Effect of fire on lark sparrow nesting densities


Lark sparrows Chondestes grammacus in Texas (southern USA) are a common ground-nesting bird associated with mesquite grasslands. Prescribed burning is used to manage honey mesquite Prosopis glandulosa var. glandulosa - tobosagrass Hilaria mutica communities, burns reducing mesquite cover and enhancing grass growth. A study was undertaken on the Renderbrook-Spade Ranch in 1975 to determine lark sparrow nest densities and nest characteristics on seven different ages of burns.

Nests were censused on seven different ages of burns: burned in 1969 (109.7 ha), 1970 (57.1 ha), 1971(60.2 ha), 1972 (123.1 ha), 1973 (71.2 ha), 1974 (73.2 ha) and 1975 (91.1 ha). Nest searches were conducted on 10-17 June 1975 by walking three random transects totaling a distance of 2,000 m per treatment. The flushing distance was approximately 2 m either side of the observer, thus 0.82 ha was censused per treatment. The type of vegetation that served as the nest site and the number of eggs per nest, were recorded.
Plant height, frequency and percent cover were recorded in 25 randomly located 0.11 m² quadrats per treatment.

Nest densities were highest in most recent burns: 1969 - 6; 1970 - 4; 1971 - 9; 1972 - 6; 1973 - 12; 1974 - 19; and 1975 - 23. Lark sparrow nest sites were typically within a limited cover range of tobosagrass i.e. between 32 to 55% cover.
Of the 79 nests found, 65 (82.3%) were in tobosagrass, 12 (15.2%) in buffalograss Buchloe dactyloides and two (2.5%) in purple threeawn Aristida purpurea.
Number of nests was negatively correlated with tobosagrass cover (dead and alive), declining as litter accumulated (stands of matted grass) and tobosagrass production reduced. No differences in clutch sizes between burns was apparent, clutch sizes averaging 3.7 eggs per nest.
The author concludes that the usual burn management practice of mesquite-tobosagrass communities (i.e. fires in spring before breeding pair arrival and a. 5-8 year burning frequency) should generally benefit ground-nesting lark sparrows.
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