Lion Manes and Global Warming

One of the most common questions we get asked, particularly by school children, is why do lions have a mane? Lions are the only wild cat species that are sexually dimorphic, that is, you can tell the males and females apart just by looking, and this has always invited questions.

While we’ve always said no one knows for sure, we give the two most popular theories. One theory is that they need the protection for fighting with other males for dominance over females. As all wild cats have the same sharp teeth and claws, and all the males fight over females, this doesn’t really define things.

The other theory is that the manes are an indication of the health and virility of the lion sporting them. Female lions looking for a mate will always choose the healthiest male, as he will give them the best chance of healthy cubs. Young male lions will try to avoid a fight with an older, experienced male.

Lion manes start to grow around puberty, and reach full size in about four years. The mane becomes darker as the cat ages.

Poor nutrition decreases hair pigmentation and weakens hair shafts, visibly pointing out a lion that may not be a good hunter. Luxurious, dark hair growth is regulated by testosterone, which also influences male aggression, giving indications  this lion may be a strong, healthy male.

By assessing mane length and darkness, males avoid healthier, older, more aggressive individuals, thereby lowering the potential costs of fighting. By preferring males with darker manes, females gain mature, better-fed, more aggressive mates, and their preference confers direct fitness benefits. Annual survival rates for yearlings are higher for the offspring of dark-maned coalitions. This might reflect superior genes, but yearling offspring of dark-maned coalitions are also less likely to be wounded, suggesting that their improved survival was due to better paternal protection.

Scientists have now found that lions living in hot climates have smaller, lighter-colored manes, suggesting the growth of the mane is temperature sensitive.

From 1964-2000, scientists in the Ngorongoro Crater and the nearby Serengeti National Park, Tanzania analyzed photographs of 568 subadult and adult male lions.

Their findings showed manes lengthened and darkened with age-related rises in testosterone, and the length and darkness of adult manes can vary monthly. Variations in length and color were associated with age, injury, testosterone and nutrition. Short manes were associated with serious injury,and manes darkened with age and with testosterone.

Ngorongoro males had the darkest manes, whereas those born in the hotter Serengeti woodlands had the shortest manes.Changes in ambient temperature also influence mane characteristics: Manes are darker during the cooler months of the year, and males that reached adult size during hotter-than-average years maintained significantly shorter manes throughout their lives. Manes were also longer if they reached maturity in cooler years.

One worrying aspect to come out of this study was that heat appears to be the dominant ecological factor shaping the lion’s mane. Mane length showed a significant relationship to annual temperature fluctuations, and manes are darker in cooler habitats and seasons. Long-term climate forecasts predict an increase of 1.3° to 4.6°C in this region by the year 2080; thus, manes are likely to become shorter and lighter in these populations.

Lions are conditioned to seek out the males with the longest, darkest manes. With the steadily rising global temperatures, it will require a complete behavioural change over several generations to adjust their survival instincts.

Citation: West, P, Packer, C. (2002) Sexual Selection, Temperature, and the Lion’s Mane. Science, 297(5585), 1339-1343. DOI: 10.1126/science.1073257