A Loggerhead Larder - Colorado Field Ornithologists

THE HUNGRY BIRD
A Loggerhead Larder
Dave Leatherman
The job opening is that of biological technician for a natural resource agency with land management responsibilities on the northeastern plains of Colorado. It’s the kind of job I would have jumped
at back in the 1970s with a formal description that might read something like this: “Inventory, collect and curate fauna from within an
assigned area of native grassland. Applicants must be familiar with
the life histories and diurnal habits of the insects, small mammals,
passerine birds, reptiles and amphibians of Weld and surrounding
counties. Work conditions include variable and potentially harsh
weather, venomous snakes, barbed wire, cattle (including bulls),
truck traffic and plants with thorns. Must be willing to have work
habits and performance evaluated by at least one other technician on
a regular basis. Pay commensurate with education and experience.”
In the text and photographs that follow, I intend to make a case
for the United States Forest Service or Colorado Department of
Parks and Wildlife hiring a certain male Loggerhead Shrike (Lanius
ludovicianus) to fill the job opening described above. This one bird,
operating on Weld County Road 37 between Roads 114 and 122 during the summer of 2015, would not only warrant hiring, but a promotion, a letter of commendation and a 2016 rehire. In fact it did such
a good job of collecting and displaying biota that I was in awe of its
appreciation for diversity and was taken aback on more than one occasion by its lethal efficiency. He was an exhibitionist in every sense
of the word.
No doubt, as soon as humans began noticing shrikes in the natural
world around them, their habit of sticking objects on sharp things
became a source of curiosity. Our grandparents called them “butcher
birds” and probably never used benign descriptors in their company.
From our perspective, impaling creatures on sharp objects, especially
when often the stickees are alive at the time of the act, and not eaten
right away, or at all, can easily be interpreted as “mean” or “macabre.”
So why do they do it? These unique raptorial songbirds have sharp,
falcon-like beaks equipped with a pair of tomial teeth on the maxilla
for severing the spinal columns of their prey (Craig 1978). And like
hawks they have the skills to discover and catch things. But why
stick them? The answer seems partly attributable to their relatively
weak feet that lack talons (Yosef 1996). In essence, the act of prey
consumption is made easier by use of sharp objects, both natural and
unnatural, that function as “forks.”
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Fig. 1. Redshank grasshopper impaled
intact by Loggerhead Shrike as found 18
June 2015 on Weld CR37 0.9 miles north
of CR114. This particular species is perhaps the most commonly utilized insect by
shrikes on the eastern plains of CO.
Fig. 3. Robust camel cricket, second
most commonly impaled insect in many
parts of eastern Colorado.
Fig. 5. Field cricket.
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Fig. 2. Redshank grasshopper. Legs removed by
shrike to make the handling
and impaling easier.
Fig. 4. A second species
of robust camel cricket.
Fig. 6. Ground beetle
head and thorax.
Fig. 7. Darkling beetle.
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But there’s more to impaling potential food items than that. A
common theme throughout the Animal Kingdom is males showing
off in various ways to females as a prelude to reproduction. The Loggerhead Shrike, the only one out of 30 true shrike species in the
world that occurs wholly within North America, is mostly migratory
throughout the northern part of its range, including Weld County,
CO (Kingery 1998, Craig 2014, Yosef 1996). In spring males arrive
on breeding grounds before females.
All photos taken on either 18 June or 22
Usually for a period of weeks afJune (except for the one showing a pellet)
ter the males arrive, an increasing
frenzy of “bulletin board” activity
by Dave Leatherman within 0.9 and 1.1
occurs, with these hormone-driven
miles north of Weld CR114 along CR 37.
individuals impaling things all over
territories they think would be productive places to raise families.
Colorado Breeding Bird Atlas I fieldworkers documented shrike
courtship as basically a May activity (30 April to 6 June) (Kingery
1998). During this timeframe, males show off their skills at providing
food for prospective mates and their resultant broods. During the two
mid-June visits in this episode, I believe the nest was occupied and
that the adults were in the process of whittling away at the male’s
stash of food.
I have long been enamored of shrikes and their penchant for impaling prey. Odd objects on barbed wire fences catch my eye. Seeing an impaled grasshopper here, a cricket there is not uncommon
anywhere in Colorado where shrikes breed, and particularly not at a
known stronghold like the Pawnee Grasslands. But I wasn’t prepared
for what I saw on 18 June 2015 along CR37 north of CR114 between
the Owl Creek Bridge and the Central Plains Experimental Range
Headquarters complex to the north. There on metal fence barbs on
both sides of the road within about 100 meters both north and south
of a lone Siberian elm (1.1 miles north of CR114), was an exceptional assortment of shrike-impaled biota. I did not do an exact count
but would estimate at least 75 objects.
Insects were by far the most common animal group impaled. Most
were what I have learned to be the “favorite” of shrikes on the eastern
plains of Colorado, the redshank grasshopper (Xanthippus corallipes)
(Figs. 1 & 2). These large, band-winged hoppers (family Acrididae,
subfamily Oedipodinae) are widely distributed in the West and usually abundant on the arid plains. Their bright red inner “thighs” on
the hind jumping legs are distinctive, although my friend Tim McNary, an orthopteran expert extraordinaire, reminds me that there
are a few other lookalike species in this genus.
Next in abundance among the six-legged larder were large crickets
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in the family Gryllacrididae, mostly reddish-brown but some creamytan. These so-called robust camel crickets (Udeopsylla robusta) (Fig.
3) and perhaps another species (Daihinia brevipes?) (Fig. 4) live in
burrows in the soil or hide under objects like dry cow pies and are
most active at night (Cranshaw 1995). Because male crickets are
more apt to forage away from burrows (for other insects and a limited amount of plant material), it is likely more males are caught and
impaled by shrikes than females, however, this needs to be verified.
Several black field crickets of both genders (Gryllus sp.) decorated
the fences (Fig. 5).
There was one large predaceous ground beetle head (family Carabidae, genus Pasimachus) (Fig. 6) and one medium-sized darkling
beetle (family Tenebrionidae, probably Eleodes sp.) (Fig. 7).
As for reptiles, on 18 June the only representative taxon were four,
small (about half-grown), intact, Short-horned Lizards (Phrysonoma
hernandesi) (Fig. 8). On 22 June the number of “horny toads” was the
same but it was obvious something, presumably a shrike, had eaten
part of the upper torso of one, accessed from the underside (Fig. 9).
Added to the reptilian ranks of the run-through were a Lesser Earless
Lizard (Holbrookia maculata) (Fig. 11) and a small Western Hognose
Snake (Heterodon nasicus) (Fig. 12). This lizard, multiple individuals of which I have seen impaled in other eastern CO locations, was
partially shriveled, but its inner organs appeared to have been at least
partly removed. The head end of the snake was missing.
Loggerhead Shrikes are known to impale small mammals, at times
in good numbers, but never as commonly as their relative, the Northern Shrike (Lanius excubitor) (Yosef 1996). The remains of only one
mammal hung from a barb in this situation, what I think was a young
Thirteen-lined Ground-Squirrel (Ictidomys tridecemlineatus) based on
the shape of the skull and the color of hairs still attached to the carcass (Fig. 13).
What seemed exceptional to me about this situation, in addition
to the sheer number of objects, was what this shrike imposed on other
birds. In addition to finding adults, it also found new nestlings, some
that were essentially featherless (Figs. 15 & 16). Not only did it find
birds smaller than itself, it apparently killed one bigger than itself, a
juvenile Western Meadowlark (Sturnella neglecta) (Fig. 14). Some of
its bird victims were affixed to a wire whole, others were beheaded.
I must admit that on 18 June, even as a lifelong biologist, coming
across the beautiful, unbloodied head of a Brewer’s Sparrow (Spizella
breweri) with its lifeless, hollow stare, stopped me in my tracks (Fig.
17). I later found a headless Brewer’s Sparrow body over a hundred
meters away that may have been its match. This shrike was not mess250
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Fig. 8. Young short-horned lizard intact
on 18 June 2015.
Fig. 9. Same individual shorthorned lizad as shown in Fig. 8 as
discovered on 22 June 2015 showing partial consumption after being
impaled.
Fig. 10. Short-horned lizard head as discovered on 7 August 2015.
Fig. 11. Lesser earless lizard.
Fig. 12. Western hognose snake.
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Fig. 13. Unknown mammal (probably
young 13-lined ground-squirrel). Skull
showing black mouth cavity at lower left
part of carcass.
Fig. 14. Young Western Meadowlark,
presumably impaled by shrike.
Fig. 15. Nestling bird (species unknown).
Fig. 16. Nestling bird (species unknown).
Fig. 17. Brewer’s Sparrow head.
Fig. 18. Pellet, presumably of shrike,
impaled by shrike.
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ing around. Altogether I would estimate I saw a total of 10 impaled
birds, most quite young, that had to have been taken from nests.
So a total of about 75 objects: 6 reptiles, about 10 birds, one mammal and roughly 58 insects, most of the latter group being rather large
grasshoppers and crickets. The major differences in the larder between 18 and 22 June were that many of the objects that were whole
on the first visit were partially or mostly consumed on the second
visit. Plus there was the addition of two reptile species. The male
shrike doing the impaling seemed to accomplish what were likely
his two primary objectives: storing food for later consumption and
attracting a mate.
As a follow up, I revisited the site on 7 August 2015. Mostly I
drove the stretch of road on either side of the nest tree, but also
walked some of it. The only identifiable object I found from the June
larder was the head of one Short-horned Lizard (see Fig. 10). A regurgitated bird pellet, which appeared to be the right size for a shrike,
was also new on the fence very near the shrikes’ nest elm (Fig. 18).
And yes, I saw at least three fledged shrikes. Asking them the question, “who’s your daddy?” seemed unnecessary. They were hunting on
their own, usually by flying down to the ground from the top strand
of the fence. Twice I observed them returning to the fence with small
insects, probably grasshopper nymphs, which they held against the
wire with a toe, and consumed on the spot.
In closing, my curiosity keeps returning to that impaled Brewer’s
Sparrow head and those nestling birds. These objects perhaps fit
within the standard reasons for impaling by shrikes cited in the literature, but struck me as possibly serving a third purpose–that of intimidation. It reminded me of something I saw once as a kid in a National Geographic Magazine involving cannibals in Borneo who, as
a warning to would-be intruders, displayed heads on sticks. If whole
birds are usually impaled (as was the meadowlark and most of the
nestling birds), why did this male shrike go to the trouble of carefully
beheading a sparrow and then, apparently, place the resultant two
body parts at opposite ends of his territory? Did this, along with the
impaling of nestlings, convey to other species nesting, or even considering nesting within this shrike’s territory, that competing with
him for food resources might be a bad idea? No way to prove any of
this, but one has to wonder.
Regardless of answers to these last conjectures, if I was an HR person looking to fill a biodiversity surveyor position, and a male shrike
was sitting across the desk, I’d ignore the bad recommendation in the
application folder from somebody’s grandmother. Hire him!
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ACKNOWLEDGMENTS
I thank Tim McNary and Dr. Boris Kondratieff, both affiliated with the C.P.
Gillette Museum of Arthropod Diversity at Colorado State University, for
assisting with identifications of impaled insects.
LITERATURE CITED
Craig, R. B. 1978. An analysis of the predatory behavior of the Loggerhead
Shrike. Auk 95:221-234.
Craig, Susan. 2014. Movements, migration and breeding by Loggerhead
Shrikes (Lanius ludovicianus) in eastern El Paso County, Colorado. CO
Birds 48(2):266-271.
Cranshaw, Whitney and Boris Kondratieff. 1995. Bagging big bugs. Fulcrum
Publishing, Golden, CO.
Kingery, Hugh E. (ed.). 1998. Colorado breeding bird atlas (I). Co-published
by Colorado Bird Atlas Partnership and Colorado Division of Wildlife,
Denver.
Yosef, Reuven. 1996. Loggerhead Shrike (Lanius ludovicianus), The Birds of
North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.
cornell.edu/bna/species/231
Dave Leatherman, [email protected]
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