Tag Archives: goose eggs

Polar bear consumption of terrestrial foods – new paper misses the point

A new paper by polar bear biologists (Rode et al. 2015) argues that terrestrial (land-based) foods are not important to polar bears now and will not be in the future – a conclusion I totally agree with – but they miss the point entirely regarding the importance of this issue.

Fat bears on land in the Southern Beaufort, Sue Miller photo, well-prepared for a brief summer fast.

Whatever food polar bears consume in the summer – whether they are on land or on the ice – doesn’t really matter. What matters is how many fat-rich seals they can consume between March and June each year. The fat put on in late winter/spring from gorging on baby seals carries polar bears over the summer, no matter where they spend it.

USGS polar bear biologist Karyn Rode and colleagues (press release here) have tried to frame this issue as one about future survival of polar bears in the face of declining sea ice. However, the fact that polar bears in the Chukchi Sea and Southern Davis Strait are thriving despite dramatic declines in summer sea ice (aka an extended open-water season), proves my point and disproves their premise. Bears in these regions are doing extremely well – contrary to all predictions – because they have had abundant baby seals to eat during the spring (see here and here).

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Journalists still pushing the “polar bears eat snow geese story,” as if it matters

I wrote about this issue in January (January – and journalists are still pushing it).

Courtesy NY Times, Sept. 22 2014.

Figure 1. Courtesy NY Times, Sept. 22 2014. Click to enlarge.

This month, the New York Times (September 22, 2014 James Gorman, “For Polar Bears, a Climate Change Twist”) is pushing it big-time (and so it’s been picked up elsewhere, like by the Anchorage Daily News).

Myths and misinformation about this phenomenon dispelled below.
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Andrew Derocher raises the “starving polar bears” issue in DailyMail interview

In what looks like a follow-up to last week’s CBC documentary, The Politics of Polar Bears, the London (UK) based DailyMail published interviews with polar bear biologists Mitch Taylor and Andrew Derocher (September 9, 2014).

The CBC film did have a one scientist vs. another” flavor about it and this article definitely echoes that approach. My comments below on Derocher’s insinuations and questions about starving bears and global warming.
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Churchill polar bears eat more caribou and geese now than in 1968 because there are more caribou and geese, new research reveals

The press release (pdf here) issued by the American Museum of Natural History (AMNH) a few days ago, regarding several recent papers on polar bear consumption of terrestrial foods around Churchill, Manitoba (Western Hudson Bay), left a lot to be desired in terms of relaying accurate information.

21 August 2021 UPDATE: I have amended this post to correct some comments I made originally about the definition of ‘spring breakup’ of sea ice on Hudson Bay. While the ice indeed begins to break up in spring (usually defined for the Arctic as April-June, bears rarely come ashore before July 1 (summer being July-September). Confusion comes from the standard meteorological method of the defining ‘breakup’ for Western Hudson Bay as the date when ice coverage drops below 50% of the area, rather than the newer, more relevant date when most polar bears have actually come ashore after the date ice coverage reaches 30% (Castro de la Guardia et al. 2017). Using the modern method, the earliest breakup date was in 1999 (17 June), which was still the case in 2021).

Recent research on polar bear diets by Robert Rockwell and Linda Gormezano, it says, suggests that an increase in the consumption of caribou and snow geese since 1968 is a sign that the polar bears are nutritionally stressed due to recent sea ice changes in spring (blamed on global warming) but may be adapting by changing their summer/fall diet.

As the AMNH press release puts it:

polar bears in the warming Arctic are turning to alternate food sources.”

Figure 1. Polar bear feeding on a caribou carcass, taken July 26, 2010. This photo was included in one of the papers cited in the January 2014 press release (Gormezano and Rockwell 2013:3518) and was clearly taken from the air. The caption in the paper says simply, “a polar bear looks up from the recently killed caribou it was eating,” so the bear may not have killed the caribou – some other predator (wolf or grizzly) may have made the actual kill. The dark spots on the bear appear to be flies. Credit Copyright American Museum of Natural History/ R. Rockwell.

Figure 1. Polar bear feeding on a caribou carcass, taken July 26, 2010, from the air. This photo was included in virtually all media reports and in Gormezano and Rockwell (2013a:3518, Fig. 3). The caption in the paper says, “a polar bear looks up from the recently killed caribou it was eating,” implying the bear may not have actually killed the caribou – some other predator (wolf or grizzly) may have made the kill. The dark spots on the bear appear to be flies. Credit: Copyright American Museum of Natural History/R. Rockwell.

However, the AMNH press release fails to mention – as the papers it publicizes certainly do – that Western Hudson Bay populations of caribou and snow geese have increased exponentially since a similar polar bear diet study was done in 1968/69. In other words, there were hardly any caribou or geese around back in the late 60s — little wonder polar bears weren’t eating any.

While evidence of polar bears consuming caribou and geese in recent years is certainly an “increase” over late 1960s levels, that fact says more about the status of caribou and geese populations than it does about polar bears and global warming. Media outlets that quoted the press release verbatim, as many do these days (e.g. here, here, and here), missed this essential part of the story – and of course, so did their readers.

[one story picked up the goose population increase and another revealed the caribou population increase, but none that I saw caught both]

In addition, the AMNH press release makes this erroneous statement that was picked up by every media outlet I saw except one (either exactly as written or reworded slightly):

Climate warming is reducing the availability of their ice habitat, especially in the spring when polar bears gain most of their annual fat reserves by consuming seal pups before coming ashore for the summer.” [my bold]

The earliest breakup dates since 1991 for Western Hudson Bay, where this research was done, have been mid-June (according to the most recent study by Cherry et al. 2013) and for the last few years breakup has occurred in July.

Overall, the press release and resulting media reports seem to be further examples of hyping global warming at the expense of the actual science involved and I have to agree with Andrew Derocher’s interpretation of the significance of terrestrial food items for polar bears. See what you think.
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