Effects of fire on the distribution and abundance of Sprague's pipit (Anthus spragueii) and their invertebrate prey

摘要

The Sprague's pipit is a small, threatened grassland songbird endemic to the Canadian prairies and to the northern Great Plains of the United States. Between 1968 and 2006, the population of Sprague's pipit in Canada experienced a significant annual decline of 4.5%. The prairie provinces also experienced declines within this reporting period. Pipits are more abundant in native prairie grasslands, however much of their preferred habitat has been lost due to the influence of human activities. Furthermore, management of remaining grasslands has impacted the quality of habitat through suppression of natural disturbances such as fire. Few studies have addressed how fire affects the occurrence and abundance of Sprague's pipit, thus pipit response to fire is poorly understood. This study investigated the effect of fire on the density and distribution of Sprague's pipit in south-western Manitoba by examining the associations between pipit density, invertebrate food resources and vegetation structure with fire history. Surveys to determine pipit abundance, invertebrate resources and vegetation structure were conducted in 2007; in 2008 only pipit abundance and vegetation surveys were conducted. Although there was no significant effect of invertebrate resource abundance on Sprague's pipit density, the abundance of grasshoppers and ground beetles declined with increasing time since last burn, which suggests that longer fire-return intervals may reduce the availability of these prey species for pipits. Fire did not significantly influence the distribution and density of Sprague's pipit in this region. However the response of the vegetation to fire may indicate that the existing fire-return interval is not contributing to the population decline of Sprague's pipit, but that in the absence of fire, the habitat could regress to a state that does not meet the critical habitat needs of this species.