Horned lark, strigata subspecies COSEWIC assessment and status report: chapter 8

Limiting Factors and Threats

The primary limiting factor is the lack of suitable breeding habitat. Although habitat was never large in extent, suitable habitat has been in decline over the last few decades.

The range of this subspecies overlaps with areas and habitats that have become increasingly developed for human activities such as housing, recreation, and light industry. This development has fragmented or destroyed most suitable habitat (Campbell et al. 1997). Continuing development pressures will, in the future, likely alienate most of the remaining habitat.  None of these sites are managed specifically for ground nesting birds such as Horned Larks.

The intensification of agriculture has reduced the suitability of some farmlands that were previously used for nesting. Improved dyking of the Fraser delta has reduced the amount of sparsely-vegetated sandy shoreline along the edges of the Fraser River. In addition, industrial agricultural practices increasingly rely on chemicals, which have unknown consequences for most species of birds (Gard et al. 1993).

Invasions of exotic plants such as Scotch broom (Cytisus scoparius), gorse (Ulex europaeus), Himalayan blackberry (Rubus discolor), and tall non-native grasses have alienated most of the remaining field, Garry oak and sand dune habitats (Fraser et al. 1999).

The effects of predators in increasingly urbanized landscapes may also limit this bird. It is possible that increased predation pressure from domestic cats and native species such as Northwestern Crows may tip the balance. Increasing human disturbance, which logically goes along with increasing human populations, may affect ground-nesting birds as well. Activities such as horse back riding, dog walking, bird watching, and trail bike riding may be incompatible with ground-nesting birds (Rogers 2000).

Populations in Washington and Oregon are becoming increasingly unlikely to be the source of dispersing birds that might re-establish breeding populations in British Columbia because numbers there are also declining.

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