Great Wildebeest Migration - Tanzania & Kenya | Rhino Africa
Whether plant species were eaten or not was examined in relation to .. in the Saadani Game Reserve such as wildebeest and zebra, originally adapted to methodological advice on the preparation and identification of the dung samples. risk areas for zebra poaching within and around Tarangire National Park, a core area of the Tarangire ecosystem. significant relationships. comments, guidance and suggestions. Figure Wildebeest grazing in Tarangire national. It's incredible to watch: each year thousands of animals, including zebras, wildebeests and gazelles, migrate in turn with the seasons between.
Due to the placement of their eyes on the side of their head, zebras can use monocular and binocular vision Barnett As a result, they can see to their side using monocular vision while they forage Harman et al.
This ability could potentially allow zebra to be passively vigilant while they feed and thus detect approaching predators. However, because zebra head placement while feeding is pointing toward the ground, we are unable to differentiate between zebra being passively vigilant looking for potential predators using monocular vision or searching for another foraging patch.
Furthermore, it is unlikely that the level of passive vigilance shown by zebra while foraging will differ between zebra-only and zebra—giraffe herds. Thus, we restricted our data collection to active forms of vigilance Scheel ; Creel and Winnie ; Creel et al. To explore whether the presence of giraffes influenced zebra vigilance, we compared active head raised zebra vigilance when herding in zebra-only herds, with zebra herding in zebra—giraffe herds. We observed a zebra for 3min and recorded: We defined a general scan as a zebra scanning with its head up without fixing its attention vision or ears in a particular direction zebra-only: A focused scan comprised a zebra staring in a fixed direction, with its ears pricked, either looking toward another herd mate i.
We sampled both herd types in both reserves iMfolozi: With regard to source of information, when herding in a zebra-only herd, a zebra could obtain information about predation risk by looking at a conspecific, conducting its own scan of the environment, or both. For zebra, binocular vision oriented in the direction of the muzzle provides better depth perception compared with their side-orientated monocular vision Harman et al.
As a result, it is more likely that these herbivores would use binocular vision to actively scan for approaching predators. Thus, we considered zebra being actively vigilant when their head was raised and their muzzle was directed toward a zebra, giraffe, or out to the environment.
If zebra looked at 2 sources separately in a scan e. However, if a zebra directed a scan toward a zebra and a giraffe, and we could not discern which individual was the focus of the scan, we recorded the scan as toward an unknown target. We used a subset of our total samples to determine information source because we only began collecting these data midway through our data collection iMfolozi: Finally, to explore the relative influence that giraffe have on zebra vigilance behavior, we compared the amount of time zebra spent vigilant when herding with giraffe and when herding with a known diluting partner—wildebeest.
We collected zebra vigilance behavior in the same manner as described above. These data come from Schmitt et al. Data analysis Prior to statistical analysis, we calculated mean individual vigilance per herd i.
To test whether time devoted to vigilance was influenced by herding with giraffe, we tested for herd independence to ensure the data could be pooled. There was no herd effect; thus, individual herds were independent. Therefore, we used the mean time a herd was vigilant as our dependent factor. We used an analysis of covariance ANCOVA to test whether the mean time spent vigilant by the herds varied with herd type zebra-only and zebra—giraffe.
The covariates such as number of giraffe, total number of ungulates, and season were nonsignificant and thus removed from the final model. Data were box—cox y transformed prior to analysis. To determine the relative impact of giraffe herding with zebra compared with when zebra herd with a known diluting partner, wildebeest, we used an ANCOVA with time spent vigilant as the dependent variable. We used herd type zebra—giraffe and zebra—wildebeest as the main effect and number of zebra in a herd as the covariate.
Initially, we also included site, season, and total number of ungulates as covariates. However, these were nonsignificant and thus removed from the final model. These data are from Schmitt et al. To test whether the intensity of vigilance events varied between zebra in zebra-only or zebra—giraffe herds, we compared the proportion of general versus focused scans within each herd.
Therefore, each herd had a proportion for a general and a fixed scan. We were able to differentiate between these proportions by including the independent variable, scan type.
By including both these proportions for each herd type, we were able to determine if there was any change in the proportional use of each behavior as herd type changed. Covariates site iMfolozi, Krugertotal number of ungulate individuals in a herd, and season were nonsignificant and removed. Data were transformed using arcsine square root. Finally, to determine the source s that zebras used to gather information about perceived predation risk, we used an Anova with proportion of scans regardless of the scan intensity directed toward an information source i.
We then used the interaction of herd type zebra-only and zebra—giraffe and information source as the main effects. Covariates site, season, and total number of ungulates were nonsignificant and thus removed.
Blue Wildebeest | Etosha National Park | Namibian Animals & Wildlife
Data were arcsine square root transformed prior to analysis. The covariate number of giraffe was nonsignificant, indicating that the presence rather than number of giraffe reduced zebra vigilance. This reduction indicates that zebra perceive information gleaned from giraffe to be more valuable than that from wildebeest.
When herding alone, zebra used focused scans proportionally more 0. However, when herding with giraffe, zebra used general scans proportionally more 0. This pattern was consistent across sites. Zebras herding alone actively scanned the environment 0. In contrast, zebra herding with giraffe actively scanned herd mates 0. Neither herd types extensively scanned both herd mates and the environment.
However, for this to be possible, group members must be able to obtain information about potential threats from other group members Metcalfe ; Elgar A number of studies have shown that information about predators can be conveyed through alarm calls Seyfarth et al. Our results show that when one or more giraffe were present in a group of foraging zebra, the time zebra devoted to vigilance dropped by nearly two-thirds compared with when herding with conspecifics.
Furthermore, in mixed-species herds, the majority of zebra scans were directed toward giraffe. Therefore, we hypothesize that the mechanisms through which this reduction occurs is likely because zebra are able to interpret the leaked cues e. As a result, zebra are able to reduce their perceived predation risk even in the absence of alarm calls. Interestingly, the amount of time that zebra devoted to vigilance when herding with giraffe was half as much as when they herded with wildebeest, a known diluting partner Schmitt et al.
Thus, it seems that zebra perceive these leaked cues from giraffe to be more valuable, and more reliable, than information from a similar-sized diluting partner. Furthermore, in zebra—giraffe herds, zebra relied more on general vigilance scans compared with the focused scans i. Moreover, there was a near complete switch in behavior from relying on direct personal assessment of risk in zebra-only herds, to primarily using social information i.
The switch in information source used by zebra is surprising because in mixed-species herds, zebra theoretically should use both conspecific and heterospecific cues equally to better determine predation risk Goodale and Kotagamarather than relying mainly on cues from giraffe. However, this shift can potentially be explained by 2 reasons.
This is similar to other species that rely on elevated conspecific sentinels for antipredator information, such as meerkats Suricata suricatta Santema and Clutton-Brock Second, the large body size and the characteristic body language displayed by giraffe when they detect the presence of lion i.
The information gained by zebra from giraffe is perhaps more accurate than information from conspecifics or other coherding species, such as wildebeest, because the height of the giraffe makes it less likely to be obstructed by vegetation. For example, a study on 2 species of shorebirds Arenaria interpres and Calidris maritime found that with decreasing visibility there was an increase in individual vigilance Metcalfe This was because the shorebirds could not rely as much on antipredator information gathered from other members in the flock because they were obstructed from view, in addition to a greater risk of predation from hidden predators with decreasing visibility Metcalfe Thus, the information from giraffe is likely more valuable to zebra than information from conspecifics or similar-sized heterospecifics sharing the same predation risk.
This is likely because zebra can gain more information about predators e. If our interpretation is correct, this then raises the question, if zebra gain so much by moving with giraffe, then why do not they always herd with them?
Zebra attack wildebeest calf
A potential reason for this is that giraffe may experience lower levels of predation by lions compared with zebra. Their horns curve outwards and upwards. Neither species is presently under threat and they are a common sight on grasslands wherever they occur.
Wildebeest are a shade loving species, preferring to rest up under the trees during the heat of the day. They usually confine their feeding habits to morning and late afternoon. Wildebeest consume around a quarter of their body weight in grass every day and prefer to drink daily. In other places, their movement is restricted by fences and the encroachment of human settlements.
Although they mass together in their thousands during the migration, most wildebeest herds consist of 20 to 40 individuals.
There's a Zebra Hiding Amongst This Huge Herd of Wildebeest: Can You Spot it?
These are made up of a male leader and his harem of females with their young. Bachelor bulls gather in loose herds of their own. Both these types of herds are very often found in the company of zebras. They have a symbiotic relationship with these herbivores, eating the taller parts of the grasses, leaving the shorter stalks which the zebras prefer behind.
This relationship is also based on the theory that more is always better when it comes to anticipating and surviving attacks from predators.