The Remarkable Cardiovascular System of Giraffes.

Gravity affects the physiology of many animals, and the effect is, for good reason, most pronounced in tall species. The physiology-in particular, cardiovascular function-of giraffes has therefore captivated the interest of physiologists for centuries. Several studies document high mean arterial blood pressure of giraffes of about 200 mm Hg. This appears necessary to establish a cerebral perfusion pressure on the order of 100 mm Hg at the cranial end of the carotid arteries. Here, we discuss the unique characteristics of blood vessels, the heart, and the kidney of giraffes and how these functional and structural adaptations are related to very high blood pressure. We also discuss how the cerebral circulation of giraffes is established and what we know about how the blood flow and arterial and venous pressures in giraffes change when they stop to drink and subsequently lift their heads 5-6 m in one sweeping movement.

Wild herbivores and cattle have differing effects on postfire herbaceous vegetation recovery in an African savanna.

Fire and herbivory have profound effects on vegetation in savanna ecosystems, but little is known about how different herbivore groups influence vegetation dynamics after fire. We assessed the separate and combined effects of herbivory by cattle and wild meso- and megaherbivores on postfire herbaceous vegetation cover, species richness, and species turnover in a savanna ecosystem in central Kenya. We measured these vegetation attributes for five sampling periods (from 2013 to 2017) in prescribed burns and unburned areas located within a series of replicated long-term herbivore exclosures that allow six different combinations of cattle and wild meso- and megaherbivores (elephants and giraffes). Vegetation cover (grasses, mainly) and species richness were initially reduced by burning but recovered by 15-27 months after fire, suggesting strong resilience to infrequent fire. However, the rates of recovery differed in plots accessible by different wild and domestic herbivore guilds. Wildlife (but not cattle) delayed postfire recovery of grasses, and the absence of wildlife (with or without cattle) delayed recovery of forbs. Herbivory by only cattle increased grass species richness in burned relative to unburned areas. Herbivory by cattle (with or without wildlife), however, reduced forb species richness in burned relative to unburned areas. Herbivory by wild ungulates (but not cattle) increased herbaceous species turnover in burned relative to unburned areas. Megaherbivores had negligible modifying effects on these results. This study demonstrates that savanna ecosystems are remarkably resilient to infrequent fires, but postfire grazing by cattle and wild mesoherbivores exerts different effects on recovery trajectories of herbaceous vegetation.

Effects of altering diet carbohydrate profile and physical form on zoo-housed giraffe Giraffa camelopardalis reticulata.

Unlike wild giraffe that primarily consume low starch browse, the preference of zoo-housed giraffe for consuming supplemental feeds over forage could increase the risk of digestive disorders such as ruminal acidosis. Our objective was to evaluate the effects of modifying a supplemental feed's non-fibre carbohydrate profile and physical form on nutritional, behavioural, and blood measures of giraffe in a zoological setting. Six non-lactating, adult, female reticulated giraffes were used in a two-pen modified reversal study using two dietary treatments in seven 21-day periods with data collected on days 15-21. Dietary treatments were a control feed comprised of commercially available products used at the time as the giraffe feed (GF) and an unpelleted experimental feed (EF). On a dry matter basis, GF and EF, respectively, contained 17.0% and 17.4% crude protein, 14.2% and 1.5% starch, 14.9% and 21.3% ethanol-soluble carbohydrates, 22.9% and 26.0% acid detergent fibre (ADF) and 9.50% and 14.9% ND-soluble fibre (NDSF), with modulus of fineness values of 3.62 and 4.82. Supplemental feeds, alfalfa hay, salt, and water were available for ad libitum consumption. Significance was declared at p ≤ 0.05. Intakes of hay, supplemental feeds, and total feed did not differ by diet (p > 0.28), though intakes of starch (0.93 and 0.12 kg; p = 0.05) and ADF (1.83 and 2.23 kg; p = 0.04) differed between GF and EF respectively. Giraffe behaviour values (min/48 h) were greater with EF for total eating (p = 0.04); diets were not detected as different for engagement in oral stereotypes (GF = 433, EF = 318 min/48 h; p = 0.22). Blood glucose was higher on GF than EF (99.0 and 82.3 mg/dL; p = 0.03). The lower EF blood glucose value is more similar to ranges reported for domesticated ruminants. No differences were detected for changes in body weight or body condition score in the 21-day periods (p > 0.32). Modification of supplemental feed carbohydrate profile and physical form can influence behaviour and blood glucose values of zoo-housed giraffe.

The cardiovascular challenges in giraffes.

Giraffes are the highest living animals on Earth and therefore are challenged by gravity more than any other species. In particular the cardiovascular system needs to adapt to this challenge. Giraffes have a mean blood pressure around 200 mmHg, which ensures a mean arterial pressure near the head of 100 mmHg when the giraffe is standing with the neck in a near vertical position. This immediately raises several questions. How do giraffes avoid edema in the legs where the arterial pressure is 300 mmHg or higher? How does the heart produce a pressure of 200 mmHg, and what is the energy required for this endeavor? How can the kidney tolerate a pressure of about 200 mmHg and does this mean that giraffes have a high glomerular filtration rate? What is the arterial pressure in the head of giraffes when they drink, and how is perfusion of the brain maintained when they lift their head after drinking? In this short review, we present some answers to these questions.

Factors affecting captive female giraffe stress response: Male presence, small enclosure, and low temperature.

To improve animal welfare based on suitable social housing conditions, it is important to understand the factors that trigger high-stress responses. Wild giraffes live in a fission-fusion society and males and females are rarely in the same herd for a long period. The captive condition of belonging to a herd with the same individuals for months or years is uncommon in nature. To understand the effect of male presence on female stress levels, fecal glucocorticoid metabolite (fGCM) levels and social interactions in two captive female giraffes were investigated. Additionally, the effect of enclosure size and temperature on fGCM level and social interactions were examined. The results showed no significant difference in the fGCM levels of females based on male presence. The frequency of agonistic behavior by the dominant female toward the subordinate female was significantly increased when a male was present. The subordinate female was significantly less likely to approach the dominant female and showed decreased affiliative and agonistic interactions toward the dominant female when a male was present. The frequencies of agonistic interactions between females were higher in the small enclosure regardless of male presence. Low temperature triggered higher fGCM levels and increased agonistic interaction in an aged female. The findings of this study suggest that these multiple factors should be considered individually to promote the welfare of captive giraffes.

Effects of browsing enrichment associated with the temperature-humidity index and landscaping trees in giraffes (Giraffa camelopardalisreticulata).

Enclosure environments for captive giraffes can be improved by promoting species-specific behaviors and extending foraging behavior. To date, however, the effects of climatic (temperature-humidity index, THI) and environmental factors (landscaping trees) on the enrichment of captive settings have not been studied. Therefore, the present study explored the effects of browsing enrichment on the licking behavior of captive giraffes. From May 2019 to February 2020, three giraffes in the Kyoto City Zoo, Japan, were observed for 270 h over two consecutive seasons (pre- and post-deciduous). Overall, branch foraging behavior and licking behavior were weakly and negatively correlated. In the pre-deciduous period, THI was significantly and negatively correlated with giraffe activity, and some individuals exhibited significantly reduced foraging behavior. Therefore, browsing enrichment under extreme heat may not improve giraffe rearing environments. Moreover, in the post-deciduous period, with decreased availability of leaves on landscaping trees, the non-branch foraging behavior of giraffes was significantly increased, with a corresponding significant increase in licking behavior. Therefore, landscaping trees affect the foraging behavior of captive giraffes.

MANDIBULAR FRACTURES IN GIRAFFES (GIRAFFA CAMELOPARDALIS) IN EUROPEAN ZOOS.

Following a case of mandibular fracture in a giraffe (Giraffa camelopardalis) at the Budapest Zoo, a survey was conducted across European zoological institutions with the support of the European Association of Zoos and Aquariums Giraffe Ex situ Programme (EAZA Giraffe EEP) to help identify the incidence, potential causes, and management of such injuries. Two hundred sixteen zoos keeping giraffes were invited to participate in the survey. Eighty-six responses were received, 14 of which (16.3%) reported jaw fractures with various causes in their giraffes. Of these responses, hay racks, where the muzzle of the giraffe could fit between the grid of feeding contraptions, were associated with mandibular fractures in seven cases (50.0%). Most giraffes were managed surgically (10/14; 71.4%), two were managed medically (14.3%), one was euthanized because of the severity of the injury (7.1%), and one was only diagnosed with a mandibular fracture postmortem. One giraffe died owing to postanesthetic complications; all other individuals had a full recovery. Most mandible fractures occurred in relatively young giraffes (between 5 wk and 8 yr with an average of 3.4 yr). Based on these findings, facilities with giraffe should evaluate their hay feeders for mandible entrapment risk, especially if they house young individuals.

Biological and environmental factors as sources of variation in nocturnal behavior of giraffe.

Upon a drastic decline of the giraffe population in the wild, conservation efforts and therefore the role of zoos have become more important than ever. With their unique opportunities, zoos provide excellent conditions to study animal behavior, expanding the knowledge about the giraffe's behavior repertoire and their ability to adapt. This study therefore examined the nocturnal behavior of 63 giraffe living in 13 different EAZA zoos across Germany and the Netherlands. Giraffe were observed and videos recorded via infrared sensitive cameras during the winter seasons 2015-2018. The observation period spanned nightly from 17:00 to 7:00. Thus, 198 nights, with a total of 2772 h were recorded and analyzed. Linear mixed models were then used to assess potential biological and environmental factors influencing behavior during the dark phase. Results show that individual variables such as age, subspecies and motherhood determined nocturnal activity and sleep behavior most. Among the variables studied, husbandry conditions and environmental factors complying with EAZA standards had no influence on the giraffe's nocturnal behavior. By combining nocturnal activity analyses and an assessment of potential influencing factors, our findings present a holistic approach to a better understanding of captive giraffe behavior and allow for management implications.

Nighttime Suckling Behavior in Captive Giraffe (Giraffa camelopardalis reticulata).

Suckling behaviors are useful to better understand mother-offspring relationships. However, in many species, knowledge about nighttime suckling behavior is sparse. In the present study, we investigated suckling behavior in four calves of the reticulated giraffe (Giraffa camelopardalis reticulata) and their mother in the Kyoto City Zoo, Japan, by analyzing video clips of 9614 h. The relation between a calf's age and the mean duration and frequency of suckling were consistent with the results of previous daytime studies: the longest duration (80 ± 4 s) and highest frequency (0.41/h) of suckling occurred when the calves were young, and decreased thereafter. Suckling frequency was lower at night than during the day, probably because the mother spent much of the time resting at night. The mother initiated suckling behavior in offspring until six months of age. Most often, the mother terminated suckling except during the first few weeks after birth. Additionally, we reported that the average weaning period was 448 days (n = 5) and that the last born (sixth) continued to suckle for more than 750 days, which is a rare phenomenon. We believe the present report helps to fill the lack of knowledge about nighttime suckling behavior in giraffe.

The locomotor kinematics and ground reaction forces of walking giraffes.

Giraffes (Giraffa camelopardalis) possess specialised anatomy. Their disproportionately elongate limbs and neck confer recognised feeding advantages, but little is known about how their morphology affects locomotor function. In this study, we examined the stride parameters and ground reaction forces from three adult giraffes in a zoological park, across a range of walking speeds. The patterns of GRFs during walking indicate that giraffes, similar to other mammalian quadrupeds, maintain a forelimb-biased weight distribution. The angular excursion of the neck has functional links with locomotor dynamics in giraffes, and was exaggerated at faster speeds. The horizontal accelerations of the neck and trunk were out of phase compared with the vertical accelerations, which were intermediate between in and out of phase. Despite possessing specialised morphology, giraffes' stride parameters were broadly predicted from dynamic similarity, facilitating the use of other quadrupedal locomotion models to generate testable hypotheses in giraffes.

GROWTH, HUSBANDRY, AND DIETS OF FIVE SUCCESSFULLY HAND-REARED ORPHANED GIRAFFE CALVES (GIRAFFA CAMELOPARDALIS ROTHSCHILDI AND GIRAFFA CAMELOPARDALIS RETICULATA).

Giraffe in the wild are in ongoing decline because of poaching and habitat loss and fragmentation, and were recently assessed as "vulnerable" on the IUCN (International Union for Conservation of Nature) Red List of Threatened Species. Captive breeding and saving each individual are therefore becoming more important to save this species from extinction. This paper describes the husbandry and diets of successfully hand-reared Rothschild's giraffes (Giraffa camelopardalis rothschildi; n = 3) and reticulated giraffes (Giraffa camelopardalis reticulata; n = 2). All calves were initially fed with bovine colostrum followed by cow's milk (Holstein milk; Holstein milk with 10% of bovine colostrum; Jersey and Guernsey milk). Additionally, lactase enzymes (Lactaidt, Johnson & Johnson Inc., Guelp, Ontario N1K1A5, Canada) and probiotics (Probiost, Vets Plus, Inc., Menomonie, WI 54751, USA) were used. Average growth varied from 764 to 1,239 g/day from birth until 2 mo of age and between 508 and 1,161 g/day from birth until last measurement before weaning. Hand-reared calves gained up to 21 cm in height within the first month and 82-138% of their birth weight during the first 2 mo. The giraffes were weaned at 6 (n = 1), 8 (n = 3), and 11.5 (n = 1) mo and successfully socialized and introduced to other giraffes. The described diets and husbandry proved to be effective in all five calves. Large amounts of cow's milk per feeding (up to 6 L) did not result in gastrointestinal problems.

Influence of ration composition on nutritive and digestive variables in captive giraffes (Giraffa camelopardalis) indicating the appropriateness of feeding practice.

The nutrition of captive giraffe (Giraffa camelopardalis), a browsing ruminant, is challenging because browse availability is limited in zoos and rations need to be composed of compensatory feeds. In this study, ration composition for giraffes in 12 German zoos was documented and linked to animal variables that indicate suitability of nutrition. Rations differed in proportion of ration items and chemical composition resulting in various grades of accordance with feeding recommendations. An estimated daily metabolisable energy (ME) intake (MEI; mean ± SD) of 0.61 MJ ME/kg0.75 body weight (BW; ±0.1) was sufficient to cover estimated energy requirements. Daily dry matter (DM) intake (DMI) was 61 g DM/kg0.75 BW (±10) and correlated negatively to dietary ME content (p = .009; r = -.596). Apparently, feed intake was regulated by energetic satiety and not by physical properties of forage. A negative correlation between produce proportion and DMI (p = .002; r = -.676) led to the assumption of a low ruminal pH in giraffes fed high proportions of produce. Increasing dietary forage proportions led to an increasing duration of feed intake (p = .045; r = .477) and decreasing occurrence of oral stereotypies (p = .047; r = -.474). The weighted average faecal particle size was larger than reported for free-ranging giraffes, but no relation to ration characteristics among the facilities existed. The abrasiveness of rations was not excessive, as contents of silicate in faeces were similar to values from the wild. Body condition was generally acceptable, but there was no evident relation to ration characteristics. The capacity to self-regulate DM and ME intakes with lucerne hay may work at higher forage proportions than often assumed for captive giraffes. Rations with less energetic density can result in a greater DMI, including maximisation of forage intake and reduction of oral stereotypies.

Stress and social behaviors of maternally deprived captive giraffes (Giraffa camelopardalis).

Maternal deprivation can cause long-term behavioral changes in captive mammals. Studies regarding captive ungulates have also indicated behavioral shifts in the presence of the animal keeping staff; however, little is known about these effects in captive giraffes (Giraffa camelopardalis). To examine this, we observed a population of reticulated giraffes composed of maternally raised and maternally deprived individuals by direct and camera observations at Binder Park Zoo, Battle Creek, Michigan. We conducted observations using a unique ethogram with special regard for behaviors that might indicate stress or anti-social tendencies. Several variables can interact to create behavioral changes; to account for this, our study design examined the interactive effects of observation technique, raising style, and temperature on giraffe behavior. The results of these observations showed a significant increase in the rate of stereotypic and antisocial behaviors resulting from the interaction of observation technique and raising style. Stereotypic behaviors in particular showed a marked increased during cooler temperatures among giraffes of all raising style. Likewise, raising style, observation technique, and their interaction significantly impacted the time spent rubbing the enclosure. The findings of this study suggest that captive giraffe behavior can be a complex response to multiple factors and studies only examining single factors might oversimplify behavioral shifts.

The effects of increased hay-to-grain ratio on behavior, metabolic health measures, and fecal bacterial communities in four Masai giraffe (Giraffa camelopardalis tippelskirchi) at Cleveland Metroparks Zoo.

We evaluated whether increasing the hay-to-grain ratio offered to Masai giraffe (Giraffa camelopardalis tippelskirchi) at Cleveland Metroparks Zoo would reduce oral stereotypies and alter feeding behaviors, maintain or increase serum calcium-to-phosphorus ratio, decrease serum insulin-to-glucose ratio and salivary insulin, and alter fecal bacterial community structure. Giraffe transitioned to a ∼90:10 hay-to-grain ratio in even increments over 8 weeks. A ration balancer was added during the seventh week of transition to ensure proper mineral and nutrient balance. We collected (1) behavioral data collected approximately daily using instantaneous focal sampling; (2) serum collections every other week for insulin-to-glucose and calcium-to-phosphorus ratio analysis and saliva weekly for insulin analysis; and (3) weekly fecal sample collections to examine changes in bacterial community structure during the 8 weeks preceding and following the diet change. After the diet change, giraffe spent significantly more time feeding and less time performing tongue and mouth stereotypies, people-directed and alert behaviors. Salivary and serum insulin and serum insulin-to-glucose ratio decreased, and fecal bacterial community structure changed significantly. However, serum calcium-to-phosphorus ratio remained >1:1 throughout the study. While further studies are needed to elucidate the nature and implications of the change in fecal bacterial community structure and metabolic hormones, the results of this study show promise for incremental improvements in health and welfare from feeding a higher proportion of forage in the diet.

Influence of cattle on browsing and grazing wildlife varies with rainfall and presence of megaherbivores.

In many savanna ecosystems worldwide, livestock share the landscape and its resources with wildlife. The nature of interactions between livestock and wildlife is a subject of considerable interest and speculation, yet little controlled experimental research has been carried out. Since 1995, we have been manipulating the presence and absence of cattle and large mammalian herbivore wildlife in a Kenyan savanna in order to better understand how different herbivore guilds influence habitat use by specific wildlife species. Using dung counts as a relative assay of herbivore use of the different experimental plots, we found that cattle had a range of effects, mostly negative, on common mesoherbivore species, including both grazers and mixed feeders, but did not have significant effects on megaherbivores. The effect of cattle on most of the mesoherbivore species was contingent on both the presence of megaherbivores and rainfall. In the absence of megaherbivores, wild mesoherbivore dung density was 36% lower in plots that they shared with cattle than in plots they used exclusively, whereas in the presence of megaherbivores, wild mesoherbivore dung density was only 9% lower in plots shared with cattle than plots used exclusively. Cattle appeared to have a positive effect on habitat use by zebra (a grazer) and steinbuck (a browser) during wetter periods of the year but a negative effect during drier periods. Plots to which cattle had access had lower grass and forb cover than plots from which they were excluded, while plots to which megaherbivores had access had more grass cover but less forb cover. Grass cover was positively correlated with zebra and oryx dung density while forb cover was positively correlated with eland dung density. Overall these results suggest that interactions between livestock and wildlife are contingent on rainfall and herbivore assemblage and represent a more richly nuanced set of interactions than the longstanding assertion that cattle simply compete with (grazing) wildlife. Specifically, rainfall and megaherbivores seemed to moderate the negative effects of cattle on some mesoherbivore species. Even if cattle tend to reduce wildlife use of the landscape, managing simultaneously for livestock production (at moderate levels) and biodiversity conservation is possible.

ACCURACY OF NONINVASIVE ANESTHETIC MONITORING IN THE ANESTHETIZED GIRAFFE (GIRAFFA CAMELOPARDALIS).

This study evaluated the accuracy of pulse oximetry, capnography, and oscillometric blood pressure during general anesthesia in giraffes (Giraffa camelopardalis). Thirty-two giraffes anesthetized for physiologic experiments were instrumented with a pulse oximeter transmittance probe positioned on the tongue and a capnograph sampling line placed at the oral end of the endotracheal tube. A human size 10 blood pressure cuff was placed around the base of the tail, and an indwelling arterial catheter in the auricular artery continuously measured blood pressure. Giraffes were intermittently ventilated using a Hudson demand valve throughout the procedures. Arterial blood for blood gas analysis was collected at multiple time points. Relationships between oxygen saturation as determined by pulse oximetry and arterial oxygen saturation, between arterial carbon dioxide partial pressure and end-tidal carbon dioxide, and between oscillometric pressure and invasive arterial blood pressure were assessed, and the accuracy of pulse oximetry, capnography, and oscillometric blood pressure monitoring evaluated using Bland-Altman analysis. All three noninvasive methods provided relatively poor estimates of the reference values. Receiver operating characteristic curve fitting was used to determine cut-off values for hypoxia, hypocapnia, hypercapnia, and hypotension for dichotomous decision-making. Applying these cut-off values, there was reasonable sensitivity for detection of hypocapnia, hypercapnia, and hypotension, but not for hypoxemia. Noninvasive anesthetic monitoring should be interpreted with caution in giraffes and, ideally, invasive monitoring should be employed.

The thick left ventricular wall of the giraffe heart normalises wall tension, but limits stroke volume and cardiac output.

Giraffes--the tallest extant animals on Earth--are renowned for their high central arterial blood pressure, which is necessary to secure brain perfusion. Arterial pressure may exceed 300 mmHg and has historically been attributed to an exceptionally large heart. Recently, this has been refuted by several studies demonstrating that the mass of giraffe heart is similar to that of other mammals when expressed relative to body mass. It thus remains unexplained how the normal-sized giraffe heart generates such massive arterial pressures. We hypothesized that giraffe hearts have a small intraventricular cavity and a relatively thick ventricular wall, allowing for generation of high arterial pressures at normal left ventricular wall tension. In nine anaesthetized giraffes (495±38 kg), we determined in vivo ventricular dimensions using echocardiography along with intraventricular and aortic pressures to calculate left ventricular wall stress. Cardiac output was also determined by inert gas rebreathing to provide an additional and independent estimate of stroke volume. Echocardiography and inert gas-rebreathing yielded similar cardiac outputs of 16.1±2.5 and 16.4±1.4 l min(-1), respectively. End-diastolic and end-systolic volumes were 521±61 ml and 228±42 ml, respectively, yielding an ejection fraction of 56±4% and a stroke volume of 0.59 ml kg(-1). Left ventricular circumferential wall stress was 7.83±1.76 kPa. We conclude that, relative to body mass, a small left ventricular cavity and a low stroke volume characterizes the giraffe heart. The adaptations result in typical mammalian left ventricular wall tensions, but produce a lowered cardiac output.

Nocturnal behavior in captive giraffe (Giraffa camelopardalis)--A pilot study.

Captive giraffes (Giraffa camelopardalis) are known to perform oral and locomotor stereotypies. However, many studies do not consider the behavioral repertoire of these animals during the time when animals are confined to night quarters. At two zoological institutions, a total of six captive giraffes were observed via camera trap technology throughout six diurnal and nocturnal periods to record feeding, ruminating, and stereotypic behaviors. The effect of browse enrichment was assessed on alternate nights to determine how behaviors may be altered in the presence of natural forage. Results need to be interpreted with caution due to a high proportion of time when animals were out of camera range. For the observed time, stereotypical licking behavior was significantly higher at night compared to daytime at both facilities, while tongue play increased at the same time, but not significantly. The provision of browse enrichment during the night decreased the rate of tongue playing, but not significantly; however, browse did significantly reduce pacing behavior. Across treatments and institutions, observed oral stereotypies tended to correlate negatively with increased feeding behavior. Apart from a short-term effect of enrichment, this study indicates relevant differences in the frequencies of behaviors observed during the day and night, suggesting that assessing nocturnal behavior specifically may be important in many species.

The weight of Rothschild giraffe-Is it really well known?

Despite being regularly bred in zoos, giraffes remain a challenge, especially in terms of feeding. Assessment of factors influencing growth and weight changes during ontogeny, as well as analysis of weight fluctuations in adult individuals, may become a critical point in captive diet evaluation. Knowledge about weight is a crucial husbandry tool; however, such data are rarely acquired. Using a unique dataset from regularly weighed Rothschild giraffes (Giraffa camelopardalis rothschildi) from Prague zoo, we determined the growth functions of male and female giraffes and calculated weight gains during giraffe ontogeny. The mean weights of adult males and females were 1307 ± 52 and 835 ± 45 kg, respectively confirming the large overall dimensions of G. c. rothschildi in comparison with other giraffe subspecies. As the giraffe is a polygynous species showing considerable sexual dimorphism, we expected male calves to have larger first weights and faster growth during the most intensive period of maternal care. Growth rates and daily weight gains were higher in males than in females during the whole postnatal period. Males grew faster and longer than females. However, differences in weight between males and females appeared as late as after 1 year of age. The weight of adult males and non-pregnant adult females fluctuated significantly across seasons, being the highest during the autumn and winter months, respectively which may reflect the different effects of sexual activity and feeding ratios in males and females. Zoo Biol. 35:423-431, 2016. © Wiley Periodicals, Inc.