EA 105 – Field Ornithology, Class I

Last night was the first class of the second half of the 14-class series of Field Ornithology classes I’ve been taking since February. Since the second half is a separate fee from the first, and due to normal class attrition, there were only perhaps half as many people there as there were on the first day of the first half.

Below are my notes on the topics covered:

• Pellets
  • Nearly all birds spit up pellets, which contain the indigestible portions of their food, but non-owl pellets are not commonly seen because 1) they’re often very small, and 2) the food of many birds (eg Robins, which eat worms) is mostly digestible.
  • One should be very careful handling owl pellets, as their common prey species often harbor Hanta virus
• Factoid: birds don’t urinate per se.
• Osmotic membranes
  • All birds have what is called an osmotic membrane as well as a salt gland. The membrane serves to desalinate water, and the salt gland accrues the excess sodium.
  • Unsurprisingly, shorebirds and seabirds have much larger salt glands than inland birds.
  • If you see a coastal gull that has a persistent drip of water on its beak tip, it’s often discharged salt from the salt gland, which hangs on the tip of the beak due to its higher surface tension compared to normal water.
• Factoid #2: The California Gull is the state bird of … wait for it … Utah! This is because shortly after their arrival at the Great Salt Lake, the Mormons were beset by a plague of locusts. A flock of California Gulls arrived and ate them all, which the Mormons regarded as a miracle.
• Vultures (continued from last week)
  • African Vultures, for example, are similar to North American Vultures (Turkey Vulture & Black Vulture), but are actually in the Hawk family.
  • The Turkey Vulture (TV) is expanding its range north and east throughout the US.
  • TVs have a keen sense of smell, unlike most birds, which have a very poor sense of smell.
  • Where TVs and Black Vultures ranges overlap, Turkey Vultures tend to favor forests (since they can smell carrion therein), while Black Vultures prefer open areas (so they can see the carrion).
  • TV & BV cannot generally kill their prey – their bills and feet are not strong enough.
  • TV’s expansion in the NE USA may be due to reforestation and second-growth forests providing more/better habitat for them.
• Factoid #3: “Bird of prey” is a silly term for referring to raptors, since all non-vegetarian birds (hawks, kingfishers, herons, flycatchers, warblers, etc etc etc) are birds of prey!
• Hawks, Kites, & Eagles
  • Golden Eagles have very high rod & cone counts in their eyes. Some have posited that this gives them something akin to built-in 12x binocular vision.
  • cere, n.: the leathery skin at the base of the bill, found on many raptors
  • Golden Eagles migrate during the day and ride thermals to conserve energy. Being as there are no thermals over water, this explains why raptors often accumulate at Hawk Hill in Marin Headlands, since it’s a tapering land peninsula, and once they reach it, they either have to turn around and go back north, or figure out a way across the Golden Gate.
  • Golden Eagles take up to 6 years to fully acquire adult plumage, and are in a constant state of molt once they’ve acquired their first full set of feathers.
  • Eagles return to and reuse the same nest (or set of nests in some cases) year after year, adding to them each time.
• Falcons
  • Peregrine Falcons catch their prey (other birds) mid-air
  • Peregrine speed:
    • For years it was thought Peregrines could exceed 200mph in a dive until a closer examination revealed that this had never actually been measured
    • A group of mathematicians then concluded after doing the physics, that it is physically impossible for them to achieve that speed – they would be torn to pieces!
    • An enterprising falconer borrowed a police friend’s radar gun and clocked some Peregrines doing their dives. They routinely clocked at up to 220mph – so much for the mathematicians!
  • Peregrines endangerment and recovery:
    • One reason for Peregrine’s decline was poachers stealing young for captive raising and falconry. On Morro Rock in the ’70s, the local Audubon society finally had to install a burglar alarm all the way around the rock to catch the poachers, who were stealing all of the young hatched every year.
    • Another reason was DDT, which metabolizes into DDE, which causes thinning of the eggshell and either the drying out or drowning of the embryo (it doesn’t cause egg breakage, however, as one might think the thinning would).
    • Captive breeding programs helped to reestablish the population
    • Populations went from 19 fledged birds in 1977 to 31 in ’78, 105 in ’85, and 120 breeding pairs in ’94. Eggshell thickness during this period, however, was unchanged, at about -17% of the thickness of turn-of-the-century egg specimens.
    • UC Santa Cruz lead the captive breeding program on the west coast, Cornell on the east. Cornell didn’t have enough “anatum” subspecies (the one that was most in danger), so they cross-bred them with “pealei” Peregrines, resulting in a rather dark population of so-called “anatum” birds in the East.
  • Peregrines fastidiously pluck the feathers from their prey.
• Factoid #3: Southern Florida and South America have many bird species which are either the same or very similar, leading to the thought that Florida was once attached to S. America and drifted north as the continents separated.
• Gruiformes (Rails, Coots, Limpkins, Gallinules)
  • They have no crop, and so cannot store extra food for later consumption
  • Limpkins exist mostly in S. Florida
  • Coots have precocial chicks that can swim immediately upon hatching.
  • They feed mostly on algae
  • They have webbed toes (like grebes, whose family name in Latin actually translates to “Coot-footed birds”), but not webbed feet
  • Coots are extremely abundant, pretty much everywhere in the US. Why?
  • Because they are very adaptable, do not require a lot of territory per bird, leading to a large carrying capacity, and they can live in many habitats
• Cranes
  • Don’t confuse them with herons (not that I would, as they look quite different to my eyes!)
  • About 50% of their diet consists of grain, the rest small animals.
  • Cranes have a vestigal rear toe, and cannot roost in trees
  • Their windpipe curls around inside of their breastplate, giving them their characteristic long-carrying calls.
  • The Sandhill Crane is the most common crane in North America
  • Cranes have long upper-tail coverts that hang over the ends of their tail feathers, giving them a “bustle”-like appearance.
  • Whooping Cranes:
    • Are endangered, with only about 200 wild individuals left.
    • They overwinter at Arranzas(?sp) NWR in Texas
    • Lay only one egg, but if it is taken, they lay another, so researchers took advantage of this for some time to establish a captive flock, most of which was killed in a recent storm in Florida 😦