Stadials, the coldest stages of Ice Ages, fostered an expansion of arid grassland habitat all across Eurasia, Beringia, and North America. Droughts were frequent and low CO2 levels slowed plant growth. Grass and conifers outcompeted broad-leafed trees in these conditions. Arid environments favored grass-eating herbivores, and a variety of smaller animals that prefer wide open spaces. The horned lark (Ermophila alpestris) is an example of a species that likely abounded in large numbers during stadials. They inhabit environments consisting of sparse grass and bare ground.
Horned larks require a landscape consisting of bare ground and sparse grass. This type of environment was common during Ice Ages.
The horned lark nests on bare ground, laying their eggs next to a tuft of grass. Like most ground-nesting birds, they will feign injury to lure a predator away, but they do wait longer than other species before taking this evasive action. Today, horned larks breed and nest from northern Canada to as far south as Maryland. They winter as far south as Georgia. In the east they find the type of environment they like in salt marshes, beach dunes, and winter-fallow agricultural fields. They are also known as shore larks. During the Ice Ages much of their modern day American breeding grounds were under glacial ice, so it is likely they bred farther south in the steppe-like landscapes that occurred adjacent to the glacial boundary.
Pleistocene fossil evidence of horned larks is scant in the south, but specimens have been recovered from Cheek Bend Cave in middle Tennessee. The lark specimens were found associated with bones of other northern bird species absent or uncommon in Tennessee today, including gray jays, boreal owls, saw-whet owls, purple finches, and prairie chickens. Evidence of other bird species from the cave represent those still common in the region today–blue jay, red-bellied woodpecker, flicker, sparrows, meadowlark, and others. (The eastern meadowlark (Sturnella magna) is not a true lark but instead is more closely related to blackbirds and starlings. It too prefers open spaces.) During winter horned larks join large nomadic flocks of sparrows, juncos, lapland longspurs, and snow buntings as they edge toward more southerly latitudes, though the larks are among the first to return north in the spring. All of these birds were likely common on Ice Age plains.
Horned larks feed on insects and grass seeds, even foraging in horse manure for undigested seeds. Horned larks and other birds scratching through mammoth and horse dung on frozen ground was probably a common sight during the Pleistocene.
Chickens foraging for worms and undigested grain in horse manure. Horned larks also like to forage through horse manure. Horse manure would have been one of their important food sources during Ice Ages. Just think about this next time you are sitting in front of a plate of fried chicken.
Horned larks belong to the Alaulidae family which includes 20 genera and 99 species, but they are the only true lark that managed to cross the Bering Landbridge. All the other species are confined to Africa, Eurasia, and Australia. The horned lark is a successful widespread species, living in both Eurasia, and North America. At present they are still considered a common bird but in steep decline. The conversion of open agricultural land to 2nd growth forest is eliminating their preferred habitat.