Role of birds in seed dispersal, dormancy, and germination

Text extracted from portions of "Ecology: The guts of seed dispersal," by Peter D. Moore.

"Hitching a lift in the gut of a bird is a pretty effective answer to the mobility problem that faces every plant. A bird eats a fruit and flies off, in due course depositing the seeds it has ingested elsewhere, allowing a new plant generation a fresh start in life. But passing through an avian alimentary system can also affect the overall viability of seeds, as well as their dormancy characteristics and germination rate" as found by Traveset and colleagues (2001).

"Some birds are seed predators, destroying and digesting seeds for their nutrient content. But even these can act as dispersal agents if they die with viable seeds in their gizzards, or if some seeds fortuitously evade destruction in the gut. Other birds consume entire fruits and digest only the fleshy parts, allowing the seeds to pass on through the gut. These can be efficient dispersers."

"Darwin speculated about the dispersal of seeds in bird guts, calculating -- perhaps optimistically -- that a propagule could travel 500 miles in this way before the host evacuated its bowels or died. It has also been recognized that passage through the gut can increase the germinability of seeds..."

The "germination behaviour of seeds may be modified in various ways as a result of gut passage, by either shortening or lengthening the period of dormancy" and "different bird species have different effects on a given species of plant. The control of germination time in seeds is known to have repercussions in terms of the overall ability of a plant to grow and reproduce. Variability in germination times can have considerable advantages for a plant, particularly when it has to deal with unpredictable habitats or those prone to catastrophic events. The destruction of a cohort of seedlings by a factor such as drought can be counteracted by a second wave of germination by dormant seeds in the soil. Early germination, on the other hand, may assist the seed in escaping predation or fungal attack, or allow it to take advantage of unusual conditions, such as the early arrival of rain. So a combination of both options -- achieved by the fruit passing through different birds -- could diversify the germination strategies available to the plant. For a seed travelling by bird, therefore, the long haul is by no means the only benefit available; the choice of transport and the in-flight service could be even more important."