posted January 15th, 2010; last edited November 18th, 2010 –– David Sibley

Causes of Bird Mortality

A chart showing estimated numbers of birds killed annually by each of several different causes. Data from various sources.

This chart and the following text were prepared in 2003. Any updates would be welcome.

First, it should be stated that the single most significant threat to bird populations is habitat destruction, in all of its forms and with all of its causes. The various causes of mortality outlined below kill individual birds directly, and can certainly have an adverse effect on population size, but can actually have a beneficial effect in some cases. Studies of hunting have documented that in certain cases killing small numbers of birds can improve the health and survival of the remaining birds. As long as the habitat is intact, the population has the potential to replace the lost birds.

In simplest terms, habitat destruction reduces the population by reducing the available resources, denying birds the chance to reproduce, and effectively putting a cap on the population size.
The problems outlined below are serious threats and are implicated in the declines of many species. They should be addressed.

Collisions

Window strikes – estimated to kill 97 to 976 million birds/year – Millions of houses and buildings, with their billions of windows, pose a significant threat to birds. Birds see the natural habitat mirrored in the glass and fly directly into the window, causing injury and, in 50% or more of the cases, death. Simple steps can be taken to reduce the number of birds striking windows. Decals that stick to the glass are not very effective, but strips of tape on the outside of the glass, or strings or feathers hanging outside the window, each no more than 10 inches apart, are fairly effective. Decorative features like stained glass designs or window dividers can achieve the same result. Outside screens are very effective both to reduce the reflection and to cushion the impact. In short, anything that reduces or breaks up the window’s reflection will reduce bird strikes. Lots of excellent info at FLAP (Fatal Light Awareness Program) ; follow the link to collision prevention and be sure to check out the “CollidEscape” film.

Communication towers – estimates of bird kills are impossible to make because of the lack of data, but totals could easily be over 5 million birds/year, and possibly as many as 50 million. Towers have proliferated in recent years, with an estimated 5000 new towers erected per year during the 1990s, mainly for the cell phone and digital TV industries. Any tall structure will kill birds by collision, and lighted towers attract birds at night. Theoretically cellphone towers are less dangerous than the taller structures, but there is no data either way, and the sheer number of cell phone towers may outweigh any other advantage. More info at FLAP (Fatal Light Awareness Program) and TOWERKILL .

High tension line collisions – may kill up to 174 million birds per year. This figure extrapolates from European studies to the millions of miles of aerial wires in North America. There are very few data in North America.

Electrocutions kill tens of thousands of birds per year. This occurs mainly when large birds such as raptors make contact between a live electrical wire and a ground such as a pole. The relatively small number of birds affected belies the significance of this threat, since species such as Golden Eagle are more susceptible. Large predators like eagles have smaller population sizes and lower reproduction rates than songbirds, so removing a few thousand birds from the population will have a much larger impact than removing the same number of, say, Savannah Sparrows. Studies byHawkWatch International revealed an electrocution rate of just under 1 bird per 100 poles per year, or 547 birds at 74,000 poles in Utah in 2001-2002. About 10% of the birds killed were Golden Eagles, 34% Ravens, and another 25%Buteos (Red-tailed, Swainson’s and Ferruginous Hawks). Fortunately PacifiCorp, the owner of the poles, is committed to making changes to reduce electrocutions, and hopefully other regions will follow.

Cars may kill 60 million birds per year.  Of over 8 million lane miles of roads in the US, 6.3 million, or over ¾, are in rural areas where most birds are presumably killed. There’s not much we can do about this source of bird mortality short of changing our driving habits, but landscaping the roadside to discourage birds from congregating there is helpful. My own sense is that small cars with more aerodynamic designs hit fewer birds, while large boxy vans and trucks hit more birds, but I don’t think this has been studied. By the way, 100 years ago there were fewer than 250 miles of paved roads in North America, all in urban centers.

Wind turbines may kill 33,000 birds per year, and, as in the case of electrocutions, these birds tend to be large and scarce (e.g. raptors). The recent surge of interest in wind power has heightened concerns about their effect on birds, and has led to at least the discussion of efforts by the wind power industry to design more benign windmills and to choose locations that are less “birdy”. It’s difficult for an environmentalist to come out against renewable energy like wind turbines, but as long as the electricity generated is considered a “supplement” to satisfy increasing demand, wind power will not really help the fight against global warming. Establishment of wind farms should go hand-in-hand with drastic cuts in electricity use, and there is a real need for more study of the relationship between birds and wind farms.

Poisoning

Pesticides may kill 72 million birds per year or possibly many more. The sub lethal effects of pesticides may also make the birds more susceptible to predators or unable to reproduce, essentially killing them. A New York study in 2000 found that common “over-the-counter” pesticides were responsible for more bird deaths there than West Nile Virus. More info about pesticides and birds can be found at The American Bird Conservancy, and BIRDSOURCE atCornell University. The Canadian Wildlife Service maintains a website with information about pesticides at http://www.cws-scf.ec.gc.ca/nwrc-cnrf/toxic/what_e.cfm

Oil spills kill hundreds of thousands of birds a year or more. Some of this occurs in dramatic large spills, but most probably occurs in thousands of small incidental spills that are never reported or documented.

Oil and wastewater pits may kill up to 2 million birds per year.

Lead poisoning – kills unknown numbers of birds each year, but Bellrose (many years ago) estimated that about 4% of the waterfowl population dies annually due to lead poisoning, and the California Condor recovery team stated that lead poisoning was the primary cause of the condor population decline over the last 50 years. This lead in the form of bullets and shot and fishing sinkers is ingested by the birds, ground up in the gizzard and absorbed by the body. More info is available from HawkWatch International. Alternative materials are now widely available and should be promoted. In Britain the use of lead fishing sinkers has been banned.

PollutionAcid rain has been linked to calcium problems.

Predation

Hunting - as a point of reference the carefully-managed annual waterfowl hunt kills about 15 million birds a year in North America. This, of course, is balanced by extensive and well-funded management and conservation efforts so hunting is not a threat to the population of any North American bird, and conservation efforts led by hunters have been hugely beneficial to many species in addition to the ones being hunted.

Domestic and Feral Cats – may kill 500 million birds per year or more. More information can be found at The American Bird Conservancy Predators, of course, account for the vast majority of bird deaths each year, and most of this predation is natural. Domestic cats are not natural predators, but kill many birds.  It is worth noting that house cats have been blamed for the extinction of two species of small mammals in the southeastern  United States, and feral cats continue to be a huge problem where they have been introduced on many oceanic islands.

By-catch – Tens to hundreds of thousands of seabirds are caught each year in nets and on hooks intended for fish. Although the total number is small this source of mortality is having a profound impact on a few species of birds.
See my newspaper column HERE about long-line fisheries and albatross. The BirdLife International site (an excellent source of global bird conservation information) has detailed information about the albatross declines here .

Disease

Disease – Unknown numbers. Disease is a major source of mortality for birds, and may be the underlying cause of death in many cases of predation. Most avian diseases are fairly specific, such as the conjunctivitis eye disease that hit House Finches hard in the eastern states. Botulism can be a serious problem in wetlands where water is drying up. The West Nile Virus has recently caused concern because it affects a wide range of species and has spread rapidly. TheHawaiian Islands have been particularly hard hit by avian disease, and offer a sobering example of the dangers of introduced diseases to naïve local bird populations; detailed info can be found here.

32 comments to Causes of Bird Mortality

  • Eric Luesebrink

    With regard to wind turbines, I don’t think the description that “as in the case of electrocutions, these birds tend to be large and scarce (e.g. raptors)” is accurate. With the exception of the Altamont Pass in CA (where raptor deaths have occured but in much smaller numbers than quoted above) very few raptors or large birds have been killed by wind turbines. I would suggest you look up the work of Paul Kerlinger who has studied this issue for 20+ years.

    Thanks,
    Eric

  • bruce

    Domestic cats most certainly are predators. Turned loose from human captivity they will readily revert to feral and do quite well, assuming they have the natural tools. And cats have been “blamed” for many things, including the supernatural. But when a cat ventures out and raids a pheasant nest, it does so because that’s what cats do. If one believes in a “Creator”, then the cat has an absolute right to kill the pheasants. People kill them for entertainment in most all cases.

    • Robert

      Bruce, while many cats are able to survive in the wild after domestication, it is a myth to say that they all do so “readily”. We have a serious problem in my area of people dumping cats because they believe this. The result is a large number of cats starving to death or living on garbage.

    • Chris

      Bruce,

      Regardless of whether you are convinced of the existence of a “Creator” house cats were CREATED by Humans from a wild species that is native to Europe, Asia and Africa. Domestic cats and their wild ancestor, the Wild Cat (Felis silvestris) were never part of the North American fauna. It’s unfortunate that you used another non-native species in your example. Feral cats as well as free-roaming pets kill large numbers of native birds, mammals and other small animals each year. You seem to imply that people killing pheasants for “entertainment” may be “wrong.” A cat allowed to roam freely or released to fend for itself is no different than a human indiscriminently firing a shotgun while walking blindfolded through the forest.

    • Susan

      Cats, if hungry, do indeed kill to eat. But any well-fed cat will hunt and kill FOR THEIR PLEASURE– it is their nature to do so. We are talking domestic cats, NOT NATIVE, NOT part of nature.

  • Van

    Bruce, what does believing in a creator have to do with having a right to kill ??? Killing for entertainment? Huh?

    Thanks for this overview, David!

    • Carole

      If one believes in a creator who created the various species, then one would necessary have to believe that the creator intended predators to kill. Indeed, many species have to kill to live. I don’t think a cat could survive on a vegetarian diet. So either the cat kills or is fed animals that others have killed and made into cat food.

  • The ‘impacts’ paper on the below web page estimates mortality of birds due to cat predation to be one billion.

    http://www.abcbirds.org/abcprograms/policy/cats/tnr.html

    Collision mortality updates:
    http://www.abcbirds.org/abcprograms/policy/collisions/index.html

    A variety of other threats are covered. ABC’s website has been recently redone and updated.

  • Rich

    This article and many others only track birds killed unnaturally by external factors, such as cars or cats. Of course birds, like people and other creatures, have finite lifetimes. It would be interesting to know how many die of “normal” effects of aging, such as heart disease and cancer. That would make the number of “unnatural” deaths more significant.

  • This sounds like the spineless ‘above the law’ spew of “that’s what cats Do” impudent monsters …isn’t that like telling the neighborhood if you don’t like my unlicensed, unneutered, marauding predator in your yard thrill killing the birds that you’ve opened your yard up to, a personal sanctuary if you please, Tough S— ‘Get used to it’. This is what the majority of predator Cats owners think and personally, they themselves are but impudent monsters – put here by a loving flying spagetti monster to Kill billions of birds for pleasure.
    A few months ago i caught this marauding predator with 1 of my 5 Blue Jays who daily came to my feeder,in its mouth, it killed a chick-a-dee too and that mate was soo soo soo unhappy it cried all around me as i picked up the little torn up carcass, this feral cat was on a killing spree mostly sparrows and one Eurasian Ring-neck that i could see in my tiny little sanctuary thanks to predator lovers. No We won’t get used to it.

  • Charles Holt

    Hello I am a ninth grade student in an iowa high school and my physical science teacher has givin me a new project. That is to wright the pros and cons of wind turbinds and make a debate in front of the class. During the debate the oppsing team brought up that wind turbinds kill birds but on this site it says that birds die more from windows than wind turbinds. so do you think that killing birds is a liable reason not to build wind turbinds?

    • Nick

      yes there should be no wind turbinds they kill valubal wild life and year apart familys

    • jack

      Charles,

      From your post it is clear that you are smart enough to make up your own mind from the data available to you. Clearly emotional responses often indicate an opinion formed on the basis of events not related to the issue at hand.

      No energy source has no impact on the environment. The challenge is to try to use energy sources that represent the best long-term compromises with the least impact and are sustainable. If birds are the only issue of importance (and in my opinion, this is one of several important issues regarding energy) then you ought to compare how many birds are killed or habitat destroyed by acid rain or the construction of other types of power plants. Those are just two examples.

      Stay scientific. Let facts lead you. We need learned and calm consideration of our alternatives or we will never solve our problems. Your post gives me hope for our future.

      Good luck with your investigation!

  • Getachew

    I am afried by what wind power is doing on birds.

  • Re: wind turbines and raptors, I’m not sure exactly why that assumption is being perpetuated – Altamont Pass was hell on raptors, but new turbine designs don’t lure raptors in for perching… Instead they kill everything from warblers to ducks and beyond. I’m sure Altamont did the same, but raptors were the primary concern there. Raptors aren’t the whole story for new turbine designs. Bats have it far worse than birds and that needs to be addressed far more seriously than it has been historically.

    I’d like to see more of the ‘bladeless’ and vertical axis designs explored; 3 blade designs are hell on wildlife.

  • dv

    Based on slovacool, “Contextualizing avian mortality: a preliminary appraisal of bird and bat fatalities from wind, fossil-fuel, and nuclear electricity”, which finds an average avian mortality of 0.3/GWh, if the entire US electrical base (3700 TWh/yr) were replaced with wind turbines, approximately 1.2 million birds would die each year from wind power. This is approximately 1/100 the minimum estimate for bird deaths from windows, and an estimated 10-fold decrease in bird fatalities relative to a coal-fired grid (based on the same paper).

    I have tried to understand the fierce opposition to wind farms by some environmental groups. I suspect it is because they make easy targets. After all, they’re suppose to be good for the environment, right?. When viewed in comparison to alternatives, they seem to be more environmentally friendly, and thus should probably not be opposed with such zeal. When looking to minimize bird deaths, it also seems that even minor efforts to reduce kills by feral cats, windows, and cars would completely dwarf any change in kill rate possible with turbines, even with vertical axis designs.

  • I see these estimate from the wind lobby are still around. In NJ they erected 5 large wind turbines near Atlantic City on an island in an estuary. There local Audubon Study concludes that 74 birds and bat were killed per turbine per year. 4 Osprey(pop 800) and 1 peregrine Falcon(pop 30) were confirmed killed and they estimate there recovery rate is only 37% so more were likely killed. There are thousand planned so the NE should plan for the extinction of many raptors… here is the the study
    http://www.ceoe.udel.edu/lewesturbine/documents/acua_quarterlyreport_fall09.pdf

    Currently in California more Golden Eagles are killed by wind turbines than reproduced. The large more modern wind turbines actually are more in the flight path of large raptors and kill more. The SF Audubon has shown an increase in kills the better searches and larger turbines.

  • How many Eagles are killed by windows? Feral cat killing Golden Eagles? I think the above estimate are a fraud places by wind turbine enthusiast. The EAgle protection act and the bird migration treaty both should be enforced against wind turbine companies, just like against oil companies. But the flow of subsidies to wind are just too great…the Gov of Maine went into the wind industry after setting up the laws to enrich himself.

  • One last comment about the estimated BILLION birds hitting building…I have seen estimated that say we have 8-10 Billion birds in the USA…do you really believe that 10-15 percent of the bird population is wiped out every year?

  • Mike Barnard

    14 million fewer birds would die annually if all fossil fuel generation world-wide were replaced with wind turbines.

    http://www.quora.com/Wind-Power/How-significant-is-bird-and-bat-mortality-due-to-wind-turbines/answer/Mike-Barnard

  • Brian Peter

    I often wonder at these studies —- do they ever ask questions of people
    outside the study group ??
    A classic case is the disappearance of song birds in our neighborhood,
    The main reason is the growth in population of MAGPIES & CROWS
    I have seven bird houses within my garden , all of them used to be occupied, but alas the magpies nesting in a neighbors garden has chased away our small birds.

  • Mike Barnard

    I redid the math: it’s 70 MILLION BIRDS SAVED ANNUALLY if all fossil fuels were replaced with wind farms.

    http://reneweconomy.com.au/2012/want-to-save-70-million-birds-a-year-build-more-wind-farms-18274

  • I wonder what this chart would look like if it incorporated the results of the recent Smithsonian / USFWS study that claims that up to 3.7 billion and no fewer than 1.1 billion birds are killed by cats annually. It is clear that the authors of this study did no cross-checking of their math, so it would be interesting to work through some of the ramifications. For instance, on this chart, every single bird death from every anthropogenic cause and then some would have to be shifted to cats.

  • Tim Kirschner

    I am extremely familiar with birds. Do you know that hawks kill millions of non-agressive songbirds doves, and pigeons a year. Cooper Hawks alone according to the last study read, kill 7 million birds a year by themselves, this does not include any of the other species of Hawks, or owls. I see many hawks in very urban neighborhoods. If you wonder where your songbirds went, they either relocated due to pressure, or were killed by the hawks. My understanding is hawks are protected? Maybe it’s time for revaluation of which species or raptor needs to be protected. My experience with turbines is the wind would have to push the birds int
    O them, it’s not something they would seek

  • Shedea

    Surely an engineer could design a strong, fine mesh guard that would protect birds and bats from the whirling blades? Obviously two drawbacks would be (a) some wind resistance, and (b) greater expense to produce. Perhaps the first problem could be offset by erecting more wind turbines. Then, with a greater demand for more turbines, they may become more affordable. If new safety standards could be introduced to the effect that all blades must be shielded, this would, in turn, generate more business for green energy industries. Even more so if a government grant towards research and development in this area could be obtained.

  • Bird Friendly

    There are already bladeless, energy efficient wind turbines out there.

  • Scottar

    I’m not so concerned with the bird deaths as weather the technology is sustainable. Yes there are better windmill designs then the props on a stalk, but bottom line it’s what do they really contribute to the grid? Since any form of wind energy device seems too frenetic and intermittent to deliver dispatchable electricity, and has to be double shadowed by gas powered peaking plants, that leads to increased infrastructure costs and increased fossil consumption then if the peaking plants operated alone, then wind is not so sustainable as it is portrayed. And for that factor they must be heavily subsidized at tax and rate payers expense.

    The best use of wind and solar cells is for heating water. They also be used for running independent heaters or coolers that are not run off the grid, sort of like supplemental energy sources.

    I have never run across a working blade-less wind energy device but here is one alternative:

    http://pseudoscientific.blogspot.com/2012/10/progressive-field-wind-turbines.html
    Progressive Field Wind Turbines

    But the lobbyists for the big market players may never let these out of the prototype stage. Renewables are mostly a scam. In fact wind farms are the original invention of ENRON and were pushed by Al Gore.

    But there is also a conflict on official reports vers unofficial reports.

    http://www.cfact.org/2013/03/18/wind-turbines-kill-up-to-39-million-birds-a-year/

    Mar 18, 2013
    Hiding the Slaughter – Up to 39 Million Birds and Bats Are Killed Each Year by Wind Turbines

    In other words the official bird death reports due to windmills looked to be greatly fudged, like global temperature increases.

  • Becky English

    David, who prepared this 2003 chart? What is the geographic basis? North America? The US? It’s always helpful to include the source and formal reference(s) when putting something like this ‘out there’ ! I wonder if these results are generalizable worldwide. Is there European research on this?

  • Michele

    Did no one notice how many WINDOWS are responsible for bird deaths? Are we not accountable? Is it in our nature to have to have them? Comments please…

  • Carolyn Doherty

    Less pollution, less would die

  • Jim Wiegand

    Every study I have looked at from West Inc. has been scientific garbage. This outfit works for the wind industry and they are behind this on going deception.

    All this is nothing more than a continuation of the decades old pattern of deceit that has been taking place with the Wind Industry and our Interior Department. In fact I have yet to come across a single credible study related to the wind industry’s mortality impacts. Peer reviewed or not it does not matter.

    As for the billions of birds being killed by communication towers, buildings, windows and domestic cats here is the truth………..Communication towers, buildings, windows and domestic cats kill very few raptors and bats. In fact raptor and bat deaths at communication towers are virtually nonexistent. While it is true that millions of more common, city dwelling birds are killed by windows, none of this mortality has anything to do with the rare and highly protected species like eagles being slaughtered by wind turbines in their remote habitats. The Interior department knows this and could correct this falsehood overnight; instead they have allowed this garbage to circulate for years. It is even on their website.

    One final thought about West Inc. and their absurd mortality analysis, they forgot to include the billions of chickens and turkeys killed each year at processing plants.

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