Horned lark, strigata subspecies COSEWIC assessment and status report: chapter 6

Biology

General

Very little is known about the ecology of the Horned Lark, strigata subspecies in British Columbia, therefore most of the following is inferred from studies done on this subspecies in southern parts of its range, or other subspecies elsewhere in the species range.

Reproduction

The Horned Lark is probably monogamous during the breeding season (Beason and Franks 1974).  Between-season pair bond maintenance is unknown (Beason 1995). The male typically arrives on the breeding ground first and establishes a breeding territory. The female probably selects a territorial male upon her arrival, and then finds a nest site within his territory. The female alone constructs the nest by scraping a small hollow on the ground, or finding an existing depression (e.g., a hoof print; Campbell et al. 1997). The nest is then lined with fine grasses and other plant fibers (Cannings 1981; Campbell et al. 1997). Nests are usually situated with a protective object (e.g., a tuft of dirt, grass or other vegetation) to one side, possibly to help maintain the temperature within the nest (With and Webb 1993; Nelson and Martin 1995). Pebbles or other paving materials may be placed around the nest, or to one side (Baicich and Harrison 1997).

A clutch of four eggs is typical for the species, although two to seven eggs are possible (Baicich and Harrison 1997). The average clutch size reported for Eremophila alpestris strigata in the Puget Sound area (Bowles 1900 in Cannings 1981) was 2.5 eggs. Three Horned Lark, strigata subspecies nests have been found with eggs in British Columbia: two with three eggs and one with four eggs (Campbell et al. 1997). Eggs are incubated by the female for 11 or 12 days (Campbell et al. 1997). The female also broods the hatchlings but both parents typically feed the nestlings (Beason 1995). Nestlings fledge after approximately 10 days (Cannings 1981; Baicich and Harrison 1997). As with many other grassland bird species, the nestling period is short, with young fledging when they can walk but before they can fly (Beason 1995).

In the Georgia Depression, the Horned Lark breeding season was reported to extend from 5 April to 25 August (Campbell et al. 1997). Elsewhere, at low elevations and low latitudes, Horned Larks are known to breed two or three times per season (Sibley 2001). It is not known if Eremophila alpestris strigata in British Columbia have more than one brood.

Horned Larks are only rarely parasitized by Brown-headed Cowbirds (Molothrus ater; Beason 1995). This may be due to the fact that they typically begin nesting before cowbirds, their nests are exposed and they have a short nestling period, such that cowbird nestlings may be left behind when the larks fledge (Friedman 1963). There are no records of cowbird parasitism of Horned Larks of any subspecies in British Columbia (Campbell et al. 1997).

Survival

Nest failure may result from predation, bad weather or accidental destruction. Adults may also succumb to predation, poisoning, and accidental trampling by machinery or livestock (Beason 1995).

There are few documented cases of direct predation of Horned Larks. However, based on what is known about other grassland bird species, potential predators of eggs, nestlings and adults in the Georgia Depression include: birds of prey (e.g., Cooper’s Hawk Accipiter cooperii and Merlin Falco columbarius); corvids (e.g., Northwestern Crow Corvus caurinus and Common Raven C. corax); small and medium-sized mammals (e.g., coyotes Canis latrans, foxes Vulpes vulpes, raccoons Procyon lotor, skunks Mephitis mephitis, domestic dogs Canis familiaris); and snakes (e.g., Common Garter Snake Thamnophis sirtalis and Western Terrestrial Garter Snake T. elegans). Domestic cats (Felis catus), however, probably represent the greatest predation threat in this region. Cats are known to be competent predators of small to medium-sized birds (George 1974; Cooper 1993; Coleman et al. undated). On southeastern Vancouver Island domestic cats were frequently seen during bird surveys at grassland sites, including the single site where a displaying Horned Lark, strigata subspecies was observed (Beauchesne 2002).

Bad weather may adversely impact nesting success. Cannings (1981) reports a nest with nestlings being abandoned during a hailstorm. Nestlings may also starve if cold wet weather precludes foraging by adults.

Agricultural practices including tilling or mowing during the breeding season may result in the accidental destruction of nests or trampling of adult birds (Kershner and Bollinger 1996). There are also documented cases of Horned Larks having been poisoned by pesticide applications (Beason 1995; Sibley 2001). The population level effect of lethal and sublethal contamination by agricultural chemicals is unknown and would be difficult to determine (Gard et al. 1993).

Movements/dispersal

Migration in Horned Larks varies between subspecies, with some entire northern populations migrating whereas some southern populations have year-round residents (Beason 1995). E. a. strigata are thought to be partial migrants. Populations from coastal British Columbia may have moved south in autumn to join permanent residents in coastal Washington and Oregon or may have moved as far as California (AOU 1957), but a few birds evidently overwintered based on winter (January) specimen records from the Fraser delta (Munro and Cowan 1947).

Horned Lark migration is diurnal. Hatch-year birds gather in the late summer and are joined by adults later in the season. Horned Larks will also form mixed flocks with other species (e.g., longspurs and buntings: Beason 1995; Sibley 2000).

Diet and foraging behaviour 

Adult Horned Larks are primarily granivorous, but feed invertebrates to their young. Invertebrates are also consumed by adults, with more taken during the spring and early summer than at other times of the year. In the winter, this species feeds almost exclusively on seeds (Beason 1995).

Horned Larks typically search for food while walking on bare ground or amongst sparse vegetation. They will also perch on a low plant and take seeds directly from the seed head. They sometimes dig up invertebrates and will chase flushed insects (Beason 1995).

Territory

The male Horned Lark establishes a territory that is to be used for courtship, nesting and foraging. The male and, occasionally, the female, defends the territory against conspecifics. Territory size is variable and is dependant upon habitat quality, population density and food availability (Beason 1995). There are no data for territory size in the Georgia Depression.

Horned Larks also exhibit interspecific territoriality (Sibley 2001). They will drive off potentially competitive species, including Vesper Sparrows (Pooecetes gramineus: Beason 1995).

Adaptability

Studies in the Great Plains suggest that Horned Larks occur mainly in grazed areas (Jones and Bock 2002) and will tolerate even heavily grazed areas (Kantrud 1981; Bock et al. 1993). Horned Larks will also occupy disturbed sites. For example, Rogers (2000) found that Horned Lark, strigata subspecies preferentially foraged in wheel ruts in a grassland area. However, Horned Larks tend to avoid hayland (Kantrud 1981) and choose habitats relatively remote from urban landscapes (Jones and Bock 2002).

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