The Daily Bucket is a nature refuge.
We amicably discuss animals, weather, climate, soil, plants, waters and note life’s patterns.
We invite you to note what you are seeing around you in your own part of the world, and to share your observations in the comments below.
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March 30, 2020
Salish Sea, PNW
Birds are pairing up these days. There are all sorts of ways they show that, and their dedication to mating success. Some hang out together foraging or resting, evidently reaffirming old or new partnerships. Others demonstrate overtly with gifts, as it appeared one crow was doing the other day.
There’s a good size flock of Northwestern crows that comes and goes as a group on my nearby beaches. Mostly they are hunting or scavenging for food, sometimes loitering around gulls and oystercatchers watching for leftovers. They are especially busy foraging when the tide is low. As crows, they are omnivorous, but these live only along the shoreline so much of their food becomes exposed as the beaches do. Their other common name is Beach Crow.
What drew my attention this time wasn’t that a crow had dug up a clam — they do that frequently. But this time it called another crow over and offered it the clam. That’s unusual. While they socialize readily, they generally feed independently.
Ordinarily crows aren’t so generous, although begging babies will elicit food. But we’re not into that season yet. The clam digger stood there as the other crow took the clam off to crack it open.
It took several tries. Crows use the same maneuver as gulls: fly up and drop a clam onto a hard surface to crack the shells. Unlike gulls though who fly up 10-15 feet, crows only drop a clam from a few feet. Otherwise it’s likely to get snagged by a sharp-eyed flockmember.
On the third or fourth try, the clam broke open and the crow hauled it off to a nearby dock to eat. This short video clip gives a sense of the maneuver.
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The crow ate most of the clam, although shortly a second crow appeared, and then a third. Between them every shred of clam flesh was finished off in a few minutes.
Then two of the crows perched on a railing, close together. I can’t identify exactly which crow is perched with the clam-breaker, but it’s likely the original clam-digger along with the clam-breaker. They were clearly a pair, separate from the other crows in the vicinity, and talking to each other quietly. Beach crows have long term mating relationships, according to Birds of North America. birdsoftheworld.org/...
What we’re likely looking at is a behavior known as “courtship feeding”, a subcategory of mate-feeding. In many bird species, the male of the pair offers food to the female.
From the study Mate-feeding has evolved as a compensatory energetic strategy that affects breeding success in birds:
In many animals, females are fed by males during courtship or incubation (mate-feeding). According to the mate appraisal hypothesis, females may evaluate the parental capacity of males, whereas the pair bond hypothesis suggests that feeding may strengthen the pair bonds with them. Following the nutrition hypothesis, by contrast, females obtain direct nutritional benefits from being fed by males during periods of high-energy expenditure, such as egg formation and incubation.
We tested predictions from these hypotheses in a dataset of 170 species of passerine birds. As predicted by the nutrition hypothesis, we found that mate-feeding has evolved more often in species in which the female incubates and builds the nest alone and have noncarnivorous diets. This suggests that mate-feeding is a behavioral strategy that compensates for nutritional limitations of females during breeding, as both incubation and nest building are energetically costly processes, and noncarnivorous diets are deficient in proteins.
In Northwestern crows, both parents build the nest but the female does all the incubating of their 4 eggs. He brings her food while she incubates. After the eggs hatch, the female mostly remains in the nest with the nestlings, though she leaves for longer intervals as they grow. The male brings food for the nestlings but the female must leave the nest briefly to drink, defecate and to find food for herself.
Raising babies is the most important task of the year for birds. Laying eggs and incubating and protecting the babies requires a big seasonal energy expenditure for the female of the pair. We might consider these her gifts. The male’s contributing toward her food during courtship is a gift of his.
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Sunny today in the PNW. Drying out but warming up here in the PacificNorthwest.
What’s up in nature in your area today?
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