Why don't all male lions have Black manes?

Why don’t all male lions have Black manes?

If female lions are attracted to a darker mane, then surely it would make sense, if you were a male lion, to have as dark a mane as possible. Yet, not all male lions have manes like this and there appears to be no fooling around in trying to woo perspective mates. If having a dark mane is a superior trait then there must be some cost involved in having a ‘black mane’. Inspired by the work of Craig Packer I decided to give some results and conclusions from their work conducted on this subject.

It has long been noted that lions in different regions had different mane characteristics, and even back in the early 20th century this trait was linked to variety in ambient temperature. All lions are extremely sensitive to heat: males in colder, higher-altitude habitats tend to have bigger manes than those in hot, humid climates.

The dark and thick mane of one of the Mapogo Males. Picture taken in January 2010 when this male was approximately 10 years old

A high volume to surface area ratio means that larger animals have more difficulty with high temperatures. If one looks closely at lion behaviour you will note that a large percentage of this is done to reduce heat stress. This includes: sleeping in the heat of the day and moving by night, lying on their backs to expose their thinly skinned bellies, resting on raised areas in an attempt to catch the breeze and panting after consumption of large meals.

Unlike dogs, lions do not have cool wet noses, and unlike people, they don’t sweat. Their only means of thermoregulation comes from breathing and radiation from the skin. This is where the big downside and catch of the mane comes in. The mane traps the heat in and so prevents the efficient dissipation of heat. Dark hairs, by nature, are thicker than light hairs, so they trap more heat in. The darker surface also absorbs more solar heat than the lighter ones. You begin to see the difficulty of having a dark mane.

Through the use of the technology of infrared thermography, (which can measure the precise surface temperature of a distant object) the researchers of University of Minnesota managed to get some fascinating results. They spent 3 months taking ‘heat-photographs’ of lions in east Africa. They even ventured to Tsavo…home to the notorious ‘maneless’ lions. They wanted to see if the difference in body temperature was caused by the difference in body size alone (males bigger than females) or to see if the temperature differences could be accounted for by the presence of the mane! Thus they needed ‘thermo-photos’ of male and female lions in different temperature areas.

The ‘maneless’ males in Tsavo had a similar body temperature to the lionesses in the area, regardless of their greater size. They were able to rule out body size. They found that mane length had little effect, but males with darker manes were significantly hotter than those with lighter manes, even after controlling for ambient temperature, wind, humidity and prior activity.

Remote thermography of a trio of lions shows that the surface temperature of the standing male is higher (more yellow) those of the two re-clining females (more orange). This temperature difference between sexes, which is common in the Serengeti, does not exist among lions in Tsavo National Park (a hotter and more humid area where males have slight manes), suggesting that the mane is linked to the build-up of heat – Picture and caption taken from the work by Craig Packer

One of the maneless male lions in Tsavo National Park – photo taken off Wikipedia

Through some very clever testing they had proved that the males with darker manes paid a higher price in terms of heat stress. The same team of scientists also proved that males with darker manes had higher proportions of abnormal sperm. Dark manned males were also noted, time and time again, to reduce their food intake on hot days. This was not the case with the lighter manned lions in the same area. So, in conclusion, there may be advantages to having a dark mane but this also comes at a cost. This cost comes in the form of heat stress. Many lions are not prepared to pay this price!

Picture taken from the Londolozi archives of the male lion known by the rangers as Big Black – Rowan Parry Davies

Written by Adam Bannister
Inspired by West, P. M., and C. Packer. 2002. Sexual selection, temperature and the lion’s mane. Science 297:1339–1343.