TOOL USE (?) IN THE YELLOW-BELLIED SAPSUCKER
SABAL PALMETTO FRUIT EXPLOITED FOR FOOD BY YELLOW BELLIED SAPSUCKER.
FRUIT WEDGED IN TREE TRUNK DEPRESSIONS
St. Augustine, Florida
January 15, 2019
A “tool” in regard to animal behavior has been defined as:
“The use of physical objects other than the animal’s own body or appendages as a means to extend the physical influence realized by the animal. ” (See: Janes and Kamil 1973)
Many animals have been observed to use tools—i.e. some physical object other than its own body which is employed to achieve or improve its ability to advantageously exploit its surroundings— (this author’s definition). Tool use has been described in mammals, birds, fish and even cephalopods. Ravens, Crows and rooks are well-known to actually create tools out of twigs and wood splinters used as probes and skewers employed to impale insect larvae which would normally be beyond their ability to reach within tunnels in rotting wood. But as far as I know, there has been no report of tool-use observed in the Yellow-belied Sapsucker (Sphyrapicus varius)
The Sapsucker, which is about robin-sized, feeds (as its name suggests) by excavating small holes in the bark of trees to generate sap flow. It returns to these excavations to feed on the weeping sap and the insects which are attracted to the sweet fluid. The bird exploits trees of many different species (Birch, Apple, Spruce , Hemlock, etc. ) upon which it excavates nearly horizontal and closely spaced lines of small holes. Sometimes the holes are so numerous they cut off so much sap-flow that they kill main branches or the tree itself (i.e. girdle a tree). This species is native to North America where it nests in the northern reaches of the USA, Canada and Alaska and winters in the southern states, as far south as southern Florida and Texas. Many individuals range down into South America and the Caribbean as well.
This author observed the feeding behavior of a male Yellow-bellied Sapsucker (Sphyrapicus varius) ( it had a red throat) in northern Florida during the winter of 2008. This specimen used s small borehole in the trunk of a Sabal palmetto to secure a palm berry and facilitate removal of the flesh of the berry.
About mid-day, a male Yellow-bellied Sapsucker was observed feeding on the berries of a mature Cabbage Palm (Sabal palmetto). The smooth-trunked palm—its “boots” had fallen away up to the base of the fronds—was located in an open area alongside of a public tennis court in St. Augustine, Florida. The Sapsucker was observed to be using an unusual and interesting feeding method. This author observed the bird pluck a palm-berry from the fruit-bearing flower panicle located among the spreading upper fronds of the tree. It firmly wedged the berry into an excavated hole in the woody palm tree trunk. It then proceeded to remove and ingest the thick sweet mesocarp (flesh) .
The “Cabbage Palm” or palmetto, a monocot of the Order Arecales, is a salt-tolerant species native to the coast of North America and ranging from south-eastern North Carolina, south through Florida and then west along the Gulf Coast to Texas. It is known for its edible “heart of palm” and its edible berries. The dark blue-black nutritious berries of S. palmetto are small, pea-sized, (about @ 6 mm to 10mm in diameter). The fruit has a thin skin (epicarp) and a sweet, dark-colored, edible (mesocarp) which encases a relatively large, (4mm to 8mm) hard inner pit or seed. The ratio of fleshy fruit to the hard inedible seed is low. In the winter months in Florida the S. palmetto berries have dehydrated considerably as a result of exposure to sun and wind and the epicarp or skin is often dry and papery, while the mesocarp or flesh part of the fruit for the same reason is thickened by dehydration, into a viscous, sticky and gummy mass which adheres closely to the pit or seed.
The berry of the Palmetto is known to be rich in sugar and nutrients. Zona, S. (1990) summarizes reports on the consumption of Sabal berries by both birds and mammals in a section of the report focusing on the fruit as a means of seed dispersal of this palm genus. The author (See Zona, S 1990)*, reports that the Northern Mockingbird (Mimus polyglottus), Robin (Turdus migratorius), Yellow-rumped warbler (Dendroica coronata), Fish Crow (Corvus ossifragus), and Piliated Woodpecker( Dycopus piliatus) are known to feed on Sabal fruits”. The author cites: Marin, Zim and Nelson (1951). In adddition to these species other authors (Zona 1990 cites: Cruickshank (1950)) report the Ring-billed gull (Laras delawariensis), Long-tailed grackle (Quiscalus mexicanus), Mexican Jay (?) Aphelicoma coerulean. (?ultramarina), Northern Cardinal (Cardinalis cardinalis) , and the Blue Jay (Cyanocitta cristata) and others have been observed to exploit the dark blue-black fruit of the genus Sabal. In the wilds of Florida the palmetto berry is also widely reported to be consumed by the Wild Turkey, Black Bear, and Raccoon. There is no mention of the Yellow-bellied sapsucker in these citations.
*(Zona, S. 1990, Vol 12, #4: page 613:)
The Yellow-bellied Sapsucker specimen of this report was observed flitting among the top fronds of the 25 foot (@ 8 meter) tree where several dried floral panicle sprays still bearing the dark-blue-black palm berries remained attached to the flower spadix from the tree’s last seasonal flowering . The Sapsucker plucked a berry from the branched spadix with its beak and then with the berry visible to this observer in its beak, it quickly flew down to the trunk of the tree where several small circular holes were visible. It used its beak to poke the berry into one of the small depressions in which the berry fit snugly. The woodpecker, perched below the now filled hole in typical woodpecker fashion, i.e. with feet gripping the palm trunk and its tail wedged into the trunk’s rough surface. It then proceeded to feed on the berry, pecking off small bits of the gummy bluish flesh which it apparently ingested. When finished, it repeated this same feeding method several times, removing the seed and refilling the hole as it ingested the flesh of several berries.
After it departed, I tried to examine the depression where the bird fed. It was too high above the ground, perhaps 18 feet (6 meters) for direct inspection, but from the ground I could see well enough with my binoculars to estimate that the depression was less than a half inch (@ 1 cm) wide and seemed to be excavated in the form of an inverted cone, decreasing in diameter toward the center of the tree. The sides were stained dark blue. Several other depressions and holes were noted on the same tree. These had no evidence of recent use. I did not observe the Sapsucker actually excavating the depressions, though that appeared to be likely.
Upon close inspection of the berries, which littered the ground below the tree, it is apparent that the fruit has at its center a very hard and large pit which may make it less desirable for a small bird such as the Sapsucker to ingest whole. The dark blue flesh is a tough, thin mesocarp of perhaps only several millimeters thick, coating the large seed. The Sapsucker is a winter visitor and the berries at this time of the year likely remain very nourishing but the dehydrated winter-seaon flesh is gummy, and difficult to remove from the pit.
The Sapsucker seems to have solved the problem of effectively exploiting the nutritious flesh of this large-seeded berry by seemingly pecking out small depressions (or using naturally formed holes) in the Sabal palm’s tree trunk. These small depressions provide the means of holding the berry firmly in place—as a carpenter would place his work in a bench vise— while the woodpecker pecks away at the berry to remove and ingest the nutritious but thin, sticky mesocarp which coats the pit.
Reference:
Zora, Scott, 1990
A monograph of Sabal, Aliso, 12(4) 1990, pp 583-666
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