“Liaisons dangereuses”: The invasive red‐vented bulbul (Pycnonotus cafer), a disperser of exotic plant species in New Caledonia

Abstract

The biodiversity hotspot of New Caledonia hosts high levels of endemism (74% of flora) that is threatened increasingly by climate change, habitat reduction, and invasive species. The fruit‐eating red‐vented bulbul (Pycnonotus cafer) is currently invading the main island of the archipelago, and its recent dispersal out of urbanized habitats raises questions about its potential to disperse noxious plant seeds along urban corridors and beyond. Indeed, the red‐vented bulbul is considered a vector of several introduced plant species in its alien range including Miconia calvescens, Lantana camara, and Schinus terebinthifolius. We conducted a quantitative assessment of the bulbul's fruits consumption by analyzing the gut contents of shot birds. We estimated gut passage times for four species of fruit found in gut contents (S. terebinthifolius, Myrtastrum rufopunctatum, Passiflora suberosa, and Ficus prolixa) and tested the effects of bird digestion on seed germination rates for two species. Finally, we monitored the movements of individual VHF radio‐tagged red‐vented bulbuls. All of the consumed fruit species we identified here have red fleshy diaspore, including fruit of the shrub M. rufopunctatum that occurred frequently (9.6%) in bulbul gut samples. Median gut passage times were short (15–41 min), corresponding to short‐distance seed transportation (77–92 m). The effect of gut passage was positive for the germination of the invasive S. terebinthifolius and negative for the endemic M. rufopunctatum, suggesting a potential bias in the contribution to the dispersal toward alien species. This study provides the first integrated assessment of mechanisms involved in the seed dispersal effectiveness of this high‐concern invasive bird species that is expected to face similar plant communities in most of its alien range in tropical islands. More generally, our results enhance knowledge of synergies between non‐native frugivores and plant species dispersal.

Invasive birds: global trends and impacts

“…A recent study in New Caledonia was dedicated to describing the seed disperser effectiveness of the Red-vented Bulbul (Thibault et al, 2018c). Their mean gut passage time of a fruit consumed was between 20 and 30 min.…”

“…Consumption by the Red-vented Bulbul accelerated the germination speed and enhanced the germination rate of S. terebinthifolius but lowered the germination capacity of the endemic M. rufopunctatum. Even if this observation could be partly explained by differences in fruit characteristics, such effects of favouring an invasive species could drive an 'invasional meltdown' and should be described in depth (Thibault et al, 2018c).…”

“…Red-vented Bulbuls feed on a variety of native plant species (Trail, 1994;Sherman and Fall, 2010), and dispersal of native seeds is the only service that has been explored in the Redvented Bulbul's alien range (Spotswood et al, 2012). As an example, the endemic M. rufopunctatum was found to be among the most frequently consumed species in New Caledonia during the study of Thibault et al (2018c). Interestingly, in a village-scale survey led by Daigneault and Brown (2013) in Viti Levu, Fiji, 47% of the respondents reported that the Redvented Bulbul was good for their community for three main reasons: (i) it was effective at insect control; (ii) it reduced mongoose attacks on chickens as a result of the chickens eavesdropping on bulbul alarm calls; and (iii) village focus groups responded that Red-vented Bulbuls were occasionally eaten by villagers.…”

Seed Dispersal by Frugivores and Germination Success of the Invasive Alien Shrub Pyracantha Angustifolia in the Eastern Free State Province, South Africa

“…It would be therefore expected that after avian ingestion, the germination rate of the seeds would be improved. Alternatively, pulp removal might be the factor enhancing germination; or both pulp removal and avian ingestion acting together (Thibault et al 2018).…”