Horned Lark (Eremophila Alpestris)
If a native North American bird exists whose mention conjures up a mental image of open space, the Horned Lark must be a top contender. Occupying coastal dunes, deserts, grazed grasslands and shrubsteppe, croplands, and Arctic and alpine tundra, the common denominator among favored habitats no matter what time of year is short, sparse vegetation (Beason 1995). Horned Larks perhaps receive less attention than they merit because they seem too-frequently associated with cropland monocultures, which are landscapes that bird watchers and nature lovers find particularly off-putting.
With one of the largest geographic ranges of any songbird, another impression of Horned Larks, at least in the Great Plains, is one of commonness, which also contributes to the lack of excitement the species engenders among birders. Horned Larks are often the most abundant birds year-round in short-grass and mixed-grass prairie habitats (e.g., Kantrud and Kologiski 1982, Bock and Bock 1999, Galle et al. 2009), and they often occur in flocks of several hundred to several thousand individuals as they wander expanses of prairie in winter (Beason 1995). The average population estimate for Canada and the continental U.S. from 2005 to 2014 was 97 million individuals (Rosenberg et al. 2016), which is certainly a big number. Among species that breed primarily in grasslands, only the Savannah Sparrow has a larger population estimate. Why, then, is the Horned Lark considered a species of concern in the latest Partners in Flight (PIF) Landbird Conservation Plan (Rosenberg et al. 2016)?
Some authorities have posited that Horned Lark numbers remained relatively stable during the latter decades of the 20th century (Beason 1995), but analysis of Breeding Bird Survey (BBS) data indicate a decline of 2.5% per year survey-wide from 1966–2015, and a decline of 2.1% per year from 2005–2015. On the basis of BBS data for 1970–2014, PIF estimated that Horned Lark populations declined by 65% in Canada and the U.S., with a population “half-life” of 40 years (Rosenberg et al. 2016). In other words, the forecast is that 48.5 million fewer Horned Larks will exist in Canada and the U.S. by 2055. This dire situation prompted PIF to identify the Horned Lark as one of 24 common landbirds in steep decline, each species having lost more than 50% of its population during the last four decades. The prospect for Horned Larks in Montana is equally disquieting, we regret to report.
Horned Lark numbers in Montana declined 2.3% per year from 1966–2015 and 2.7% per year from 2005–2015 (Figure 1). Trends for most surrounding states and provinces look as bad or worse, with declines of up to 5.7% and 12.2% per year, respectively, in Saskatchewan and Alberta from 2005–2015. Horned Lark declines in Montana are particularly dramatic for the Prairie Pothole and Northern Great Plains joint ventures, which encompass the prairie regions of the state east of the Continental Divide; estimated long-term declines across these two joint ventures are 70% and 81%, respectively, with half-life population projections of <30 years for each region (Rosenberg et al. 2016).
Is the decline in wintering birds across Montana similar to that exhibited during the breeding season? The Christmas Bird Count (CBC) provides the best available data for analyzing most winter bird trends across Montana. CBCs are not as structured or rigorous as the BBS, and the distribution of CBC circles across the state is not as uniform as BBS routes. Counts are adjusted for effort by converting total numbers tallied for individual species within a count circle to numbers tallied per party-hour of effort. CBC results for Montana from 1966 to 2014 show a slight, non-significant decline in Horned Larks tallied per party-hour (Figure 2). Thus, winter numbers of Horned Larks in the state appear to be relatively stable. The stark difference in breeding versus wintering trends very likely is related to the source of the populations that occur in Montana. Subspecies that breed in Montana, E. a. enthymia and E. a. leucolaema, generally winter in the central and southern Great Plains south to northern Mexico, whereas subspecies that winter here, E. a. articola and E. a. hoyti, breed at higher latitudes mostly in the Arctic and sub-Arctic (Beason 1995). The high-latitude birds that winter in Montana probably are not exposed to the same threats experienced by the individuals that breed here.
As with many bird species, what drives the decline of Horned Larks is not fully known, but several factors probably contribute to the overall trend. Foremost among them is ongoing loss of native shortgrass and mixed-grass prairie to sod-busting on the breeding and wintering grounds (Askins et al. 2007, Pool et al. 2014). Another important factor is fire suppression, which can allow encroachment of trees and shrubs, thus reducing the suitability of habitats that otherwise would be preferred by Horned Larks, and the wholesale reduction of native grazers such as prairie dogs and bison that maintain and create extensive patches of sparse prairie vegetation (Askins et al. 2007). Paradoxically, the sparse structure of croplands makes them attractive to Horned Larks, which might appear to benefit larks at first glance. Croplands, however, function as “ecological traps” in which reproductive success is particularly low (Best 1986) owing to the timing and frequency of tillage or mowing, and regular exposure to herbicides, insecticides, and rodenticides (Beason 1995, Askins et al. 2007). Too, Horned Larks do not seem to benefit from the long-term restoration of former croplands to Conservation Reserve Program (CRP) grasslands, because the grass and legume cover in CRP lands eventually becomes too dense and tall (Johnson and Igl 1995, Askins et al. 2007).
Conserving remaining native prairie, and increasing public awareness about declining population trends of this widespread prairie bird, are fundamental actions that would help improve the long-term prospects of Horned Larks in Montana and elsewhere in the West. Horned Larks should benefit from efforts that maintain a variety of vegetation structures over large native grassland tracts through use of different livestock grazing regimes, from rested to heavily grazed. Developing and following best-management practices for shortgrass and mixed-grass prairie birds also are important actions. Curbing or restricting use of poisons that kill native rodents such as Richardson’s ground squirrels and prairie dogs will reduce losses of these native grazers that naturally create the low vegetation cover Horned Larks seek for nesting, and also will limit the number of birds killed from exposure to the poisons. Switching to reduced-tillage and no-tillage of row crops (Best 1986) might provide Horned Larks the time needed to successfully breed in croplands before nests are disturbed or destroyed by conventional tillage operations. All of these alternative land-use practices could contribute to lessening the alarming decline of this abundant bird. Ultimately, however, owing to seasonal movements of larks over vast landscapes, a multi-jurisdictional approach will be necessary for effective conservation. A sustained public education campaign on behalf of all prairie birds, including seemingly common species such as the Horned Lark, may offer the best hope for reversing overall declines of prairie-nesting birds.
Askins, R. A., F. Chávez-Ramirez, B. C. Dale, C. A. Haas, J. R. Herkert, F. L. Knopf, and P. D. Vickery. 2007. Conservation of grassland birds in North America: Understanding ecological processes in different regions. Ornithological Monographs No. 64.
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Best, L. B. 1986. Conservation tillage: Ecological traps for nesting birds? Wildlife Society Bulletin 14: 308-317.
Bock, C. E., and J. H. Bock. 1999. Response of winter birds to drought and short-duration grazing in southeastern Arizona. Conservation Biology 13: 1117-1123.
Galle, A.M., G. M. Linz, H. J. Homan, and W. J. Bleier. 2009. Avian use of harvested crop fields in North Dakota during spring migration. Western North American Naturalist 69: 491-500.
Johnson, D. H., and L. D. Igl. 1995. Contributions of the Conservation Reserve Program to populations of breeding birds in North Dakota. Wilson Bulletin 107: 709-718.
Kantrud, H. A., and R. L. Kologiski. 1982. Effects of soils and grazing on breeding birds of uncultivated upland grasslands of the northern Great Plains. United States Fish and Wildlife Service, Wildlife Research Report 15.
Pool, D. P., A. O. Panjabi, A. Macias-Duarte, and D. M. Silhjem. 2014. Rapid expansion of croplands in Chihuahua, Mexico threatens declining North American grassland bird species. Biological Conservation 170: 274-281.
Rosenberg, K. V., J. A. Kennedy, R. Dettmers, and 21 others. 2016. Partners in Flight Landbird Conservation Plan: 2016 revision for Canada and Continental United States. Partners in Flight Science Committee.
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