More Migration Mysteries

37878872205_00d203885a

Monarch Butterflies, Courtesy of “Monarchs on Salvia”by cgus51@sbcglobal.net is licensed under CC PDM 1.0“>Creative Commons

Scientists have long wondered how a group of animals finds its way along the same route year after year over generations.  Monarch butterflies require multiple generations to complete a full migration cycle, so learned behavior is clearly not at work. Instead, they use a number of tools embedded in their genome, including sunlight and the earth’s magnetic pull. Homing pigeons also use magnetism. In fact, there’s a story that was passed around ornithology class back in grad school, possibly apocryphal, that during the heyday of the Concord jet, pigeon races were disrupted along the Concord’s flight, presumably due to the mechanisms that enable its supersonic flight.

A recent study added a wrinkle to this process. Do animals get lost? Yes, says this study on salmon. A lack of group consensus can lead animals astray.

Right now in North America, we are nearing the end of nighthawk migration season, but migration will continue until January in Central and South America.  How exactly these birds find their way to South America and back each year is an enduring question. But, if they group up by the hundreds and sometimes thousands, could group-think be the key?

Advertisements

What do Migrating Nighthawks Look Like?

Untitled3.png

Nighthawks only gather during migration season. Image courtesy of Suzanne Coleman.

Here’s an excellent view of migrating nighthawks low and feeding along their migration route. To see the full video, check it out here. When nighthawks are in breeding season, they will spread out and cover wide territories, as much as 40 km in a day (Ng 2013). But, when nighthawks migrate, there is strength in numbers, and as many as 1,400 can be viewed in a single day.

 

Source: Ng, J.W.M., 2013. Habitat use and home range characteristics of Common Nighthawks (Chordeiles minor) in mixed-grass prairie.

Now is the Time to See Nighthawks

coni 0819 lax

eBird map for Common Nighthawks in August, 2019. Courtesy of Cornell Lab of Ornithology

Nighthawks are one of the first birds to migrate south, and they are starting to make their move. At places like Hawk Ridge in Duluth, Minnesota, as many as 14,000 nighthawks can be seen in one day.

Here in La Crosse, Wisconsin, we have seen hundreds in one night.

If you are not near one of these places, check out eBirds’ nighthawk maps, plug in a range of recent dates and your location to find out where to check out the nighthawks.

 

In the Field with a Spotted Owl Biologist

Below is an unpublished story I wrote in 2010.

Picture1

A Northern Spotted Owl roosts during the day.  While Spotted Owls are generally more sedentary during the day, they may be awake for  extended periods. Photo: Gretchen N. Newberry

The owls know his truck.  Tom opens the driver’s side door, strides to the back, grabs a cylinder of live mice, pulls on a pair of gaiters, slings a backpack over his shoulder, and points upward. They’re usually waiting, he says.

The owl peers down at him from a branch 10 feet above his head.

Tom supervises a team of field technicians who scout for Northern Spotted Owl nests in the Oregon Coastal Range, and the data is analyzed by a team of researchers led by U.S. Forest Service ecologists at Oregon State University (OSU).

This is an effort matched by other teams in other regions across the Pacific Northwest.  The object is to estimate population trends and assess the effects of different Spotted Owl management strategies.

Various faculty at OSU have been studying the issue of the Spotted Owl for decades in an effort to find working solutions in those management strategies.  Building study protocols is essential to that effort. And it’s people like Tom who take those protocols into the field.

Picture2

An old-growth temperate coniferous forest typical of the Oregon Coast Range.  This dense vegetation is the typical habitat for the Northern Spotted Owls’ nests, and increasingly this vegetation is losing out to logging practices. Photo: Gretchen N. Newberry

It’s a relief to find a bird.  Not only because of their decreasing numbers, but because it’s exhausting work finding a nest.  Usually nests are found far off the road in old growth forests and require climbing over fallen trees, through

heavy brush, knee-deep in rich soil, splashing through streams, and climbing up and down steep hills, grabbing ferns for handholds.  It’s steep terrain, and even the birds get winded flying uphill, Tom says.

At night, Tom and his team drive through the woods calling for the birds, and noting where they hear the distinctive “Cooo-wheep” of the females and other calls of the Spotted Owl.  By day, they search the woods around the calls they heard looking for a nest.  Often, they spot the ravens and scrub jays that bother the owls before they see the actual owls.

Once they spot an owl, they look for a nearby nest.  Typically, the field technician gives a mouse to the owl and takes note of what happens next.  If the owl takes it back to the nest, they usually have young chicks to feed.  If the male and female squabble over the mouse, or if the female stuffs in a nearby tree branch for later, it’s unlikely they have any young chicks to feed.  And if it’s the right time of year, and if there are no nestlings, this might be a year the pair are skipping the arduous task of reproduction altogether.

This pair knows Tom because he scouted their nest before and they know he has mice. Today, Tom places the mouse on the ground within view of the pair of owls, backs away 10 feet, and sits down within the dense ferns.  Within a minute, one of the owls scoops up the mouse. And after a brief squabble with the male, the female stuffs the dead mouse in a nearby tree branch for later and Tom takes note.

What Tom has been doing for the past six years has fed into a larger project that spans decades.  Teams of researchers have been tracking population trends in the Spotted Owl south of Oregon and up into the Pacific Northwest, where its subspecies, the Northern Spotted Owl, prevails.  And since its 1990 listing on the endangered species list, the public has become more aware of the species’ progress.

Overall, the trend indicates that populations numbers have decreased with the loss of old growth forests. According to the Wildlife Ecology Team’s annual report, last published in January 2010, the survey found 220 individuals in 1990 and 125 individuals in 2009 in the Oregon Coast Range study area.

The decreasing population numbers have also been due to the expanding range of the Barred Owl, and changes in climate [Note: This is a hyperlink to another OSU press release talking about these two factors].  Even accounting for fluctuations year-to-year due to normal food availability fluctuations, the overall trend indicates overall decline.

So, what’s new about the owls this year? “Every year is interesting,” Tom says.  But this year was an especially difficult year for the Spotted Owl, he adds.  Due to a warm month of March, a higher than usual percentage of pairs nested.  But because of the unusually cold and wet months following March, many of the owls failed to produce young.

The type of nests they build make them unusually vulnerable to weather, he says.  The Northern Spotted Owl assembles its nests atop trees in the broken top of a trunk, leaving it exposed to the elements.  This is typical of the Northern Spotted Owl in Oregon.  But as you travel northward or southward the Spotted Owl constructs different types of nests along a gradient of tree-trunk-cavity types of nests.  In California, he says, the nests are more exposed but experience warmer temperatures.  North of Oregon, the nests are in more sheltered cavities lower on the tree and covered by more branches that shield it from the colder temperatures.

In Oregon, the middle range of its habitat, the owl’s exposed nests atop the trees are within the dense old-growth forests and are fairly exposed to the elements.  And in a colder year, such as 2010, that can have an impact on the success of producing viable eggs.

So, what’s ahead for the Northern Spotted Owl survey project? Tom expects the same field techniques and project strategies will remain in the coming years to match the past 20 years of strategy for  consistency in data analysis.

Future challenges include a change in the guard as the projects’ principle investigators , its key scientists, reach retirement age, the ever-present budget crises, the deterioration of roads which hampers technicians’ ability to access the birds, and the loss of the Spotted Owl  populations.  For, as some areas, like in the Olympic Peninsula, lose their bird populations, researchers cannot find birds to survey.

And, what’s ahead for Tom?  It’s another change in the guard as Tom takes a new job this fall.

As stimulus moneys pours into the development of alternative energy, many wildlife biologists are finding work and research in risk assessment for birds and mammals whose migration takes them through the growing fields of wind turbines in the Columbia Gorge and other areas.

Tom will be working for a private consulting firm.  It’s a sign of things to come that field biologists like Tom will be scouting planned constructions sites for wind farms for risk to wildlife.

For the Spotted Owl survey in the Oregon Coast Ranges Study Area, it’s unknown who will lead the team of field technicians.  But the project will continue, says Tom.  “It’s a key part of monitoring the species.”

The Air

01f1076cc1b9b44f0e247329e3a278e26bdb5c7c_m (1)

Art by JR Goodwin

Ecologists have a hard time explaining what’s happening on land, and even more so, in the water, to folks who haven’t spent their life studying a single animal or habitat. Now we have the air. Increasingly, we are realizing the air above is partitioned off by species. Some fly higher at different times of the day or or year. Migrating birds might fly higher than usual. Dispersing birds might move fly higher on the way to their evening roost. Species might specialize on insects that fly lower or higher. Lower flying animals might be out-competing others that are forced to flyer higher. Many factors make this space complex, and we are just starting to understand it.

Facts versus Emotions

Tebe Interesno

It’s not often I encounter someone whose opinions diverge from mine that there is no middle ground. When I do, I know that it is not about me. We each have strong emotions about our opinions, and often the common ground can be found when we talk about the elements of survival: food, water, warmth, and the people that surrounds us.

Occasionally, common ground cannot be found because we don’t agree on how those fundamentals can be met, and our emotions take over. Are emotions or facts best used in such an interaction? I imagine it depends on the situation. This video has some thoughts on the issue.

Prairies and Drought

Jim Richardson

Prairies are in trouble. According to Worldwide Wildlife Fund’s 2016 plowprint, we have lost in grasslands the equivalent of the size of Kansas in North America in the previous decade due to conversion to row crop. We wanted more corn for ethanol.

In addition to the loss of wildlife habitat, we might lose a few other things, carbon sequestration, prairie plants are sometimes capable of withstanding droughts and preventing soil erosion that might become more frequent under climate change. Check out the photo above — prairie plants have longer roots than row crops and can reach water that other plants can’t. And during times like the dust bowl, native prairie plants have the ability to hang onto the soil.

What eats what others won’t?

b4608def-4ba8-4480-aa7b-5dcccea34659-2

Vultures!

I have written before about vultures here, here, here, here and here. But have you seen this video? Most vultures specialize on dead leftover flesh, but the bearded vulture wants only the bones. It swallows the bones whole. According to Houston and Copsey 1994, their digestive tract might have additional acids to deal with bones and that the additional nutritive qualities of a bone-only diet make it all worth it, especially in barren landscapes with fewer carcasses to find.