Saturday, June 14, 2014

Heavy Metal Drummer

Red-bellied woodpecker - Wikimedia
Every spring we watch the red-bellied woodpecker drum on the metal birdfeeder before chowing down.  The rhythm is different than the intermittent methodical pecking when they dig into a tree for insects or cavity building.  We hear drumming identical to the bursts we hear around the valley on hollow trees but the metal creates a much sharper sound.  Watch this video of the woodpecker pair, before reading on.

Why do woodpeckers drum on a metal box?  It is all about territory.  Their rhythm can be distinctive for their species, saying "I am male, big and strong so stay out of my territory."  It also serves to attract a female although the sexual attraction of a male beating its head against a metal surface is a turn-on that escapes me.
Female red-bellied-Wikimedia
We also get to see them transporting food to another bird.  The male will fly to a distant tree and deposit it on the branch next to the other bird, even occasionally making a beak to beak transfer.  I wondered if some of this might be so called courtship feeding, a.k.a. mate-feeding.  Also known as a nuptial gift, this is seen in animals as diverse as insects, spiders and mammals.  This is commonly seen in cardinals and bluebirds but Charlie Burwick gave me the answer.
"Really interesting thing about red-bellied woodpeckers. The female hatches the chick, and the male, as you are watching, is feeding the young chick after it has fledged. This is common behavior among woodpeckers."
Reviewing the video I can see that this is a rather drab chick with no red like an adult female.  By now the juvenile is flying and able to run up and down a tree like an adult.  It either can't get its own food or chooses to wait and be fed.  Any of you parents can relate to this behavior.

Feeding a juvenile - Bron Praslicka
To us sentimental humans the idea a "courtship feeding" is an "Aww, isn't that sweet," moment but before we get too mushy, look at the evidence.  A rather soberly titled study,  Mate-feeding has evolved as a compensatory energetic strategy that affects breeding success in birds, published in 2011 in Behavioral Ecology tends to shift the emphasis from romance to survival.  Their findings from studying 170 species of passerine birds:
  •  "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"
  • "Incubation feeding has evolved more often in species that place nests at elevated sites, suggesting that these species face low predation risk that allows males to feed females. In the particular case of incubation feeding, we found that species that have evolved this behavior produce larger clutch size and have higher hatching success."
So rather than a romantic come-on, mate-feeding is more like bringing in carryout dinner for her after a hard day with nest building or child care.  I too found this to be a good nesting strategy during our child rearing years.

In the video you can see the adult male getting seed from the feeders, then storing some in the bark of trees and delivering others to a rather drab appearing juvenile high in a distant dead tree branch.  Now that you know what is going on, feel free to watch the video again to catch the quick beak-to-beak feeding.

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