What Is The Size Of The Giraffe Population?

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Enquiry Article

Population structure of giraffes is afflicted past management in the Great Rift Valley, Kenya

Population structure of giraffes is afflicted past management in the Great Rift Valley, Republic of kenya

• Zoe Muller

ten

• Published: January iii, 2018
• https://doi.org/10.1371/periodical.pone.0189678

Figures

Abstruse

Giraffe populations in East Africa have declined in the by thirty years even so there has been limited research on this species. This study had four objectives: i) to provide a baseline population assessment for the two largest populations of Rothschild's giraffes in Kenya, 2) to assess whether at that place are differences in population structure between the two enclosed populations, three) to assess the potential and possible implications of different direction practices on enclosed giraffe populations to inform future decision-making, and four) to add to the availability of data available about giraffes in the wild. I used individual identification to assess the size and structure of the two populations; in Soysambu Conservancy betwixt May 2010 and January 2011, I identified 77 giraffes; in Lake Nakuru National Park betwixt May 2011 and Jan 2012, I identified 89. Population structure differed significantly betwixt the two sites; Soysambu Conservancy independent a high percentage of juveniles (34%) and subadults (29%) compared to Lake Nakuru NP, which contained fewer juveniles (five%) and subadults (15%). During the time of this written report Soysambu Conservancy independent no lions while Lake Nakuru NP contained a high density of lions (30 lions per 100km²). Lions are the main predator of giraffes, and preferential predation on juvenile giraffes has previously been identified in Lake Nakuru NP. My results suggest that high king of beasts density in Lake Nakuru NP may take influenced the structure of the giraffe population by removing juveniles and, consequently, may affect futurity population growth. I suggest that wildlife managers consider lion densities alongside breeding plans for Endangered species, since the presence of lions appears to influence the population construction of giraffes in enclosed habitats.

Citation: Muller Z (2018) Population construction of giraffes is affected by management in the Dandy Rift Valley, Kenya. PLoS I 13(1): e0189678. https://doi.org/10.1371/journal.pone.0189678

Editor: Elissa Z. Cameron, University of Tasmania, AUSTRALIA

Received: October iv, 2017; Accepted: November 30, 2017; Published: January 3, 2018

Copyright: © 2018 Zoe Muller. This is an open access article distributed under the terms of the Artistic Commons Attribution License, which permits unrestricted use, distribution, and reproduction in whatever medium, provided the original author and source are credited.

Data Availability: All relevant information are within the newspaper and its Supporting Information files.

Funding: This written report was funded by Chicago Zoological Social club, grant no. not available, www.czs.org; Chester Zoo, grant no. not available, www.chesterzoo.org; People's Trust for Endangered Species, grant no. not available, https://ptes.org; SeaWorld & Busch Gardens Conservation Fund, grant no. not available, https://swbg-conservationfund.org/; Fresno Chaffee Zoo, grant no. not available, www.fresnochaffeezoo.org; Denver Zoo, grant no. non bachelor, www.denverzoo.org. The funders had no role in written report design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Information near the size and distribution of giraffe populations is deficient and often outdated. A species-wide assessment by the IUCN Giraffe and Okapi Specialist Grouping was completed in 2016 [1], just information on subspecies population sizes and distributions is yet incomplete. Most population size information for giraffes is gleaned from general wildlife counts carried out across large areas [two–5], which give incomplete indications of affluence and distribution. Currently, information about giraffe population construction or census is express and comes from a few studies of single populations. Despite their scarcity, such data are condign increasingly important for understanding population changes, ecosystem dynamics and for the purposes of population monitoring, management and species conservation [1]. The 2016 IUCN Giraffa camelopardalis assessment and increasing bear witness of steeply declining populations [1] has highlighted a lack of cognition about this species and an urgent demand for research into conservation and management.

In this study I used individual identification to study the two of the largest populations of Rothschild's giraffes in Kenya; those inside Lake Nakuru National Park (LNNP) and Soysambu Conservancy (SC). LNNP has a high density of lions and is Kenya'south most visited National Park [6, 7]. Consequently, the giraffe population in LNNP is exposed to a high gamble of predation and frequent disturbance from loftier levels of tourist activity and vehicular traffic. In the adjacent SC at the time of this study there were no lions and minimal tourism activities, so giraffes in this site were exposed to depression, or no, risk of predation, and minimal disturbance from limited vehicular activity. Reports have previously suggested that lions in LNNP preferentially casualty on giraffe calves [viii] but it is unclear what the consequences of this are, if any. If predation chance by lions has a significant impact upon giraffe calf survival, and then I expect that LNNP will accept significantly fewer calves than the population in SC.

This written report had the following aims: i) to provide a baseline population assessment for each population, ii) to compare age class structures, grouping composition and sexual activity ratio between sites, iii) to analyse the patterns of giraffe population size alter over time in LNNP alongside lion densities, iv) to add to the availability of information about giraffes in the wild. All four objectives were achieved, and I provide give-and-take and commentary almost how the results can be applied to conservation exercise.

Methods

Study sites

The study was conducted in the Swell Rift Valley region of Kenya betwixt May 2010 and Jan 2012. This region is classified every bit dry sub-humid to semi-barren with a hateful annual rainfall of 920 mm/year [9]. The giraffe population here is fragmented and but exists within confined conservation areas [1, 8]. I studied 2 discrete populations of giraffes; one confined within Soysambu Salvation (SC) and 1 confined within Lake Nakuru National Park (LNNP). Both areas are enclosed and protected wildlife conservation areas situated adjacent to i another and part of the aforementioned biome, only separated by an electrified game fence across which there is no motility of large mammals (Fig 1). The habitat in both written report sites consists of large patches of Acacia species and mixed woodland interspersed with open savannah grassland. SC is a privately-endemic wildlife conservancy, 190km² in size surrounding Lake Elementeita (00°46'S, 036°23'East; 1670m asl). LNNP is a National Park, 188kmⁱⁱ in size surrounding Lake Nakuru (0°22'Southward 36°05'E; 1759m asl).

At the time of this written report SC was costless of lions, and had been for several decades. Inside LNNP there were 56 lions [x], i.due east. a loftier density of 0.3 individuals per km². In areas with no exposure to hunting, typical panthera leo densities are between 0.08 and 0.xiv individuals per km² [eleven, 12]. Lions are the only predator to pose a significant threat to giraffes [13–17] and the preferential preying of lions upon giraffes has been identified every bit a potential trouble in LNNP [8].

Data collection

To satisfy objectives i) and ii) I monitored the giraffe population in each study site for a menstruation of nine continuous months (in SC from May 2010 to January 2011, in LNNP from May 2011 to January 2012). It was non possible to conduct concurrent monitoring so I time-matched data drove periods between consecutive years, to reduce any possible seasonal effects as far every bit possible. All data were collected by driving a 4x4 vehicle along transects to search for giraffes opportunistically. Each study site was split into four blocks (NE, SE, SW, NW); each mean solar day the order that the blocks were searched was randomised, and the road network within each cake was driven in a random society (direction and route chosen). All roads in all blocks were driven each solar day then that all areas were searched. Information were collected between sunrise at 06:30 and dusk at 18:30 (UTC + 3h Standard Time). Upon sighting an individual or group of giraffes, I stopped the vehicle at an appropriate distance and then as not to disturb the animals (typically 100 to 500 metres) and group composition information were recorded. I defined a group of giraffes as 'all individuals being within 1km of each other and engaged in generally similar behaviour' [18–23]. There were no instances where an individual could be considered at the threshold of this definition.

Upon stopping the vehicle I took a photo of each individual in the group from the furthermost left animate being to the far-off right fauna, to create a digital record of the observation. I took farther photographs of group members opportunistically as they moved or turned around, to provide farther records of group members and to verify identifications. I used a Nikon D90 digital SLR camera with a 50-500mm Sigma lens. I initially made all identifications in the field, but afterward checked these for accuracy using the digital images. I examined every digital photograph to ensure I had allocated the correct identification, age class and sex activity to each animal. Group blazon was categorised as ane of six types: lone male, lone female person, mixed sex, females, males, females and juveniles. At that place were no instances where but males and juveniles were found in a group together.

Individual identification

All giraffes in each report site were individually recognised and classified by sex and age class. Each giraffe was identified using its unique coat pattern [22, 24, 25] (S1 Fig) and was allocated a unique identifying code (S2 Fig). An identification (ID) file was created for each giraffe including photos of its left and right sides (S3 Fig). Sex was determined by observing general physical characteristics (S4 Fig) and the shape of the giraffe's skull; the skulls of female giraffes are narrower in bending when viewed side-on than those of males [26–28] (females S5 Fig; males S6 Fig). Accurate age classification of wild giraffes is difficult without an individual's nascency data so historic period classes are widely used in field studies [13, 19, 22, 24, 29–31]. Age classes were categorised as juvenile (<12 months), subadult (12 months to < 4 years), or adult (4+ years). Mature adult males with dark coats and skull nodules, estimated to exist 9+ years [25, 32] were classified as big bulls [29, 31] (S7 and S8 Figs). For comparison with recent literature which uses an A/B/C system of classifying males [29, 33], in this study 'big bulls' are equivalent to category A males, and 'adult males' are equivalent to category B and C males combined. Juveniles were non sexed because the presence of the umbilicus and small body size made accurate sexual practice-identification challenging (S9 Fig).

Individuals were allocated unique identifying codes on the first instance that I reliably observed both the left and correct sides in one observation. If I failed to photograph both sides of an animal at the same observation, then that individual was not allocated an identifying code until a time when both sides could be photographed in the aforementioned observation to ensure accuracy. I considered the ID catalogue complete when no new individuals had been identified for a period of two consecutive weeks. Post-obit completion of the ID catalogue in each site no new individuals were constitute (except for juveniles built-in during the study period).

Population size and survey effort summaries

Full population size and structure in each study site was established past examining the completed private identification records, and totalling the number of giraffes identified in each age and sex form. I used SOCPROG 2.7 [34] to generate summary statistics to describe the min., max. and mean times each giraffe was seen, and the mean percentage of the population observed on each survey. I used a t-examination to cheque for bias in the book of observations between study sites, and a chi-square test to bank check for differences in population structure between sites, both in R [35].

Approvals and permissions

The methods used in this written report were observational and non-invasive. Ethical blessing was granted past the Academy of Bristol Upstanding Review Group, and the study was carried out under permit number NCST/RRI/12/1/MAS/08/5 with the authorisation of the Kenya Wildlife Service and the Kenya National Council for Science and Engineering science.

Results

Volume of encounters

In SC 1,442 sightings of individual giraffes were recorded in 298 groups with a mean of 23 giraffes (32% of the population) sighted each survey (i.eastward. each day). Each individual giraffe was sighted between ane and 36 times (mean = 16, SD = 8). Males were sighted a mean of 15 times (SD = 5.13) and females a mean of 23 times (SD = 7.91). In LNNP i,438 sightings of individual giraffes were recorded in 293 groups with a mean of 25 giraffes (28% of the population) sighted per survey. Each private giraffe was observed betwixt 1 and 26 times (mean = sixteen, SD = six). Males were sighted a mean of sixteen times (SD = 5.61) and females a hateful of 17 times (SD = 4.75). There was no significant departure in the number of times each individual was observed between study sites (t(163) = 0.11, p = 0.913). S1 Table lists the individuals present in each written report site with age and sex class information, and number of times sighted. Individuals sighted fewer than v times either died at the start of the study period or were born towards the end of the report catamenia.

Population size and construction

In SC I identified 77 giraffes; in LNNP I identified 89 giraffes. The proportions of each age grade betwixt the two populations were significantly different (χ^two = 34.225, df = 5, p < 0.0001) (Fig 2). Of the giraffes which could be sexed (i.e. those which were not juveniles: SC, northward = 51; LNNP, n = 84), there were 51% females and 49% males in SC and 52% females and 48% males in LNNP.

Group blazon frequency

The well-nigh frequently observed grouping type was 'mixed sexual activity' in both report sites, followed by 'females and juveniles' in SC, and 'lone males' in LNNP. Group blazon 'lone female' was the least observed in SC, while 'lone female' and 'females and juveniles' were the to the lowest degree observed group types in LNNP (Fig 3).

Discussion

Population size

Population figures for Rothschild'southward giraffe in Kenya are scarce; the only population counts available for giraffes in Lake Nakuru National Park are 153 individuals in 1994 and 62 individuals in 2002 [36], implying that the population crashed by 91 individuals (59%) in an 8-year period. This crash is thought to have occurred due to a combination of factors including inbreeding depression, over-browsing of Acacia species, the heavy predation of giraffe calves by lions, and climatic effects [eight]. My results suggest that the population within LNNP has grown by 27 individuals (44%) in the 9 years since the last published survey in 2002. It has been suggested that LNNP is able to support 150 giraffes [8], so this growth may exist the natural furnishings of a population recovering from a previous period of challenging weather. The population growth could as well be a outcome of a decrease in panthera leo density; in 2002 there were an estimated 65 lions inside LNNP [36] compared to the 56 individuals counted in 2011 [10] (i.e. 35 lions/100km² in 2002 vs. 30 lions/km² in 2011). This represents a xiv% decrease in lions during the catamenia 2002 to 2011 and may be a factor contributing to the 44% growth of the giraffe population during that aforementioned catamenia. Although it is impossible to decide the verbal causes of the population growth, this study provides a possible and preliminary indication of how a decrease in lion density may contribute to an credible recovery in the co-resident giraffe population. My observation of 77 giraffes within SC provide the first published population figure for the area, which can be used as a baseline for ongoing population monitoring.

Population structure

The sex and historic period structure of the 2 populations differed significantly between the 2 sites; LNNP had a smaller proportion of juveniles and subadults, and a larger proportion of adults compared to SC (Fig ii). Given previous suggestions that king of beasts predation contributed to the population decline observed between 1994 and 2002 [8] and previous reports of lions in LNNP preferentially preying on juvenile giraffes [36], it is likely that the observed age construction in LNNP is a result of king of beasts predation removing juveniles from the population. Climatic factors or the corporeality of suitable nutrition bachelor may as well have influenced or restricted growth rates. Previous studies have shown that giraffes use provender resources differently co-ordinate to age and sex class [37–39]. However, information technology would be expected that any climatic factors touch all age classes of giraffes similarly, and should not create the unequally distributed age structure observed in this study. Lion predation is the main cause of death for giraffe calves [15]; they are a preferred target for lions and rarely survive an assail [14]. My observation that LNNP contains so few juveniles appears to support this. The small number of subadults in LNNP (n = 14, 15% of total population vs. n = 22, 29% in SC) could indicate that the risk of panthera leo predation is increasing, since previously enough juveniles have survived (i.due east. 14) to reach subadulthood, while only 5 juveniles were alive during my observations. Future surveys may detect fewer subadults every bit juveniles neglect to reach their side by side life stage.

The sexual activity structure of the population was inside the typical range reported past previous studies [21] and the ratio of adult males to developed females was like between the two written report sites. This may suggest that lions do non discriminate between giraffes by sex when attacking. If juveniles are a preferred target for lions in LNNP [viii, 36] then both male person and female calves are as equally probable to be predated upon, leading to a 50–fifty sex split in those which survive to be subadults and adults. In the Serengeti the prevalence of lion hook marks on giraffes were significantly higher in females than in males, just the authors suggested this was likely to reverberate dogie defence rather than a preference for attacking females, or that females appoint in riskier behaviour [14].

Group blazon frequency

Frequency of different grouping types of giraffes appears to vary between studies; with the most frequent group blazon having been reported to be males [31, xl] or mixed-sex groups [xix, 21]. Such variation is probable to be due to seasonal effects and differing environmental weather condition between studies. Group types of 'mixed sex' were the most oft observed in both report sites and typically comprised adults, subadults and juveniles. 'Females and young' was the second most frequent group blazon observed in SC, but was one of the least observed group types in LNNP, which is likely to be an artefact of the different number of juveniles between each site. Grouping type 'lone male' was the 2d most often observed grouping blazon in LNNP, and third well-nigh in SC, which is unsurprising as adult males are known to spend more fourth dimension alone, regardless of predation risk [15, 20, 21, twoscore–42]. The least frequently observed group type in both sites was 'lone female'; the proportion of lone female groups was smallest in SC and is likely to exist a reflection of limited opportunities to be solitary, due to the loftier number of juveniles present.

Suggestions for conservation

Giraffes are classified as Vulnerable on the IUCN Reddish List of Threatened Species [1] and populations in Due east Africa are generally in decline. Declines in the Lake Nakuru population between 1995 (153 individuals) and 2002 (63 individuals) have been attributed to climatic factors and a failure to recruit young into the population during those years [8] however this written report demonstrates that the recruitment of young is an ongoing problem, which may be linked to high lion densities. In areas where the main objective is to encourage the population growth and range expansion of giraffes, I advise that the presence of lions should be limited equally far as possible. Future translocations intending to establish new populations of giraffes should select new areas of occupancy known to contain small densities of lions.

Conclusion

This study demonstrates how wild fauna direction practices tin impact the population structure and population growth potential of giraffes, and careful monitoring of the lion population in LNNP is necessary to further understand the human relationship between lion density and giraffe population size in this area.

The four objectives of this written report were accomplished: i) I have provided a baseline population assessment for the ii largest populations of Rothschild'due south giraffes in Kenya for 2010–2011, which tin be used for futurity monitoring; ii) I uncovered of import structural differences betwixt the two populations, and showed how individual identification tin provide robust assessments of small populations of threatened species, 3) I propose that high lion densities may have an impact on giraffe population growth potential in enclosed habitats, and iv) this manuscript adds to the amount of information available about giraffes in the wild, and highlights the need for further enquiry to contribute even basic information about this understudied species.

Supporting information

S6 Fig. Photographs of eight different male Rothschild'southward giraffe to bear witness general male head shape.

Note, in comparison to females, a broader head shape, wider angle from the cage to back of the skull, prominent protrusion on the front of the skull and large, upright ossicones.

https://doi.org/10.1371/periodical.pone.0189678.s006

(TIF)

S1 Tabular array. Listing of individual giraffes within each written report site with sexual practice and age class characteristics defined, and the number of times they were observed during the written report catamenia listed.

Individuals which were observed < 5 times either died towards the showtime of the study period, or were born towards the end.

https://doi.org/x.1371/journal.pone.0189678.s010

(DOCX)

Acknowledgments

I thank the Republic of kenya National Quango for Scientific discipline and Technology, Kenya Wild animals Service and Soysambu Conservancy for permissions and access to report sites. Thanks to Professor Innes Cuthill for comments on an earlier version of this manuscript, to Professor Stephen Harris for general support and feedback, and to the Giraffe Conservation Foundation for field support. Thank y'all to OpenStreetMap and its contributors for employ of the basemap in Fig 1. I am grateful for the feedback offered by 2 anonymous reviewers which profoundly improved the paper.

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What Is The Size Of The Giraffe Population?,

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