L4KE 

 VICTORIA 



Masai Mara 



H Short-grass plains 

 Woodland and 

 transitional zones 

 Migration routes 

 I — I Range of western white- 

 ' — ' bearded wildebeest 



Current ranges of the recognized species and subspecies 

 of wildebeests are shown at right; only the western white- 

 bearded subspecies survives in substantial numbers, 

 largely because it can migrate with the seasons to find suit- 

 able pasture (above). Elsewhere, wildebeest populations 

 have crashed because people have encroached on their 

 ranges, often fencing off vital migration routes. 



k it 



I C. t. taurinus 

 blue wildebeest 

 (brindled gnu) 



I Connochaetes taurinus mearnsi 

 western white-bearded wildebeest 



C. t. albojubatus 

 eastern white- 

 bearded wildebeest 



I C. gnou 

 black wildebeest 

 (white-tailed wildebeest) 



C. t. johnstoni 

 Nyasa wildebeest 

 (white-banded wildebeest) 



I C. t. cooksoni 

 Cookson's wildebeest 



the short-grass plains as soon as the rains begin anew, 

 usually in November. Births among all three species 

 peak there from December through March. Even at 

 the height of the calving season, however, wildebeests 

 keep on the move from pasture to pasture. That need 

 has led wildebeests to abandon a strategy practically 

 universal among other antelope species, as well as 

 deer. The calves of most antelopes remain too feeble 

 to outrun predators for days or even weeks after they 

 are born. So the prevailing survival strategy among 

 those species is for newborns to hide until they grow 

 strong enough to flee. 



But for wildebeests the hiding strategy is really not 

 an option. With the constant movement of the herd, 

 a mother that stayed behind with a calf still in the 

 hiding stage would expose both herself and her calf 

 to far too much danger. Moreover, the calves retain 

 the ancestral, tan coloration of most antelope new- 

 borns. That color is well adapted for concealment in 

 tall grasslands, but in a mobile population that ag- 

 gregates on short green pastures, the calves' color 

 simply makes them more identifiable to predators. 



In large part, wildebeests solved those problems by 

 developing what are probably the most preco- 

 cious calves of any ungulate. Newborns can gain 

 their feet in as little as three minutes, and the aver- 

 age is only seven minutes [see photograph on opposite 

 page]. Furthermore, instead of seeking seclusion be- 



fore and after calving, as do typical "hider" antelopes, 

 pregnant wildebeests in migratory populations 

 gather together on calving grounds and drop calves 

 by the dozens between dawn and midday. Once 

 the newborns have gained their feet and have suck- 

 led for the first time, they are led into the nearest 

 nursery herd, an association of mothers and their 

 nursing young. The presence of calves that are a few 

 days older — and by then hard to catch — helps con- 

 ceal the most vulnerable day-old calves. 



Wildebeests also took another important evolu- 

 tionary step for protecting their calves: about four- 

 fifths of the yearly crop is born within just a few 

 weeks. The concentrated calving season is compara- 

 ble to that of caribou in the Arctic. The difference is 

 that the abbreviated caribou calving period is an 

 adaptation to the short Arctic summer, when new- 

 born calves are most likely to survive. Among wilde- 

 beests, the principal environmental pressure that 

 drives the calving pattern comes from predators: 

 spotted hyenas, first and foremost, but also cheetahs, 

 lions, and wild dogs. The most obvious advantage of 

 the wildebeest's short calving season is glutting the 

 predators, which enables many calves to survive and 

 at the same time keeps the predator population from 

 increasing. Predator numbers would balloon if the 

 births of the calves were spread out over the year. 



M igration is another key factor in minimizing pre- 

 dation. After ranging the short-grass plains for six or 



September 2006 NATURAL HISTORY 



31 



