Cooperation and conflict over the struggle to reproduce in harsh environments : An experimental field study on ostriches

Sammanfattning: People are used to hearing that evolution is about the survival of the fittest. Theyimagine a world full of bullies that ruthlessly fight their way to the top in the struggle for life, leaving the weak behind. But this doesn’t need be the case. This thesis reveals a different side of evolution, where survival means working together, and where the weak can ride on the shoulders of the fit.Ostriches are awkward and goofy-looking. They are the biggest bird alive, easilyreaching 2.5 meters in height, and can weigh over 150 kg. These massive birds are adapted to dry and hot environments. In the past, their habitat extended from the Arabian Peninsula to the southernmost tip of Africa. But their habitat is nowconfined to Africa, south of the Sahara Desert, and it keeps shrinking due to human activities.Ostriches are social animals. They breed in groups (often several males and several females), and their nests are communal, which means that females lay eggs in the same nest. Adult ostriches cooperate over the incubation of eggs and in the protection of young chicks. They are caring parents and go through a lot of trouble to raise their chicks in the harsh and dangerous environment in which they thrive. And no, ostriches do not bury their heads in the sand at the first sign of trouble. I know from first-hand experience that they can chase you down if they feel threatened. In nature, ostriches fight cheetahs. They are definitely not head-burying cowards.In this thesis, I experimentally manipulated more than one hundred groups ofbreeding ostriches. This allowed me to study the social behaviour of thesefascinating birds. I did this using a pair of binoculars and a birding telescope, sitting hidden on top of a 10-meter tall camouflaged tower in a research farm inOudtshoorn, South Africa.Studying ostriches has taught me many things about living in a group. Being in agroup can lead to conflict, of course. Ostrich males in particular do not want other males around. In groups with several males, they often compete with each other over females. This competition can get so frantic that, in their crazed attempts to mate before their rivals do, males sometimes break the eggs in their own nest.Females are generally at ease with having other females in their group; they evenbenefit from it. Given that incubating eggs is tedious and time consuming, havingmore females around is welcomed, since it means that there are more bottoms tohelp with incubation. Males incubate as well, but they mostly take the night shift.During the day, they are busy fighting each other and breaking the eggs!Under the peaceful surface of female coexistence, however, trouble lurks: somefemales sneak their eggs into the communal nest, without contributing to incubation.These cheats let other females do all the hard work. This kind of cheating behaviour is most common in big groups. This is probably because cheats can easily pass unnoticed when there are lots of females in the group, or maybe because the other females don’t mind a cheat or two when there are plenty of others that do help with incubation.Cheat are very uncommon small in small groups, but do occasionally occur. Whencheats do occur in small groups, they are often discovered. What happens next isstriking. When a hard-working female discovers that the other female in her group is not contributing to incubation, she herself stops incubating. This is bad for both females, because the nest fails completely. Does this reaction to cheating mean that ostriches have a sense of fairness? If you don’t do your fair share, I won’t either! I don’t know if this is about fairness in the human sense. Nonetheless, it is incredibly relatable behaviour.Enough about conflict. What about the kinder side of evolution I promised? Well,this relates to heat-stress. Some female ostriches can tolerate high temperatures but others are sensitive to the heat and struggle to lay eggs in hot conditions. Even 25°C is too hot for some females, suggesting that heat-sensitive females should avoid hot environments. But wait! Ostriches are supposed to be adapted to hot and dry habitats, like the savannahs of sub-Saharan Africa. How can it be that some female ostriches would suffer on a nice summer day in Sweden? The answer to this question lies in shared incubation. Females that can tolerate the heat incubate more. This lets heat-sensitive females survive and reproduce in environments where they probably couldn’t breed on their own.This shows how nature’s fittest help the vulnerable survive. Evolution may not beso ruthless after all and cooperation could be a way for ostriches, and other species, to cope with climate change.