Similar seed dispersal systems by local frugivorous birds in native and alien plant species in a coastal seawall forest

Frugivorous birds play an important role in seed dispersal. Alien plant species’ seeds are dispersed by local birds in order to establish populations in new habitats. Alien plant species that produce fruits similar to that of native species have the potential to attract local birds, creating new mutualistic systems that are similar to the local ones. In autumn 2018 and 2019, we studied the seed dispersal systems of an alien plant species, Phytolacca americana, and a native species, Cayratia japonica, in a coastal seawall forest. Both plant species’ fruit, frugivorous bird foraging behaviors, seed germination rates, and seedling microhabitats were examined to determine whether the alien species had a similar seed dispersal system to that of the native species. Our results showed that P. americana and C. japonica had similar fruit type, color, and ripening period. There was a positive correlation between the percentage rate of fruit ripening and the percentage rate of fruit missing for both plant species, indicating that local frugivorous birds have the potential to sufficiently disperse the alien seeds to enable its spread in the coastal seawall forest (simple linear regression, P. americana: β = 0.863 ± 0.017, R2adj = 0.978, P < 0.01; C. japonica: β = 0.787 ± 0.034, R2adj = 0.898, P < 0.01). Eleven bird species consumed the fruits of the alien species or native species during the study period. Similar results were shown across alien and native species in bird foraging behavior (feeding frequency, feeding duration and first stop distance) indicating that a similar seed dispersal relationship had been established between local frugivorous and both plant species. The alien plant had a higher number of fruits carried by birds, suggesting that P. americana had a slightly higher fruit consumption than that of C. japonica (t-test, P < 0.01). Alien plant seedlings grow more abundant in forest gap microhabitat (t-test, P < 0.01). Our results confirmed that bird digestion promotes seed germination success in both plant species. Our study suggests that in a narrow coastal seawall forest, alien plant species can successfully establish their populations by relying on similar seed dispersal systems as the local species.

The contour feathers of water birds exhibit adaptations to the impact forces of diving, plunging and alighting

The contour feathers of water birds are well-known to show structural details in their distal one-third that optimally confer water repellency and resistance to water penetration. In this study, these details were further examined to see if they also provide resistance to the impact forces of diving and alighting. To this end, 49 species representing 37 water bird families were grouped into nine foraging niches before measurement of length, diameter, and spacing of their barbs. Twelve land bird species grouped into two foraging niches were included in this study for comparison. These measurements allowed the calculation of the ranges and medians for barb stiffness and vane deflection for each foraging niche. A phylogenetic ANOVA approach was followed to determine if the foraging niches for water and land birds explain differences in feather microstructure while accounting for phylogenetic relationships. There were no significant group aggregations for water or land birds confirming the statistical reliability of the ANOVA approach. Differences between the deflection parameter medians of water and land bird foraging niches proved significant demonstrating an evolutionary distinction between these groups. No such difference was observed for the two land bird foraging niches indicating similarity in feather structure. For the water birds, significance was found among all aquatic niches showing that differences in feather microstructure are associated with respect to differences in aquatic feeding niches. These findings support the notion that evolutionary adaptations of feather traits are significant across bird species and their respective foraging niches. The observed mechanical and morphological variations of feathers are therefore considered adaptations to different habitats and behavioral patterns.