Rabbits are what they eat

Rabbit debarking bittersweet (all photos in this post by Zas Ispa-Landa)

What: You are what you eat. And in this case rabbits are a whole lot of things. Zac and I were impressed at the abundance of rabbit sign (from the introduced eastern cottontail, Sylvilagus floridanus, as opposed to the native New England cottontail, Sylvilagus transitionalis) when we went tracking on Saturday down at Bread and Butter Farm in Shelburne. We even spooked a cottontail as we walked past the driveway. Rabbits seemed to prefer shrubby non-natives, or at least those were the most prolific species in the area and so were the most foraged upon. We found feeding sign (debarking and/or twigs clipped) on forsythia, common buckthorn, barberry, domestic apple, honeysuckle, staghorn sumac, and oriental bittersweet.

45o angle snips on twigs, charateristic feeding sign from cottontails
on woody species (forsythia in this case)

The story got even cooler at the end of the day when we found another high traffic area for cottontails under the powerlines. Buckthorn predominates in that area and the rabbits must have been eating fallen buckthorn berries as their urine was died blue (image on the right is blue tinted urine, on the right is more typical orange). Buckthorn berries are unpallatable, if not inedible to most things so the berries persist into late winter, when they become a last resort for many winter active species.

Ecological notes: Many plants contain phenolics (tannins, which cause the dry taste in wines, the bitterness in aspen bark) as a defense against herbivory. During spring and summer these are concentrated in leaves and flowers, but during winter they are translocated to the bark. Animals have a variety of ways of dealing with these phenolics (e.g. beavers will soak witchhazel before eating to leach tannins, birds and will eat clay, which absorbs phenolics). Buckthorn (Rhamnus cathartica) is high in phenolic compounds. Rabbits presumably can handle the phenolics by breaking them down in their kidneys, or maybe eating clay. The anthocyanins (pigments in the fruits) are also excreted in the urine. I'd assume that eating buckthorn fruits later in the season gives more time for the tannic acids to break down and makes the fruits more palatable. That's speculation though, and I couldn't find any articles to confirm/deny that.

Little leaves

What: Quiz Time! This seems to be the hardest part of the year for telling which trees are which: the buds are bursting, becoming unrecognizable, and the little leaves, just emerging, haven't quite yet taken full shape. It's like looking baby photos of friends and trying to guess who they are. The leaves in the photos below are some of the early ones to come out. Roll over each to test your ID skills (there are both shrubs and trees). 

Ecological notes: You can compare the male boxelder shown above to the female boxelder from my post on boxelder bugs. Also, the last photo shows the seeds from an ornamental Siberian elm in Centennial Woods. Ryan Morra and I were pondering over greenness of the seeds. One possibility is that they're actually photosynthetic when they're young (boxelder, white pine, oaks, walnuts, and probably other seeds that invest a lot in endosperm are also green when young). I would imagine that this would take away pressure on the leaves to produce energy for the developing seed. In the elm photo it's a fly on the seed, but other pests can destroy a seed. If leaves were producing energy for growth, winter storage, and the seed, they might be more likely to be at a net loss each year. Having seeds responsible for their own growth is energy insurance for the rest of the plant.

Spoiler alert: The species above are, in order, Populus tremuloides, Cornus alternifolia, Rhamnus cathartica, Acer rubrum, Rhus typhina, Acer platanoides, Acer negundo, Acer negundo, Ulmus pumila.

Other notes: Just a pattern I noticed - willow family and maple family seem to be among our earliest trees to leaf out. Big-tooth isn't out yet, birches are barely opening up, and the buds on some of our more southern species are only beginning to open (e.g. walnut, oak, hickory)