Volume 40 Number 3 157 any other sites in the Great Lakes region or along the Gulf of Mexico, the only opportunity for a cormorant to swallow a fish that may have itself swallowed a Chaff-flower seed would be somewhere on the Mississippi or Ohio Rivers. Dou- ble-crested Cormorants, including birds from Ontario colonies, do migrate along the Mississippi in both spring and fall, but their passage is rapid, with a total mean duration of 12 days in spring and 34 days in fall (Dorr et al. 2020). Mi- gratory flights continue throughout the day (Dorr et al. 2020). Achyranthes japonica fruits ripen in the fall, but as cormorants normally re- gurgitate pellets daily (Dorr et al. 2020; van Leeuwen et al. 2017), it is unlikely that a seed from a swallowed fish taken during autumn migration would remain in a cormorant’s digestive system until it returned to its breeding grounds the fol- lowing spring. As the seeds remain viable for months it is possible that a fish could have swallowed a seed in early spring that had fallen into the river in the previous autumn, and the fish could then have been eaten by a cormorant during its northward migration (assuming that northward migrants stop to feed during their short spring passage), but surely this is less likely than other explanations for the plant’s presence on Middle Island. Previous studies suggest that cor- morants are less likely than many other bird groups to be vectors for a plant, such as A. japonica, that spreads its seeds by epizoochory because of their morpholo- gy and behaviour. A. japonica is adapted to transmit its seeds to the fur or feathers of an animal walking past it (Neal 2013), and cormorants, unlike other aquatic birds such as gulls, rarely walk. Their short hindlimbs which are adapted for foot-propelled diving, confine walking to a limited speed range (White et al. 2008). Walking is often confined to short journeys within a nesting colony; the average distance travelled when walking Imperial Cormorants (Pha- lacrocorax atriceps), a ground-nesting species, was 1.19 m (range = 0.32–2.10; Gómez Laich et al. 2011). Double-crest- ed cormorants, which do nest on the ground but normally nest in trees on Middle and East Sister Islands, may walk even less, though they may descend to the ground in search of nesting mate- rials. When necessary, cormorants can move on land with a bounding gait, sometimes assisted by wing movements (White et al. 2008), but the occasions on which they would move along a for- est trail or through a thicket of weeds where they could encounter A. japonica, particularly when away from the breed- ing colony while on migration, are prob- ably rare at best. Double-crested Cormorants, in sum, lack the behavioral and morphological features that would make them good candidates for the spread of A. japonica to the Lake Erie Islands. The establish- ment of plants under their breeding colonies may have less to do with disper- sal than with a supply of nitrogen-rich guano from their droppings (Kolb et al. 2010; Zólkos ´ and Meissner 2010). This benefit may decrease as chemicals such as uric acid increase soil acidification and affect seed germination (Klimaszyk and Rzymski 2016), and cormorant