U.S. Bank Stadium's Bird Toll

Posted on November 27, 2019
Tags: economics

Over the last few years of living in Minneapolis, there has been a substantial amount of conversation about the new Vikings stadium, particularly about its cost (substantial) and its toll on migrating birds (uncertain). In 2017, the Audubon Chapter of Minneapolis published a study they performed during the Fall migration season in 2016, concluding “this level of migratory bird mortality … will establish U.S.Bank Stadium as the top bird-killing building in the Twin Cities.” Minneapolis Audobon Society US Bank Stadium Bird Mortality Report

Lots of people are paying attention to the risk to birds presented by the US Bank Stadium, and the Vikings funded “a two-year, $300,000 bird collision study” MPR U.S.Bank Study Summary to quantify that threat. This was performed by Scott R. Loss and a team of researchers from Oklahoma State and the University of Minnesota. They did surveys near the stadium for 6 months of the year, finding 111 dead birds near the stadium. They conducted surveys at the buildings in the study for six months, and though these observation times include the peak migration times, this isn’t the full toll the stadium takes on birds annually.

As best as I can tell, this study resulted in 2 papers: one hosted by the MSFA and prepared with them as an audience, and one published in PLOS, an open-access publisher. The MSFA one gives some suggested window treatments, and I looked at their first suggested treatment, CollidEscape. The ceiling on cost of materials for all the stadium’s windows given the listed prices on their website would be around $600,000, and though there should be ways to cut down on that number, I’m not sure what installation costs would be, so lets take that as a very rough cost estimate. 200,000 square feet of glass, according to the Audubon Chapter of Minneapolis’ initial report presented on February 24, 2017. The listed price for 50 square feet of “CollidEscape Guaranteed - White” treatment is $149. 200,000 * (149/50) = $596,000. I imagine buying 4,000 of these would lower the price substantially. I don’t have a good estimate of installation costs. I will take the life of the stadium to be 31 years. This is the lifetime of the Vikings’ last stadium, the Metrodome, which they occupied from 1982-2013. Assuming the window treatment lasts the entire lifetime of the stadium, this will total to 3,441 birds. With the generous assumption that a bird in 2050 is worth the same as a bird today, this treatment has an efficiency of around $175/bird. A reminder that these are very rough numbers, but they ought to at least be in the ballpark (pun intentional). Michael W. Fox’s Star Tribune Op-Ed mentions Minnesota’s Animal Humane Society’s release of 3,175 cats over four years. If each cat from this policy lives 5 years outdoors (cats often live to be 15), and this rate of release continues, this translates to 3,969 feral cats in Minnesota at a time attributable to this policy. Loss’ previous work with Will & Marra estimates that each of these feral cats is likely to kill 38 birds annually, bringing the annual bird toll from this trap-neuter-release (TNR) program to 150,425 birds a year. Per feral cat bird predation in the United States is roughly (51.4 + 24.4)/2 = 37.9 birds per cat annually, or one third of a stadium. The same paper estimate’s the impact of owned cats with outdoor access, at roughly (1.0 + 34.1) /2 = 17.55 birds per cat annually, or a sixth of a stadium. From a little searching online, it looks like spaying or neutering a cat is comparable to euthanasia: if anything, it’s more expensive, meaning replacing the TNR policy with euthanasia may save money and birds at the same time. Regardless of price, it’s worth putting in perspective: the Minnesota Humane Society’s policy’s bird toll is equivalent to over a thousand stadiums 150,425/111 = 1,355 , and it would be much, much cheaper to change.

I understand that the suggestion of euthanasia may be morally repugnant to some, and that the Vikings are unlikely to support this proposal. I don’t expect they will pursue a window treatment, given the small estimated number of bird deaths that would be avoided with it. If someone wanted to do something comparable, they could sponsor the culling of 3/5 feral cats a year. I’m not sure what this would cost, but this is the math you have to do if you’re genuinely interested in saving birds. The only way to responsibly make policy decisions is to compare the means to accomplish your desired ends based on something like price A great start to thinking in terms of utility is Eliezer Yudkowsky’s post Coherent decisions imply consistent utilities , and the truth of the matter is that the cost of window treatment is very high.

There are some considerations that still might make the math defending a stadium window treatment. I would defend such a proposal if:

  • I could be convinced that the selection pressure presented by reflective windows could not be adapted to.
  • The population of birds killed by cats and windows were very different. For example, if birds too large to be hunted by feral housecats disproportionally died colliding with reflective windows, or if reflective buildings impacted many more migratory birds than local birds (this seems to be the case), and
  • the population selected for by reflective windows was undesirable: reflective windows killed more valuable birds for some definition of “valuable”
  • there was not a cheaper way to save a comparable number of these birds
  • I could be convinced these birds were a more valuable policy goal than other low-hanging policy fruit

The point, though, is that all of these considerations can fit into your definition of “utility,” and they should! It’s not responsible to have a policy opinion without making at least some vague consideration of efficiency. You may highly value feral cats, and value outdoor-access for owned cats, and find it unreasonable to suggest impacting cat numbers. If you also value birds, you may support treatment of window glass to save birds, but it’s still worth knowing the tradeoffs you are supporting. It’s worth thinking about that when arguing for window treatment, you should also be ready to defend feral cats. There is a feral cat ↔︎️ stadium window exchange rate, and it is good to have some vague idea what sort of trades on that exchange strike you as fair.