NWA 9/30/2016

A Northwoods Almanac for 9/30 – 10/13, 2016

Sightings

Let’s start with a non-sighting: Frost! As of 9/26, we haven’t even come close to a frost (38°F is the lowest in Manitowish so far), and the long-term weather forecast suggests we won’t experience one until sometime in October. While this is great for gardeners – we’re still picking tomatoes, which is unheard of for us – the implications may not be so positive.

9/17 – Jim Swartout photographed a male American kestrel resting on the roof of a building on his property near Minocqua. His gorgeous photo clearly shows the rufous tail and back, and the mustached black-and-white facial pattern.

Given that a kestrel’s diet consists mainly of insects and small rodents, kestrels leave our area for warmer climes beginning in early September and are usually long gone by early October, wintering from northern Illinois into Central America.

9/21 – Sarah Krembs in Manitowish Waters sent this note: “After a couple weeks of wondering what was making weird sounds in the trees in our yard . . . Yesterday, we were moving the birdhouse, so I decided to clean out the chickadee nest in it. I opened the front, and I was eyeball to eyeball with two tree frogs!” She shut the birdhouse, but questioned what the frogs were doing in there.

I suspect she was visiting with two eastern gray tree frogs who are known for singing from trees and shrubs, and also for showing up around homes in odd places. They’re quite arboreal and often hang out on tree branches. They’re also known to congregate around windows, porch lights, and window wells, in swimming pool covers, potted plants, etc.

They’ll soon be burying themselves in the leaf litter to hibernate, so Sarah’s weird sounds should rapidly become a memory.

9/22 – Witch hazel came into flower in our yard. I don’t know of a later blooming shrub than witch hazel, and the flowers will last for many weeks.

9/22 – Carol Pfister on Big Crooked Lake in Lac du Flambeau sent this note: “We have an exotic bloom of freshwater jellyfish in our lake. My neighbor found it about 1 1/2 weeks ago and looked it up on line and found out what they were. They are really interesting to watch. My question is, if we have them now, will we have them every year? It says they live on zooplankton and they live on the bottom of the lake during winter. I’ve never seen them before on our lake and have some in a jar. You can catch them with your hands as they don't sting.”

Freshwater jellyfish have been seen in dozens of lakes in Wisconsin, but they are highly inconsistent from year to year for reasons that are unclear. The Yantzge River in China is considered to be the original home of these tiny jellyfish, and they’ve now spread throughout most of North America.

9/22 – Marthe and Rex Jones on Twin Island Lake observed three baby snapping turtles walking across their front step toward the lake during a light rain. They took a photo next to a Bic pen for a size comparison. Rex noted in his email, “Since we never saw evidence of a nest raid this year, we thought it possible these baby turtles came from our driveway nest site. We checked and saw a small circular hole, but no egg remnants. We were surprised by the size and precision of the hole, and by the lack of egg remnants, so we aren’t convinced the baby turtles came from this nest location. A little research indicates the incubation period of common snapping turtles is temperature dependent and ranges from nine to 18 weeks. We saw a turtle burying eggs on our driveway on June 11. The June 11 to September 22 period totals almost 15 weeks.” Which leads us to:

Snapping into Fall

Snapping turtles go to astonishing extremes to survive winter. Snappers hibernate in shallow waters by burying themselves in the mud. While some snapping turtles are still moving around at the beginning of October, they all will have moved to their hibernating areas by mid-October, about half traveling up to two-and-a-half miles to find just the right place.  

Hibernating sites have to offer access to oxygen. In lakes and ponds that freeze over, hibernating areas need to be deep enough so the water doesn’t freeze to the bottom. There are only a few favorite sites in each body of water, so many snapping turtles aggregate and hibernate literally in a pile, staying less than 6 feet away from the other turtles, and often stacked directly on top of each other. Males hibernate on top of females, so it is possible that they serve to protect the females from both predation and thickening ice. While the exact reasons for the group hibernating behavior are unclear, it unfortunately exposes them to predation by otters. At the site of a long-term study of snapping turtles in Algonquin Park, Ontario, the whole population of snapping turtles was effectively exterminated during a single winter when otters ate the defenseless turtles.

During hibernation, a snapper’s body temperature drops to about 34°F, or just above freezing. They also don’t breathe for as long as six months, though they can get oxygen by pushing their head out of the mud and allowing gas exchange to take place through the membranes of their mouth and throat, a process known as extrapulmonary respiration.

No one really knows how wintering turtles survive and why they act as they do. What is death to a turtle? For half their lives, turtles live under ice, buried in mud, not breathing, not moving, and likely living without any heart activity. In the spring, they rise to the surface, presumably take a few breaths, and swim away as turtles have done for millions of years. Spring brings many resurrections, but the rebirth of turtles may be one of the most remarkable.

Hawk Ridge Migration

A couple reports from Hawk Ridge in Duluth:

9/13: The best day for broad-winged hawks – 8,163!

9/19: “Massive morning flight of birds, especially warblers (18,680 warblers of 16 species)! We counted a total of 24,632 migrating non-raptors.” Of those, 2631 were cedar waxwings.

9/20: 15,830 migrating non-raptors crossed over the ridge, among them 1,155 American Goldfinches, 2,890 Blue Jays, and 5,075 unidentified warblers. As for the raptor migration, 1,454 sharp-shinned hawks

9/21: A good day for broad-winged hawks as 1,227 soared over the ridge.

And then just to show how important the right winds are, the count on 9/24 totaled just 1, a merlin.

Differential Migration

            I was asked recently why male hummingbirds leave before female and juvenile hummingbirds. Well, I don’t know for sure about hummers, but the situation in which all individuals of a population migrate but the distance traveled varies according to sex and/or age is known as differential migration. It’s a complicated matter, given that adults and juveniles, and females and males, may have different abilities and different needs that have to be balanced. If not calculated correctly, it can be life or death for songbirds since around 85% of their annual mortality occurs during migration. Birds need to figure out the perfect timing, the best stopover sites, the best routes to take, how to avoid predation, how to anticipate weather, and where the best places for wintering may be.

For songbird migration in spring, males generally precede females in order to take possession of the best breeding areas. But the timing of migration in fall has a different purpose, and thus varies between sexes and age classes. Four single-factor hypotheses try to explain why differential migration occurs.

One: The body-size hypothesis. Smaller-bodied birds may have to fly further south simply to survive winter at higher latitudes. Bigger-bodied birds should have greater energy reserves than smaller birds, and thus be able to survive unexpected severe conditions.

Two: The dominance hypothesis. Social dominance may contribute to age and sex differences in how far south an individual goes, whereby dominant males and adults take the best northern wintering grounds and force subordinate females and juveniles to fly further south.

Three: The arrival-time hypothesis. Males often leave first in the fall in order to capture the northernmost wintering areas so they’re a leg up on getting back to the spring breeding grounds. Many juveniles also leave later in the fall than the adults in order to maximize their development prior to the rigors of migration.

Four: The migration-threshold hypothesis. Birds migrate at the point at which the advantages of staying at a particular site are outweighed by the advantages of leaving it, a cost-benefit model based on the risks of moving on and the potential gain or loss in reproductive success the coming spring.

It turns out that none of these hypotheses works on its own, and every species has its own story of what makes the most sense for individuals of varying ages and genders.

Back to our ruby-throated hummers. Given that the males leave first in the fall and return first in the spring, and given how incredibly territorial they are once they arrive in the spring, my bet is that the males leave first in the fall in order to occupy the furthest north wintering habitat they can find. This way they will have the best shot at returning earliest in the spring and getting the prime real estate.

Celestial Events

            New moon tonight, 9/30. On 10/3, look after dusk for Venus about five degrees south of the waxing crescent moon. As of 10/4, we’ll be down to 11 ½ hours of daylight. On 10/11, look before dawn low in the east for Mercury and Jupiter to be within one degree of the other.