Carnivores living in the wild and zoos give birth at the same time of the year in a phenomenon called reproductive seasonality.

Researchers at the Clinic for Zoo Animals, Exotic Pets, and Wildlife at the University of Zurich took 150,000 birth records in zoos submitted to the nonprofit organization Species360 and cross-analyzed it with the natural birthing season of carnivores in the wild.

The study was published May 7 in the Journal Biological Rhythms.

Influence Of Climate On Birthing

Environmental factors like climate and availability of food source dictate mating and birthing season. Some animals are born in spring when the conditions are less hostile to survival.

The study was meant to determine if animals have the same reproductive seasonality that they have in the wild as they do in captivity, where they have a constant supply of food all-year-round. They found that births occurring in the wild and in captivity are closely the same, with 80 percent of the species born at the same time.

"Seasonality is an evolutionary feature and thus a fixed characteristic of a species - most probably through a genetically determined reaction to a signal given by the length of daylight," said lead author Marcus Clauss, a professor at the Vetsuisse Faculty, University of Zurich.

Relationship Of Habitat And Reproduction

Researchers found that the farther the animal is from the equator, the more seasonal their reproductive behaviors are. This is especially true in carnivores with more distinct seasonality features like the red wolf, the mink, the yellow-throated marten, the wolverine, the red panda, and the Canadian lynx.

On the other hand, carnivores like the bush dog, the jaguar, and the spotted hyena do not reproduce at any particular time of the year.

How Body Sizes Affect Gestation

Interestingly, researchers noted that seasonal carnivores have shorter gestation periods relative to their body size. The reason being is to accommodate the growth of the embryo in time for the birth in spring.

Other animals would have longer gestation periods so they can give birth at the most appropriate time of the year. The extension of the gestation happens not by slowing down the embryo growth but by delaying the time in which the fertilized ovum is attached to the womb.

The exception to this rule is the sea otter, which is a native species in the Alaskan coast. Scientists hypothesized that sea otters do not need to extend or prolong their gestation because they eat sea urchins and mussels, which are abundant all-year-round.

"Living in the ocean provides more uniform conditions throughout the year compared with life on land because resource abundance is relatively stable across seasons and marine mammals are less affected by adverse weather conditions compared with land-living species, potentially allowing sea otters to give birth year-round," the authors explained.

Clauss said the results of their study show the little influence zoos can make in reproductive seasonality. However, they did not specify if this connection still exists among domestic pets.

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