About those claims of declining bird populations due to 'climate change'

Guest Essay by Kip Hansen

The Audubon Society and other conservationist groups have recently been getting publicity for the idea that bird populations in the United States are declining and that the cause of the decline is Climate Change or Global Warming. Dr. Tim Ball recently wrote about this in an essay here with a long criticism of the alarmism involved in this claim, but didn’t really tell us anything about the birds, their decline, or the true causes of population shifts. Here I try to shed some of the light of data on this issue.

“Audubon’s unprecedented analysis of forty years of citizen-science bird population data from our own Christmas Bird Count plus the Breeding Bird Survey reveals the alarming decline of many of our most common and beloved birds.” [ link ]

“Of the 314 species at risk from global warming, 126 of them are classified as climate endangered. These birds are projected to lose more than 50 percent of their current range by 2050. The other 188 species are classified as climate threatened and expected to lose more than 50% of their current range by 2080 if global warming continues at its current pace.” [ link ]

Well now, that all sounds pretty serious. There is actually an organization established to keep us all up to date on the state of the birds called, erhm, The State of the Birds. The State of the Birds website was produced for the U.S. Fish and Wildlife Service by the Cornell Lab of Ornithology and is a jointly supported project by the following organizations:

This broad list of supporters allows us to rule out simple financial gain as a biasing factor for any particular organization, as we might suspect of, say, the Audubon Society report.

Note that while I complained that Dr. Ball’s essay hadn’t supplied data on bird numbers, I find I will do the same. Counting birds is difficult and imprecise – birds you see in your yard on Monday might not be back until Friday. I am happy to accept the two different counts – one by Audubon and one by the USGS Breeding Bird Survey – as being the only useful data easily found. Care should be taken when interpreting the numbers. In the following essay, the large block quotes are from The State of the Birds 2014 report, unless otherwise noted.

What does the State of the Birds tell us? Like Audubon, they present a list of common birds in steep decline. 33 birds on the SOTB list:

Northern Pintail, American Wigeon, Cinnamon Teal, Greater Scaup, Long-tailed Duck, Scaled Quail, Northern Bobwhite, Purple Gallinule, Franklin’s Gull, Herring Gull, Black Tern, Yellow-billed Cuckoo, Snowy Owl, Short-eared Owl, Common Nighthawk, Chimney Swift, Loggerhead Shrike, Horned Lark, Bank Swallow, Verdin, Varied Thrush, Snow Bunting, Cape May Warbler, Blackpoll Warbler, Wilson’s Warbler, Field Sparrow, Lark Bunting, Grasshopper Sparrow, Eastern Meadowlark [mentioned later], Rusty Blackbird, Brewer’s Blackbird, Common Grackle and the Pine Siskin.

What is happening that brought about these declines?

Now that is very clear. First, notice that birds are actually increasing. Green, positive change, far outweighs declines. Second, notice that the focus in on habitat – not species.

“Where conservation investments have been made in healthy habitats and cleaner water, birds are doing well. Due to conservation action, many wetland birds are showing strong population gains, and grassland bird populations are showing signs of improvement. Bird populations in eastern and western forests and aridlands are all in decline, reflecting the urgent need for conservation in these habitats.”

and

“Coastal birds, shorebirds, and island birds are squeezed into shrinking strips of habitat impacted by development and invasive species. Some seabird populations are recovering from prior declines, though threats remain from fishing operations, offshore energy development, and climate change.”

We have our first mention of climate change….what are they actually referring to?

COASTAL BIRDS, SHORELINE BIRDS

Coastal Birds:

“Meanwhile, Gulf coastal wetlands loss continues; coastal habitats will need additional conservation measures to counter wetlands loss and sea-level rise. Birds along the Atlantic Coast are squeezed for habitat in this most densely human-populated region of the U.S. Additionally, coastal engineering projects—such as sea walls being built to defend against sea-level rise—are impacting beach-nesting species such as Piping Plover and tidal marsh birds such as Saltmarsh Sparrow. “

In the Gulf states, as everywhere else, sea level rise means the change of the sea level compared to the adjacent land – and in the vast delta areas the land is subsiding (“sinking”) as the sea slowly rises. NOAA’s Tides and Currents Sea Level Trends map shows the story.

Notice that here we find the first indications that the possible future is being confused with the present. I could find no reports of seawalls being built in the US on beaches to defend against sea level rise. There are seawalls being built, such as that in Seattle, but it is to provide level seas for their piers. In the present, seawall construction is not underway to defend against sea level rise – that is a potential future threat – and it is highly unlikely that fabulously expensive seawalls will ever be built to protect the secluded beaches needed by plovers for nesting. Note that the claim seems to come from a self-repeating claim made in Maine such as this example:

“Today, because of the construction of seawalls, jetties, piers, homes, parking lots and other structures, the available shoreline habitat for these two species has been reduced by more than 75 percent.” [ link ]

Of course, coastal construction projects, some of which are built with protecting seawalls, which disturb the “just above the high tide line” dunes, preferred nesting sites for plovers, are affecting and will affect their populations. On Merritt Island, in Florida, where I have spent the last two winters, plovers nest in the 50 foot wide strip of dunes directly in front of the condos and high-rise apartment buildings along the beach – nesting sites protected only by signs during the nesting season. Piping Plovers are not on the list of 33 common birds in steep decline.

Shorebirds:

“Long-distance migrants are steeply declining and need international conservation. Shorebirds are declining more than many other species groups. Long-term migration counts for 19 shorebird species show an alarming 50% decline since 1974. Declines are particularly strong for long-distance migrants that breed in the Arctic and boreal forest. Species with the steepest declines include Red Knot, Hudsonian Godwit, and Ruddy Turnstone. Long-distance migrants require healthy stopover habitats along their entire pathway, and the chain of sites is only as strong as the weakest link. For example, overharvesting of horseshoe crab eggs in Delaware Bay can threaten the entire Atlantic coastal population of Red Knots, as they depend on this food source during their intercontinental migration.”

Take home: Coastal and Shoreline birds are affected by coastal development – not climate change – coastal species are gaining for the most part, they are not in decline. Some long-distance migrating shoreline birds are in trouble due to habitat changes along their migration routes.

GRASSLANDS BIRDS:

“Since 1968, the grasslands indicator for 24 obligate breeding birds declined by nearly 40%, but the decline flattened out beginning in 1990. This recent stabilization noted in the 2009 report continues today, reflecting the significant investments made in grassland bird conservation. Reductions in Farm Bill conservation funding, however, threaten those investments.

Eastern grassland birds (such as Eastern Meadowlark and Bobolink) have continued a steady and precipitous decline, associated with declines in pasturelands due to changing dairy farming practices and suburban sprawl.

A sub-group of shortgrass prairie-nesting birds in the Western Great Plains—including Sprague’s Pipit and McCown’s and Chestnut-collared longspurs—also continue steep declines, which may be driven by large-scale agricultural conversion and overgrazing on their wintering grounds in the Chihuahuan Desert that spans the U.S.–Mexico border.” (emphasis mine)

Grassland birds are not in decline, they are gaining. Individual species are suffering from changes in habitat availability, such as the Eastern Meadowlark, which is typical of the group:

“Their [Eastern Meadowlark ] status and distribution has undergone historic changes in the northeastern U.S. where meadowlarks noticeably increased during the nineteenth century as a result of deforestation and the spread of agriculture (Andrle and Carroll 1988, Laughlin and Kibbe 1985). These population trends were reversed during the twentieth century, and Eastern Meadowlarks show some of the most consistent declines of any grassland bird on the BBS.” [BBS = USGS Breeding Bird Survey ] [ link ]”

Take home: Grassland birds are gaining, but negatively affected in some cases by changes in agricultural practices (sometimes reversing gains from previous shifts in the very same practices) which change available habitat – for the most part, they are not in decline.

WETLAND BIRDS:

“The inland wetlands indicator for 87 obligate freshwater breeding birds shows strong growth, with a more than 40% gain since 1968. These gains among wetland birds are the continuing legacy of important legislation such as the Clean Water Act and the Farm Bill’s conservation provisions.”

Take home: Wetland birds are doing well after heroic efforts at wetlands restoration – habitat restoration.

ARIDLANDS BIRDS:

“The aridlands indicator for 17 obligate birds—breeding birds of desert, sagebrush, and chaparral habitats in the West—is the most steeply declining of all habitat indicators, with an overall loss of 46% since 1968. Just since 2009 this indicator dropped 6%, extending a nearly continuous 44-year decline. Habitat loss and fragmentation due to residential and energy development are the most consistent and widespread threats. Long-term habitat degradation from unsustainable land use, invasions of non-native grasses, and encroachment by trees and shrubs also play significant (and underappreciated) roles in the decline. These negative effects have been exacerbated over the past decade by severe drought, creating extremely difficult conditions for aridland birds such as Bendire’s and Le Conte’s thrashers, the two fastest declining species in the aridlands indicator.”

Aridland birds are the category most adversely affected according to the chart at the top of this essay. They are, however, being affected by the same thing — habitat loss or habitat change. They could be rightly classified as being adversely impacted by a climatic condition – yet another extended drought that plagues a good portion of the southwestern United States. The causes of the drought are controversial, but seem to be settling out to be natural variability – “[Martin] Hoerling’s conclusions echo those of another longtime student of western drought, Richard Seager of Columbia University…. “I’m pretty sure the severity of this thing is due to natural variability.”

Take home: Aridlands birds are negatively affected by habitat loss and naturally hit hard by the extended drought which is not attributable to climate change.

FOREST BIRDS:

“The eastern forests indicator for 26 obligate breeding birds shows an overall drop of 32%, with a continued steady decline since 2009. Species dependent on either young forests (such as Golden-winged Warbler and Eastern Towhee) or mature deciduous forest (such as Wood Thrush and Cerulean Warbler) are showing the steepest declines. Because 84% of eastern forests are privately owned, timber companies and other forest owners can greatly benefit bird populations by maintaining large forest blocks and participating in sustainable forestry initiatives.

The western forests indicator, based on 39 obligate breeding species, has declined nearly 20% and has continued to decline since 2009. More than half of western forests are on public lands. Species dependent on oak and pinyon- juniper woodlands (such as Oak Titmouse and Pinyon Jay) are showing the steepest declines. As in the East, both early successional species (such as Rufous Hummingbird and MacGillivray’s Warbler) and mature forest species (such as Vaux’s Swift and Cassin’s Finch) are declining. Major threats to U.S. forests include urban and ex-urban development, changes in natural disturbance regimes including fire, and exotic insect pests and diseases.”

What about this?: “Major threats to U.S. forests include urban and ex-urban development”. Here is a satellite image of the Northeastern US – the most densely populated and the most developed region of the United States:

One can clearly see NY City, Brooklyn, the Bronx, Boston, Providence, Albany, etc. The rest is forest and mostly abandoned farmland.

Note that Early-Successional Forest means “Young trees and shrubs, often occupying recently disturbed sites and areas such as abandoned farm fields, provide unique and important habitat for many wildlife.” Where there are less changes, birds of this habitat suffer. This means less clear-cutting, less abandoned farms, fewer fires that clear the land.

Take home: Forest birds showing some declines are affected by loss of and changes to habitat. There is no climate change indictment here.

* * * *

There are a few more categories – but this post is getting much too long as it is. We see the general situation – bird populations follow the general formula for all populations as follows:

“…a simple model assumes that the population in the next year will depend only on the population in the current year. So, if x_n is the population in year n, then x_n+1 will be some function of x_n.

One very simple model assumes that a proportion, ax_n, say, breed successfully and that bx_n² die from overcrowding [or outstripping the carrying capacity of their habitat]. To simplify the equations we may re-scale the coordinates to obtain the following quadratic equation:

x_n+1 = rx_n(1-x_n)

for some fixed number r >0 and initial population x₁.” [ link ]

Those of you who have followed Dr. Robert G. Brown’s recent essay here, and some of his subsequent comments there, will be aware of the role of Chaos Theory in climate science. Chaos Theory plays a prominent role in population dynamics as well – the above equation produces a population graph like this one:

[ link ]

This graph is the above formula, applied for initial population of x₁=0.2 (solid line) and then x₁=0.2001(dotted line). After just a dozen years or so, the lines diverge, and produce near extinctions three or four times in 30 years, but at different times. This behavior is typical of population dynamics.

What this means for bird populations is this: “A population will exhibit chaotic behavior, if reproductive output is high and there are strong density effects regulating population size [for example highly dependent on specific, limited habitat features for nesting or feeding during migration].” Other populations may be subject to other dynamics which result in populations that settle down to a figure centered on habitat carrying capacity, or, for those characterized by a limit cycle, will alternate between 2, 4, or possibly 8 population sizes in succession.

Small changes initial conditions – either population or the term “r” representing the combined forces that mean “growth” for the species (and according to The State of the Birds this means area of habitat and health of habitat) in some combinations lead to chaotic results – sudden crashes and sudden booms maybe interspersed with years of stability. In the real world, the populations of Pacific sardines or anchovies – possibly some species of salmon – clearly exhibit this behavior.

The point here is that we don’t really know what many of the individual bird species are reacting to – not all cases are as simple as the Eastern Meadowlark for whom availability of “meadows” apparently directly determines populations. But, we can be fairly sure that if there are only 50% as many meadows, there will be fewer meadowlarks.

It is this feature of the modern world that is credited with increases and decreases in apparent bird populations – habitats for birds change from year to year, decade to decade, and century to century – both for natural reasons and anthropogenic reasons.

I call your attention to the lack of climate change or global warming in the attribution statements from The State of the Birds. [There are a few species that seem to be affected by changes in the sub-Artic regions of Canada and some species limited to drought stricken areas.] Changes in bird populations appear to be almost entirely caused by changes in habitats – both negative changes and positive changes.

So where does all this alarm over bird populations come from? From here:

“Audubon scientists used three decades of citizen-scientist observations from the Audubon Christmas Bird Count and the North American Breeding Bird Survey to define the “climatic suitability” for each bird species—the range of temperatures, precipitation, and seasonal changes each species needs to survive. Then, using internationally recognized greenhouse gas emissions scenarios, they mapped where each bird’s ideal climatic range may be found in the future as the climate changes. These maps serve as a guide to how each bird’s current range could expand, contract, or shift across three future time periods (2020, 2050, and 2080).” (emphasis mine) [ link ]

“Of the 314 species at risk from global warming, 126 of them are classified as climate endangered. These birds are projected to lose more than 50 percent of their current range by 2050. The other 188 species are classified as climate threatened and expected to lose more than 50% of their current range by 2080 if global warming continues at its current pace.” [ link ]

ADDITONAL DRIVERS OF POPULATION CHANGE:

CATS, CATS, CATS and CATS

SUMMARY:

Bird populations in the United States are changing – some for better, some for worse – the primary driver of changing populations is habitat change – both natural and anthropogenic – including such natural variations as precipitation, seasonal changes, drought and fire and anthropogenic factors like development and changing agricultural practices.

Climate, so far, has had very little (or no) effect. Posited Climate Change is not even in the running.

Housecats (pets and feral) have a disproportionately large negative effect on populations of small, low- and ground- nesting birds.

Alarm about bird populations is based on barely understood population dynamics blended with so-far-unsuccessful IPCC climate predictions, which some scientists believe to be fanciful at best.

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Authors Replies Policy: I will be glad to respond to your questions about sources for bird population data, the basis of the population dynamics formula and to supply links to information not already linked in this essay. I have little interest in (and am generally not qualified to speak to) the larger issues of AGW, CAGW, Global Warming, Global Cooling or Climate Change and will not be responding to comments on those topics. I am lukewarm on house cats and believe that they should be precisely that – in-the-house cats. I do, however, like birds.