We love fat!

Yesterday’s climatic drama here in MN included thunder and lightning (in the winter!), rain, freezing rain, sleet, snow, and then bright sunshine for 5 minutes before more gray drizzle.  There was also a lot of wind, making outdoor activity quite uncomfortable.  The birds visited the feeders frantically early in the morning, perhaps in anticipation of the weather drama soon to hit them. It was entertaining to watch the woodpeckers scramble for access to the suet feeder — I usually never see all four resident species within the space of 10 minutes.

Mr. Yellow-shafted Flicker was first and dominated for a few minutes until he was completely sated and went and sat in a tree to digest his heavy meal.

So full of fat now — that’s about 100 calories per gram of suet eaten, and this guy ate a lot!

Mrs. Hairy Woodpecker fed noisily, chipping continuously as she warned others to stay away until she had her fill.

However, Mrs. Red-bellied Woodpecker was not to be denied access and finally drove Mrs. Hairy off. She vigorously attacked the suet, drilling multiple holes in the block.

Finally when everyone else was satisfied, Mr. Downy Woodpecker got his chance, and spent a few minutes cramming big chunks down his gullet.

You’ve probably noticed the order of my suet visitors seemed to be organized by size, and it certainly seems to be the case that smaller birds do yield to larger-bodied ones when both want the same resource.

But the intensity of the feeding activity observed made me wonder if precipitation that day was more of driving force, or was it the drop in temperature??  Do all birds respond the same way to these two climate variables?  Well, it turns out that someone else was interested in these questions, using the data generated by Project Feeder Watch collected from backyard feeders in the northeastern U.S. by the folks at the Cornell Lab of Ornithology.  And some of the results were a little surprising, summarized in the graph below.

Gray bars next to the species name indicate the extent to which birds might increase their feeder activity in response to decreased temperature. Black bars indicate the feeder activity response to increased precipitation.  Obviously, not all species respond the same way!

According to the authors’ findings, Yellow-bellied Sapsuckers showed the greatest probability of increased feeder activity with decreased temperatures, but the diminutive Downy Woodpecker’s feeding activity did not change with temperature — probably because they are such regular visitors every day anyway.

Red-bellied Woodpeckers are more responsive to temperature changes than Hairy Woodpeckers, even though the two species are very similar in size, and presumably in their daily energy needs.  So, perhaps this reflects differences in the two species’ reliance on backyard feeders for their total food intake?

House Finches and Cardinals are more likely to be seen at feeders when there is marked precipitation, but the House Finches, like Downy Woodpeckers don’t seem to care if it’s colder — just wetter.

It’s amazing what one can learn from observing birds at a feeder.  Do these results jive with what you’ve seen at your bird feeders?

Brrrr…., it’s cold!

A week of subzero temperatures, and then strong winds and blizzard conditions brought lots of hungry birds to the feeder this morning.  I was pleased to see the Yellow-bellied Sapsucker back at the suet feeder.

Even though this bird has twice the body mass of a Downy Woodpecker, it seems less tolerant of the extreme cold than the smaller Downy.  The sapsucker seems less active than the Downys do, spends more time sitting either perched or feeding, and erects its plumage until it resembles a feathered ball of fluff, while Downy Woodpeckers maintain their sleek contour even on extremely cold days.

And this nicely excavated hole is a great place to get away from the bitter cold and wind chill.

The map of Yellow-bellied Sapsucker winter range shows most birds spending their time no further north than central Kansas, Missouri, Illinois, and Indiana, not the Arctic north of Minnesota in the winter.  So perhaps they are actually not as well insulated or as capable of revving up their internal metabolic furnace as the resident Downy Woodpeckers are.

After this little Sapsucker finished probing all the holes full of peanut butter suet, it flew over to the Buckeye tree to huddle up against the bark and gain some protection from the wind.

Doesn’t this photo say — “I’m so cold!”
(I took the photo through the window and had to cut out the distortion from the glass.)

Do you think the bird could get those feathers any more fluffed out? Brrr…., it’s cold out here!

 

Woodpecker delight

After 10 days of fog so thick I couldn’t see the neighbor’s house across the street in the morning, we have a partially sunny morning at last.  That, and temperatures hovering at 0 F brought the woodpeckers into the backyard suet feeders all at once. In the space of about five minutes, four woodpecker species snacked on the peanut-enriched suet in my new feeders.

The diminutive Downy Woodpeckers are frequent visitors to the suet.

Mrs. Downy was quickly chased away by a much larger Hairy Woodpecker — this one a male, indicated by the red on the back of his head.  The Hairy Woodpeckers don’t seem to like suet feeders as much as the rest of the birds do in my backyard.

Mr. Red-bellied Woodpecker never can decide which hole provides the best tasting suet. He tries several each feeding bout.

And over on the other side of the yard, a Northern Flicker male pounds away at the peanut suet in a natural log feeder.

I have learned that all suet is not the same — woodpeckers really delight in the peanut variety, over just fat and bird seed pressed together.  They also seem to prefer logs over cakes, whether because they like the idea of drilling in a hole, or because the log variety of suet just tastes better.  So this is what I buy for them now.

It costs a little more than regular suet, doesn’t melt in the summer, and can easily be molded and pressed into the holes in the feeder logs.

I found I could save quite a bit on buying suet feeders by just converting appropriate sized logs from tree branch clean-up into log feeders.  My husband drilled the 1 inch holes with his largest drill bit, fastened an eye-bolt into the top of the log, and voila — log feeder ready for filling.  Plus, with the rough surface of the log easier to cling to, no additional grooves need to be cut into its surface. Chickadees, nuthatches, woodpeckers, and even Blue Jays visit these log feeders often.

The woodpecker and the weevil

It’s unusual to see Downy Woodpeckers foraging on herbaceous plants in the middle of a prairie landscape, even if the flower stalks do reach 5-6 feet tall.  But the mature seed pods of Common Mullein may harbor a feast of insect larvae that Downy Woodpeckers have learned to harvest.

This Downy female spent quite a long time exploring every bit of all the Common Mullein flower stalks on a small patch of prairie. She worked around the bottom half of the flower stalks, then flew to the next stalk to start another search.

Common Mullein is a fuzzy-leaved biennial weed, introduced from Europe.  During its first year of growth, it produces a large rosette of furry leaves, followed by one to several tall spikes of small yellow flowers the following year.

Only a few small, yellow flowers open each day (and they last just one day), but the woodpecker isn’t interested in insects on the flowers.

Mullein is famous for its seed production — putting out as many as 175,000 seeds per plant.  But the woodpecker isn’t interested in eating the Mullein seed either.  But that much seed in one place becomes highly attractive to insects, like Mullein Weevils, whose larvae specialize in devouring mullein seeds.

Each of the knobby seed capsules that surround the flower stalk harbors as many as 500-600 seeds. A weevil larva develops inside one seed capsule where it consumes 100% of the developing seeds, and finally pupates there. 

The lower and middle thirds of the Mullein flower stalk seem to suffer the heaviest infestation of weevil larvae, with the top being relatively weevil free.  In all, weevils destroy/consume about 50% of the mullein seeds, which still leaves a lot of seed production from just one plant (~80,000!).  But without this semi-effective control of mullein seed production, that species would be a lot more invasive.

Then as seeds are maturing, along come Downy Woodpeckers who probe the seed capsules for larvae and pupae, thus keeping the weevil population in check. A nice system of biological control at a couple of different levels.

Nesting

Nest construction seems to be in full swing now that the snow has melted and the temperature seems to stay above freezing (but barely).  On our walk through the flooded cottonwood and silver maple forest at Roberts Bird Sanctuary in Minneapolis, we saw several birds hard at work readying their abodes.

This downy woodpecker male dug out this perfectly round hole and was busy removing wood from the interior. He was still working on it when we walked by him 20 minutes later.  I’m pretty sure I couldn’t make a hole this round and perfectly smooth in a tree given a hammer and chisel.  I wonder how the woodpeckers do it?

He’s really getting into his work, getting it ready for inspection by Mrs. Downy.  It looks like a bit of a tight squeeze there.  You would think going in and out of this tiny hole so frequently would damage their feathers.

Robins build their nests in a variety of places: bushes, eaves, under decks, but this one chose a fork in a cottonwood tree about 40 feet up, where it is fairly visible and probably won’t be obscured by tree leaves.   Not a great site when it  comes to protecting nestlings from predators.

This Canada Goose has added sticks, cattail heads, and a few other random objects to her nest which is just barely above the water.

Next the goose plucks some down from beneath its breast feathers to line the nest. It can’t be very comfortable resting for hours on sharp, pointed sticks.

Settling in for the duration.  I couldn’t really see if there were actually eggs in the nest, but why else would she sit there?

Eat to stay warm

On these intensely cold days, the birds hit the feeders before sunrise to replenish their energy for the day.  I found this cardinal digging around at the base of one of the feeders and realized it must be mostly empty.

A bunch of sunflower seeds had piled up underneath the feeder, and I assume the cardinal dug through the snow to find them.  Smart bird!

Sub-zero temperatures make the suet cakes concrete-hard so that the woodpeckers have to drill them to get a bite.

“This stuff is as harder than tree bark at -12F.”  Red-bellied Woodpecker

Peanut butter suet seems more attractive to the Downy Woodpecker and easier to extract.

Animals convert their daily food intake to fat stores, which are then metabolized overnight at a prodigious rate.  Black-capped Chickadees, for example, can turn-over 25% of their body weight overnight on a very cold night.

But energy costs (metabolic rate on the Y-axis below) go up as the temperatures go down (on the X-axis below), and the smaller the animal, the higher that rate of fuel consumption and energy burn, as shown in the graph below.

Avian Energy Balance and Thermoregulation (http://people.eku.edu/ritchisong/birdmetabolism.html)

At some point, there is a limit to how much heat a small animal like a Downy Woodpecker can produce in order to stay warm, and still make it through the night revving its furnace to that high level.  A friend of mine found that 80% of the Downy Woodpeckers they tested in the winter in South Dakota became hypothermic (3-5 degrees below normal) after 30 min exposure to 5F, which leads me to wonder how these birds are faring at our current below 0F temperatures.

More than one way to find a meal

You get a different view of what might be hidden beneath loose bark on a stem or branch by looking at it from all sides, as Downy Woodpeckers often demonstrate.

Downy Woodpeckers work their way around the circumference of a branch or stem, but usually remain in a head up position.  Their four toes, pointed two front and two back, and stiff tail feathers help them keep a grip on the surface.

Now, looking at it from the top side…not fighting gravity.

A White-breasted Nuthatch might explore the same branch, but uses a different technique and gets a different view.

A specialized and elongated first toe of the Nuthatch can swivel to the side or back and helps them cling to the tree in a head-down, upside down posture.

Woodpeckers typically explore the convoluted landscape of tree bark from the head-up perspective, which allows the bird to see small food items beneath the top section of bark.  But what little critters might be hiding on the bottom of that same section?  Head-up foragers would miss it, because they can’t see beneath the bottom overhang.  But Nuthatches foraging in a head-down position can exploit this overlooked resource.

Another good example of how competition for food can produce specialized (and different) foraging techniques.

Sunbathing

Believe it or not, sunbathing is an essential behavior for birds.  Not only do birds spread their feathers and bask in sunlight to warm themselves passively (e.g., vultures) or dry their feathers after swimming (e.g., anhingas and cormorants), but they sunbathe for their health.

This juvenile Downy Woodpecker found a bright sunny spot in the forest to take a sunbath. Juveniles are recognized by their red cap, unlike the adult male which sports just a red spot on the back of its head and the adult female which has no red on its head.

Find a nice sheltered spot, protected from predators and wind, spread out those feathers and expose the skin and oil gland at the base of the tail to the direct rays of the sun.  Sunlight helps convert inactive Vitamin D to its active form in the skin (just like it does in humans), and the excess heat of direct sunlight dislodges feather parasites which are then removed by the bird by preening.

Downy Jr spent many minutes in this posture, alternating with a lot of digging through feathers on the back and sides of its body. Fledglings probably pick up a lot of ectoparasites (on skin and feathers) in their crowded tree nest hole.  

And beyond the general health value of sunlight, it just feels good to sit in the sun and think about what to do next.

Sated!

Falling asleep after a big meal is commonplace among us humans that over-indulge on festive occasions like Thanksgiving.  But I have never seen it happen to a bird until I saw this Downy Woodpecker male fall asleep at a suet feeder.  Here is the sequence of action I observed the other day.

“Oh boy, a nice meal of fat to start the day.”  Actually I have seen more birds at the suet feeder lately and I wonder if it has something to do with our up and down “spring” weather.  

There was much pecking and gobbling of suet for a few minutes.

Then, a long pause in the feeding activity.  Feeling a little full?  The woodpecker’s third eyelid (nictatating membrane) is closed over its eyes. The neck is contracted and the bird seems to be hunching down on its legs.

Feeling really sleepy — too much fat intake at one time?  The posture is really relaxed in this last frame.

Why does food, especially food high in fat, make us (and animals) lethargic?  Some say it is the chemicals in the food itself (e.g., the tryptophan in the turkey), and others believe it is the chemicals that the body releases as the food is ingested (e.g., hormones that communicate from the gut to the brain telling it what has been eaten and how much).  Either way, the signal the brain receives (indicating satiation) causes a dramatic change in behavior to cease eating and relax.

There is a good reason to relax after a full meal, allowing more blood flow to the gut to absorb the ingested nutrients.  It’s the old law of supply and demand.  The limited volume of blood needs to go where the demand is highest — in this case, the gut.

But…small birds that go to sleep in plain sight of the abundant natural predators are going to be dead ones, so this is kind of unexpected behavior.  Lucky for this bird there weren’t any Cooper’s or Sharp-shinned Hawks in the neighborhood.

Small, medium, and really big — Woodpeckers

Three species of woodpeckers at the suet feeders in one day!

I managed to trim the photos of the Downy and Hairy Woodpeckers to the same relative magnification using the suet feeder as a guide, so you can see the size difference between them. (Click on the image below for max resolution)

Downy Woodpeckers (left) weigh 20-30 grams and are 5-7 inches long, while Hairy Woodpeckers (right) weigh 40-90 grams and are 7-10 inches long.  These particular birds are both females — there might be larger differences between males of the two species.

Downy and Hairy Woodpeckers are common and inhabit the same range over most of North America, where both species are year-round residents.  They compete for nest sites, as well as food, in mature forest, and can be aggressive toward one another.  Although they seem to have identical plumage as adults, Downy and Hairy Woodpeckers are actually not very closely related genetically.  It is thought that the two species have converged on a single black and white plumage pattern, maximizing their ability to recognize each other and defend feeding and nesting territories from each other (interspecific territoriality).

And then, there’s this guy, a handsome male Pileated Woodpecker, whose head and neck are about the same length as the little Downy.

This might be one of the pair of Pileateds I keep hearing back in the woods, but have never seen.  Our subfreezing night time temperatures have made the suet feeders quite attractive to all sorts of birds, even these mammoth wood chippers.  He doesn’t have the right body shape to utilize this tiny feeder, though.