;Balme et al. 2012), and to examine meta-population dynamics(e.g., determining the reproductive output of source popula-tions; Smith and McDougal 1991; Chapron et al. 2008).

    Reproductive data are available for some long-lived carni-vores (i.e., lions Panthera leo; Packer et al. 1988), cheetahs(Acinonyx jubatus; Kelly et al. 1998); leopard (Pantherapardus; Balme et al. 2012), and pumas (Puma concolor;Logan and Sweanor 2001). Yet reproductive parameters ofwild tiger (Panthera tigris) populations are sparsely availableand may vary over their global range. The limited informationon reproductive parameters has been obtained from studies inIndia (Schaller 1967; Sankhala 1978; Chundawat et al. 2002;Singh et al. 2013a), Nepal (Sunquist 1981; Smith andMcDougal 1991; Smith 1993), and the Russian Far East(Smirnov and Miquelle 1999; Kerley et al. 2003). Reproduc-tive parameters may vary among the subspecies of the popu-lations because of the different climatic conditions, habitats,prey densities, and other environmental parameters (Kerleyet al. 2003). Information on how reproductive parameters varyamong subpopulations of the same subspecies surviving indifferent habitats is essential for range-wide conservationplanning (Kerley et al. 2003).

    We present reproductive data collected from 2005 to 2010on a protected tiger population in the dry, tropical habitat of

    Communicated by C. Gortzar

    R. Singh (*) :Q. Qureshi :K. Sankar : S. P. GoyalWildlife Institute of India, Post Box # 18,Dehradun 248 001, Uttarakahnd, Indiae-mail: randeep04@rediffmail.com

    P. R. KrausmanBoone and Crockett Program in Wildlife Conservation,University of Montana, Missoula 59812, USA

    Eur J Wildl ResDOI 10.1007/s10344-014-0822-3

  • Ranthambhore Tiger Reserve (RTR), Rajasthan India. Thepopulation in RTR represents a unique gene pool (Sharmaet al. 2008), which is adapted to survive harsh and inclementweather conditions during summer. The open, thorny, decid-uous forest with scanty vegetation and a good road network inRTR provided ideal conditions for tiger sightings (particularlyin the valley and other low-lying areas). Geographic closure ofthe population and easy accessibility provided an opportunityto monitor reproduction through a combination of direct ob-servations and camera trapping. We used an extensive datasetcompiled on tigers (Singh et al. 2013a, b) to establish baselineinformation on reproductive parameters and enhance the un-derstanding of tiger reproductive ecology to facilitate theconservation to improve management strategies for thespecies.

    Materials and methods

    Study area

    The study was conducted in RTR (25 54 to 26 12 N, 7622 to 76 39 E), in Sawai Madhopur district of Rajasthan,India. Intensive data collection was undertaken in the corezone (392 km2). The RTR is located on the Aravalli andVindhya hill ranges. The region received an average annualrainfall of 800 mm, and temperatures were as low as 2 C inJanuary and as high as 47 C in May. The vegetation of RTRcorresponded to those of northern tropical, dry, deciduousforests and the northern tropical thorn forest (Champion andSeth 1968). The vegetation of RTR is representative of atypical, dry, and deciduous dhok (Anogeissus pendula) forest.Apart from dhok, the other species commonly found arekadaya (Sterculia urens), salai (Boswellia serrata), raunj(Acacia leucophloea), amaltas (Cassia fistula), palash (Buteamonosperma), tendu (Diospyros melanoxylon), gurjan(Lannea coromandelica), and jamun (Syzigium cumini).Ranthambhore was characterized by a subtropical dry climatewith four distinct seasons as follows: winter (DecemberFeb-ruary), summer (MarchJune), monsoon (JulySeptember),and post monsoon (OctoberNovember). Carnivores in-cluded tigers, leopards (P. pardus), sloth bears (Melursusursinus), and striped hyaenas (Hyaena hyaena). The RTRsupported five species of wild ungulates, including the chital(Axis axis), sambar (Rusa unicolor), nilgai (Boselaphustragocamelus), chinkara (Gazella gazelle), and wild pig (Susscrofa).

    Camera trapping

    An intensive camera trapping study was conducted in the corearea of RTR in 2005 (Chauhan et al. 2005) after the decline ofthe tiger population from unknown causes in 2004 (S. P.

    Goyal, personal observation). During 2005, the tiger popula-tion in RTR consisted of 19 individual tigers (4 M, 10 F, and 5cubs [3 M and 2 F 1 month in a camera trap, we attempted toobserve them on foot patrols during the day and at night (usingsearch lights in a vehicle near water points and roads). Themonitoring of tigers in RTR provided information about the

    Eur J Wildl Res

  • reproductive characteristics of female tigers including theproportion of females that reproduce each year, annual birthrate, age at first reproduction, seasonality of birth, meaninterval between litters, mean litter size, recruitment rate,cub mortality, sex ratio of litters, and cub age at dispersal,emigration, immigration, and mortality.

    We used the following age categories (Karanth 2003): cubs(1 year old, associated with, and dependent on theirmothers), juveniles (2 years old), subadults or post dispersalfloaters or transients (>2 years old, no longer associating withtheir mothers but not reproducing), and breeding adults

    (3 years old). The proportion of females (3 years old) thathad reproduced was based on direct observations and photo-graphic evidence from camera traps.

    Breeding time and litter monitoring

    We assumed that breeding occurred if we observed lactatingtigers or could estimate the breeding time based on the ap-pearance of cubs. We did not have any radio-collared individ-ual that gave us actual information, breeding month of femaletiger, and when cubs start moving with the mother. Thus, we

    Fig. 1 Area of intensive sampling in Ranthambhore Tiger Reserve, India using camera traps 20052010

    Table 1 Sampling efforts from April 2005 to March 2010 in Ranthambhore Tiger Reserve, India

    S.N. Season Duration Sampled area (km2) No. camera trapping station Trapping days Trap nights No. photo-captures

    1. Summer Apr-05 to May-05 160 30 60 358 31

    2. Winter Oct-06 to Mar-07 140 106 226 3,380 110

    3. Winter Nov-07 to Feb-08 233 224 80 4,480 173

    4. Summer Apr-08 to Jun-08 233 167 60 3,340 76

    5. Post monsoon Oct-08 to Nov-08 233 140 60 2,800 137

    6. Winter Jan-09 to Mar-09 233 194 60 3,880 206

    7. Summer Apr-09 to Jun 09 233 178 60 3,560 163

    8. Post monsoon Oct-09 to Dec-09 233 181 60 3,620 128

    9. Winter Jan-10 to Mar-10 233 165 60 3300 122

    Eur J Wildl Res

  • used backdating following published studies on tiger to esti-mate the breeding month of female tigers by backdating2 months from the first appearance of cubs because cubs startmoving with the mother when 2 months old (Smith et al.1987; Majumder et al. 2012). Litters were divided into fourdifferent seasons based on birth dates winter (DecemberFebruary), summer (MarchJune), monsoon (JulySeptember), and post monsoon (OctoberNovember).

    Therefore, once cubs were captured in a camera trap, wemade an intensive effort to observe litter size through pug-marks on the road, by direct sighting, or photo-capture in othercamera traps. We compiled the photographic data set of tigercubs starting from 2 months through 36 months and wecompared the photo-capture of cubs with our data setand estimated the approximate age of the cubs. The tigerpopulation, including cubs, was monitored throughout theyear (Table 1). We sexed animals as they aged andmatured based on size differences between male and fe-male siblings. Sex of cubs was identified by a combina-tion of opportunistic sightings and photographs obtainedthrough camera traps or by observing their genital inphotographs. The open, thorny, deciduous forest withscanty vegetation and a good road network in RTR pro-vided ideal conditions for tiger sightings. When monitor-ing tigers, we often encountered females with cubs and wespent 13 h in a particular place to observe the behaviorand activity of females and their cubs, which strengthenedour data to identify more accurately the sex of the cubs.In addition to camera traps, it provided an opportunity forus to know more accurately the liter size and sex of cubs.The sex of cubs was estimated after they were >12 monthsold.

    Reproductive rate

    We determined the proportion of females that reproduced eachyear, annual birth rate, mean individual birth rate, and recruit-ment rate. The proportion of breeding females that reproducedeach year was recorded through intensive monitoring usingcamera traps, intensive searches (i.e., foot patrolling in dayand night patrolling using search lights and vehicles) oppor-tunistic sighting, and pugmarks. The annual birth rate wasestimated as the number of cubs produced by all femalesdivided by the number of females in the population(>3 years; Persson et al. 2006). The annual mean proportionof breeding females producing cubs was calculated using themethod described by Persson et al. (2006). To estimate thelifetime productivity of individual tigers, the reproductivelyactive age of females was calculated (i.e., tigers were repro-ductively active from 4 to 14 years of age; Crandall 1964;Kleiman 1974; Nowell and Jackson 1996) and multiplied bythe mean annual birth rate.

    Estimation of survival rate at different ages

    The percentage of tigers alive was divided into stages:12 month old, juveniles (12 to 24 months old), and post-dispersal floaters or transients (>24 month old). Tiger cubsstart moving with their mother when they are 2 months old,and tracks of 34-month-old cubs were regularly seen withthose of the mother. Cubs frequently remain with the motheruntil they were 1824 months old (Smith 1993). Survival ofcubs 4 times/month until the cubs were12 months old to estimate the number of cubs that survived.Survival between the ages of 1224 and >24 months (dispers-al age) was determined through photo capture of individualsby camera traps and continuous individual-based monitoringprotocol (Singh 2011). We used the KaplanMeier methodwith a staggered-entry design (Pollock et al. 1989) to estimatethe survival rates of cubs of the different age classes. Wepooled data from all years to obtain a sufficient sample size.Confidence intervals (95 %) for survival rates were derivedaccording to Pollock et al. (1989).

    Results

    Sampling efforts

    Camera traps were operated for from April 2005 to March2010 (726 days, 28,718 trap nights over 3 different seasons,1,231 photo-captures of tigers; Table 1).

    Breeding population and productivity

    During the study period, 13 breeding females were identifiedby camera traps and monitored. All 13 females gave birth atleast once, and 2 females gave birth twice during the studyperiod (15 litters; Table 2). The minimum number of breedingfemales in a year was 2, and the maximum was 5 (Fig. 2). Wedid not document any litter in 2009. Two of 13 females weremonitored from birth, and they reproduced for the first time at33 and 48 months. Two females bred twice, and the periodbetween successive births was 24 and 65 months. The meaninterbirth interval was 33.43.7 months.

    Birth period, litter size, and sex ratio

    The mean litter size was 2.260.39 (n=15, range=13).There were three cubs in five of the litters, two cubs in ninelitters, and one cub in one litter (Table 3). One female raisedfive cubs (1 M and 4 F) in two litters. Of 34 cubs from 15litters, we recorded the sex of 32 cubs produced by 12

    Eur J Wildl Res

  • breeding females. There was no significant difference in thesex ratio of cubs at birth, although it was slightly male biasedwith 1.29 M:1.00 F (2=1.82, df=3; P=0.61). Ten breedingfemales gave birth to more males than to females (Fig. 3). Ourdata suggested that most of the litters were born in early and latewinter (n=15 litters from 13 mothers). Most births reported inthe post monsoon, 27 % in winter, and 6 % in monsoon. Nobirths were reported during summer (Fig. 4).

    Reproductive rate

    Twenty-seven individual tigers 4 years old (11 F and 16 M)survived until March 2010. The annual mean proportion offemales producing cubs was 0.260.08 and ranged from 0.15to 0.63 (Table 4). The mean annual birth rate was 0.590.23

    cubs/female (Table 4). Assuming a female is reproductivelyactive from 4 to 15 years of age, the total lifetime productivitywould be 6.49 cubs/breeding female in RTR.

    Mortality and survival rate of cubs

    Cubs died due to several causes (Table 3). The survival rate ofcubs

  • 0.610.91; n=29; Table 5). Two juvenile males survived>1 year and died when
  • tigers in the Russian Far East gave birth all through the year,most frequently in late summer (AugustOctober, >50 %),which indicates that conceptions are most frequent duringMarchMay (Kerley et al. 2003). Data on 530 litters of Amurtigers born in zoos in the northern hemisphere indicate thatmost cubs are born between April and June (Seal et al. 1987).Our findings on the breeding period of the tiger in the tropical,dry, deciduous h...

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