Mean chick-aging accuracy without and with the tool for observers in field and laboratory tests.

<p>Chick-aging accuracy is the percentage of chicks aged correctly by observers when not using (dark gray) and when using (light gray) and the aging tool. Error bars are ±1 SE.</p

Are Morphometrics Sufficient for Estimating Age of Pre-Fledging Birds in the Field? A Test Using Common Terns (<i>Sterna hirundo)</i>

<div><p>Age is a key component of fitness, affecting survival and reproductive capacities. Where it is not possible to study known individuals from birth, morphometrics (predominantly patterns of plumage development for birds) are most often used to estimate age. Although criteria for age estimations exist for many species, the degree to which these criteria improve the precision of estimates remains to be tested, restricting their widespread acceptance. We develop a photographic tool for estimating ages of Common Tern (<i>Sterna hirundo</i>) chicks and test it using 100 human observers of varying prior experience across four breeding colonies (three North American sites and one European site) and under controlled laboratory conditions. We followed the design approach of other morphometric tools, expanding it to create a user-friendly guide (divided into six age groupings). The majority (86%) of observers improved in chick-aging accuracy when using the tool by an average of 20.1% (±1.4 SE) and correctly estimated 60.3% (±1.4) of chick ages. This was similar to the intrinsic aging ability of our best field observer (63.3%). Observers with limited experience showed the greatest increases in chick-aging accuracy over experienced observers who likely had established a method for estimating chick ages prior to using the tool. Even the best observers only correctly estimated ages of chicks 62.9% (±2.8) of the time in the field and 84.0% (±2.9) of the time in the lab when using the tool and typically underestimated ages. This indicates that developmental variation between individual chicks can prevent completely reliable age estimates and corroborates the few existing data that suggest that morphometric criteria fail to achieve robust levels of accuracy and may introduce error into studies that rely on them. We conclude that novel approaches for estimating age, not only morphometric criteria, must be pursued.</p></div

Morphometric features most often used for aging estimates prior to and when using the tool.

<p>Data are percents of responses of observers in laboratory tests (n = 87) when asked which criteria they used to estimate age.</p><p>Morphometric features most often used for aging estimates prior to and when using the tool.</p

Example of age group from the tool.

<p>Age group 6 (chicks 20–23 days old) is shown (full tool is provided as <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0111987#pone.0111987.s001" target="_blank">Fig. S1</a>). Within the age group, pictured chicks increase in age from left to right; an image of the outstretched wing of the oldest chick is provided. Morphometric data summaries and key diagnostic characteristics are also shown.</p

Boxplots of improvement in chick-aging accuracy when using tool for observers of different prior experience in (a) field and (b) laboratory tests.

<p>Improvement in chick-aging accuracy is the difference in the percentage of chicks aged correctly when using the tool versus without the tool. Sample sizes of observers are given in parentheses next to axis labels. “No Experience” = no prior experience working with any birds, “Some Experience” = <1 year working with birds (including Common Terns) [for laboratory trials this was any previous experience with birds], and “Most Experience” = 1+ years working with Common Terns.</p

hoisting engine

hoisting engine[PT] No engine; only th'hoisting engine,that's all.YesJ. D. A. WIDDOWSON JUL 1973Not UsedNot usedWithdrawnChecked by Jordyn Hughes on Wed 22 Apr 201