Bursae, Reproductive Structures, and Scapular Color in Wintering Female Oldsquaws

Peterson, Steven R.; Ellarson, Robert S.

doi:10.2307/4085501

Cited by 11 publications

(4 citation statements)

References 9 publications

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“…As birds mature, the bursa regresses and eventually disappears, being absent altogether from adult birds (Esler and Grand 1994). For sea ducks, the degree of bursal involution provides an accurate measure of age, especially when used to separate first‐year birds (0–1 yr of age) from adults (>1 yr of age; Peterson and Ellarson 1978, Mather and Esler 1999). In the most complete study to date, Mather and Esler (1999) found that, of 217 known‐age harlequin ducks ( Histrionicus histrionicus ), 0% of second‐year or younger birds (≤14 months of age) and 2% of adults (≥26 months of age) had their ages misclassified based on bursal depth.…”

Section: Methodsmentioning

confidence: 99%

Reliability of External Characteristics to Age Barrow's Goldeneye

Lewis

Esler

Hogan

et al. 2020

Wildlife Society Bulletin

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Accurate assignment of age class is critical for understanding most demographic processes. For waterfowl, most techniques for determining age class require birds in hand, reducing utility for quickly and efficiently sampling a large portion of the population. As an alternative, we sought to establish an observation-based methodology, achievable in the field with standard optics, for determining age class of Barrow's goldeneyes (Bucephala islandica). We photographed heads, wings, and bellies of 232 Barrow's goldeneyes captured during late winter (February-April) of 2007-2015 along the north Pacific Coast. From these photographs, we focused on 5 external characteristics for both males and females, with binary states that putatively corresponded to 2 age classes-first-year birds (<1 yr) and adults (>1 yr). For males, all 5 external traits (belly color, head color, eye color, facial crescent, median secondary coverts color) had binary states that were reliably distinguishable by observers. Moreover, all 5 external traits were highly predictive of age class (≥96% concordance between external vs. bursal-derived ages), and novice observers, after receiving training, were able to accurately age 96% of first-year and 99% of adult males. In contrast, patterns were weaker for females; putative external characteristics of female age class (belly color, bill radiance, bill blackness, eye color, median secondary coverts color) had 77-91% concordance with bursalderived age, compared with 96-100% for males, and observers misidentified age classes of 15% of females, compared with only 2% of males. Overall, age classes of male Barrow's goldeneyes were accurately and reliably distinguishable during winter based on several external characteristics, whereas those of females were not. Our technique may be used to estimate age composition of male Barrow's goldeneyes during winter, providing a useful metric for monitoring annual changes in adult-to-juvenile ratios and other important demographic parameters.

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Section: Methodsmentioning

confidence: 99%

Reliability of External Characteristics to Age Barrow's Goldeneye

Lewis

Esler

Hogan

et al. 2020

Wildlife Society Bulletin

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“…Age and sex of afterhatching-year birds were determined by cloacal examination (hatching-year birds were not caught in our sample). Birds that possessed a bursa of Fabricius were classified as young birds in their second or third calendar year (Peterson and Ellarson 1978). Each bird was marked with a standard U.S.…”

Section: Methodsmentioning

confidence: 99%

Spacing Patterns, Mating Systems, and Winter Philopatry in Harlequin Ducks

Robertson

Cooke

Goudie³

et al. 2000

The Auk

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“…The drakes were rounded up with sea kayaks and corralled into funnel traps. Individuals were sexed and aged (yearling or adult) by measuring the depth of the bursa of Fabricius during cloacal examination (Peterson & Ellarson 1978). It is not possible to catch juveniles with this technique because they do not moult their flight feathers in their first year.…”

Section: Study Area and Field Methodsmentioning

confidence: 99%