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Friday, June 17, 2016

2016 Tejon Ranch Breeding Bird Blitz

2016 Tejon Ranch Breeding Bird Blitz

Ellery Mayence, Tejon Ranch Conservancy Senior Ecologist

On June 4th, 2016, Tejon Ranch Conservancy staff and a suite of keen birding enthusiasts (three teams in total) branched out in different directions across Tejon Ranch, spending eight hours per team censusing all birds heard and/or seen.  One team targeted portions of the San Joaquin Valley, while the other two canvased the Antelope Valley (East and West).  With conditions being warm, sunny, and generally agreeable for bird watching, a total of 2533 birds were observed (Figure 1).  The greatest number of birds was observed in the Western Antelope Valley grasslands and associated riparian and oak woodland habitat (1076), followed by similar habitat in the San Joaquin Valley (836), and the Eastern Antelope Valley (621), where observers targeted Joshua tree woodland, higher elevation scrub oak and chaparral vegetation, and ultimately montane mixed conifer forest.  A different pattern was observed when the total number of species is considered, with the San Joaquin exhibiting the greatest number of species (55), followed by the West Antelope Valley (44) and the East Antelope Valley (40).

Figure 1.  Total number of a) birds and b) bird species observed by region of Tejon Ranch as part of the 2016 Breeding Bird Blitz.

A total of 70 species were observed by the three teams, with more than 100 individuals observed for five species (horned lark, European starling, mourning dove, tricolored blackbird, and acorn woodpecker), and fewer than 10 individuals observed for 37 species (Figure 2).  Of the 70 species observed, 69 are native to the region, with the one non-native being the European starling.

Figure 2.  Number of birds observed by species for the 39 most commonly encountered species.  Five or fewer individuals were observed for the remaining 31 species including: great horned owl, hairy woodpecker, Stellar’s jay, tree swallow, Bewick’s wren, Cooper’s hawk, barn owl, northern flicker, black phoebe, northern mockingbird, purple finch, California condor, greater roadrunner, spotted towhee, western tanager, Scott’s oriole, mallard duck, turkey vulture, prairie falcon, mountain quail, Pacific-slope flycatcher, wrentit, yellow warbler, great-tailed grackle, killdeer, downy woodpecker, Say’s phoebe, ruby-crowned kinglet, Swainson’s thrush, American robin, and American goldfinch.

With respect to the five most encountered species, a few conclusions can be drawn.  It should not come as a surprise that a large number of horned larks were observed, as Tejon Ranch supports more than 100,000 acres of grassland habitat, horned larks are obligate grassland species, and two of the teams spent a considerable amount of their survey time traversing through grassland habitat.  European starlings, much like acorn woodpeckers, are cavity nesters and the large number of mature valley oaks on Tejon Ranch provide ideal nesting habitat for such species.  Oak woodland is the second most dominant habitat type on the ranch and two teams dedicated a large proportion of their survey time to oak woodland – so high tallies for these two species was expected.  Mourning doves, to a large degree, forage in grassland and roost in woodland, so when the amount of these two habitat types is combined, this species’ habitat requirements are well supported on the ranch (and it was frequently observed).  However, when it comes to the tricolored blackbird, neither grassland nor oak woodland is necessarily required nesting habitat, so why were so many observed?  Their presence and the approximately 200 observations made during the survey is primarily a result of an 1/8 of an acre cattail-filled stock pond in the West Antelope Valley portion of the survey.  Interestingly, this same stock pond is also where the majority of the red winged and Brewer’s blackbirds and great-tailed grackles were observed.

Though none were observed as part of the official Breeding Bird Blitz, purple martin enthusiasts can rest assured by the fact that numerous breeding pairs (and colonies) have been observed on the ranch this year.  Tejon Ranch Conservancy will continue to search for and observe purple martins until early July to better understand the condition of their preferred and/or required habitat, nesting site preferences and other behavioral attributes.

The Breeding Bird Blitz was conducted at a time when many bird species are establishing nest sites, incubating eggs, or feeding chicks yet to fledge.  As stated before, with grassland being the dominant vegetation type on Tejon Ranch, it is not uncommon to encounter ground nesting birds (Figure 3) as one peruses grassland habitat (with not all nests being those of obligate ground nesting species).  When a bird is flushed from grassy habitat during breeding season, spend time looking because a nest is often nearby.

Figure 3.  Shown (left to right) are nests of horned lark, mourning dove, and lark sparrow, all found in grassland habitat of Tejon Ranch in May and June of 2016.

As with previous avifauna surveys, the 2016 Breeding Bird Blitz was successful, fun and informative.  All participants enjoyed their time afield and are eagerly looking forward to their next opportunity to take part in similar Tejon Ranch Conservancy-based activities.  Please consider monitoring Tejon Ranch Conservancy’s website and social media pages for news on membership, upcoming events and outing opportunities.