When the sea ice begins to recede, the ‘Polar Bear’ has to live on land without food for several months. This period of starvation is challenging for all bears, especially for female polar bears who breastfeed their babies. Our research, published in ‘Marine Ecology Progress Series’, shows that increasing time spent on land as sea ice melts has a negative impact on polar bears’ lactation. Poor lactation is likely a factor in recent declines in polar bear populations. This research shows how polar bears may be affected in the future by the melting of sea ice due to global warming.
Sea ice may seem like a vast and useless thing, but in the Arctic ice polar bears find energy-rich seals, which they hunt to feed themselves. Polar bears in the western Hudson Bay region of Canada experience seasonal sea ice, which melts during the summer months. This forces them to move to land until the cold temperatures of winter allow the sea ice to freeze again. While on land, there are few opportunities for hunting and polar bears usually spend their time in a fasted state. During these difficult months, polar bears rely on the vast fat reserves in their bodies to survive. When these bears come ashore in early summer, some of them have lost as much as 50 percent of their body fat.
While on land, polar bears can lose about a kilogram per day, so they need to spend their energy carefully. For this, most polar bears reduce activities and save energy. Females also have to take into account the additional burden of breastfeeding their children. Polar bear milk contains a lot of energy. It contains up to 35 percent fat and is like cream. This high-fat milk helps in the rapid growth of babies, who weigh only 600 grams at birth, growing to more than 100 kilograms when they reach about two and a half years of age and become independent after leaving their mothers. Are.
Female polar bears face difficult conditions during their time spent on land. If they stop breastfeeding, they risk putting the health of their growing children at risk, while continuing to breastfeed puts their own lives at risk as their energy reserves begin to deplete. To better understand how females breastfeed, our research team looked at data from milk samples collected during polar bears’ stay on land in the 1980s and 1990s. We estimated how long each female polar bear had been fasting based on the dates of sea ice melt.
During this time we found that the quality and quantity of their milk declined due to spending more days at the coast.Some female bears had stopped giving milk completely. Bears who lactated less had the advantage of expending less energy. However, the development of children who received low-energy milk was affected. In the long term, this may reduce the survival of children and ultimately have a negative impact on population dynamics.
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