Accounting for misclassification of subspecies provides insights about habitat use and dynamics of the Florida Grasshopper Sparrow in response to fire

Abstract

Monitoring populations is critical to understanding habitat use, especially for endangered species and is important for determining the effectiveness of land management strategies. The Florida Grasshopper Sparrow ( Ammodramus savannarum floridanus ) is a critically endangered non-migratory grassland bird that has been monitored since the 1990s. It resides primarily in dry prairie habitat managed by frequent (2–3 years) prescribed fires. Monitoring is confounded by the presence of the migratory and wintering eastern Grasshopper Sparrow ( A. s. pratensis ), that has vocal and morphological similarities. These similarities could lead to misclassifications and erroneous conclusions about land management. Our goal was to determine the impact of fires on Florida Grasshopper Sparrow habitat use at two spatial scales, 100 m and 400 m buffers surrounding point count locations, while controlling for the presence of the eastern Grasshopper Sparrow. We combined point count data (1996–2011), external sources of data (eBird), and Bayesian dynamic occupancy models that accounted for misclassifications to evaluate habitat use and dynamics in response to prescribed fires. The probability of misclassifying a Florida Grasshopper Sparrow peaked in April and then decreased to near zero after May 1. The probability of persistence at point count stations decreased as years-since-fire (maximum of pixels within 400 m buffer) increased and was greatest for recent burns (< 1 year). Seasonality of the most recent burn (i.e., ordinal date of burn for pixels within 100 m buffer) also influenced probability of persistence with Florida Grasshopper Sparrows having greater-than-average persistence when burns occurred during January and July, peaking in early April. The probability of colonization peaked approximately two months after a fire and rapidly decreased to negligible values. This is the first long-term study to examine the effect of prescribed burn on Florida Grasshopper Sparrow occupancy that accounts for the presence of eastern Grasshopper Sparrows. This modeling framework may also provide utility for other species and subspecies that are difficult to distinguish during surveys.

Keywords

• conservation
• florida grasshopper sparrow
• misclassification model
• occupancy modeling