Yellow-bellied Sapsuckers make holes in trees (as do other sapsuckers) to get at the sap, and other birds drink from them - (See: 'Why a Sapsucker may be a Hummingbird's Best friend'). Artificial hummingbird feeders and sapsucker holes help the Ruby-throated Hummingbird (and other hummingbirds) live in Canada.
Sapsuckers
The Yellow-bellied Sapsucker (Sphyrapicus varius) flies south in the autumn to places like Mexico and the West Indies.
In the spring they fly back north as far as Canada and Alaska to breed.
Male birds arrive first to choose territory and begin hollowing out a nest cavity in a tree trunk.
As breeding gets underway both males and females step up their 'sap-sucking' activities.
Drilling Holes to Suck Sap
Yellow-bellied Sapsuckers drill horizontal rows of holes into selected trees and drink the sap (from the 'phloem' coming down the tree and rich in nutrients).
The sap soon begins to block these holes from above, so the birds then drill another row of holes a little way above the first. This goes on until trees can be riddled with holes forming a regular grid, with the newest holes in the top row (see image below).
Sapsuckers are similar to all woodpeckers in that they eat insects they find in the trees – but sapsuckers like theirs to be soaked in tasty sap.
Ruby-throated Hummingbirds
At the northern end of their range (in parts of Canada) there are insufficient nectar-bearing flowers to allow Ruby-throated Hummingbirds (Archilochus colubris) to breed successfully every year. Sapsuckers come to their aid by providing an alternative food source – the hummingbirds visit sapsucker holes.
Many animals and birds (and other animals) take advantage of the sapsuckers' drilling activities, but it seems to be a crucial factor in Ruby-throated Hummingbird survival in the far north of their range. Their arrival in the north coincides with peak sapsucker activity.
Humans have also recently entered this relationship by hanging out hummingbird feeders filled with syrupy liquid (a 4:1 water:sugar solution). The birds benefit from the extra food source, and the humans get a good close look at the beautiful birds.
Birds and Humans Influencing Hummingbird Breeding Range
When sapsuckers developed the habit of drilling holes in trees to drink sap (and eat the insects that are attracted to it) is not known, but it must have been very long ago because they are thought to have developed a phloem anti-coagulent in their saliva – other holes drilled in trees block much quicker than those made by sapsuckers.
Once the sapsuckers had perfected the trick the way was open for the hummingbirds to follow them north. Much more recently humans have joined the party, and by providing syrups in hummingbird feeders humans are helping hummingbirds keep their foothold in the north.
This story is a very good illustration of the reason why it is important to consider many animal interactions if behaviour and distribution are to be understood. 'Interaction Webs' take into account the ways in which all the animals and plants in an ecosystem affect one another, and goes much further than simply looking at who eats who.
Source:
- 'The Master Sap Tapper', Mary Deinlein, Smithsonian National Zoo, 2003.
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