Henslow's Sparrow shows positive response to prescribed fire rotation

ABSTRACT We examined Henslow's Sparrow (Centronyx henslowii) response to prescribed fire at 32 grasslands at Big Oaks National Wildlife Refuge in southeastern Indiana from 1999 to 2009. We burned grasslands in the spring between 1999 and 2007 and monitored Henslow's Sparrows for up to 4 yr after treatment. We used linear mixed models to analyze our data. Henslow's Sparrow counts were correlated with time since prescribed fire and grassland size. The estimated changes in mean Henslow's Sparrow density relative to pre-burn densities were –0.19, 1.15, 0.74, and –0.68 birds ha–1 for 1–4 breeding seasons after a spring burn, respectively. We found that Henslow's Sparrows preferred larger grasslands both during the first breeding season after prescribed fire, when vegetation was presumed to possess less litter and structural density, and during the fourth breeding season after fire, when vegetation was presumed to be a more ideal composition, but preferred smaller grasslands in the interim. Thus, grassland size shapes the magnitude of Henslow's Sparrow population response to fire, with populations in smaller grasslands experiencing greater amplitude changes. Larger grasslands might provide more habitat diversity following prescribed fire, attenuating population change. On average, Henslow's Sparrows responded positively to prescribed fire in a network of grasslands and cumulative net change in densities were highest three breeding seasons after a burn suggesting that maintaining this burn frequency would be beneficial to Henslow's Sparrow abundance. How to Cite Keating, M. P., P. J. Williams, J. R. Robb, F. E. Buderman, J. P. Lewis, T. Vanosdol, and R. Harer (2023). Henslow's Sparrow shows positive response to prescribed fire rotation. Ornithological Applications 125:duad018. LAY SUMMARY Henslow's Sparrow (Centronyx henslowii) abundance has declined across much of its range, leading to its designation as one of the highest priorities for grassland bird conservation according to the U.S. Fish and Wildlife Service. Research has shown that habitat loss and alteration, such as woody vegetation encroachment, is strongly associated with these population declines. Prescribed fire is often used to prevent woody encroachment into grasslands. In southeastern Indiana, grasslands are organized as a network of patches distributed within forested habitat. These heterogeneous patches, which vary in size and degree of isolation, make it difficult to predict the response of sparrows to prescribed fire and therefore to develop an optimal burn schedule. We studied Henslow's Sparrow response to a prescribed-fire regime by systematically burning grassland patches and performing Henslow's Sparrow counts for up to four breeding seasons post-burn. Our results suggest that a 3-yr burn cycle (i.e., burning in years 1 and 4) is an optimal strategy for promoting sparrow density. RESUMEN Examinamos la respuesta de Centronyx henslowii al fuego prescrito en 32 pastizales en el Refugio Nacional de Vida Silvestre Big Oaks en el sureste de Indiana, desde 1999 hasta 2009. Quemamos pastizales en primavera entre 1999 y 2007 y monitoreamos a C. henslowii hasta 4 años después del tratamiento. Utilizamos modelos lineales mixtos para analizar nuestros datos. El número de individuos de C. henslowii estuvo correlacionado con el tiempo transcurrido desde el fuego prescrito y el tamaño del pastizal. Los cambios estimados en la densidad promedio de C. henslowii en relación con las densidades previas al fuego fueron de –0,19, 1,15, 0,74 y –0,68 aves por ha para la primera a la cuarta temporada reproductiva después de un incendio en primavera, respectivamente. Encontramos que C. henslowii prefirió pastizales más grandes tanto durante la primera temporada reproductiva después del fuego prescrito, cuando se supone que la vegetación tuvo menos hojarasca y densidad estructural, como durante la cuarta temporada reproductiva después del fuego, cuando se supone que la vegetación tuvo una composición más ideal, y prefirió pastizales más pequeños en el ínterin. Por lo tanto, el tamaño del pastizal moldea la magnitud de la respuesta de la población de C. henslowii al fuego, con las poblaciones en pastizales más pequeños experimentando cambios de amplitud mayores. Los pastizales más grandes podrían proporcionar una mayor diversidad de hábitats después del fuego prescrito, atenuando el cambio poblacional. En promedio, los individuos de C. henslowii respondieron positivamente al fuego prescrito en una red de pastizales y el cambio acumulativo en las densidades fue mayor durante las tres temporadas reproductivas posteriores a un incendio, lo que sugiere que mantener esta frecuencia de quema sería beneficioso para la abundancia de C. henslowii.