Exploring Phenological Asynchrony Between Avian Diversity and Vegetation in Temperate Deciduous Forests Through Bioacoustic Monitoring and Camera Trapping

Climate change has had significant effects on the phenology of spring-time vegetative growth and bird reproduction, however, increasing evidence exists that reproduction in long-distance migratory bird species is not keeping pace with the emergence of vegetation in temperate habitats. The aim of this study was to explore whether such asynchrony could be occurring in Scottish deciduous forests using acoustic monitoring and camera traps to track the phenologies of migrant birds and vegetation growth from January to July 2019. A series of images was obtained using time-lapse settings of camera traps to determine a ‘greenness score’ as vegetation emerged from winter dormancy. Simultaneous bioacoustic monitoring was used to estimate the arrival date of eleven species of singing passerine and the difference between green-up and arrival was calculated to measure the phonological interval. Acoustic indices were also calculated and compared against avian and invertebrate diversity, measured through mist-netting and trapping studies respectively, to determine whether acoustic diversity could be an effective measure of overall biodiversity before being compared with greenness index. The Bioacoustic Index was determined to be the most promising index for estimating avian diversity. The Bioacoustic Index and Normalised Difference Soundscape Index also showed strong positive associations with photoperiod, likely as a consequence of increased daylength triggering mating behaviour and increased bird song in the soundscape. Short-distance migrant species tended to arrive earlier than long-distance species, in keeping with trends observed elsewhere. In summary, there did appear to be phenological asynchrony between migrant birds and vegetation within these forests, however more work is needed to connect bioacoustic indices with measured avian and invertebrate diversity