Some winters I install a feeder for the birds in the garden.
The activity is moderate because I cannot invest as much in abundant supplies.
However, as the snow melts but the ground is yet unfrozen, I observe many tiny droppings scattered around the tree.
As the soil unfreezes, these droppings would become accessible to the roots of the plants below the tree and to the tree itself.
At least poultry manure is an excellent fertilizer and I cannot see why wild bird droppings would be lesser to farm-fed birds (especially, farm-fed birds who are sustained on very basic, non-diversified diets).
Thereby, I began wondering whether trees that bear fruit and seed (that birds consume) might have a chemical composition which is different from trees that do not attract flocks of birds.
Similarly, it might be beneficial to have a nest in one’s branches as the resident pair and its chicks fertilize the soil all season round and these droppings are not subject to spring aboveground flows washing the nutrients off the base of the tree.
However, a resident pair can only produce as much fertilizer and it might all become consumed by the plants below the tree that have shallower roots systems intercepting the nutrients as they enter the soil.
Meanwhile, fruit and seed (/nut) trees can attract flocks of birds that spend considerable time in the tree.
We feed birds during winter and many fruit/seeds also remain available during winter.
However, the droppings enter the soil in late summer/autumn and in early spring which is the most significant period for root development.
Root development, in its turn, is an investment in the overall productivity (biomass and seed) of the tree throughout the following season.
One would assume that producing fleshy fruit and seeds/nuts rich in protein and lipids (attractive to birds) but also hardy enough to survive the foraging process (digestion) is also an energy demanding strategy.
Thereby, I wonder whether such trees and shrubs have coevolved with their bird herbivores in a manner whereby the woody plant produces an attractive fruit/seed which is consumed by flocks of birds which leave their droppings.
These droppings enhance the nutrient availability for the woody plant compared to other trees/shrubs that might not have such high visitation rates by the winged gardeners.
The enhanced nutrient availability allows to increase new root production rates and to store nutrients in the old roots.
The nutrients stored in the old roots are used to ensure new aboveground growth (shoots, leaves) while the new roots expand the belowground nutrient acquisition network.
Thus, the fruit- and seed-bearing trees might become enabled to produce the attractive (rich in sugars, fat and protein) resources to further the cycle and to both raise fertility/productivity rates as well as promote seed dispersal by birds.
Perhaps the evolution of fruit and seed (/nut) bearing trees has been closely linked with their bird herbivores in that they each provide nutrients for the other; and the more attractive products the woody plant can offer, the greater the fertilization rate by the birds which furthers the potential to develop even more nutritious products.
Notes by Ieva 