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Bird-plant entanglement: a review and addition of the Least Flycatcher.

Article Excerpt
Entanglement in plants is among many factors affecting survival of birds. Little is known about circumstances of how birds become entrapped. Seed-eating species, such as American Goldfinch (Carduelis tristis), may get caught while trying to extract seeds from seed heads (McNicholl 1988). Needham (1909) speculated that kinglets (Regulus spp.) may be caught in burdock (Arctium spp.) inflorescences while attempting to forage insect larvae of moths and weevils present on seed heads. Aerial predators hawking insects may brush up against plants during pursuit of prey. Initial entanglement for most individuals is probably minor, but as a bird struggles to free itself, more and more feathers may become lodged in the seed head until the bird is effectively immobilized. Feathers may attach to the hardened and hooked phyllaries of seed heads (e.g., burdock), similar to the hook and loop system of Velcro[R] (Craves 1998). Alternatively, birds may adhere to sticky resin associated with some seeds (e.g., the tropical tree Pisonia grandis), affecting bird mobility off of plants (Gauger 1999, Burger 2005). Plant entanglement in North America is reported for 25 avian species (Table 1). Burdock, one of 15 plant taxa reported, accounted for 56% of the bird species affected.

McNicholl (1988, 1994) compiled the literature on birds caught in burdock. Reports continue to identify bird entanglement in burdock and other plants known to impact birds. Our objectives were to: (1) summarize published accounts of bird/plant entanglement in North America, since most observations come from this region, and (2) document the first case of a Least Flycatcher (Empidonax minimus) fatally snared in burdock (A. minus).

OBSERVATIONS

We add the first documented account of mortality of the...

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