Don’t Look Up, but Bird Poop Promotes Plant Health

My dread of early summer is the horde of birds that descend on our backyard and strip our trees and bushes of most of their fruit. I do gain a little solace, however, in recognizing that birds fulfill a critical role in spreading the seeds of plants far from their initial locations. Thus, birds help promote the survival, health, and proliferation of the plants they feed on.

Birds spread the seeds of plants in two ways. One way is with their beaks. Some seeds fall out of their beaks by accident when they fly away or land. Others are spit out after the birds consume the fruit surrounding the seeds.

The second way birds spread seeds is through their digestive tracts. They consume the fruit of plants—seeds and all––digest the fruit and eliminate the seeds.

Now, a team of seven biologists has discovered that birds do much more than just transport seeds to further the health and well-being of plants.¹ The biologists noted that one of the most important benefits of seed transfer by birds is that the birds deposit seeds to locations bearing fewer plant pathogens and fewer plant-consuming animals. However, they also deduced that this benefit should be much reduced for plants that are densely populated throughout very large habitats. Yet, their observations did not confirm their deduction. They concluded, therefore, that birds must provide additional help.

The team used a common bird-dispersed chili pepper to conduct an experiment. Researchers learned that seeds dispersed by birds consuming the peppers and passing the pepper seeds through their digestive tracts had an increased survival rate of 370 percent compared to pepper seeds dispersed by birds’ beaks.

This finding led the biologists to another discovery: seed passage through the birds’ digestive tracts removed––to a large degree––both fungal pathogens and chemical attractants to herbivores. (Ants can infect seeds with fungal pathogens while the seeds are still on the plants, and chemicals in the seeds emit odors that attract predators.) Gut passage removed volatile compounds from the seeds that resulted in a one hundredfold decrease in emission rates of volatile attractants from the seeds during the first three days after gut passage. Those days are the times when seeds are most subject to consumption by herbivores. The researchers also determined that gut passage reduced fungal loads on seeds to such a degree that it doubled the seed survival rate, yielding an overall net 370-percent superior survival rate.

Once again, scientists have uncovered a remarkable example of symbiosis. Pepper plants provide birds with a valuable food source while the birds (in two different ways) process the seeds and later distribute them in a manner that greatly enhances the population, health, and habitat range of the plants. The necessary simultaneous designs of the plants, birds, birds’ digestive tracts, and birds’ behaviors to make this symbiotic relationship operate as effectively and beneficially as it does strains the evolutionary paradigm but argues strongly for the intelligent, purposeful design of the God of the Bible.