Ill.: Clipartkey, Clipartbank & pgitem.com, montage: laidbackgardener.blog
Question: I was wondering if bird droppings can harm plants. Birds love to roost on the trees in the yard, but leave their droppings everywhere.
Answer: In general, no, they aren’t harmful. But…
If the droppings land directly on young, still fragile tissues, yes, they can “burn” them, the damage being caused by the high concentration of minerals in the droppings, but this is generally a very minor effect. Mature leaves and plant parts are usually unharmed in any way.
Aside from this small defect, droppings are normally highly beneficial to plants and are, in fact, a major source of natural fertilizer. They are rich in minerals, especially phosphorus (P), nitrogen (N), calcium (C), potassium (K) and magnesium (Mg), but also many others. The exact percentage will vary according to the species of bird and its diet.
A case in point, you can usually readily find pelletized chicken manure fertilizer (a mixture of droppings and litter) wherever fertilizers are sold. Yes, you’re actually paying for bird crap! Also, bird guano (accumulated droppings of seabirds) was for a long time the most widely used fertilizer in agriculture and is still available to this day.
Thus, birds generously distribute rich minerals wherever they perch and plants benefit from them.
The white coloration of bird droppings comes from uric acid (C5H4N4O3). This compound sometimes sticks to objects (cars, walls, roofs, lawn furniture, clothes on the clothesline, etc.) where, once it has dried, it may be difficult to remove. Mostly, though, it’s quickly washed into the soil by rain.
Downsides of Bird Droppings
If in general, droppings are distributed in a random enough way so that their concentration causes few problems, there are exceptions.
In places where there are a large number of birds in a small space, such as in trees where seabirds or wading birds (cormorants and herons, in particular) form nesting colonies, coming back year after year to raise their young and poop, the accumulation of droppings eventually leads to a severe concentration of minerals and ends up killing most or all of the vegetation below. It eventually even kills the trees that support the nests.
Droppings also contain microbes (bacteria, microscopic fungi, viruses, etc.) and even parasites. There is no risk to plants (in fact, passing through a bird’s gut actually sterilizes the outside of seeds, killing the pathogens they originally bore), but there can be to gardeners, plus pets, not to mention other birds. Generally, any risk of infection decreases quickly, because bird poop microbes rarely survive long after they are ejected from their bird host, but where droppings build up, some undesirable microbes survive while others can move in. If you have to collect bird droppings (from a chicken coop, a bird cage, a pigeon-infested ledge, etc.), it’s better to wear a mask and gloves.
Otherwise, bird droppings are pretty innocuous, although you’ll certainly want to wash them off, then clean your hands, when any land on you. Of course, being splattered with bird feces is supposed to bring good luck! So when it happens, maybe you should get out and back that lotto ticket!
Also, droppings often contain viable seeds. In fact, some seeds won’t germinate readily until they have passed through a bird’s digestive system, as this frees them from germination inhibitors. Thus, birds play a very important role in the distribution of plants in the wild. However, sometimes the plants thus distributed turn out to be weeds, so some monitoring is necessary.
Under a bird feeder, you often notice the original plants dying back, but this is generally more related to the accumulation of seed hulls, some of which, like those of sunflowers, are allelopathic (toxic to other plants) than to the presence of droppings. Regular cleaning can help alleviate this problem. Or install a seed catcher under the feeder.
If you have an abundant source of bird droppings (if you keep cage birds or have a chicken coop, for example), ideally you shouldn’t apply them directly to garden plants, as they’re probably too concentrated and could damage plant tissues. Instead, add the nitrogen-rich manure to your backyard composter, mixing them with carbon-rich brown materials. Not only does this dilute the minerals, but the droppings help the brown materials decompose more rapidly. And you end up with a particularly rich compost. Again, gloves and a mask should be worn whenever you directly handle bird droppings.
Bird poop: it’s here, it’s there, it’s pretty much everywhere… and that’s a good thing!
In the Pacific Northwest, birds who eat the salmon that die after spawning deliver microdoses of magnesium to the forests above the rivers where the salmon live. The soil is otherwise deficient of magnesium and other micronutrients. The forest appreciates what the birds do for it.