Collision Mortality Has No Discernible Effect on Population Trends of North American Birds

[kristopher]

Collision Mortality Has No Discernible Effect on Population Trends of North American Birds

Todd W. Arnold1*, Robert M. Zink2

1 Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota, St. Paul, Minnesota, United States of America, 2 Bell Museum and Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, Minnesota, United States of America

Abstract Top
Avian biodiversity is threatened by numerous anthropogenic factors and migratory species are especially at risk. Migrating birds frequently collide with manmade structures and such losses are believed to represent the majority of anthropogenic mortality for North American birds. However, estimates of total collision mortality range across several orders of magnitude and effects on population dynamics remain unknown. Herein, we develop a novel method to assess relative vulnerability to anthropogenic threats, which we demonstrate using 243,103 collision records from 188 species of eastern North American landbirds. After correcting mortality estimates for variation attributable to population size and geographic overlap with potential collision structures, we found that per capita vulnerability to collision with buildings and towers varied over more than four orders of magnitude among species. Species that migrate long distances or at night were much more likely to be killed by collisions than year-round residents or diurnal migrants. However, there was no correlation between relative collision mortality and long-term population trends for these same species. Thus, although millions of North American birds are killed annually by collisions with manmade structures, this source of mortality has no discernible effect on populations.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0024708&annotationId=info%3Adoi%2F10.1371%2Fannotation%2F45166fd2-e951-48f7-902e-113f9e37ac81

[joshcryer]

1. Promising report.

We believe that many poorly quantified conservation threats, ranging from topics as diverse as house cat predation (24), wind towers (11) and bushmeat consumption (25), could be assessed using similar methodology.

[XemaSab]

2. .

[kristopher]

3. Promising?

Not sure what that means? It sounds like straight-forward good news for those who are invested in cumulative human impact on avian mortality.

[FBaggins]

6. Do you think that those with this concern...

... Are worried about birds becoming extinct?

While I don't share their concern, a million dead birds is a million birds that they would prefer not to see die.

Also... While the holocaust reference is hyperbolic, it's relevant. Fukushima (heck even Chernobyl) has no discernible impact on population growth. Does that have any impact on your opinion re: the safety of nuclear power?

[GliderGuider]

9. Yes, you understand the wrinkle exactly. n/t

[OKIsItJustMe]

11. For what it's worth

This study doesn’t actually deal with bird deaths attributed to wind turbines at all.

[font face=Times, Serif][font size=3]… Our analysis was based on existing summaries of birds that accidentally killed themselves by colliding with towers or buildings …[/font][/font]

Given the complexity of the ecosystem, and the amount of effect we have on it, it is difficult to say that “a million birds” who are killed in collisions with human structures would not have been killed in some other fashion. (All birds will die eventually from something, and most not from “natural causes.”)

Those who are concerned by this issue should step back for a moment, and ask themselves, Is it better for a percentage of a species to die, flying into artificial structures (like wind turbines) or for their entire species to go extinct due to more rapid climate change.

The Audubon Society recommends a balanced approach. They strongly support the expanded use of wind power, but stress that wind farms should be constructed in such a way as to minimize bird deaths. (This, I feel, is a rational approach.)

[FBaggins]

14. Seems about right to me

Though, from my perspective, a cat eating a bird is a "natural cause"

But you're right... There isn't a scenario where humanity doesn't have an impact on the rest of the ecosystem. Absent a desire to return to a pre-electrification standard of living, wind turbines seem an acceptable impact for their benefits.

[kristopher]

17. That is their position as they often articulate it, yes.

Are you going in the direction of "it's ok to eat a chicken but killing a robin is a sin"?

You either:
hold deep moral beliefs about the sanctity of all life, or
you hold deep moral beliefs about the sanctity of some life and no deep oral beliefs about the sanctity of other life, or
you hold no deep moral beliefs about the sanctity of life.

Could you fit your explanation into that structure so that it becomes clear?

[FBaggins]

22. Really?

I've never seen anyone come close to implying that wind power is going to kill all of the birds.

Are you going in the direction of "it's ok to eat a chicken but killing a robin is a sin"?

Didn't I esentially say the opposite? I don't consider bird deaths a factor to consider when supporting wind power. I would support reasonable design modification to limit such deaths where they make sense... but I think that's already been done.

Could you fit your explanation into that structure so that it becomes clear?

No... but I can come close.

Remove "sanctity" (a word with different meaning for different people) from the equation and I'm close to the second position. I'm human and happen to consider humans different in some essential way from other creatures. I'm willing to eat the ones that I find tasty/nutritious and don't mind "using" others (for work, entertainment, leather, etc)... but that doesn't mean that there are no "moral beliefs" related to animals. I'm willing to eat a chicken, but that doesn't mean that I don't care how it was raised or cared for. If birds consistently strike a large window and hurt/kill themselves I'm willing to try to modify the look/usage of that window in a way that will help them see it... not because there's a moral equivelence between human and avian... but because I prefer that even "lesser" animals not suffer unecessarily on my part.

Close enough?

[jpak]

25. What peer reviewed studies conclude that wind turbines threaten any bird species with "extinction"

waiting

[FBaggins]

26. None at all that I'm aware of.

As I said... I can't even think of a most-wildly-anti-wind advocate who would try to spin that turbines actually endanger the very existence of birds. That's why I thought the OP was a non sequitur. I can't justify abusing my dog by claiming that that the overall population of dogs will not be impacted by the loss of a single dog.

There are plenty of good defenses against the attack that wind power should be restrained because it kills birds... but "ah! There's still tons of birds out there... we can hardly count them!" isn't one of them.

[joshcryer]

19. Yes, it is promising that we have a new method to define poorly quantified conservation threats.

[GliderGuider]

4. The Holocaust had no discernible effect on population trends of European humans either.

Last edited Wed Dec 21, 2011, 12:08 PM - Edit history (1)

We should find that encouraging too.

[kristopher]

5. Comparing avian mortality to the Holocaust?

Yes, I'd say that is a definite "WTF?"

[GliderGuider]

7. No. Dig a little deeper, and don't let your knee jerk so hard.

Now try again.

[OKIsItJustMe]

10. It certainly had a discernible effect on a subset of the population

Approximately 2/3’s of the European Jewish population was killed.

Do you mean to suggest that wind farms will have a similarly dramatic effect on some variety of birds?

[Dead_Parrot]

12. Well, there's the question

It irks me that most of these studies lump 10,000-odd species together and treat them as one. Sigh...

[OKIsItJustMe]

15. Which, by the way, is something this study quite specifically does not do

It’s well worth a read (if you ask me.)

[Dead_Parrot]

18. I'm about half way through it...

Last edited Wed Dec 21, 2011, 07:02 PM - Edit history (1)

...and should really finish it. Yes, this is one of the rare exceptions and it's a pity they didn't include turbines, but at least they prompt it and give a methodology.

The impression I get - and don't ask me to back this up with hard numbers - is that turbines affect large, low-population birds more than small, high-population ones. In the majority of cases this could probably be avoided with proper siting, but just raising the topic seems to be anathema.

[GliderGuider]

13. I'm not an ornithologist. However, I'm very aware of the dangers of over-aggregation.

Examining population aggregates is of very little value. Too much important information gets lost if we step back too far and squint too hard. If some species of birds in some regions were being placed at extraordinary risk by wind farms, studies like this won't detect it.

[OKIsItJustMe]

16. Did you actually read the study?

[font size=3]…

These residuals represent relative collision vulnerability, which varied enormously among species. For buildings, the top five species (“super colliders”) were 25 to 57 times more likely to collide with a building than expected by chance (Fig. 1; Table S1). By contrast, the bottom five species of super avoiders were 105 to 208 times less likely to collide with a building than expected by chance. For towers, super colliders were 96 to 236 times more likely to collide than expected by chance, whereas super avoiders were 222 to 688 times less likely to collide. Only two species identified as super colliders based on relative collision vulnerability were also among the top five species based on simple body counts (swamp sparrow at buildings, bay-breasted warbler at towers; for scientific names see Table S1). Black-throated blue warblers were super colliders at both buildings and towers, whereas cliff swallows and horned larks were super avoiders for both structure types.

There was a strong taxonomic component to collision vulnerability. For 13 avian families that contributed five or more species to the tower collision data, relative vulnerability varied significantly among families (F12,132 = 12.47, P<0.0001) with wood warblers (Parulidae, n = 36) averaging 18-fold greater vulnerability and swallows (Hirundinidae, n = 6) averaging 54-fold lower vulnerability (Table S2). Taxonomic effects were also prominent for building collisions (F12,101 = 9.88, P<0.0001), with wood warblers and swallows once again representing the extremes. Although there were notable differences between towers and buildings in relative vulnerabilities for some species, residuals from the two data sets were highly correlated (r = 0.60, P<0.0001, n = 147; see Figure S2) indicating that most species had similar vulnerability to both mortality sources.

…[/font]

[GliderGuider]

20. Yes, I know the study looked at individual species.

My hackles were raised by this offhand conclusion: "Thus, although millions of North American birds are killed annually by collisions with manmade structures, this source of mortality has no discernible effect on populations."

The implication seems to be that as long as population numbers aren't affected, the lethality of human behaviour doesn't really matter. Unfortunately, there are many other genus and species for which even that cavalier dismissal is off the mark.

[OKIsItJustMe]

21. OK, is there any indication that these deaths are significantly affecting of these species?

Your reference to the Holocaust was a rather cavalier dismissal as well. (Don’t you agree?)


Honestly, you rather calmly discuss the deaths of Billions of people in your analyses; yet you get ticked off that someone discusses the deaths of Millions of birds without what you consider to be an appropriate level of contrition?

[Bob Wallace]

23. Thanks for saying that....

n/t

[GliderGuider]

24. My reference was intended to illustrate one simple point.

Last edited Thu Dec 22, 2011, 03:57 AM - Edit history (2)

Human actions can have horrific consequences while not interrupting the population growth of a species. The damage that human actions cause may be utterly unacceptable even if they don't have a species-scale impact. The line that triggered me seemed to imply that as long as there was no species-scale impact there was no "real" harm done.

Of course, deliberate or avoidable species-scale impacts involve a much higher level of harm. When I talk about the deaths of billions of humans, I am under no illusion that this would be a positive thing from the human viewpoint. It could easily be the most horrific human tragedy since Toba.

My willingness to accept this possibility stems from my conviction that there is something even more important at stake than human life. What is at stake may be Life itself, due to multiple species-level impacts that have been made unavoidable by the sheer and ever-growing number of humans.

The only circumstance I see that would reduce the existential threat we pose to countless other species is a reduction in our numbers. I don't think we will deliberately engineer that outcome, but I'm ever more convinced that we are unwittingly engineering a situation where an involuntary decline is inevitable. I would like to see us do as little harm as possible to other life on the planet while we figure out what the hell we're on about. That of course includes birds as well as cetaceans and land fauna large and small.

[OKIsItJustMe]

8. Nothing really new here

http://election.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=314944&mesg_id=314975