Archive for August, 2012

At this time of year, all across the northern hemisphere, people are starting to go out to particular places that combine specific geographic characteristics.  They are places that generally have reliable winds out of the north, they are elevated up above the surrounding landscape and so give a good vantage of the area, and they are situated where the land is constrained in some way (by coastlines or mountain ranges), and they are at mid-latitudes such that there is a large amount of potential breeding areas to the north and is not south of the wintering areas.  The places that meet these requirements and have these characteristics are places where migratory birds of prey tend to concentrate.  If you look at a map of the world, you can predict where the good hawkwatch sites are.  Anywhere that is shaped like a funnel with the wide end to the north and the narrow tip to the south will likely be the site of a fall hawk migration.  There is a hawkwatch on the Rock of Gibraltar at the tip of the Iberian peninsula funneling birds out of western Europe and constrained by the Mediterranean Sea and the Atlantic Ocean.  There is a hawkwatch in Ilat, Israel funneling birds out of eastern Europe and western Asia and constrained by the Mediterranean and the Black and Caspian Seas.  There is a hawkwatch on the Thailand/Malaysian peninsula funneling birds out of eastern Asia and constrained by the Gulf of Thailand and the South China Sea to the east and the Bay of Bengal and the Andaman Sea to the wet.  There are a series of hawkwatches along the funnel of central America funneling birds out of North America and constrained by the Pacific Ocean and the Gulf of Mexico.  The largest of these hawkwatches is also the largest hawkwatch in the world at Vera Cruz, Mexico.  The birds are drawn by the tailwinds that help to push them south and guided by the coastlines and ridges in the attempt to avoid large bodies of water or open land that lack the aerodynamic aid of thermals and updrafts.

And the people are going out to high points in such areas to count the raptors as they pass by.  Hawkwatchers all around the world are starting their yearly endeavors to monitor the populations of migrating birds of prey.  Some of these counts are done only one or two days a week while others have people out every day of the season.  A large majority of them use volunteers, to at least some extent, and this is an excellent way for anyone to become a citizen scientist and add to the understanding of birds of prey.

By conducting these counts every year, the size of raptor populations can be tracked.  If drops are seen, the causes of these drops can be investigated.  One of the most famous example of this process was when Rachel Carson noted a drop in the numbers of the young Bald Eagles and Peregrine Falcons during migration.  The investigation of the extremely high rates of nest failures in these species, led to the finding that the nests were failing because the eggs being laid in them had very thin shells and so cracked when an adult bird attempted to incubate them.   When egg shell fragments were tested, they were found to contain very high levels of the pesticide DDT and its derivative DDE.  All this led to two major events.  One was that Carson wrote the book “Silent Spring” which grabbed the attention of the nation and was one of the large steps in getting DDT banned.  The second was that researchers began taking eggs out of nests and incubating them in captivity.  With the help and knowledge of falconers, they were able to raise the chicks that hatched from these eggs and release them into the wild where they have succeeded in thriving and breeding and so bringing the populations of a number of species back from the edge of extinction to large and stable populations.  And none of this would have happened if people had not been going out into hill tops and mountain ridge-lines to count the birds as they pass by each year.

So go out and join a hawkwatch near you, or start your own!  There are many organizations that either run hawkwatches or can help you start one.  The data from all these sites is compiled so that trends across large area, or even continents, can be monitored.  But it only works if there are people out counting.

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I went birding at the Yolo Bypass Wildlife Refuge, yesterday morning.  It was lovely to watch the refuge wake up in the morning to a beautiful sunrise over the Sierra.  Got lost of close and excellent looks a bunch of Ciconiiforms: Green Heron, Great Blue Heron, Great Egret, Snowy Egret, White-faced Ibis, Black-crowned Night-Heron, American Bittern.  Also watched a Barn Owl hunting over the marsh just went I arrived.  It was soon replaced by Northern Harriers and White-tailed Kites quartering above the cattails and tules and rice paddies.  It has often been observed that no two species can occupy the same ecological niche in the same place at the same time.  The Harrier, Kite and Owl all are hunting for the same basic prey, but they are active at different times.  This is an example of temporal partitioning.  The water level at the refuge is still being kept pretty low, but in areas that did have standing water I found Mallards, Gadwalls, Black-necked Stilts, Marsh Wrens, Pied-billed Grebe, and Double-crested Cormorant.  Lots of Black Phoebes and Savannah Sparrows, and a few Red-tailed Hawks, were also present.  An early migrant that was exciting to find was a group of about a dozen Northern Pintail!  Northern Pintail are one of the earliest migrating species of waterfowl, so this is just the start of the massive migration of ducks and geese that will be arriving in central California in the next few months.  Two species that I found that I do not get to see often were a couple of small groups of Horned Larks foraging on the roads and three Yellow-headed Blackbirds (two males, one female) mixed in a group of Red-winged Blackbirds.  Both beautiful species.  All in all, it was a really wonderful, relaxing and refreshing morning.

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In the western U.S., Spotted Owls (Strix occidentalis) are one of the banner species for the protection of old growth forests, and several subspecies are federally endangered.  A small owl, it has a huge impact on conservation in North America.  But now they face a threat that is harder to deal with even than human disturbance and habitat loss.  It is a fellow owl, the Barred Owl (Strix varia).  The two species are very closely related.  The Barred Owl is most commonly found in the eastern portion of the continent, but that is changing.

Due to an increase in the number of planted trees in the central parts of the continent, the breaking up of large tracts of continuous forests by timber harvesting, and probably other factors that we do not yet understand, the Barred Owl has been expanding its range westward.  There are now breeding populations of Barred Owls in Washington, Oregon, and California, and this posses a special problem for the Spotted Owl.  With their larger size and more aggressive behavior, Barred Owls can drive out Spotted Owls from nesting territories, sometimes eating the Spotted Owls!  However, even when the Spotted Owls stand their ground (and don’t end up being a meal) a problem still exists.  Since the two species are so closely related, they can interbreed.  The hybrid, or Sparred Owl, can then mate with other Sparred Owls or members of their parent species.  Since the total Spotted Owl population is small and the total Barred Owl population is large, and getting larger, the overall result is that the Spotted Owl is getting absorbed into the Barred Owl.

Now, we face a dilemma: what should we do to save the Spotted Owl?  For that matter, what can we do to save the Spotted Owl?  Ideas abound across a wide spectrum.  At one end are those that feel that the Spotted Owl must fend for itself.  This viewpoint is generally driven by the idea that a species its range is a natural process and should not be interfered with.  If one species out competes  another where they come in contact, that is just how the world works.  Many advocates of this viewpoint point out that if the two species are so closely related that they can interbreed, they probably should not have been categorized as two different species in the first place, but are rather two populations of the same species.

At the other end of the spectrum are those that feel that the Spotted Owl should be protected at almost any cost.  Proponents of this viewpoint feel that a large part of what brought these two species together were human induced changes to the land, and we are therefore responsible for the results.  Among the most drastic of the plans that have been suggested is to actually kill Barred Owls when they are found near known Spotted Owl nesting territories.

So, who is right?  The debate continues.  There may be nothing we can do to stop the Spotted Owl from disappearing.  But we can learn.  Ecosystems are incredibly complex, and we did change the landscape in such a way as to allow this situation to occur.  In the future, we need to consider carefully the possible consequences of our actions and perhaps apply the precautionary principle a bit more often.

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Here in central California, most of the bird species are replacing the feathers that have been worn out during the breeding season.  The feathers that are falling out are being replaced by the feathers they will use to migrate to their non-breeding grounds.  This molt that they are going through is called the prebasic molt.  The general pattern that most birds have is a prebasic molt in the fall that leads to their basic plumage.  This is their simpler, duller, non-breeding plumage.  Basic.  When they are ready to return, they will go through a prealternate molt that will lead to their alternate plumage.  This is the bright showy plumage of the breeding season.  Not all species adhere to this pattern, but is a quite common one that is adopted by a lot of birds.  Different species have different details of the timing of their molts.  For example, the Yellow-billed Magpies have largely just finished their molt, while the Western Scrub Jays are in the middle of theirs.  How far a bird migrates, how it fared in the breeding season, if it had a single brood or had multiple broods, even how hard its spring migration or non-breeding season before may have been can all effect the timing of molt.

Molt is a significant endeavor to undertake twice a year.  The feathers of a bird can account for between 4% and 12% of a birds body mass, so it takes a large amount of energy and resources to replace them.  Mass for mass, this is equivalent to a human replacing all the tissue in their brain, liver, heart, lungs and skin!  But, replacing them is necessary.  As feathers age, they ware and break down.  This reduces their ability to keep a bird dry and temperature controlled.  It also causes a drop in flight efficiency.

Molt can also be used to determine a birds’ age.  Since feathers get more and more worn the longer they are retained by a bird, it is sometimes possible to see different feathers that have different amounts of ware side by side.  Depending on the pattern of where these feathers are, and how many different ‘generations’ of feathers are present, a trained eye can tell if a particular bird hatched this year, the year before, or the year before that!  So as you go out birding, pay attention to the feathers of the birds you see.  There are all kinds if details to be learned about their lives.

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As I was exiting off one of the major freeways in Davis, I passed by a big group of Yellow-billed Magpies.  Around 35 or 40 of these birds were foraging on the ground in an open grassy space or sitting in some low trees nearby.  It turns out that, according to the Oxford English Dictionary, a group of magpies is called a tiding!  These tidings tend to form at this time of year as hatch-year birds group together, and wander around looking for food and prepare to survive their first winter.  For most birds, the largest source of mortality is young birds not finding enough food or shelter in their first winter.  Some species have been found to have as high as 80% mortality in this period.  So by grouping together, Yellow-billed Magpies may be hoping to gain safety in numbers, and they may also be hoping to learn various tricks of the trade from one another.  Yellow-billed Magpies are endemic to central California and are non-migratory, so after they get through our wet winter, the tidings will break up as individuals go off to find mates and establish breeding territories.

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I went out to the Fremont Weir National Wildlife Refuge this morning and spent a lovely few hours before the heat of the day began to sink in.  Saw lots of great birds including, but not limited to, Western Kingbirds that are still paired up even though most have finished breeding, Blue Grosbeaks singing all over the place, a hatch-year Red-shouldered Hawk that flew right in front of me, and an adult Red-tailed Hawk being harassed by a Red-winged Blackbird.  Among all these bird sightings I did have one really notable mammal sighting.  I was poking around through the underbrush near the edge of a small water way that runs through the refuge and came across a number of small trees that displayed the clear tooth marks of having been chewed through by a Beaver.  A few steps farther, and I saw the Beaver itself standing on the far bank at the waters’ edge.  It was eating some greenery, and when it was finished it walked up the bank, picked another plant, brought it down to the water and swam in pulling the plant in with it.  It only swam for a few seconds before it turned around, came back to shore, and began munching on the, now wet, plant.  I have no idea why it did this rinsing behavior, but it was interesting to see!  After it finished its’ breakfast, the Beaver returned to the water and swam off down the channel.  It really was a very nice morning indeed.

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