It`s not trails that disturb forest birds, but the people on them
(PHYSorg.com Biology)

The first study to disentangle the effect of forest trails from the presence of humans shows the number of birds, as well as bird species, is lower when trails are used on a more regular basis. This is also the case when trails have been used for many years, suggesting that forest birds do not get used to this recreational activity. Published in Frontiers in Ecology and Evolution, the finding suggests the physical presence of trails has less of an impact on forest birds than how frequently these recreational paths are used by people. To minimize the impact on these forest creatures, people should avoid roaming from designated pathways.