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A second critique of ‘Collision mortality has no discernable effect on population trends of North American Birds’

Posted by kdegroot on 03 May 2012 at 17:54 GMT

Klem, Daniel Jr.1, K.L De Groot2, E.A. Krebs3, K.T. Fort2, S. B. Elbin4 and A. Prince5

1 Acopian Center for Ornithology, Department of Biology, Muhlenberg College, Allentown, PA, 18104, USA; e-mail:

2 Canadian Wildlife Service, Environment Canada, Pacific Wildlife Research Centre, 5421 Robertson Rd., RR#1, Delta, BC, V4K 3N2

3 Science and Technology Branch, Pacific Wildlife Research Centre, Environment Canada, 5421 Robertson Rd., RR#1, Delta, BC, V4K 3N2

4 New York City Audubon, 71 W. 23rd St., New York, NY 10010, USA

5 Chicago Bird Collision Monitors, Chicago Audubon Society, 5801-C N. Pulaski Road, Chicago, IL 60646 USA; email:

Many species of North American birds are showing strong regional and/or range-wide declines (Berlanga et al. 2010). However, due to their complex life cycles it is often difficult to partition out specific factors that drive or contribute to these declines. Arnold and Zink therefore have tackled a highly relevant question for the conservation and management of birds. While we acknowledge the appeal and potential applications of Arnold and Zink’s approach, we believe that the authors have overstated the robustness and scope of their conclusions.

The general nature of the title, “Collision Mortality has No Discernable Effect on Population Trends of North American Birds” is not an accurate reflection of the limited types of data used in this analysis. Data included in Arnold and Zink’s analysis consists of collision mortality during fall and spring migratory periods from: communication towers at 39 sites; a group of multistory buildings in the cities of Toronto and New York; and a long-term dataset from one building in Chicago (McCormick Place). Collisions with glass on a range of low-rise and residential buildings as well other structures, high-tension wires, vehicles etc. are not represented. While this may reflect a reality in the accessibility or availability of these other types of collision data, we clearly should be very cautious in accepting that “collisions with manmade structures” have “no discernable effect on populations” as Arnold and Zink assert.

Secondly, the nature of the collisions and the time of day during which birds were collected for the particular data included in this analysis (M. Mesure pers comm., S. Elbin pers. comm., and D. Willard pers. comm.) indicates that these datasets consist of mainly nocturnal collisions, or at the very least do not contain a representative sample of diurnal collisions. The authors note a strongly significant increase in vulnerability to collisions for nocturnal migrants versus diurnal migrants. We argue that this is a result of significantly oversampling nocturnal collisions, i.e., diurnal migrants should not be vulnerable to the effects of lighting of communication towers and urban buildings as they tend not to be migrating at night. However, both diurnal migrants and nocturnal migrants are susceptible to colliding with glass during the daytime.

We know that diurnal collisions occur throughout the year, and with great frequency at buildings of all sizes, including residential homes (Klem 2010, Klem 1989, Klem 1979, Wedeles 2010). A truly accurate assessment of relative vulnerability to collisions may portray a result quite different from Arnold and Zink’s. Indeed, the entire construct of “super-avoiders” and “super-colliders” might fall apart when looking at a complete picture of avian collision mortality.

Clearly there is a strong need for broad-scale investigations of avian collisions of all types. It is also clear that these investigations need to account for collisions throughout the annual cycle of birds in order to assess the relative magnitude of the effect of collisions on populations. We thank the authors Arnold and Zink for publishing thought-provoking work, generating interest and opening up discussion on the topic of avian collisions.

Literature Cited:

Arnold, T. W., Zink R.M. 2011. Collision mortality has no discernable effect on population trends of North American birds. Plos ONE 6: e24708.

Berlanga, H., J.A. Kennedy, T.D. Rich, M.C. Arizmendi, C.J. Beardmore, P.J. Blancher, G.S. Butcher, A. R. Couturier, A.A. Dayer, D.W. Demarest, W. E. Easton, M. Gustafson, E. Iñigo-Elias, E. A. Krebs, A.O. Panjabi, V. Rodriguez Contreras, K.V. Rosenberg, J.M. Ruth, E. Santana Castellón, R. Ma. Vidal and T. Will. 2010. Saving Our Shared Birds: Partners in Flight Tri-National Vision for Landbird Conservation: Cornell Lab of Ornithology: Ithaca, NY

Klem, D. Jr. 1979. Biology of collisions between birds and windows. Ph.D. dissertation, Southern Illinois University at Carbondale.

Klem, D. Jr. 1989. Bird-window collisions. Wilson Bulletin 101:606-620.

Klem, D. Jr. 2010. Sheet glass as a principal human-associated avian mortality factor. In Chapter 20. Avian Ecology and Conservation: A Pennsylvania Focus with National Implications, 276-289 pp. Eds. S. K. Majumdar, T. L. Master, R. M. Ross, R. Mulvihill, M. Brittingham, and J. Huffman. Pennsylvania Academy of Sciences, Easton, PA.

Wedeles, C.H.R. 2010. Avian Incidental take due to Buildings in Canada. Report Prepared by ArborVitae Environmental Services Ltd. for Environment Canada. 43 p.

No competing interests declared.