Readers’ wildlife photos (and moar science)

Because of his extraordinary and information-packed posts on bird research (mostly his), Bruce Lyon has now been appointed our Official Website Ornithologist™, though he’s really a professor of ecology and evolution at the University of California at Santa Cruz. Here’s his latest post—on pygmy owls—and his commentary is indented. Did you know that some owls have fake eyespots on the back of their heads?

Here is another post about owls, one of my favorites, the pint-sized Northern Pygmy Owl (Glaucidium gnoma). It is fairly common in coniferous forests (especially pines and Douglas fir) in western North America but can be hard to see. At 60 grams, it is slightly smaller than an American Robin but the small size should not fool anyone. This is a serious bird killer—mostly songbirds, but they sometimes take down birds much larger than themselves, with exceptional records of quail and even mammals as large as red squirrels. They often take prey that are too big to fly with so they have to consume the prey on the spot. Rodents and lizards round out the diet.

The ferocity of pygmy owls has long been appreciated. Arthur Cleveland Bent, who wrote the first detailed life history accounts for North American birds, described the pygmy owl as “blood-thirsty, rapacious . . . fiend . . . from the top of its gory beak to the tips of its needle-like-claws.”  It sometimes hangs around bird feeders picking off the songbird visitors. Cooper’s and Sharp-shinned Hawks do the same. Henry Horn, a professor where I went to grad school, jokingly referred to bird feeders visited by raptors as ‘two trophic level bird feeders’—the seeds feed the seed-eating birds and the seed-eaters feed the raptors.

Below: Here is the bird killer in all of its glory. We found it in Del Puerto Canyon, Stanislaus County California, but they also occur very close to my home in Santa Cruz (they are heard more than seen). We heard this bird calling and eventually tracked it down—tooting away in the top of tree.

Below: Another photo of the same bird.

Given the threat that pygmy owls pose to small birds, songbirds often enthusiastically mob pygmy owls. Even an audio playback of owl toots can bring in a group of excited mobbers. When the first bird discovers an owl, it gives off a mobbing call that functions to recruit other mobbers to the scene. Our owl was being mobbed by several birds, including Oak TitmiceBewick’s WrensViolet-green SwallowsAsh-throated Flycatchers, and Anna’s Hummingbirds. The photo below shows an Anna’s Hummingbird about to buzz the perched owl. We had hoped to get really nice photos of the mobbing, but the damn mobbers always perched just outside the photo. Mobbing is interesting in its own right, so I will send a future posting about it.

Below. Video of the tooting owl. A small owl with a high-pitched toot seems cute to us but this tooting is harbinger of death to small songbirds.

Some mobbing birds will actually strike the predators, typically attacking from behind. Pygmy owls, along with other small raptors like American kestrels, have a trait that appears to have evolved to reduce the risk of strikes from behind—plumage markings on the back of the head that resemble eyes. The two photos below show the front and back of the head. This bird had really distinctive fake eyes—they are not always so clear.

Below: One idea for why pygmy owls and other small raptors (and even cats like bobcats) have fake eyes on the back of their head (or ears for cats) is that the eyes reduce the risk that mobbing birds strike them from behind. If birds attack and strike from behind, fake eyes work by the appearance of all sides having a face, which should reduce strikes. A clever study tested this idea with balsa wood pygmy owls, one with fake eyes and one without. The authors placed the models conspicuously on branches in pygmy owl habitat near Missoula Montana and used audio playbacks of pygmy owl toots to recruit in mobbing songbirds. They scored the responses to the two different models and found that the model with the fake eyes had fewer close approaches from the rear.

Below: People have adopted the fake eye ruse too, but it seems not as effective over the longer term as the owl eyes.  There are places in south India where tigers (Panthera tigris) kill a lot of people (up to 60 per year in a fairly small area), such as the coastal Sundarban swamps. Apparently, tigers typically strike from behind so people began wearing masks with eyes on the back of the head to reduces the risk of attacks. According to Wikipedia this worked for a while but then the tigers figured the deception out and started preying on people again (photo ‘borrowed’ from the web).

A mask is shown being put on the back of honey collector Madhusudhan Mondal’s head, in Bali, a village in the Sundarbans, India, Tuesday, Aug. 5, 2008. The Sundarbans forest, a remote tangle of unforgiving islands dangling off the eastern edge of India, is home to perhaps the world’s largest population of tigers, prone to attacking humans, as well as 4 million people who are among the poorest in India. Locals believe that tigers do not attack humans from the front and wear masks on the back of their heads in the hope of warding them off. (AP Photo/Gautam Singh)

 

I love watching pygmy owls because of the mobbing and alarm calls they incite. Even a playback of owl toots is enough to bring in birds, and this has been used to study mobbing behavior. A study of the Eurasian Pygmy Owl (Glaucidium passerinum)used owl playbacks to figure out if species vary in their mobbing response in relation to their risk of being preyed on. The authors used the literature to determine how likely a species is to be taken by a pygmy owl. They found that species that are never preyed on by the owls did not respond to toots, birds that are occasionally eaten showed a modest response, and species that are frequently eaten went ballistic. It makes sense that mobbing intensity reflects mortality risk. Their authors were also able to reject the long–standing hypothesis that mobbing is mostly about protecting vulnerable chicks in the breeding season—the authors found the same pattern in spring and in winter.

Bird alarm calls contain information about predation risk. When an attacking predator is on the move and there is a risk of being taken, birds use a high frequency alarm call—the high frequency makes it hard for the predator to locate the caller. In contrast, when birds are mobbing a perched predator, they give harsh calls that are easy to locate. This makes it easy for other birds to find the location and join the fun. The information in alarm calls goes beyond this simple “run for your life” versus “let’s gang up this bad guy” dichotomy. Two friends of mine, Chris Templeton (Pacific University) and Erick Greene (University of Montana), teamed up with a Kate Davis, a raptor person, to conduct a neat study of whether birds include information about the type of predator in their alarm call. Davis founded and runs Raptors of the Rockies, an education and conservation organization. The study took advantage of her many captive raptors and used live raptors in an aviary setting to see if Black-capped Chickadees (Poecile atricapillus) vary their mobbing calls for different predators. It turns out that the body size of the predator is key: for the small owls that are likely to eat them, including pygmy owls, the chickadees include more ‘dee’ syllables per call (see graph below from the paper). Alarm calls for large raptors that are mostly too big to pose much of a threat contain fewer dee syllables. The paper can be downloaded for free from Templeton’s website:

Templeton et al. 2005. Allometry of Alarm Calls: Black-Capped Chickadees Encode Information About Predator Size. Science 308: 1934-37.

Below: Pygmy owls nest in cavities in trees, most often old woodpecker cavities. On a birding trip to Arizona this spring, we heard a pygmy owl tooting away but could not find it. After a couple of minutes somebody realized it was calling from a nest cavity right over our head. Their calls can be really hard to locate.

The photo below shows a rare photo of a pygmy owl inside its nest. The photo was taken with a nest camera on a pole pointing directly down from the nest hole to the bottom of the cavity, where the little owl is peering up, with some of her eggs showing. Like all owls, pygmy owls have white eggs. The photo was taken by Eric Walters and Walt Koenig, who are studying Acorn Woodpeckers at Hastings Reserve in the Carmel Valley of California.  This is a very long-term study (population continuously studied since 1974!) and each year the researchers check a large number of old woodpecker holes to look for active woodpecker nests (the woodpeckers often reuse old nest cavities). Recently they began using nest cameras on long poles to check cavities (to reduce the risk of researchers falling 60 feet to their deaths) and last year they got a big surprise—they found three different pygmy owl nests in old acorn woodpecker cavities. This is particularly surprising because they have been checking cavities for many years and never had any pygmy owls nests before. This suggests that a bunch of owls moved into the area, perhaps to capitalize on a local abundance of some prey item. Other species of owls sometimes do this too.

 

33 Comments

  1. BobTerrace
    Posted July 12, 2018 at 7:47 am | Permalink

    Thanks for the science.

  2. Debbie Coplan
    Posted July 12, 2018 at 8:10 am | Permalink

    Wonderful post! Thank you so much.
    What a cute little killer….

  3. Serendipitydawg
    Posted July 12, 2018 at 8:12 am | Permalink

    Fascinating post, many thanks.

  4. ThyroidPlanet
    Posted July 12, 2018 at 8:30 am | Permalink

    Congratulations!

    I think there are owls that hang out near me, but it’s not convenient to go look … expect they’ll fly away…

    One night, I’ll look….

  5. TJR
    Posted July 12, 2018 at 8:46 am | Permalink

    Songbirds mobbing pygmy owls – a *real* twitterstorm.

    The owls really do balance on the cute/threatening borderline.

  6. Kevin
    Posted July 12, 2018 at 8:51 am | Permalink

    A friend of my father’s woke up in the morning and found an owl perched on his wardrobe watching him with its owlish stare: it had fallen down the chimney.
    An alarming way to start the day!

    I went to a lecture in Oxford in the 80’s given by Mrs Dawkins (Richard’s wife): it was all about the sensory system of owls required to spot prey and home in on it at night. Velocity and timing constraints of the nervous system responses etc. speed of flight.

  7. Posted July 12, 2018 at 9:00 am | Permalink

    That was really interesting. The effectiveness of the fake eyes proves that not just humans are subject to pareidolia.

  8. Terry Sheldon
    Posted July 12, 2018 at 9:24 am | Permalink

    Fascinating information and great photos. Thanks!!

    • Terry Sheldon
      Posted July 12, 2018 at 9:27 am | Permalink

      Just noticed that in the photo with the hummingbird the owl is turned with the “fake eyes” toward the attacker.

  9. phar84
    Posted July 12, 2018 at 10:46 am | Permalink

    Nice article, thank you.
    Seems like a lot of mimicry involves just the eyes.

  10. nicky
    Posted July 12, 2018 at 11:05 am | Permalink

    There are several -not mutually exclusive- theories why the bengal tigers (the smallest of extant tigers) in the Sundarbans are preying so much on humans. The two I find most probable:
    – the Sundarbans are a swampy, ‘difficult’ terrain, so ‘rifled’ hunters did not often hunt tigers there. These tigers did not ‘learn’ to fear humans.
    – The Sundarbans are regularly hit by tropical storms causing flooding and many humans drowning. The scavenging tigers learned to consider humans as part of their diet.
    I’m very sorry those masks do not appear to work anymore, it apparently was to good to be true in the long run

    • Jenny Haniver
      Posted July 12, 2018 at 9:13 pm | Permalink

      I hadn’t known about the Sundarbans man-eating tigers, but I recall reading a book long ago by Jim Corbett, “The Man-Eaters of Kumaon”; Kumaon being in the north of India, mostly in the Himalayas.

      • nicky
        Posted July 15, 2018 at 3:06 am | Permalink

        Correction: the Bengal tiger is not the smallest of extant tigers, that is the Malayan tiger. The Indochinese tiger is also smaller. Apparently the Bengal tiger is the second largest subspecies.
        Most of the tigers (and leopards and lions) that hunt humans are individuals (or mother & cub), often old or disabled, that find humans an easy prey.
        It is only in the Sundarbans that healthy tigers routinely hunt humans.

  11. Glenda Palmer
    Posted July 12, 2018 at 11:17 am | Permalink

    Thank you for very interesting post. Sending on to a few other people.

    Have seen crows mobbing an owl on two occasions along the creek behind my home. Did not see any Northern Flickers involved in the sport even though they are long term residents here.

  12. Posted July 12, 2018 at 11:31 am | Permalink

    Very interesting. I have noticed on my morning walks that crows mob hawks and are, in turn, mobbed by blackbirds.

  13. Christopher
    Posted July 12, 2018 at 11:39 am | Permalink

    I recently listened to a BBC 4 program, Lindsey Chapman’s LIving World (from the archives) about Blackbirds andit discussed how blackbirds in the UK have different predator calls for ground vs. air predators. Do we know if the chickadees and other birds taking part in a mobbing having different calls in a similar way? Would they call differently if mobbing a blacksnake or a cat than they would a pygmy owl or a red tailed hawk?

    • Michael Fisher
      Posted July 12, 2018 at 3:22 pm | Permalink

      Bruce Lyon above: “Two friends of mine, Chris Templeton (Pacific University) and Erick Greene (University of Montana), teamed up with a Kate Davis, a raptor person, to conduct a neat study of whether birds include information about the type of predator in their alarm call. […] for the small owls that are likely to eat them, including pygmy owls, the chickadees include more ‘dee’ syllables per call (see graph below from the paper). Alarm calls for large raptors that are mostly too big to pose much of a threat contain fewer dee syllables”

      My question is – do non-chickadees avians & small tasty snack mammals understand & react to the chickadee alarm call ‘language’?

      • Christopher
        Posted July 12, 2018 at 4:31 pm | Permalink

        I have certainly seen a mixed species flock mob a black snake climbing a tree here in Missouri, so I would say probably (though I lack data or studies to back that up), and as chickadees often forage with or near other small birds in the same mixed flocks (sparrow species, kinglets, titmouse, for example) then there may be a comprehension between these unrelated flock foragers.

    • Bruce Lyon
      Posted July 13, 2018 at 9:52 am | Permalink

      I will address the questions by Christopher and Michael at the same time.

      1) I don’t know if chickadees differ in their response to ground versus aerial predators

      2) Templeton and Greene have a paper out showing that nuthatches ‘eavesdrop’ on the alarm calls of the chickadees and they behave appropriately to the variation. In other words they understand the body size information that is encoded in the chickadee alarm calls. Templeton talked about unpublished work during his recent talk at UCSC and for other species the story is a bit more complex but I do not recall the details. It might be something like the nuthatches pay attention to the details in a chickadee call but do not themselves pass the information on or it could have been that another species pays attention to some of the information in the chickadee call but not all of it. Cannot recall.

      • Michael Fisher
        Posted July 13, 2018 at 11:47 am | Permalink

        Thank you. More posts please!

  14. Posted July 12, 2018 at 11:44 am | Permalink

    People in various places seem to regard tigers (of various species [?]) to be “the intelligent creature which needs respect” – e.g., the Siberian tiger in Dersu Uzala. (Cf. the attitude to bears amongst the Inuit.)

  15. Posted July 12, 2018 at 1:41 pm | Permalink

    Thank you for this enlightening post.

  16. Mark R.
    Posted July 12, 2018 at 3:17 pm | Permalink

    Thanks, this is terrific post…as are all your posts. Congratulations for your WEIT promotion as well.

    I didn’t know about some owls having eyes on the back of their head…nor that all owls have white eggs. That fact seems strange to me for some reason.

    I gather from your descriptions that pygmy owls are diurnal. I doubt a nocturnal owl would evolve fake eyes.

    • Diane G
      Posted July 12, 2018 at 6:30 pm | Permalink

      Nice point.

      I’ve observed “fake eyes” on Northern Hawk Owls, also a diurnal species.

    • Bruce Lyon
      Posted July 13, 2018 at 9:55 am | Permalink

      This is a very astute observation that I had not fully grasped! Saw-whet owls are pretty small too but are nocturnal and I am pretty sure they do not have false eyes.

  17. Kiwi Dave
    Posted July 12, 2018 at 4:20 pm | Permalink

    As others have said, a really interesting post.

    And on an entirely non-scientific, anthropomorphic note, it’s easy to believe the pigmy owl is an aggressive predator from the first two pictures – the face of someone with anger-management issues.

    • Jenny Haniver
      Posted July 12, 2018 at 9:07 pm | Permalink

      Napoleon complex?

      • Michael Fisher
        Posted July 12, 2018 at 9:38 pm | Permalink

        I see owls as baleful in look rather than angry.

        Napoleon was of average height. One of Napoleon’s best marshals was Laurent de Gouvion Saint-Cyr AKA “The Owl” – I don’t know why, maybe intelligence. It is the little chaps who are the scrappers & get especially good at it – from having to be good when small of course.

  18. Diane G
    Posted July 12, 2018 at 6:31 pm | Permalink

    Informative, delightful post with beautiful pictures–thanks, Bruce!

  19. Andrea Kenner
    Posted July 14, 2018 at 5:15 am | Permalink

    Interesting article! Thank you!


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