Migratory herds of wildebeests and zebras indirectly affect calf survival of giraffes

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Sociability increases survival of adult female giraffes

Studies increasingly show that social connectedness plays a key role in determining survival, in addition to natural and anthropogenic environmental factors. Few studies, however, integrated social, non-social and demographic data to elucidate what components of an animal''s socio-ecological environment are most important to their survival. Female giraffes (Giraffa camelopardalis) form structured societies with highly dynamic group membership but stable long-term associations. We examined the relative contributions of sociability (relationship strength, gregariousness and betweenness), together with those of the natural (food sources and vegetation types) and anthropogenic environment (distance from human settlements), to adult female giraffe survival. We tested predictions about the influence of sociability and natural and human factors at two social levels: the individual and the social community. Survival was primarily driven by individual- rather than community-level social factors. Gregariousness (the number of other females each individual was observed with on average) was most important in explaining variation in female adult survival, more than other social traits and any natural or anthropogenic environmental factors. For adult female giraffes, grouping with more other females, even as group membership frequently changes, is correlated with better survival, and this sociability appears to be more important than several attributes of their non-social environment.     

Movements and source–sink dynamics of a Masai giraffe metapopulation

Spatial variation in habitat quality and anthropogenic factors, as well as social structure, can lead to spatially structured populations of animals. Demographic approaches can be used to improve our understanding of the dynamics of spatially structured populations and help identify subpopulations critical for the long-term persistence of regional metapopulations. We provide a regional metapopulation analysis to inform conservation management for Masai giraffes (Giraffa camelopardalis tippelskirchi) in five subpopulations defined by land management designations. We used data from an individual-based mark–recapture study to estimate subpopulation sizes, subpopulation growth rates, and movement probabilities among subpopulations. We assessed the source–sink structure of the study population by calculating source–sink statistics, and we created a female-based matrix metapopulation model composed of all subpopulations to examine how variation in demographic components of survival, reproduction, and movement affected metapopulation growth rate. Movement data indicated no subpopulation was completely isolated, but movement probabilities varied among subpopulations. Source–sink statistics and net flow of individuals indicated three subpopulations were sources, while two subpopulations were sinks. We found areas with higher wildlife protection efforts and fewer anthropogenic impacts were sources, and less-protected areas were identified as sinks. Our results highlight the importance of identifying source–sink dynamics among subpopulations for effective conservation planning and emphasize how protected areas can play an important role in sustaining metapopulations.     

Food supply and poaching limit giraffe abundance in the Serengeti

The iconic giraffe, an ecologically important browser, has shown a substantial decline in numbers across Africa since the 1990s. In Serengeti National Park, Tanzania, giraffes reached densities of 1.5–2.6 individuals km⁻² in the 1970s coincident with a pulse of Acacia tree recruitment. However, despite continued increases in woody cover between the 1980s and the 2000s, giraffe recruitment and survival rates have declined and density has dropped to only 0.3–0.4 giraffes km⁻². We used a decision table to investigate how four extrinsic factors may have contributed to these declines: food supply, predation, parasites, and poaching, which have all been previously shown to limit Serengeti ungulate populations. Lower recruitment likely resulted from a reduction in diet quality, owing to the replacement of preferred trees with unpalatable species, while decreased adult survival resulted from illegal harvesting, which appears to have had a greater impact on giraffe populations bordering the western and northern Serengeti. The Serengeti giraffe population will likely persist at low-to-moderate densities until palatable tree species regain their former abundance. Leslie matrix models suggest that park managers should meanwhile redouble their efforts to reduce poaching, thereby improving adult survival.     

Demographic balancing of migrant and resident elk in a partially migratory population through forage–predation tradeoffs

Partial migration is widespread in ungulates, yet few studies have assessed demographic mechanisms for how these alternative strategies are maintained in populations. Over the past two decades the number of resident individuals of the Ya Ha Tinda elk herd near Banff National Park has been increasing proportionally despite an overall population decline. We compared demographic rates of migrant and resident elk to test for demographic mechanisms partial migration. We determined adult female survival for 132 elk, pregnancy rates for 150 female elk, and elk calf survival for 79 calves. Population vital rates were combined in Leslie‐matrix models to estimate demographic fitness, which we defined as the migration strategy‐specific population growth rate. We also tested for differences in factors influencing risk of mortality between migratory strategies for adult females using Cox‐proportional hazards regression and time‐varying covariates of exposure to forage biomass, wolf predation risk, and group size. Despite higher pregnancy rates and winter calf weights associated with higher forage quality, survival of migrant adult females and calves were lower than resident elk. Resident elk traded high quality food to reduce predation risk by selecting areas close to human activity, and by living in group sizes 20% larger than migrants. Thus, residents experienced higher adult female survival and calf survival, but lower pregnancy and calf weights. Cause‐specific mortality of migrants was dominated by wolf and grizzly bear mortality, whereas resident mortality was dominated by human hunting. Demographic differences translated into slightly higher (2–3%), but non‐significant, resident population growth rate compared to migrant elk, suggesting demographic balancing between resident strategies during our study. Despite statistical equivalence, our results are also consistent with slow long‐term declines in migrants because of high predation because of higher wolf‐caused mortality in migrants. These results emphasize that migrants and residents will make different tradeoffs between forage and risk may affect the demographic balance of partially migratory populations, which may explain recent declines in migratory behavior in many ungulate populations around the world.     

Giraffe (Giraffa camelopardalis) social networks in areas of contrasting human activity and lion density

The adaptive value of close social bonds and social networks has been demonstrated in a variety of vertebrate taxa. While the effect of predators on populations is well established, disturbance by humans is increasingly being identified as affecting the behaviour and reproductive success of animals and can have significant impacts on their survival. We used a concurrent analysis of two adjacent giraffe Giraffa camelopardalis populations in Kenya to determine whether human activities and high predation affected their social networks. One study site was a premier tourist destination with a high volume of human activity in the form of tourist traffic and lodge infrastructure, alongside a high density of lions which preferentially prey on giraffe calves; the other was a private wildlife conservancy with minimal human activity and no lion population. Giraffes in both networks showed preferred associations and avoidances of other individuals, which were independent of space use. Bond strength was lower in the population exposed to high levels of human activity and lions, and the network had lower density and clustering, and shorter path lengths, suggesting that it was more fragmented. We suggest that human activity and predator density may influence the patterns of social interactions in giraffes and highlight the importance of understanding the impact of tourism and management on the survival and success of wild animal populations.     

Oviposition pattern and within-season spatial and temporal variation of pre-dispersal seed predation in a population of Mimosa bimucronata trees

Spatial and temporal variation of pre-dispersal seed predation was investigated in a population of Mimosa bimucronata trees located in the south-east region of Brazil. Three main hypotheses were addressed: (1) that the life stages of the seed predator Acanthoscelides schrankiae are synchronised with the reproductive stages of its host plant; (2) that seed predation levels vary spatially as a result of differences in fruiting phenology synchrony and fruit production among trees; and (3) that predation levels should be affected by the proximity of trees, showing a spatial structure. Also investigated was the oviposition pattern of A. schrankiae among seeds and fruits. Twenty spatially referenced trees were monitored throughout a year to examine tree phenology and egg laying and adult emergence. The bruchine’s life stages were synchronised with the reproductive stages of M. bimucronata trees. Egg distribution among seeds and fruits was aggregated. Infestation rates of adult bruchines were not spatially related to fruiting phenology and there is evidence that seed predation is a spatially density-independent process, because the relationship between infestation rates and fruit production was not significant. Finally, it was observed that the distribution of adult bruchines was spatially structured, because similar levels of infestation were found among nearby trees.     

Spatial patterns in age- and colony-specific survival in a long-lived seabird across 14 contrasting colonies

Demographic rates such as recruitment and survival probability can vary considerably among populations of the same species due to variation in underlying environmental processes. If environmental processes are spatially correlated, nearby populations are expected to have more similar demographic rates than those further apart. Breeding populations and foraging ranges are spatially segregated in colonial seabirds, making them ideal for studying spatial patterns in demographic rates and their effects on local population dynamics. Here we explored variation in age-dependent survival probabilities across 14 colonies of Herring Gulls Larus argentatus breeding along the Dutch North Sea coast. We used long-term mark–recapture data of marked fledglings to estimate survival, and estimated spatial autocorrelation of survival probabilities. We assessed whether survival until recruitment age or until 10 years old (close to their expected lifespan) explained variation in population trajectories of each colony. Juvenile and adult survival showed a strong, but different, north-to-south gradient in survival probability, with lower juvenile but higher adult survival in northern colonies than southern colonies, whereas the spatial pattern of immature survival was less distinct. Neither recruitment nor the proportion of 10-year-old adults alive predicted whether a colony collapsed, declined, remained stable or increased. The distinct spatial pattern in survival suggests variation in regional food availability, which do not seem to drive local population dynamics. The absence of a link between survival and colony trajectories implies that connectivity between populations plays an important role affecting population dynamics.     

Giraffe birth locations in the South Luangwa National Park,Zambia: site fidelity or microhabitat selection?

Birth site location can have enormous implications for female reproductive success. Some ungulate species demonstrate consistent birth site fidelity, while others shift birth locations during their lifetimes as a function of ecological and social factors. We plotted 39 years of birth records from a wild population of Thornicroft's giraffe, Giraffa camelopardalis thornicrofti, to test the hypothesis that giraffe use consistent locations for birth. Data from 29 calves born to nine females revealed that birth seasonality was absent and that ecological zone had no significant impact on birth locations. Consecutive births by individual females were not limited to certain locations, with the distance between sequential birth sites tending to be greater if a calf failed to survive the first year of life. Our evidence conflicts with the suggestion that giraffe cows regularly return to special locations for bearing calves. We suggest that the choice of birth location is a function of nonseasonal breeding, predator pressure and extensive variation in microhabitat characteristics within ecological zones. Female giraffe have evolved a flexible reproductive strategy, whereby they regulate choice of birth site location based upon their past reproductive history, current ecological conditions (including both resource availability and predator pressure) and present social surroundings.     

Androgen changes and flexible rutting behaviour in male giraffes

The social organization of giraffes (Giraffa camelopardalis) imposes a high-cost reproductive strategy on bulls, which adopt a ‘roving male’ tactic. Our observations on wild giraffes confirm that bulls indeed have unsynchronized rut-like periods, not unlike another tropical megaherbivore, the elephant, but on a much shorter timescale. We found profound changes in male sexual and social activities at the scale of about two weeks. This so far undescribed rutting behaviour is closely correlated with changes in androgen concentrations and appears to be driven by them. The short time scale of the changes in sexual and social activity may explain why dominance and reproductive status in male giraffe in the field seem to be unstable.     

Bionomics of Aedes aegypti subpopulations (Diptera: Culicidae) from Argentina

Differences in biological features of immature and adult Aedes aegypti, as well as variability in vector competence, seem consistent with the existence of genetic variation among subpopulations and adaptation to local conditions. This work aims to compare the bionomics of four Ae. aegypti subpopulations derived from different geographical regions reared under temperate conditions. Life statistics of three Ae. aegypti subpopulations from the provinces of Córdoba, Salta, and Misiones were studied based on horizontal life tables. The Rockefeller strain was used as a control. The development time required to complete the larva and pupa stages varied from 6.91 to 7.95 and 1.87 to 2.41 days, respectively. Significant differences were found in mean larval development time between the Córdoba and Orán subpopulations. The larva‐pupa development time was similar in all the subpopulations. However, survival values varied significantly between the Orán and San Javier subpopulations. The proportion of emergent males did not differ from females within each subpopulation nor among them. Adult longevity was similar among the subpopulations. The average number of eggs laid by each female was significantly different. The Rockefeller strain laid a significantly greater number of eggs (463.99 eggs/female) than the rest of the subpopulations. Moreover, differences in the demographic growth parameter R_o were detected among the four subpopulations. The differences obtained in larval development time, larva‐pupa survival values, and net reproductive rates among the subpopulations might reflect underlying genetic differences as a result of colonization from different regions that probably involve adaptations to local conditions.     

A comparison of sex ratio,birth periods and calf survival among Serengeti wildebeest sub‐populations,Tanzania

Although adaptation and environmental conditions can easily predict demographic variation in most savannah ungulates, no study on demographic consequences arising from natural and anthropogenic factors among Serengeti wildebeest (Connochaetes taurinus) sub‐populations in Tanzania has been carried out. Here, I report estimates of annual sex ratio, calf and yearling survival rate and birth seasonality between resident and migratory sub‐populations to explore demographic patterns arising from the different age and sex structure. The results indicate significantly higher female‐biased sex ratios in the resident and almost even sex ratios among individual migrants. The calf recruitment estimated as mother: offspring ratios indicate a more synchronous birth in the migrant than the resident sub‐population. Also, birth seasonality in the migratory sub‐population coincided with seasonal variability of rainfall and the timing of the birth peak was more variable in the migrants than the resident sub‐population. The migratory sub‐population had a higher annual proportional mean calf survival estimate (0.84) than that of the residents (0.44) probably due to higher mortality resulting from predation in the western corridor. However, the proportion of yearling survival estimates was much lower (0.31) in the migrants and relatively higher (0.39) in the residents. Different demographic outcomes resulting from environment, predation, movements and ecological factors including resource competition have conservation implications for the two sub‐populations.     

Spatial explicit demography: The effects habitat patch isolation have on vole matrilines

Populations of many species are spatially structured in matrilines, and their dynamics may be determined by matriline specific demographic processes. We examined whether the isolation of habitat patches (i.e. interpatch distance) affected the demography of matrilines in 14 experimentally fragmented populations of the root vole. Matrilines inhabiting the most isolated patches decreased in size over the breeding season, while matrilines in less isolated patches increased. The survival rate of adult females was the main factor underlying the variation in growth rates among matrilines. Low survival when patches were isolated seemed to be due to long-distance interpatch movements exposing females to increased predation rate.
The differential success of matrilines in patchy populations with variable interpatch distances acted to decrease the matrilineal diversity at the population level. Furthermore, isolated patches may function as sinks. Thus spatially explicit landscape features may affect both population demography and genetics.     

Influence of adult and egg predation on reproductive success of Epirrita autumnata (Lepidoptera: Geometridae)

We studied the effects of predation and oviposition activity on reproductive success of a late-season moth, Epirrita autumnata by exposing adult females and eggs to predation in their natural habitat in two successive years. Daily survival rates of adult females ranged from 0.4 to 0.8, average being 0.7. Most predation occurred during nights and was caused by harvestmen and other invertebrate predators. Avian predation did not have an effect on adult survival rates, most likely because of the lateness of E. autumnata flight season. Eggs were also preyed upon by invertebrate predators, although a notable proportion of egg mortality was attributable to causes other than predation. Daily survival rates of eggs were more than 0.99. Using modeling based on empirical data on eclosion of female adults, their oviposition behavior and survival rates of adults and eggs, the daily survival rates were translated into population level consequences. Adult predation was estimated to decrease reproductive success of non-outbreaking E. autumnata by 60–85 percent and egg mortality by 20–40 percent. Predation on adult lepidopterans is a mortality factor potentially as relevant as predation in any other life history stage and thus, should not be ignored in studies of population regulation.     

Life expectancy,maximum longevity and lifetime reproductive success in female Thornicroft's giraffe in Zambia

Gestation and longevity scale with body mass across taxa, yet within size dimorphic taxa, males tend to have reduced lifespans compared with females. Testing life history models, and accounting for sex differences in longevity, requires obtaining accurate longitudinal data from wild populations. We provide the first report describing key life history parameters from a long‐term study of giraffes in Africa. We followed a population of Thornicroft's giraffe (Giraffa camelopardalis thornicrofti) in Zambia for over 40 years. Maximum longevity among females was approximately 28 years, with lifespan accounting for 81% of the variance in lifetime reproductive success. Average adult female life expectancy was no different than average adult male life expectancy. However, the breeding lifespan of males was about half that of females, while maximum lifespan of males was 75% that of females. Our findings support the suggestion that sex differences in maximum lifespan arise from stronger selection for lengthy lives in females than in males. Among females, longer lives are associated with greater reproductive output.     

Behavioral development in okapis and giraffes

Observations on the behavioral development of two okapi calves and one giraffe calf were made at Brookfield Zoo. The following behaviors were monitored for 4 to 6 mo after birth; nursing duration and nursing attempts, mother-infant distance, bunting the mother's udder, lying, moving, maternal grooming, mother and infant autogrooming, object licking, tail chewing, and contact by others in the herd. Behaviors in both species showed oscillating patterns with high levels of mother-infant contact behaviors at 3–4 wk, 9–11 wk, and 14–15 wk in okapis. Giraffe infants showed similar oscillations with high periods of contact about 2–5 wk later than those in okapis. Other behaviors oscillated in concert with these, with specific correlations occurring between nursing behaviors and grooming behaviors. A main difference between okapi and giraffe development centered around maternal motivation during the high contact (regressive) periods. In okapis, after 10–12 wk there was a low rate of nursing success, whereas in giraffes the percentage of success in nursing rose with later behavioral oscillations. The regressive periods became conflict periods in okapis, whereas in the giraffe, the mother initiated the periods. This difference was in accordance with the unique strategy of infant rearing in wild giraffes in which there is an extended “hider” period when older calves are left together in shaded areas with an adult sentry. Field studies also indicated probable oscillations of mother-infant contact and a prolonged period of the mother initiating contact with her calf.     

Regional Differences in Seasonal Timing of Rainfall Discriminate between Genetically Distinct East African Giraffe Taxa

Masai (Giraffa tippelskirchi), Reticulated (G. reticulata) and Rothschild''s (G. camelopardalis) giraffe lineages in East Africa are morphologically and genetically distinct, yet in Kenya their ranges abut. This raises the question of how divergence is maintained among populations of a large mammal capable of long-distance travel, and which readily hybridize in zoos. Here we test four hypotheses concerning the maintenance of the phylogeographic boundaries among the three taxa: 1) isolation-by-distance; 2) physical barriers to dispersal; 3) general habitat differences resulting in habitat segregation; or 4) regional differences in the seasonal timing of rainfall, and resultant timing of browse availability. We used satellite remotely sensed and climate data to characterize the environment at the locations of genotyped giraffes. Canonical variate analysis, random forest algorithms, and generalized dissimilarity modelling were employed in a landscape genetics framework to identify the predictor variables that best explained giraffes'' genetic divergence. We found that regional differences in the timing of precipitation, and resulting green-up associated with the abundance of browse, effectively discriminate between taxa. Local habitat conditions, topographic and human-induced barriers, and geographic distance did not aid in discriminating among lineages. Our results suggest that selection associated with regional timing of events in the annual climatic cycle may help maintain genetic and phenotypic divergence in giraffes. We discuss potential mechanisms of maintaining divergence, and suggest that synchronization of reproduction with seasonal rainfall cycles that are geographically distinct may contribute to reproductive isolation. Coordination of weaning with green-up cycles could minimize the costs of lactation and predation on the young. Our findings are consistent with theory and empirical results demonstrating the efficacy of seasonal or phenologically dictated selection pressures in contributing to the reproductive isolation of parapatric populations.     

Reproductive life history of Thornicroft’s giraffe in Zambia

Knowledge of the reproductive life history of giraffe in the wild is sparse. Giraffe have two fairly unusual reproductive patterns among large mammals: they can become pregnant while lactating, and calf mortality is extremely high. Longitudinal records are largely absent, so tracking reproductive parameters tends to combine information from captive and field studies. In this study, we examine longitudinal data obtained over a 33‐year period in one population of Thornicroft’s giraffe in order to chart their reproductive careers. We found that age at first parturition was 6.4 years, or slightly later than in captivity. Giraffe bred throughout the year, with cows producing offspring on average every 677.7 days. About half of the calves died before one year of age, but death of a calf did not reduce interbirth interval. We conclude that the lifetime reproductive success of giraffe is more dependent on longevity and calf survivorship than on reproductive rate.     

Sonomorphology of the reproductive tract in male and pregnant and non-pregnant female Rothschild's giraffes (Giraffa camelopardalis rotschildi)

The application of real-time-B-mode ultrasonography to wild and zoo animal medicine has been shown to improve the understanding of reproductive physiology in many species. Ultrasound technology is especially helpful for monitoring urogenital health, which in turn has advantages for giraffe breeding and welfare in captivity.This study aimed to ultrasonographically describe the genital organs of reproductively healthy male and female giraffes. Through the use of a restrainer, repeated rectal ultrasound examinations were performed over a 2 year period in 2.6 Rothschild's giraffes. Changes in ovarian activity were monitored throughout four different reproductive stages in the females and included immature, mature-cycling, pregnancy, post-partum-period. In the immature giraffes the ovaries showed multiple follicles of which larger ones luteinized to form pseudo-corpora lutea. By comparison, in the mature giraffes the dominant follicle reached an ovulatory diameter of 18.5 ± 0.89 mm. After ovulation, a single corpus luteum rapidly formed and reached a maximum diameter of 33.0 ± 2.4 mm on average. Pregnancy was detected for the first time by the embryonic vesicle, visualized around 28 days post copulation. Follicular development remained ongoing during early pregnancy. In the males, as in other ruminants, the bulbourethral glands and the seminal vesicles were prominent, whereas the prostate gland was indistinct.Knowledge about the reproductive tract morphology and physiology is necessary for diagnosing medical disorders and abnormalities in giraffes. The aim of this study was to help consolidate the current knowledge on basic reproductive parameters for this species.     

Fitness and extra-group reproduction in male Verreaux's sifaka: An analysis of reproductive success from 1989-1999

Adult males in social groups often compete with other male group members for access to adult females. In some primate species, males also seek mating opportunities in neighboring social groups. Such extra-group fertilizations (EGFs) provide an additional source of variation in male fitness. This additional component of fitness provided by EGFs must be incorporated into analyses that investigate sources of variation in male lifetime reproductive success. In this study, a model is analyzed in which male fitness over a 10-year sample period is decomposed into additive and multiplicative variance and covariance components. The data come from an ongoing study of a wild population of Verreaux's sifaka (Propithecus verreauxi verreauxi) located at Beza Mahafaly Special Reserve, Southwest Madagascar. Paternity and demographic data for 134 males are used to decompose male fitness into the following three multiplicative components: reproductive lifespan during sample period, fertility, and offspring survival. These multiplicative components are estimated for males reproducing within their resident groups plus (i.e., the additive portion) for males reproducing in neighboring social groups. The analysis shows that variation in fertility makes the largest contribution to variation in total fitness, followed by variation in amount of time spent in sample period (which is a proxy of total reproductive lifespan) and variation in offspring survival. EGFs contribute an important source of variation to male fitness, and numerous factors enhance the opportunities for EGFs in male sifaka. These include female choice, a high degree of home range overlap, and a limited mating season.