There are a number of birds that have returned to New England from their southern wintering grounds and are working hard to find enough to sustain themselves until food is more plentiful. Eastern Bluebirds, Hermit Thrushes, Northern Mockingbirds, Eastern Phoebes and Yellow-bellied Sapsuckers adapt their diets to whatever is available at this time of year, which can mean going from eating insects to consuming fruit. Fruits that persist through the winter are few and far between, but one of the plants that provides the most sustenance to birds in early spring is Poison Ivy. The off-white, berry-like fruits are extremely popular with at least 60 species of birds, including the early returning migrants previously mentioned, as well as Gray Catbirds, Yellow-shafted Flickers, Wild Turkeys, and Downy, Hairy, Red-bellied and Pileated Woodpeckers. The popularity of Poison Ivy fruit with birds explains why this plant is common along fencerows and other areas where birds roost (and pass the seeds). (Caution – irritating urushiol, an oily resin found in the sap of Poison Ivy, is present in the leaves, stems, flowers, roots and fruit of this plant.)
Poison Ivy is in the Anacardiaceae family, which also includes cashews, mangos and sumacs. The sap of the stems, roots, fruit and leaves of many species in this family contains urushiol oil, which is what causes the allergic rash in 80% of humans that come in contact with these species. Poison Ivy is very sensitive to carbon dioxide, and even slightly elevated levels of CO2 have proven to increase its growth. In the past 50 or 60 years, during which time the amount of carbon dioxide in the atmosphere has increased by roughly 22%, Poison Ivy’s growth rate has doubled. The amount of urushiol oil has not only increased, but it is also more potent…leaves of three, let them be.