At the recent Colorado Field Ornithologists' Convention in Trinidad (May 17-20)
we conducted two field trips with the slant of looking at bird food habits. A
few participants and non-participants have requested a summary of the things we
saw or talked about during the trips, so, to the best of my notes and
recollection, here goes....
OVER-ARCHING THEMES:
Evolution is not a theory and the details of predator-prey relationships (how
to find food, how to avoid being eaten) are constantly changing.
Much of the daily activity of birds relates to food acquisition (with
procreation being a second dominant time-consumer).
Birds are both habitual and opportunistic.
Resident, 12-month birds probably go thru major dietary shifts during the year
(lots of insects in summer, seeds/fruit in winter).
Many bird species migrate mostly for reasons related to food. Cold temperature
plays a role, but mostly as it affects food availability, not any sort of
direct aversion to it by the birds.
Fruit and insects are heavily utilized by migrant songbirds.
We live in an increasingly homogenized, shrinking world where human
international commerce and other forms of intercontinental contact facilitates
introduction of exotic species, including birds and their food.
Birds heavily utilize search-imaging (both to locate situations/objects that
have paid off in the past and to find "defect" or "difference" in their habitat
substrates that often allows detection of what it was that created or currently
resides at the abnormal-looking site (namely, some sort of feeding insect,
hiding spider, etc.).
It's all connected and the ramifications of climate change on producers
(plants) and their direct or indirect consumers (animals) are many.
Alterations of the synchrony of plant and animal phenologies (that is, the
sequence and timing of biological events) can be profound in their effects.
Things we saw at various stops:
1) Trinidad Lanes (bowling alley) parking lot (southwest corner of Sante Fe
Trail and Van Buren):
European Elm Flea Weevil (Orchestes alni) in the leaves of Siberian Elm - An
introduced species from Europe, this insect has recently expanded in major
fashion from the Midwest into Colorado, and largely replaced another European
exotic, the Elm Leaf Beetle. At this time of year the flea weevil is mostly
present as larvae mining the outer margins of leaves. At this stop and others
we saw many bird species eating these larvae by biting the browned portion of
leaves with the insect morsel inside. Species included: Evening Grosbeak,
Black-headed Grosbeak, Bullock's Oriole, Western Kingbird, Yellow Warbler, and
House Sparrow. We also found adult weevils. This insect overwinters as adults
in the leaf litter, lays eggs on the newly emerged leaves, larvae feed as
leafminers, pupation is in the leaves, adults emerge and feed all summer
(causing round "shotholes" in the leaves), drop to the ground for overwintering
in late summer/fall, one generation per year (I mistakenly said two during one
of the field trips).
Robust Camel Cricket (Udeopsylla robusta) - one found semi-smashed on the
asphalt. This was unexpected at this location and is a prairie species often
utilized for food by Burrowing Owls, and probably many other birds such as
American Kestrel.
Sap wells made by a sapsucker species, probably Red-naped, on the trunk of a
Siberian elm sapling along the golf course. The symbiotic relationship between
sapsuckers and many other animals, including hummingbirds, visiting "taps" was
discussed.
On the trunk of a barkless telephone pole: mechanical marks in perfect rows
made at the sawmill during the turning process that might be confused with the
regular (but not perfect) row arrangement of sapsucker sap wells.
Additionally, sapsuckers always peck living trees with the prospect of sap
flow, never barkless, dead trunkwood. Other woodpeckers seeking wood-boring
larvae down in the outer rings of wood may chisel dead trunkwood, but their
efforts at excavation would not be particularly regular, would be rough around
the hole edges, and would almost never result in a pattern of both horizontal
and vertical rows.
On cue, a robin yanked a large earthworm from grass bordering the golf course.
We discussed the exotic nature (from Europe) of most lawn earthworms in North
America and everybody is referred to the recent Colorado Birds (April 2012, Vol
46, No.2) article on this topic.
Banded Elm Bark Beetle (Scolytus schevyrewi) in a dead Siberian Elm near the
parking lot entrance - an import from Asia (probably Walmart pallets from
China), this bark beetle has now largely replaced its European cousin the
Smaller European Elm Bark Beetle (S. multistriatus) as the default bark beetle
in elms. It is lethal to elms of all types stressed by drought but does not
appear to be as efficient a vector of the Dutch Elm Disease (DED) fungus as the
European species. In the long analysis, this may be good for survival of our
valued American Elms, which historically have been very prone to DED, but if
the drought continues on the eastern plains, may result in intensified
mortality of Siberian Elms (not a "quality" tree but in many situations better
than nothing). Like all bark beetles that exist for most of their life cycle
under the bark, they are only available as food to woodpeckers (on the plains,
primarily by Downy and Hairy).
2) Trinidad Catholic Cemetery on Main Street (= Rte. 350) just east of
downtown:
Pinyon Needle Scale (Matsucoccus acalyptus) on Pinyon Pine. This scale insect
is periodically cyclic on pinyon over large regional areas. They are small
(resemble a black pepper grain) and mostly occur on needles older than one year
old. They are common selections of small gleaner type birds such as Bushtit,
Juniper Titmouse, chickadees, and Black-throated Gray Warbler.
We talked about the cones of White Fir, and like all members of the genus
Abies, how their cones disintegrate in autumn as a form of seed dispersal. As
such, their seeds are not as available to birds over a long period of months as
would be the seeds in cones retained in the crowns of conifers like pine,
spruce, Douglas-fir, and juniper. Once on the ground, true fir seeds are
mostly eaten by mammals.
"Urn galls" on One-seed Juniper made by small midges in the family Cecidomyidae
(Walshomyia junipenna) spurred discussion of how they look different from both
green juniper berries and brown mature juniper berries, and how birds might
learn which object is an unripe "berry", which is mature and contains a single
hard seed, and which is an insect "pinata". We found the orange maggots which
caused formation of these galls. Bushtits, chickadees, titmice and like
species would be involved in such mystery solving.
On White Fir we looked at the newly-emerged, bright lime green foliage at
branch tips. Foliage uninfested with various insects tends to elongate and
push off the bud cap. Clumps of foliage infested by insects can be conspicuous
by its retention of the bud cap. We looked under bud caps still clinging to
the foliage and found Western Spruce Budworm (Choristoneura occidentalis)
larvae (the most important defoliator of native Rocky Mountain coniferous
forests) and aphids/adelgids (probably the Cooley Gall Adelgid (Adelges
cooleyi)). Birds use this same visual clue (retained bud cap) at this time of
year to find food during foraging. Budworms are favorite foods of Evening
Grosbeaks, both of which are experiencing "up" cycles at present in southern
and southwestern CO. Small sucking insects like aphids and adelgids are
utilized by many passerines. The fact they occur in clumped distributions make
the "nitpicking" effort birds must exert to obtain them worth the cost.
Spiny Elm Caterpillar (Nymphalis antiopa) on American Elm. These spiny, black
caterpillars with reddish prolegs, and which turn into Mourning Cloak
butterflies, feed on elm, willow, cottonwood, hackberry and occasionally other
deciduous trees. Something, presumably a bird like a kingbird or grackle,
found the colony of several dozen caterpillars noted during my scouting trip on
Thursday and ate most them prior to the Friday field trip. Friday's group saw
one uneaten caterpillar attaching itself to a branch, which we interpreted as a
precursor to forming a chysalis. The Saturday group discovered this to be an
act of skin-shedding, instead.
Also on American Elm we saw European Elm Flea Weevil mines, a type of
meandering moth leafminer (genus Lithocolletis, I think), and a heavy
infestation European Elm Scales (Gossyparia spuria, females are ladybird
beetle-sized, stationary, circular, and dark with a wide, whitish rim). The
latter are heavily eaten by many birds including House Finch, Black-capped
Chickadee, Downy Woodpecker, Cedar Waxwing, Pine Siskin, American Goldfinch,
orioles, European Starling, and Chipping Sparrow.
Pocket Gopher (probably Botta's (Thomomys bottae cultellus)) mounds dotted the
cemetery grounds. This large, mostly subterranean rodent, is not commonly
available to birds of prey. However, if found above ground, particularly young
animals during fall dispersal, the usual suspects like larger hawks, owls, and
eagles would take them.
Desert Cottontail (Sylvilagus audubonii) - Seen on the cemetery-wildland
interface. A mammal named for a famous ornithologist (who also studied/painted
mammals) ought to be food for birds and these rabbits, indeed, are that. The
same set of predators mentioned above in the gopher discussion catch them
alive, and many more bird species scavenge their remains on roadways and
elsewhere.
The one big Douglas-fir tree had many cones infested by some type of cone moth
(probably in the genus Dioryctria), as evidenced by missing seeds and fecal
pellets inside distorted and damaged cones. Such insects can be eaten by jays,
crossbills, and woodpeckers.
We saw no insects attacking the myriad, colorful plastic flowers adorning
gravesites at this cemetery, and, thus, no bird predation. However, judging by
the number of hummingbirds that approached the color-blotched T-shirts of field
trip participants, if a hummer predator (which is what, Dave?) hung out near
plastic flower arrangements, it might have some luck.
3) Trinidad Lake State Park including the extreme e end (Sunset Point) and the
main picnic area (near the Visitor Center/Entrance Station):
Midges (fly family Chironomidae) found in abundance in the cottonwood trees and
on other tall vegetation. These insects are aquatic as larvae. As adults on
land and in the air these harmless mosquito lookalikes constitute one of the
most abundant and valuable food resources to birds near water. That's what
those six-swallow-species flocks are getting over a reservoir in April. That's
what sitting phalaropes and Bonaparte's Gulls are getting from the water
surface.
Female cottonwood catkins prior to seed dispersal (look like hanging clusters
of small green grapes) are eaten by orioles, blackbirds, grosbeaks, waxwings,
and probably other passerines.
In the open areas among the rabbitbrush bushes was a Redshank Grasshopper
(Xanthippus corallipes), a common, large species marked by blood-red hind legs,
and talked about its high utility by many birds, including during winter when,
unlike most grasshoppers it overwinters in the adult stage. This is a common
item impaled by both shrike species on barbed wire.
On rabbitbrush we saw the white, oval galls of gall-forming fruit flies (family
Tephritidae, genus Aciurina). More pinatas for small winter bird species.
An Eastern Fence Lizard (Sceloporus undulatus) was amused by my
not-25-years-old-anymore attempts to catch it. It would not be so lucky with a
Greater Roadrunner, American Kestrel, Northern Pygmy-owl, Red-tailed Hawk, and
various corvids.
The "fruitworm", a type of free-ranging, bright lime green noctuid moth
caterpillar (probably Orthosia hibisci), found in our net after sweeping thru
the foliage of a Plains Cottonwood is a common prey of many, many passerines
foraging deciduous tree crowns in early summer. It would be a particularly
fitting food for nestlings.
The Rock Wren up on the dam face includes many spiders and other rock-dwelling
arthropods in its diet, and no doubt eats its share of midges and Darkling
Beetles (family Tenebrionidae). One large black tenebrionid (when disturbed,
lifts its rear end high in the air in characteristic posture) allowed us to
discuss how this family of beetles is key to the diet of Mountain Plover. This
bird's need to easily detect big beetles explains the types of
vegetation-challenged habitats (recent burns, fallow fields, prairie-dog towns)
in which we see them.
A small black-and-orange cicada species (Platypedia sp.) was seen on both
Thursday and Friday (also at the Catholic Cemetery). Colorado has at least 27
species of cicadas. The more noisy species generally can be divided into those
that "click" or those that make a shrill "buzzing". The type we found is one
of the clickers. Adult cicadas are highly sought after by birds, with
Mississippi Kites perhaps being best-known for this habit. Sandalid beetle
(family Sandalidae) larvae are predators of the big dog-day cicada (genus
Tibicen) nymphs in the soil, with the adult beetles being heavily predated in
late summer by birds like Blue Jays and Red-headed Woodpeckers at places like
the Lamar Community College Woods.
The omnivorous nature of American Crow was demonstrated during our lunch break
in the Picnic Area , when the fly-by corvid made an emphatic detour to eat part
of a discarded, conspicuously-yellow banana lying among the pinyons.
Among the flowers of Gambel Oak we found a very cryptic inchworm moth
caterpillar (looked just like the yellow and brown catkins). This led to
discussion of the various ways caterpillars attempt to avoid detection and
predation by birds and other predators, such as camouflage, leaf-mining between
the upper and lower layers of a leaf, leaf modification (folding, tieing, and
rolling), silk tents, hairs and stinging spines, distastefulness, mimicry of
distasteful objects (like monarch butterflies or bird droppings), etc.
The predominate odonate (member of the insect order Odonata containing
dragonflies and damselflies) present in the Trinidad Lake area was Variegated
Meadowhawk (Sympetrum corruptum). Kingbirds, swallows and many other birds eat
these predators of other insects.
4) Cokedale (mostly the small town park):
European Elm Flea Weevil was being consumed in Siberian Elms by many birds
including Evening Grosbeak and Bullock's Oriole.
Earthworms in the grass constituted lunch for robins, European Starlings, and
Common Grackles.
Both Black-chinned and Broad-tailed Hummingbirds frequented the sugar water
feeders provided on many porches.
5) Spanish Peaks State Wildlife Area (Dochter Unit) (Friday only):
We (mostly Gary Faust) pretended to be bears and tore the lower trunk bark off
a long-dead Ponderosa Pine killed by a suspected combination of drought and
engraver beetles (bark beetles in the genus Ips). We discussed the succession
of insects (greatly oversimplified) in such trees, starting with bark beetles
and progressing thru wood boring beetles ("lawyers", in that they are at the
accident but didn't do it), to carpenter ants, to the tree falling and being
utilized by isopods ("rolly-polly"), etc. Also involved in all this are yeast,
bacteria, and fungi, which all facilitate participation in the recycling
process by the other participants, including woodpeckers which both eat some
these organisms beneath the bark, and excavate homes in the decaying tree
(which in turn are used by other cavity-nesting and roosting species). One of
the nicest insects Gary found for us, and now headed to the collection at CSU,
was a dark brown adult click beetle. Larvae (often called "wireworms") of this
large beetle family feed in a variety of plant situations, including
semi-decayed wood.
Western Wood-Pewees were abundant at this site. A flying carpenter ant
(Camponotus sp.) we found would be typical of large flycatcher diets, which in
my experience appear to be comprised of many hymenopterans (bees and wasps), as
opposed to "flies".
We were entertained by what appeared to be three rival and/or courting
Plumbeous Vireos and a nearby Western Tanager. At this point we were too tired
to observe any food-related behaviors by the vireos, if there were any, and
just enjoyed the birds themselves. The tanager appeared to get a largish
insect (technical phrase) from the flowers of a chokecherry. As such, it
exemplified why we see birds at flowers. Sometimes they are actually eating
the flowers (finches, waxwings, etc.), and most of the time they are going
after flower visitors such as insects, spiders, and mites.
I am probably forgetting some things, but this is the gist of it.
I very much appreciate the curiosity, attitude, and active participation of the
field trip attendees. They got into it and made facilitation of the trips fun.
By my count we saw about 66 bird species during the scouting and actual
conducting of "hungry bird" trips. Considering pass-thru migrants were almost
non-existent during the Convention, that's a decent number. Nothing wrong with
lists and we all keep them. But what if what we counted, and contributed to
the general understanding of Colorado birds, were bird-food combinations? The
possibilities are endless when you think about figuring out the changing menus
and actual selections of 490+ species over long time spans in the varied
habitats that constitute our state.
Dave Leatherman
Fort Collins
PS I have to relate what I saw a Common Raven eat day before yesterday near
the entrance to Colorado National Monument at the Grand Junction end - a Milky
Way bar.
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