Feature Articles

Incidence of Capped American Kestrel Eggs (Falco sparverius) in a Nest Box Program.

Jill Morrow & Lance Morrow

Capped eggs occur in nests when a part of an eggshell from a previously hatched egg adheres to an unhatched egg, potentially killing the embryo within or preventing its hatching.  During the last 3 of 11 breeding seasons (2008-2018) in an American Kestrel (Falco sparverius) nest box program in the Shenandoah Valley Raptor Study Area of Virginia, we observed capped kestrel eggs at an incidence of 2.3% (n = 4 of 177 successful nests).  Detection of capped eggs is time sensitive and requires close examination of all unhatched eggs.  The significance of egg capping is unclear but is likely not a significant factor limited kestrel productivity or populations.  We hypothesize that egg capping in kestrels is a symptom of aberrant behavior by female kestrels who do not promptly remove eggshells from the nest.

 

Molt Limits Reveal Extent of Molt and Age in Black-capped Vireos

David A. Cimprich

I determined the extent of preformative and prealternate molt in the wing plumage of the Black-capped Vireo (Vireo atricapilla) by examining molt and molt limits in 619 individuals within the breeding range at Fort Hood Military Installation in central Texas.  During the first molt cycle, these birds commonly replaced more secondaries and tertials than was previously known, typically four or five and as many as eight.  A few individuals preplaced outer primaries, primary coverts, and two alular quills during the first cycle which was also not previously known.  Most of the molt occurred away from the breeding grounds as evidenced by hatching-year birds at Fort Hood, which replaced not more than the tertials and one alular quill.  The replacement of primary coverts during the first cycle has not been reported for other vireos and is also unusually extensive in this species (as many as five feathers) compared to other North American passerines.  Second-year Black-capped Vireos replaced more wing feathers during their time away from the breeding grounds than after-second-years and the resulting molt limits in the secondaries, alula, primaries, and primary coverts provide additional characters for determining age.  Previously known characters for determining the age of adults during the breeding season are rendered useless early in the prebasic molt by the loss of key feather, but these new age characters allow ageing of many individuals for an additional month.

 

Band Wear in Spotted Towhees and Other Passerines

Walter H. Sakai

The issue of band wear and band loss has been a concern of bird banders for many years, but has primarily been a concern to larger, longer lived marine birds.  There are few reports of and less concern for band wear in smaller, terrestrial, primarily passerine birds.  Forty-four worn bands from ten passerine species, California {formerly Western} Scrub-Jay (Aphelocoma californica), Bewick’s Wren (Thryomanes bewickii), Wrentit (Chamaea fasciata), California Thrasher (Toxostoma redivivum), California Towhee (Melozone = Pipilo crissalis), Spotted Towhee (Pipilo maculatus), Fox Sparrow (Passerella iliaca), Song Sparrow (Melospiza meloidia), Gambel’s White-crowned Sparrow (Zonotrichia leucophrys gambelii), and Purple Finch (Haemorhous purpureus), are reported here, coming from six of the smaller band sizes (1, 1B, 1A, 1D, 2, and 3).  The percent weight loss per year are comparable to larger marine birds.  Although the actual age at which bands would be lost is not available, the age of the band at which the bander felt that the band was worn sufficiently enough to need replacing averaged about three to four years.  This was often less than half of the longevity records for most passerines.  Thus, we should concern ourselves with life history studies relying on banding records.

 

Molt and Ageing Criteria in Eight Birds from Northwestern Costa Rica

Tyler C. Christensen and Sean P. Graesser

Detailed descriptions of molt patterns and ageing techniques are lacking for many neotropical resident bird species. Using data collected from five years of December-January bird banding on the Nicoya Peninsula of the northwestern Pacific lowlands of Costa Rica, molt patterns and external ageing criteria were described for eight neotropical resident species frequently encountered in the region.  Molt patterns are other ageing criteria observed in the species included in this study followed patterns regularly seen in North American species, but either have not been documented or are in conflict with existing literature.  This study provides the first detailed accounts of molt patterns and other external age-deterministic characteristics in Black-headed Trogon (Trogon melanocephalus), Bright-rumped Attila (Attila spadiceus), Mangrove Vireo (Vireo pallens), Cabanis’s Wren (Cantorchilis modestus), Long-billed Gnatwren (Ramphocaenus melanurus), and Gray-headed Tanager (Eucometis penicillata), and suuplements existing literature describing molts of Rufous-and-white Wren (Thryophilus rufalbus) and Clay-colored Thrush (Turdus grayi).

 

Capture Efficiency of Three Mesh Sizes of Mist Nets

Michael D. Morrison

Mist nets of three mesh sizes were used at 36 net sites in old-growth chaparral.  Each size was used for the same number of net hours, once at each net site, over a span of 38 weeks.  The 30 mm mesh nets caught 54% more birds than the 36 mm mist nets, and 237% more than the 60 mm mesh nets.  Although several small species were captured more often in the 30 mm mesh, there was no significant tendency for thrush-sized birds.