[obol] Odd (to us) BY Bird Behavior

[Dan Gleason]

Kat,

> We've seen some things lately that seem rather odd to
> us...
I'll take a guess at offering an explanation for some of these  
behaviors.

> Anna's hummingbird appeared to lick the suet block.
I suspect that if you looked closely at the suet, you might find  
small insects, spiders or mites that have been attracted to the suet.  
If the suet basket is hanging from a post in the ground, small ants  
will frequently be attracted, climbing the post to reach the suet. If  
the suet was soft enough for the hummingbird to actually feed on,  
then you should probably take it down until the weather cools. Suet  
that is soft and semi-liquid from the heat can pose some risk to the  
birds. It can adhere to feathers around the face causing problems.  
Apparently, there has been some evidence that softened suet can lead  
to some loss of feathers in the nostrils of Downy Woodpeckers. I  
don't know how big of a problem this is but it is best not to take a  
chance. Also, in hot weather, suet may turn rancid.

Like other birds, hummingbirds do utilize fats as a fuel. This is  
especially important during cool evenings when the air temperature  
drops and burning fat helps sustain the bird. Ruby-throated  
Hummingbirds in the east nearly double their weight prior to  
migration by adding fat. However, in each case, the fat is not eaten  
but produced by the bird from the sugars that it feeds upon. You will  
often notice that hummingbirds make many visits to a feeder at dusk  
to help attain the needed fuel to survive the night. I can't think of  
any account where hummingbirds were observed actually eating fat.

> Flickers and Downy's are coming to, and eating from
> tube feeders. (black oil seed)
Watch their behavior at the feeders. Most often they are not eating  
the sunflower seeds but poking through it in search of moths, beetles  
or other insects that are attracted to the seed or have infected your  
batch of seed. Sometimes, there are bad lots of seed that are  
infected with insects who laid eggs in the seed (or as the seed was  
developing on the plant) and the larvae are feeding on the dried  
endosperm of the seed within the hard seed coat. If you open these  
seeds, you will either find the larvae still within or the dust-like  
remnants of the seed it fed upon while growing.

Small seeds may occasionally be eaten by some woodpeckers but most  
often, the plant materials that they eat are berries and other small  
fruits. Poison-oak berries are sometimes eaten by Downy Woodpeckers  
and Pileated Woodpeckers eat dogwood berries, for example.

> House Finches are all eating the red hot poker
> blossoms. Our poker plants are trashed, while the
> neighbor's plants are in great shape. The Downy's have
> also been all over the pokers. (nectar?)
>

I'm not sure what to tell you about the House Finches here unless  
they are finding seeds of some kind on the plants. Poker plants have  
tubular flowers and are attractive to some insects for the nectar or  
simply as temporary shelter. Downy's might be after the nectar but  
more likely, they are after whatever insects the plants harbor. That  
they are after insects is even more probable given that your  
neighbor's plants remain untouched. If it was the plants that were  
the attractant, your neighbor's would be equally desirable.

> Finches have been trashing my spinach crop. There are
> little snippy bird beak bites out of all the outer
> leaves.
This one, I don't have a good answer for. House Finches are strictly  
vegetarians but leaves are not part of their diet. Oil-rich seeds are  
mostly what they seek. Coarse, leafy vegetation is very high in  
cellulose and cellulose is very difficult to digest. Vertebrates  
can't digest it directly and rely on the action of bacteria in their  
gut to do this work. Even so, the plant tissue must be very well  
macerated for the bacteria to get at the cellulose molecule.  
Mammalian ruminants continually regurgitate and re-chew their food  
for long periods of time. Birds need to keep their weight to a  
minimum and can't afford to have the time or excess weight that  
digesting vegetation requires. The Hoatzin of South America is one of  
the few exceptions and does eat leafy vegetation. Its crop is large  
and very muscular and begins to grind the food before it reaches the  
stomach (which is somewhat reduced from that of other birds). As in  
mammals, the digestion of cellulose is a slow process and done  
strictly by bacteria within the digestive system of the Hoatzin.

Geese eat grasses, but mostly they are eating the young grass shoots  
that have not yet developed thick ridges that are heavy in cellulose.  
These softer leaves are easier to mechanically macerate. Also, if you  
watch geese in action, you will see that while they are rapidly  
taking in food at one end, they are also constantly leaving deposits  
from the other end. They eat a lot but digest little. The constant  
eating is compensation for the fact that they do a rather poor job of  
digesting the plants. Much nutritional value remains in their  
droppings but rather than carry this around, as the Hoatzin does,  
they simply get what they can, pass it along and continue taking in  
more food.

(Have I evaded the question long enough?) Basically, I have no answer  
for House Finches eating spinach or any other leaves. One other  
thought does occur to me, however. Is there anything sweet that drips  
on the leaves? An overhanging hummingbird feeder or a plant that  
exudes a sweet, sticky liquid that would adhere to the spinach  
leaves? If so, this could possibly attract the finches. There has  
been some experimental work in the past looking at which types of  
sugars House Finches prefer (answer: 6-carbon sugars over complex  
sugars like sucrose) but this was a manipulated series of experiments  
and made no conclusions about whether sugars would attract finches  
over other foods such as seeds.

Dan Gleason
-------------
Dan Gleason
dan-gleason at comcast.net
541 345-0450



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