Bird Population Declines: New Numbers, Familiar Concerns

September 28, 2019

Recently, the esteemed magazine "Science" published an article that was short, yet impactful. Simply titled "Decline of North American Avifauna," the authors assert that the number of birds in North America has declined by almost 3 billion birds since 1970. They concluded, after analyzing, estimating and interpolating previously collected data, that in a period of 48 years, North American bird populations declined by 29%.

This shocking statistic led to articles in The Atlantic, on NPR, in The Washington Post, and The New York Times, to name a few. Television reporting was widespread, as were opinion pieces about what could or should be done.

To know more about the Science article by K. V. Rosenberg et al., I read the source article, hoping to understand the data sources and the modeling assumptions within the scientific paper.

The authors, eleven in total, reviewed two primary data sources: firstly, the Christmas Bird Count data of the National Audubon Society's annual citizen science field counts (compiled for 529 bird species), and secondly, the NEXRAD radar data from 2007 to 2017, which measured "cumulative passage across all nocturnally migrating species" by biomass detection from 143 stations. 

Using the first set of data ("long-term surveys"), the authors claim there is a "net loss in total abundance of 2.9 billion birds across all biomes", a reduction of 29% since 1970. These are the numbers that made the headlines.

The second set of data, from radar measurement of biomass of migrating birds at night, showed a 13.6% (+/-) 9.1% from 2007 to 2017. The authors state that this trend shows further support for the long-time decline.

Digging in further, we read that of "a total of 419 native migratory species experienced a net loss of 2.5 billion individuals", whereas "native resident species" showed a small net increase (26 million). More than 90% of the cumulative loss of birds, as discussed, "can be attributed to sparrows, warblers, blackbirds and finches." Some bird families (29 of them) showed a gain in population size, and some (38) showed a loss in total population size. 

In order to understand the underlying data and assumptions, one would need to review the supplementary materials that accompany the article. I have not done so, but Science magazine is peer reviewed, and with that, we can be reassured that the expertise of eleven authors met the standards of rigor that peer review implies.

Perhaps more important than the numbers themselves, the ambitious presentation reveals a "biodiversity crisis" in North America. Indeed, if the population size of all birds in North America has declined by a third, we should all be concerned. Very concerned.

What are the likely causes? The causes, as named, are familiar concerns to conservationists.

• Grassland bird populations are affected by habitat loss and harmful pesticide effects, two side effects of modern agriculture.
• Urbanization and other land use changes have caused further bird habitat loss or habitat degradation, both in North America itself, and in related bird wintering areas.
• Insect populations are declining, reducing food for insectivores (bird species that eat insects). Pesticide use is implicated.
• Coastal land disturbances incurring habitat loss or degradation affect many species.
• Anthropogenic (ie. human-caused) bird mortality is increasing, such as window collisions or cat predation.
• Further concerns include deleterious weather effects of climate change, detrimental land use policy, and degradation of wildlife protection policies.

These are all possible contributors to what the authors say is a "continued biodiversity loss and potential collapse of the continental avifauna." The most dire statement in the article was this one: "Given that birds are one of the best monitored animal groups, birds may also represent the tip of the iceberg."

The authors, then, turn towards solutions, and primarily, they recommend more research to better understand the problem and forging conservation-related policy changes. I agree. Solutions will take both scientific expertise, policy knowledge, and political will.

One of the authors, Michael Parr, is president of the American Bird Conservancy, which advances the cause of bird conservation with a multi-prong approach. Another author is Peter Marra, formerly of the Smithsonian Migratory Bird Institute, and now affiliated with the Georgetown Environmental Institute. The lead author, Kenneth Rosenberg, is director of Conservation Science at the Cornell Lab of Ornithology. All of these non-profit organizations--and more--will need to further educate the public on this topic, reliably and clearly stating what work needs to be done. The first step is to sound the alarm, and report the level of population decline, which they have done with the Science article this wekk.

In my opinion, after following the topic of cat predation on birds carefully for ten years, I think that "sounding the alarm" may be the easy part. Finding, promoting, and ultimately establishing solutions is truly difficult. Conservation policies are affected by the political climate in Washington D.C. and beyond. Slowing global climate change is not yet the strong-suit of the U.S. government. Reducing human impacts on nature relies on continuing to apply pressure on decision-makers to include non-human species in their calculations of what has value.

It will be difficult halt the avian population decline. Wildlife conservation has been a personal focus of mine since the 1970s. It is as difficult now, as it was on the first Earth Day, to lessen the cumulative impact of human actions--and now, we are racing the clock, as never before because of global climate change.

Whatever you think you can do to help, do it. As soon as possible. For the birds. For the world. Before it is too late.

Cat Predation on BIrds

Cat predation is responsible for a significant portion of the overall bird population decline. Fortunately, cat owners can easily be part of the solution.

Here is the American Bird Conservancy's website page about various solutions to the problem of cat predation on birds. It includes our own Birdsbesafe® cat collar covers, which are a suitable choice if you are letting your cat roam outdoors where they can hunt birds. If you can not or do not keep your cat indoors, do something else to prevent bird predation by your pet the best that you can.

As a bird conservationist, who works in the pet product marketplace to make a difference, I sign my company letters: "Thank you for caring about cats and birds." It is a sincere "thank you."

I can not imagine my planet without its gorgeous birds. Please help any way that you can.

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