Frugivorous birds provide important ecosystem services by transporting seeds of fleshy fruited plants. It has been assumed that seed-dispersal kernels generated by these animals are generally leptokurtic, resulting in little dispersal among habitat fragments. However, little is known about the seed-dispersal distribution generated by large frugivorous birds in fragmented landscapes. We investigated movement and seed-dispersal patterns of trumpeter hornbills (Bycanistes bucinator) in a fragmented landscape in South Africa. Novel GPS loggers provide high-quality location data without bias against recording long-distance movements. We found a very weakly bimodal seed-dispersal distribution with potential dispersal distances up to 14.5 km. Within forest, the seed-dispersal distribution was unimodal with an expected dispersal distance of 86 m. In the fragmented agricultural landscape, the distribution was strongly bimodal with peaks at 18 and 512 m. Our results demonstrate that seed-dispersal distributions differed when birds moved in different habitat types. Seed-dispersal distances in fragmented landscapes show that transport among habitat patches is more frequent than previously assumed, allowing plants to disperse among habitat patches and to track the changing climatic conditions.

Summary1. Quantifying ecosystem functions in spatially explicit ways is important for management decisions in increasingly fragmented landscapes. Between-patch dispersal of seeds by frugivores constitutes a key ecosystem function to ensure connectivity for fleshy-fruited plants. However, to date, methodological hurdles have limited our understanding of dispersal pathways on the landscape scale. 2. We made use of newly available tracking devices and combined movement data of 30 trumpeter hornbills Bycanistes bucinator with gut passage times and high-resolution habitat data in a fragmented forest landscape in South Africa. We identified each potential seed dispersal path and distinguished whether potential seed transport happened to a different forest patch (between-patch dispersal), within the same patch (within-patch dispersal) or into the habitat matrix (failed dispersal). To quantify functional landscape connectivity, we identified all possible between-patch connections and used graph networks to estimate landscape connectivity provided by hornbills. 3. Although potential between-patch dispersal events were rare (on average 7% compared to 20% failed dispersal and 73% within-patch dispersal), hornbills could cover distances of up to 15 km. Hornbills visited over 100 forest patches and connected a habitat network with an extent of about 50 km, which increased the potential functional connectivity of the landscape more than twofold. 4. We identified habitat patches that were critical stepping stones for seed dispersal pathways. Without these stepping stones, the network would likely disintegrate into separated components and lead to isolation of forest fragments. 5. Synthesis and applications. We showed that large frugivorous birds can greatly improve functional connectivity for fleshy-fruited plants across broad scales, linking habitat patches in fragmented forest landscapes. Combining high-resolution movement and landscape data in graph networks allows identifying seed dispersal pathways and critical stepping stones in fragmented landscapes. This approach addresses the general challenge of spatially explicit mapping of ecosystem services and can be widely incorporated in reserve design and landscape-level conservation planning.

Studies on the ranging behaviour of birds often suggest that ranges vary seasonally with larger ranges in the non‐breeding compared to the breeding season. However, due to limitations in tracking methods very little is known about the underlying processes driving seasonal differences in ranging behaviour, especially in fragmented, heterogeneous landscapes. Such knowledge is particularly important if movements deliver essential ecosystem functions such as seed dispersal. We contrasted the daily ranging behaviour between the breeding and non‐breeding season of a frugivorous bird and demonstrate how larger seasonal ranges in the non‐breeding season emerge through switching from a stationary home range behaviour to nomadism. We tracked movements of 29 male trumpeter hornbills Bycanistes bucinator across a fragmented landscape of eastern South Africa during different breeding and non‐breeding seasons using high temporal resolution GPS data‐loggers. Birds in the breeding seasons showed a typical, stationary home range pattern. In the non‐breeding seasons birds, rather than expanding their stationary daily ranges, switched to nomadic movements that were characterized by shifts of the general location of daily ranges to a different area every couple of days. We also found that during the breeding seasons hornbills were mostly located in large continuous forests; birds in the non‐breeding seasons frequently used forest patches within the agricultural landscape and residential areas. These seasonal differences in the movement behaviour of trumpeter hornbills may have important consequences for seed dispersal of plant species. Our findings show how seasonal range expansion of frugivorous birds may be driven by fundamental behavioural changes that have important consequences for ecosystem processes.