Polar Bear Blog – Last Call

April and May are a busy time for polar bears. Not only is it peak seal hunting conditions but its also time for bears to, well, get busy. By age four or five, females are sexually mature and ready to mate. As they go into estrous, they appear to leave a scent trail in their footsteps allowing male polar bears to track them.

Preferably, the female ‘allows’ the male to court her and they mate over several days, often find a ‘secluded’ spot for their tryst. However, there is considerable competition for mates among the males and often the female does not have much choice in her mating partner. Males will battle in fierce sparring competitions, fighting for upwards of an hour at a time, sometimes with mortal injuries, just for the opportunity to mate.

For this reason, it is very rare for a male under eight years of age to successfully breed (unless he can sneak in while the big boys are distracted’. It also seems that a genetic bottleneck is created by these battles for mates, as the largest and most aggressive males sire the vast majority of cubs in regional subpopulations.

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A recently published study has shed some light on reports of ‘last call’ bears, bears that appear to have mated well after prime season.  For years, Inuit and Hudson’s Bay Company reports have cited that mating has been witness in June and even July. These observations did not seem to fit with the scientific community but, again, you can never discount eye-witness accounts by northerners.

Last June, two polar bears were recorded mating on the sea ice near Svalbard, Norway.  Here are the details:

‘The female lay down at 18:11 and remained in the same position on the ice floe. After a few minutes, the male lay down within a few metres of her. The ship remained in position until 19:30, then moved south away from the bears, who remained lying down on the ice. During the whole observation period, there was no sign from the bears that they were reacting in any way to the presence of the ship.

The female bear (N23937) was identified from the satellite tag, which gave its GPS position on the date and time of the sighting. She was first captured in April 2008, during the annual capture–recapture programme of the Norwegian Polar Institute. Her size and the cementum lines in a rudimentary tooth extracted during her capture indicated that her birth year was 2005 (likely uncertainty ±1 year; Christensen-Dahlsgaard et al. 2010). This female, which habitually occupies the area of north-west Spitsbergen, was recaptured alone in April 2011 and in April 2012. In April 2013, at the estimated age of eight years, she was with a cub of the year. On 31 August 2013, this mother and cub were again captured, and at that time the mother was equipped with the iridium telemetry collar.

The mother and her cub were again captured on 7 April 2014. At that time, the yearling cub measured 47 kg. This is the lowest body weight measured among 41 yearling cubs in the spring from 1989 to 2014 in Svalbard (mean 77.4 kg, 95% confidence interval: 70.7 kg–84.0 kg). At 162 kg, the mother had lost 47 kg since the previous autumn. She did not seem to be lactating. We flew over the area where the bears had been handled on both 12 and 23 April, but they were then not seen in the area. When the mother was again observed, mating, on 29 June, the cub was not seen anywhere close despite prolonged observation of the area of floating pack ice.’

This is the first confirmed sighting of late season mating. It is theorized that if a female loses her cubs in the spring, that she may re-enter estrous. This seems to confirm the Inuit and fur trade observations.

This is another example how local observations and traditional knowledge are very often proven credible by science, sometimes after decades or even centuries. For instance, the recently discovered ‘scented footprints’ that females leave for potential mates corroborates a western Arctic belief that polar bears ‘sleepwalk’ sometimes. This is, of course, due to observations of a male following a female in estrous, his nose to the ground, so intent on a potential mate that he seems oblivious to the outside world.

Only recently has traditional knowledge been given a more active role in global polar bear management and research. These two examples show how important it is that both sides keep an open mind to new interpretations of polar bear behaviour.

One thought on “Polar Bear Blog – Last Call”

  1. Great topics and reports…. school sent some researchers up there to help on monitoring and locating dens. I sure hope they read your archives first. 😉
    The latest low that brought rain / thunderstorms south of the border into the Hudson Bay basin might be attributed to the decrease in ice up there as noted in the http://www.ec.gc.ca/glaces-ice/default.asp?lang=En&n=CE69E4DD-1 map.

    Thanks for the great reports and topics… Some of the images on FB page could be first place winners in National Geographic’s wildlife category. 🙂

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