AZFO FIELD EXPEDITION

Vekol Valley Survey Summary

2 February 2008

Carl Tomoff

On 2 February 2008, nine members of the Arizona Field Ornithologists (AZFO) gathered to survey tobosa grassland habitat in the Vekol Valley, located in Maricopa County southwest of Casa Grande.  Though the intent of the trip was to focus on raptors and passerines in the grasslands, we found very little of that habitat.  Creosote bush flats dominated the lower valley with legume-lined washes draining saguaro-clad bajadas on its east and west flanks.  The effects of drought were evident throughout the region.  Virtually no herbaceous plants or their remains were found between creosotes or under mesquites.  Some mesquites even had dead branches and several of the few mistletoes present were also dead.  

 About 12-15 miles south of Interstate 8, dense, nearly monospecific thickets of mesquite have developed around a series of constructed berms, providing habitat strikingly distinct from the adjacent shrublands.  Ponds form in depressions behind the dikes when sufficient runoff occurs.  The few that contained water held a handful of waterfowl and shorebirds.  Since we found only small patches of tobosa grassland at the south end of the survey area, we explored mostly mesquite habitat.  We could see more extensive grassland south and east on Tohono O’odham lands. (Our Expedition did not survey these lands, as they are inaccessible without prior permission from the Tohono O’odham.)

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We divided into two groups.  One group worked south, starting near the north end of the system while the other group drove south to the grassland mosaic and moved north.  Most of the birds the “north team” found were at this first site, including 2 male Cinnamon Teal, 9 Northern Shovelers, 1 Killdeer, 1 Greater Yellowlegs, 1 Wilson’s Snipe, a Greater Roadrunner, Gila and Ladder-backed Woodpeckers, Black and Say’s Phoebes, Ruby-crowned Kinglets, and Yellow-rumped Warblers.  An Ash-throated Flycatcher, Northern Mockingbird, Crissal Thrasher, Chipping Sparrows, and an “Oregon” Junco were nearby.  Jenness and Yerger found a Sharp-shinned Hawk here during their reconnaissance trip on 15 January.

After finding the first three tanks without water, the “south team” encountered one tank with single Killdeer and Greater Yellowlegs and another pond with 4 Killdeer and a Wilson’s Snipe.  A flock of 12 White-crowned Sparrows foraged with 18 Dark-eyed Juncos (1 “Gray-headed”, 2 “Pink-sided”, and 15 “Oregon”).  A Bewick’s Wren briefly scolded then emerged from dense mesquite.  Canyon and Abert’s Towhees flushed near water edged with seep willow where a solitary House Wren skulked.    Tomoff heard one of the Canyon Towhees, slightly darker than most, exclaim alarm notes much like with those of Abert’s Towhees.  (This observation stimulated some interesting questions.  Could this bird be an intergrade?  How does the island-like isolation and small area of these mesquite thickets influence interaction between these two species?  See this link to Rich Hoyer’s website showing a presumed hybrid at Catalina State Park: http://personal.riverusers.com/~calliope/hybridtowhee.html).  Another surprise was an adult Ferruginous Hawk that flushed from a stand of tall thick mesquites.

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The groups met, returned to their cars, and joined for lunch at the starting point to recount the morning’s observations.  An unidentified hummingbird and 2 Mourning Doves flew by.  One group then stopped at another tank north of the starting point, finding an adult Red-tailed Hawk, while the other rechecked the duck pond and watched an American Kestrel fly overhead.

Finally everyone visited a pond near corrals and a large abandoned building, presumably a never-used meat-packing plant, where we found probable Great Horned Owl pellets and Barn Owl feathers as well as a Rock Wren.  On February 1 Tomoff had found a Great Horned Owl in dense cover along a nearby wash and watched an adult Harris’s Hawk circle above.  We discussed the plumage of a female Ring-necked Duck while Black Phoebes darted about the pond.  Ruby-crowned Kinglets and Yellow-rumped Warblers danced among mesquites where 2 Phainopeplas called.  Four male and 1 female Lawrence’s Goldfinches delighted everyone as they slipped to water’s edge and drank in full view.

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Overall the group tallied 248 birds representing 44 species.  The most abundant insectivorous passerines were Black-tailed Gnatcatchers and Ruby-crowned Kinglets; 6 Crissal Thrashers were widespread, but only 3 Verdins were found.  Five Gray Flycatchers were restricted to edges or openings in dense mesquite stands.  Granivores were generally scarce.  The four most common were usually in single flocks: Chipping Sparrows (20), Black-throated Sparrows (14), “Oregon” Dark-eyed Juncos (14), and White-crowned Sparrows (12).  Vesper and Savannah Sparrows flushed only from patches of tobosa grass at the south end of the survey area.  Horned Larks, Sage Sparrows, a Loggerhead Shrike, and a Sage Thrasher occurred there but also in open habitat near the mesquites.

Most of the birds we observed (60%) were concentrated at ponds or in mesquite habitat.  Only 7 species (11% of birds) were found in creosote bush flats: Sage Thrasher, Crissal Thrasher, Ruby-crowned Kinglet, Black-tailed Gnatcatcher, Black-throated Sparrow, Sage Sparrow, and White-crowned Sparrow.  Six species (5% of birds) flew by or overhead.

Birds observed in the Vekol Valley, 2 February 2008

            AZFO thanks team members for contributing their time and expertise to explore this interesting area and document its late winter residents.  They were: Eric Hough, Brian Ison, Morgan Jackson, Doug Jenness, Diana Stuart, Carl Tomoff, Marceline Vandewater, and John Yerger. Pictures 2, 3, and 5 were provided by Marceline Vandewater; pictures 1 and 4 provided by John Yerger.