Frugivores, plying their trade

A male American Robin deftly flips a berry into its gaping maw. This bird and many of his comrades were devouring a thicketful of Amur Honeysuckle (Lonicera maackii) fruit. I made this shot last Friday morning at Glacier Ridge Metro Park in Union County, Ohio.

The likely evolution of brightly colored berries is to serve as bird attractants. Enticing strong fliers to eat and thus disperse one's fruit is an effective colonization strategy. The migratory and localized nomadic tendencies of robins makes them ideally suited to the task.

Unfortunately, robins don't discriminate between native berry crops and introduced ones, such as this honeysuckle. There are three species of Eurasian bush honeysuckles that have become well established and highly invasive in Ohio and elsewhere in the Midwest, and the shrubs have taken over with great rapidity.

Birds are the reason. Along with Cedar Waxwings and European Starlings (an invasive bird), American Robins are doing much of the heavy lifting in regards to honeysuckle dispersal. All three are highly frugivorous (fruit-eating), at least seasonally. It's very common to see mobs of these species stripping honeysuckles of their fruit, and they will expel the seed-rich fruit far from where they ate it, most likely. One could not design a better plan for a botanical takeover.

Other species of birds eat honeysuckle fruit, but I single the trio above out due to the sheer force of their numbers and strong tendency to harvest fruit crops. Collectively, those three species comprise about 9.5 million individuals in Ohio alone and that's a lot of honeysuckle harvesting power.

We can't blame the birds for this invasive scourge - well, maybe the starlings - but hopefully we can learn from our mistakes. The landscape industry and fish and wildlife agencies pushed these honeysuckles for a long time, touting their "wildlife" values and aesthetic properties (I would agree with the latter - they are quite showy). It should be very apparent by now that woody plants, especially shrubs, that develop colorful bird-dispersed fruits have a great chance of vaulting the garden fence and going rogue. Perhaps the nurseries could become more visionary and avoid selling these plants BEFORE they become problems. 

 A stone's throw from the fruit-plundering robins was this Eastern Phoebe. A tough flycatcher, phoebes will try to ride out the winter if conditions give them half a chance. This one was staying near a small stream on this chilly morning. Their odds of finding insects are higher around water. But on a few occasions I watched the phoebe duck into a patch of Multiflora Rose (Rosa multiflora) and scarf down a few berries. When push comes to shove, and food is of the essence, phoebes will turn to fruit. But because of their low numbers and ephemeral frugivory, they probably play a very minor role in invasive plant seed dispersal - certainly nothing even remotely approaching the gangs of robins, starlings, and waxwings.

HERE'S A POST from 2014 from a site where I caught a number of species in the act of honeysuckle plundering, and talk a bit about why honeysuckle is bad for birds and ecology. Here's ANOTHER POST about robins and global warming that you might find of interest.