Recreational trails are affecting bird reproduction

Many protected areas provide important habitat refugia for wildlife while also providing access for recreational activities like hiking. Research conducted by Max Henschell of the SILVIS lab shows that recreational trails reduce reproductive success and increase nest parasitism for forest birds. The effects are stronger nearer to trails but the effects extend well beyond the physical footprint of the trails.

Protected areas are often our front line to maintain wildlife populations, and their habitat for critical activities like feeding and breeding. But what happens when we also rely on these areas to provide recreational opportunities so that people can enjoy the great outdoors? Access and use in protected areas is on the rise and Max Henschell, a PhD student in the SILVIS lab has set out to answer the question of how recreational trails affect forest bird reproduction.

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Typical Trail in Devil's Lake State Park
Max says, 'We are seeing more access to protected areas via trails and the concern is that this may be affecting the quality of the habitat.' He seeks to answer some important questions. Does activity along trails affect bird community composition and reproductive success? Does size matter? To answer these questions, Max has been looking at bird reproduction in forests within the Baraboo Hills of central Wisconsin.Max has compared bird reproduction in forest with no trails with that off forest with trails. In addition to the presence of trails, he has been looking at whether the size of trails matters to these questions. He is trying to tease apart the effects of disturbance, activity that might make birds temporarily leave their nest, from habitat fragmentation, the physical break-up of large blocks of forest into smaller blocks. 'We also want to see if there are edge effects from large trails making habitat fragmentation a compounding factor.'While Max's research is ongoing, he has already found that trails do have an effect on bird reproduction. He says, 'Trails definitely affect nest success. Nest success is lower, and nest parasitism and nest predation higher, in the vicinity of trails. We are also seeing that the influence of trails extends well beyond their physical footprint.' While the results are not final, some of his findings suggest that the size of the trail matters. 'The first season we only found 30 nests, so hopefully analysis of subsequent years with more nests will help tease apart these findings.' Another factor he is working on incorporating is trail use. Adding that to the analysis should further help understand the effects of trails.

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Parasitized Acadian flycatcher nest (Brown-headed Cowbird egg, in bottom of nest)
Trails may also affect bird community composition, but whether that is the case is not clear at the moment. 'Identifying changes in the bird community can be really difficult because larger factors like climate variability can have overriding effects', says Max (the two years of the study had very different weather patterns). 'We've got one more field season', he says. Here's hoping his research concludes along happy trails.
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