| Abstract | | The literature surrounding the effects of human recreation on bird populations is rich and varied. Several studies document the negative effects on bird populations due to human recreation in general (e.g. Miller et. al 1998, Pfister et. al 1992) and dog walking in particular (Banks and Bryant 2007) at numerous locations worldwide. However, several recent studies report no adverse effect of trail use on abundance or species richness of foraging shorebirds (Trulio and Sokale 2008) and little evidence to suggest hiking trails influence abundance, detection probabilities or within and among seasonal movements of montane forest birds (Deluca and King 2014).
Abundance
We found a slight negative trend of abundance during winter and breeding seasons over the course of the study period and a slight negative effect of trail construction on seasonal abundance. Most individual species however, do not show these trends. Decline in winter and breeding season abundance of Song Sparrow in particular is worth note. Song sparrows are one of the most abundantly encountered species in the study with several hundred detected each season. Our data suggest both that Song Sparrows may be in decline, but also that the decline in this one species may be driving the overall decline in abundance found in the study. Continued study of Song Sparrow populations into the future would help elucidate this dynamic. We recommend additional analyses excluding Song Sparrow abundance on existing data as well as additional data collection (i.e. what will Song Sparrow abundance do into the future).
Diversity
We found an increase in the Shannon Diversity index in both winter and breeding seasons over the course of the study period and did not find any influence of either trail construction or distance to the trail on diversity of bird species. Increase in diversity over time is in part attributed to this type of long term study (i.e. over time observers will encounter additional species that were either not present or present but not abundant in early years). Increased diversity may also be a response to restoration throughout the study area as significant restoration planting has occurred by the Foundation along the Middle Reach of the Laguna de Santa Rosa from Highway 12 to Occidental Road as well as significant plantings in Meadowlark field directly adjacent to Kelly Farm. We also expect to see new species as a result of predicted changes in climate. Evaluating the effect of restoration and climate change is beyond the scope of this study.
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