Distribution and abundance of baling twine in the landscape near Osprey (Pandion haliaetus) nests: implications for nestling entanglement

Abstract

Polypropylene baling twine used by Ospreys (Pandion haliaetus) during nest construction creates a risk of entanglement for nestlings and adults on the yellowstone River, Montana. In 2013, we evaluated the abundance of twine in 2-km-radius buffer zones centred on 38 nests for three categories of road density. We found more twine per kilometre along roads in low (n = 19) and moderate (n = 13) road density nest buffer zones than in high road density nest buffer zones (n = 6). The estimated total amount of twine found along roads in nest buffer zones ranged from 0 to 2602 m and did not differ among road density strata. The percentage of Osprey nests containing twine was highest in low (63.2%) and moderate (61.5%) road density nest buffer zones and lowest (33.3%) in high road density buffer zones, which reflected a gradient from rural and suburban to urban landscapes. The estimated total amount of twine within a nest buffer zone did not predict whether a nest contained twine. The amount of twine found in seven nests destroyed by wind or power company personnel ranged from 0 to 206 m and was not correlated with the amount of twine found in their buffer zones. During the 2012 and 2013 breeding seasons, four of 120 nestlings (3.3%) became entangled in twine: two were cut free and fledged normally, one died, and one was euthanized. The abundance of twine in the environment surrounding nests and its slow rate of biodegradation mean that vigilance by citizen scientist nest monitors and assistance from power companies are the only short-term solution to reducing mortality resulting from entanglement.