A house full of kids always keeps parents very busy, especially if they are a hunter-gatherer family with no supermarket let alone a convenience store nearby.
This week, I encountered exactly that type of family – a family of Mountain Bluebirds, west of Lake Henrys.
Dad was sitting on a nearby fence post with a large caterpillar hanging from his mouth as I pulled up. Just as I started photographing him, a flying insect flew past him and I saw his eyes follow him. I thought I heard him thinking in passing, “a ticket full of soft food is better than chasing a crusty bug that’s mostly wings and skinny legs.” Seconds later, mom emerged from the entrance hole of the family home and nailed the spindly insect, returning to the nest as the baby birds begged for more food.
Dad patiently stayed on the post while the female went inside then came out with a dirty diaper, flew across the road and dropped her on top of a fence post. This was the first time I noticed that most of the fence posts 100 feet from the nest had several dirty layers while the posts near the nest were clean. Each parent would wait on one of the clean posts while waiting for the other parent to emerge from the nest.
As I watched the nest for over an hour, the male seemed to be attracted to “big bugs” as he brought in a June bug, two grasshoppers and three caterpillars. Before delivering them to the children, he should kill them by removing their heads. The grasshoppers were difficult to eliminate as they fought with their legs grabbing the bird’s feathers. Maybe the big bugs were meant to impress the kids, but I noticed every now and then he needed to pull out the leftovers, like the wings and legs of his big offerings.
The female seemed content with small offerings. Several times she captured flying insects, but mostly she delivered what appeared to be some kind of eggs, possibly large ant eggs. She delivered three or four in each delivery, arranged in a row on most visits to the nest.
Mountain bluebirds are cavity nesters and are among the species whose young produce their poop in faecal sacs. When a parent has entered the nest box, the young turn their backs on the adult who has grabbed the waste and walked outside to deposit it in a storage area. This usually happened after every second or third food delivery.
Each time the female removed a poo bag, she held it carefully and placed it on a post while the male usually leaked before dropping it. As a result, he would then land on a barbed wire and try to clean up the dripping guano.
Some species of birds, not these bluebirds, practice “coprophagia”, which means the adults will eat the poo sacs. Scientists believe that the digestive system of young baby birds is not well developed, leaving energy and nutrients in waste. They also believe that removing the droppings keeps the house clean and does not attract predators to the nest.
I was amazed at how busy these two parents were during the time I observed them. I learned a lot about them and enjoyed the show and hope to watch them until the baby birds take flight.