SEXUALLY frustrated female black rhinos are prone to crankiness and weight gain, new research has revealed.
Researchers at Chester Zoo teamed up with experts at Manchester and Liverpool universities to carry out the first comprehensive study into reproduction among the species.
They discovered that checking hormone levels in the giant creatures was the best way to know the likelihood of breeding success.
Females are often found to be aroused despite not outwardly showing it, according to the report, which studied animals from 11 European zoos.
A total of 9,743 samples were sent to Chester Zoo’s Wildlife Endocrinology laboratory to analyse female reproductive cycles.
Dr Katie Edwards, who led the research as part of her PhD at the University of Liverpool, said: “Our analyses showed females who had never bred were more likely to exhibit irregular oestrous cycles, indicating that underlying physiology is involved in differences in breeding success.
“As well as non-breeding females not cycling as reliably, behavioural observations showed us that these females don’t necessarily show when they are ready to mate, which can make managing breeding difficult.
“Hormone analysis helps address this problem by allowing us to predict when a female will be sexually receptive to a male, even if she doesn’t make it obvious.”
As well as looking at hormone analysis, the researchers also investigated a number of other factors that could affect breeding success.
Females that had never bred were found to be heavier than those that had, demonstrating that maintaining a suitable diet in captivity can play an important role in the success of breeding programmes.
Non-breeding females were also found to be “more unpredictable” in their temperaments.
Dr Susanne Shultz, from the Faculty of Life Sciences at the University of Manchester who was the academic supervisor for the project, said: “This research highlights how rhinos can behave in a different manner despite being kept in similar conditions.
“We think this demonstrates it is important to recognise individual differences and adjust management plans accordingly to maximise the health and reproduction across all individuals in the population.”
Dr Sue Walker, head of applied science at Chester Zoo, said the study was vital to ensure the continued survival of black rhinos.
She said: “Poaching in the wild is a serious threat to the rhino. Therefore it is important for us to understand the factors that can influence reproductive success.
“We established the project to understand why some individuals breed well, while others do not.
“The idea is that with a better understanding of factors that affect reproduction, we know where we should be focusing our efforts to support the European-wide breeding programme for this critically endangered species.”
Results of the study have been published in the Journal of General and Comparative Endocrinology.