survival rates

Researchers from the University of Toronto have directly linked the population decline in polar bears living in Canada’s Western Hudson Bay to climate change. Between 1979 and 2021, the polar bear population in this region has declined by nearly 50%.

The monitoring data over this period shows that the average size of polar bears has declined, the size of cub litters has dropped, and cub survival rates are reduced.

The primary factor is the declining amount and duration of sea ice. When there is less ice, bears have less feeding time and less energy overall. The loss of sea ice means that bears spend less time hunting seals and more time fasting on land. The lack of food leads to reduced reproduction, cub survival, and, ultimately, population decline.

The average body mass of adult females has dropped by 86 pounds and of cubs by 47 pounds. With shorter hunting periods and less food, mothers produce less milk. Not only have cub litter sizes dropped over the monitoring period, but mothers are keeping their cubs longer because they are not strong enough to live on their own. The bottom line is that the survival of cubs directly impacts the survival of the population.

Western Hudson Bay is considered to be a bellwether for polar bear populations globally. It is one of the southernmost populations of polar bears and it has been monitored for a long time. With the Arctic warming at a rate four times faster than the global average, polar bear populations in other Arctic regions are likely to be experiencing similar declines.

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Polar bear population decline the direct result of extended ‘energy deficit’ due to lack of food

Photo, posted October 23, 2015, courtesy of Anita Ritenour via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

A massive but unintended experiment in animal conservation has revealed an unexpected result. Thousands of desert tortoises moved to a translocation site in Nevada had a greater chance of surviving if they had lots of genetic variation.

From 1997 to 2014, over 9,000 Mojave desert tortoises were moved to a 39-square-mile translocation site in the Ivanpah Valley. The tortoises were either abandoned pets or were displaced by developments in suburban Las Vegas and by solar farms in the desert.

The U.S. Fish and Wildlife service took blood samples to screen for diseases and marked each animal before releasing them into the site, enabling them to be tracked in later surveys.

When the researchers compared tortoises that lived or died over the same time period after being relocated to the site, they found that survivors averaged 23% greater heterozygosity than those that perished. Heterozygosity is a measure of genetic variation. Like most organisms, tortoises have two copies of their entire genome, with one from each parent. The more those copies differ from each other, the higher the organism’s heterozygosity.

Researchers are not really sure why greater genetic variation is linked to survival rates. Potentially, individuals with higher heterozygosity have more genomic flexibility. It is the case that tortoises with more genetic variation have a better chance of having at least one copy of a gene that works really well in stressful or new environments.

Human activity and the changing climate are increasing the need to relocate plants and animals. Often the chances for success in doing this are not good, so anything we can learn about things that increase the chances for survival can be very important.

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UCLA study of threatened desert tortoises offers new conservation strategy

Photo, posted August 23, 2016, courtesy of the Bureau of Land Management California via Flickr. Photo by Dana Wilson, BLM.

Earth Wise is a production of WAMC Northeast Public Radio.