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. -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to cobirds@googlegroups.com. 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