Of Leaves & Worms

leavesEvery autumn, vibrant leaves float down from the tree tops to stitch a patchwork quilt resting on the forest floor.

Over time, leaves are broken down by fungi, bacteria and other detrivores (organisms that eat dead stuff) like earthworms. The superpower of the earthworm (Lumbricus terrestris) is its ability to compost vegetation and return vital nutrients to the soil.

Charles Darwin was fascinated by earthworms, conducting wonderful experiments to determine how much soil they moved and whether worms preferred to collect leaves from the broad end or pointed end. Worms pull leaves into their burrows (narrow end first) to plug the opening and protect themselves from ‘early birds’.

In much of North America, earthworms were killed off in the last ice age (~10,000 years ago). The worms you see now in Michigan, Maine and Minnesota are all invaders. Sounds great, right? More nutrients in the soil? Unfortunately, the northern hardwood forest ecosystem is adapted to a thicker leaf litter layer and slower release of nutrients. So now, the introduction of the earthworm changes which seeds can germinate (and which trees will continue to survive), nutrient run-off, and which animals live in the new, de-littered forest. (1)

If you’re interested in appreciating the awesome recycling power of the worm, check out a delightful little book by Amy Stewart – “The Earth Moved: On the Remarkable Achievements of Earthworms”.

Want to read more specifics about leaf-earthworm experiments? Natural History Magazine has an entertaining write-up.

  1. Hale CM et al. 2008. Exotic earthworm effects on hardword forest floor, nutrient availability and native plants a mesochosm study. Oecologia. 155:509-518.

Going Nuts for Blue Jays

bluejaysWatch out, squirrel. You’ve got competition this autumn.

Acorn gathering and burying is often considered a squirrel hobby. Turns out, Blue Jays (Cyanocitta cristata) are pretty good at it too. Okay, really good.

Blue Jays have a pouch in their throat they can use to hold acorns (up to 5!). When they reach a caching site, the birds will spit up the acorns and bury them one at a time under leaves or in the dirt.

One study showed that Blue Jays were responsible for relocating more than half the acorns in a forested plot. (1) That’s over 130,000 acorns! And yes, the birds usually remember where they’re hidden. They’ll often place the morsels near “beacons” like rocks or fences.

Another study suggested that the birds were the most likely culprit in the spread of oaks after the last Ice Age (2). Most trees with heavy seeds returned slowly to the barren lands left when the glaciers retreated. But the oaks came back quickly. Squirrels couldn’t do that, but Blue Jays could.

  1. Darley-Hill S and Johnson WC. 1981. Acorn dispersal by the blue jay. Oecologia. 50(2) 231-232.
  2. Carter JW and Adkisson CS. 1986. Airlifting the oaks. Natural History. 95(10) 40-48.

By the way, Lego(R) came out with a bird series this year – and it includes the blue jay. They should add a small Lego acorn to go along with it.