U.S. Fish & Wildlife Service

Molt and Aging Criteria 

for Four North American 

Grassland Passerines 

Biological Technical Publication

BTP-R6011-2008

Bob Gress©
U.S. Fish & Wildlife Service

Molt and Aging Criteria 

for Four North American 

Grassland Passerines 

Biological Technical Publication

BTP-R6011-2008

Peter Pyle1

Stephanie L. Jones2

Janet M. Ruth3

1 The Institute for Bird Populations, Point Reyes Station, CA 2 U.S. Fish and Wildlife Service, Nongame Migratory Bird Program Region 6, 

Denver, CO 3 U.S. Geological Survey, Arid Lands Field Station, Albuquerque, NM

Cover image: Sprague’s Pipit

Photo credit: Bob Gress©
ii Molt and Aging Criteria for Four North American Grassland Passerines

Author contact information:

Peter Pyle

The Institute for Bird Populations

P.O. Box 1346

Point Reyes Station, CA 94956

Phone: (415) 663-2053

E-mail: ppyle@birdpop.org 

Stephanie L. Jones

U.S. Fish and Wildlife Service

Region 6 Nongame Migratory Bird Coordinator 

P.O. Box 25486 DFC

Denver, CO 80225

Phone: (303) 236-4409 

E-mail: stephanie_jones@fws.gov 

Janet M. Ruth

Research Ecologist

U.S. Geological Survey

Fort Collins Science Center

Arid Lands Field Station

Biology Department MSC03 2020

1 University of New Mexico

Albuquerque, NM 87131-0001

Phone: (505) 346-2870

E-mail: janet_ruth@usgs.gov

For additional copies or information, contact:

U.S. Fish and Wildlife Service

Region 6 Nongame Migratory Bird Coordinator 

P.O. Box 25486 DFC

Denver, CO 80225

Recommended citation:

Pyle, P., S.L. Jones, and J. M. Ruth. 2008. Molt and 

aging criteria for four North American grassland 

passerines. U.S. Department of Interior, Fish and 

Wildlife Service, Biological Technical Publication, 

FWS/BTP-R6011-2008, Washington, D.C.
Table of Contents iii

Table of Contents

List of Figures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Molt and Aging by Molt Limits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Species Accounts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Sprague’s Pipit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Grasshopper Sparrow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Baird’s Sparrow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Chestnut-collared Longspur. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Literature Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Appendix. Feather Collection Protocols for Analysis (Isotope and DNA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
iv Molt and Aging Criteria for Four North American Grassland Passerines

List of Figures

Figure 1. . Molt patterns among four species of grassland passerines during the first and definitive molt 

cycles. Solid bars indicate complete molts and dashed bars indicate incomplete, limited, or partial molts. 

Locations of where molts occur are indicated above the bars: BG = breeding grounds; WG = wintering 

grounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Figure 2. Tracts of the wing for identification of molt limits in grassland passerines. The primary covert tract 

is emphasized because it is often the best tract to use to separate SYs from ASYs in spring. Primaries are 

numbered distally and secondaries are numbered proximally, reflecting the order in which they molt (except 

for the tertials, which molt before other secondaries). Note that the “tertials” are usually considered a subset 

of the secondaries, s7-s9. Illustration: Steve N.G. Howell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Figure 3. Indication of molt limits within the wings of grassland passerines. Darker feathers indicate those 

replaced during the preformative (or prealternate) molt. A-E indicate limits resulting from varying extents 

of these molts. F represents uniform feather tracts following a complete molt. Illustration: Steve N.G. 

Howell. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Figure 4. A common molt-limit pattern found in certain SY passerines, including Baird's Sparrows. Darker 

feathers are formative and paler feathers are juvenal. Illustration: Steve N.G. Howell . . . . . . . . . . . . . . . . . . . 4

Figure 5. Juvenal (white), formative (stippled), and alternate (dark) feathers following the first-prealternate 

molt in certain passerines. Illustration: Steve N.G. Howell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Figure 6. Eccentric molt pattern among the primaries and secondaries. Note the replaced formative outer 

primaries and inner secondaries contrasting with a block of juvenal feathers in the center of the wing. 

Sprague’s Pipits may show this pattern. Illustration: Steve N.G. Howell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Figure 7. Specimens of HY and ASY Sprague’s Pipits (collected in Texas) demonstrating molt limits between 

formative and juvenal feathers (HY) and alternate and basic feathers (ASY). Note that the juvenal primary 

coverts on HYs are more tapered and worn than the basic primary coverts on ASYs. The difference becomes 

more obvious when comparing SYs with ASYs in spring. Photo: Peter Pyle . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 8. Apparent SY Sprague’s Pipit (from Montana) showing eccentric preformative molt patterns. Note 

that the outer four primaries appear fresher, darker, and with darker shafts than the inner five primaries. 

The three tertials also appear to have been replaced during the preformative and/or prealternate molts, as 

would be typical in individuals replacing the outer four primaries. The left wing showed the same patterns 

of replacement. Based on images of the tail, it is difficult to determine whether or not the rectrices were 

replaced during the preformative molt. Photo: Janet M. Ruth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 9. Feather generations among wing feathers in an apparent SY Sprague’s Pipit, captured in Montana 

in June. J = juvenal, F = formative, and A = alternate feather; red indicates good feathers to sample for 

connectivity studies. Photo: Janet M. Ruth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 10. Rectrix shape and condition by age in Sprague’s Pipit specimens (collected in Texas). Note that by 

spring the juvenal outer rectrix shown above will become even more worn and frayed in comparison to the 

basic outer rectrix. Juvenal rectrices might be replaced during the preformative molt but at what frequency 

is unknown (see Figures 11 and 12). Photo: Peter Pyle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figures 11 and 12. Rectrices in two apparent SY Sprague’s Pipits captured for banding in Montana in June. 

Both of these individuals showed apparent eccentric patterns in the wings. Many passerines with eccentric 

patterns replace all rectrices during the preformative molt but more study is needed (e.g., through 

biochemical analysis) to determine rectrix-replacement patterns in this species. Photos: Janet M. Ruth . . . . 8

Figure 13. Grasshopper Sparrow captured for banding in Montana. Note that all wing feathers appear to be 

uniform in quality, part of a single generation of either formative or basic feathers. The darker tertials and 
List of Figures v

proximal greater coverts represent pseudolimits rather than replaced feathers of a newer generation. Some 

of the scapulars as indicated may represent alternate feathers. Photo: Janet M. Ruth . . . . . . . . . . . . . . . . . . 11

Figure 14. Grasshopper Sparrow captured for banding in Montana in June. Note the more worn secondaries 

(especially s2-s6) perhaps representing retained juvenal feathers. Photo: Janet M. Ruth . . . . . . . . . . . . . . . . 11

Figure 15. Grasshopper Sparrow captured for banding in Montana in June. Look for darker and fresher 

feathers among the back and scapulars that could represent alternate feathers replaced on the wintering 

grounds. It would be of interest to compare the biochemical signals from these feathers with those of older, 

adjacent feathers. Photo: Janet M. Ruth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 16. Rectrices of a Grasshopper Sparrow captured for banding in Montana in June. The central 

rectrices were likely replaced due to accident rather than molt. It would be of interest to sample one of these, 

along with one of the other rectrices, to compare locations of development. Photo: Janet M. Ruth . . . . . . . . . 11

Figure 17. Specimens of SY and ASY Baird’s Sparrows (collected in Arizona) demonstrating the molt limit 

between the formative greater coverts and juvenal primary coverts in the SY, lacking in the ASY. Note the 

difference in quality of the primary coverts, and that both individuals had replaced 2-3 inner greater coverts 

during the prealternate molt. Photo: Peter Pyle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 18. SY Baird’s Sparrow in Montana in June showing molt limits in the wing. Note that the replaced 

formative greater coverts appear fresher and of better quality than the retained juvenal primary coverts 

(compare with Figure 19). Note also that the lesser alula appears to be replaced formative whereas the 

greater alula appears to be retained juvenal. Due to possible pseudolimits among tertials, it is difficult to tell 

whether or not they were replaced at the preformative molt. The juvenal outer primary is also narrow at the 

tip. This individual appears not to have replaced any tertials or greater coverts during the prealternate molt 

(the darker inner coverts resulting from pseudolimits) but appears to have newer alternate scapulars that 

can be used for feather sampling. Photo: Janet M. Ruth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 19. ASY Baird’s Sparrow in Montana in June showing uniformly basic feathers in the wing. In contrast 

to the SY in Figure 18, note the darker and higher-quality primary coverts, not contrasting as markedly with 

the greater coverts, which are slightly darker in color (naturally) than the primary coverts but uniform in 

wear and quality. The outer primaries are also broader and fresher at the tips. No greater coverts or tertials 

appear to have been replaced during the prealternate molt but note at least two replaced scapulars near the 

joint of the wing. Photo: Janet M. Ruth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 20. Shape and condition of the rectrices in Baird’s Sparrows captured for banding in Montana in June. 

Note that the SY appears to have replaced the central rectrices during the preformative and/or prealternate 

molt and that the ASY has replaced the right central rectrix during the prealternate molt. Photos: Janet M. 

Ruth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 21. Shape and condition of the outer rectrices in SY and ASY Baird’s Sparrows collected in Arizona. 

Some individuals show intermediate conditions that would be unreliable to use for aging. Note that the 

central rectrices appear to have been replaced during preformative and/or prealternate molts (see Figure 

20). Photo: Peter Pyle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 22. SY Baird’s Sparrow in Montana in June. Biochemical signals can be obtained for this individual’s 

natal site (juvenal secondaries and primaries), wintering site (alternate scapulars, tertials, and inner greater 

coverts), and possibly other molting sites (formative greater outer coverts). Photo: Janet M. Ruth . . . . . . . 14

Figure 23. AHY female Chestnut-collared Longspur wing (collected in California) showing uniformly basic 

wing feathers. HY/SYs show uniformly juvenal wing feathers throughout the year; thus, molt limits in the 

wing cannot be used for aging Chestnut-collared Longspurs, unlike the other species treated here. Note the 

broad primary coverts and outer primary tips and the richly colored tertials and greater coverts which, for a 

female, combine to indicate an AHY/ASY (Figure 24). Photo: Peter Pyle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 24. SY female and ASY male Chestnut-collared Longspurs collected on the wintering grounds in 

Arizona. Note the more worn wing coverts on the SY, and the lack of white on the inner primary coverts; 

within each sex, ASYs have more white than SYs (e.g., compare the SY female here with the AHY female in 

Figure 23). Photo: Peter Pyle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 25. Shape and condition of the outer rectrices in Chestnut-collared Longspurs (collected in Texas). 

This criterion is reliable throughout the year. Photo: Peter Pyle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
 vii

Acknowledgments

This document resulted from a U.S. Fish and 

Wildlife Service, Migratory Bird Office Region 6, 

grant to the Institute for Bird Populations (IBP) for 

the study of molt. We thank Stephen K. Davis for 

sharing images of Sprague’s Pipits at a workshop 

in Saskatoon, Saskatchewan, Canada, and David 

DeSante (IBP) for support and help administering 

the contract. We also thank Steve N.G. Howell for 

use of illustrations (Figures 2-6) from Pyle (1997a) 

and Maureen Flannery at the California Academy of 

Science and Carla Cicero at Museum of Vertebrate 

Zoology for allowing examination of specimens. We 

thank Michael T. Green, Kevin Kritz, and Maiken 

Winter for providing helpful comments on earlier 

drafts of this manuscript. This is contribution 

number 303 of the Institute for Bird Populations.

Acknowledgments
 1

Prairie and grassland habitats in central and 

western North America have declined substantially 

since settlement by Europeans (Knopf 1994) and 

many of the birds and other organisms that inhabit 

North American grasslands have experienced steep 

declines (Peterjohn and Sauer 1999; Johnson and 

Igl 1997; Sauer, Hines, and Fallon 2007). The species 

addressed here, Sprague’s Pipit (Anthus spragueii), 

Grasshopper (Ammodramus savannarum) and 

Baird’s (A. bairdii) sparrows, and Chestnut-collared 

Longspurs (Calcarius ornatus), are grassland birds 

that are of special conservation concern throughout 

their ranges due to declining populations and the 

loss of the specific grassland habitats required on 

both their breeding and wintering ranges (Knopf 

1994, Davis and Sealy 1998, Davis 2003, Davis 2004, 

Jones and Dieni 2007). 

Population-trend data on grassland birds, while 

clearly showing declines, provides no information 

on the causes of population declines. Without 

demographic information (i.e., productivity and 

survivorship), there are no means to determine when 

in their life cycle the problems that are creating 

these declines are occurring, or to determine to what 

extent population trends are driven by factors that 

affect birth rates, death rates, or both (DeSante 

1995). For migratory birds, population declines 

may be driven by factors on breeding grounds, 

during migration, and/or on wintering grounds. 

Lack of data on productivity and survivorship thus 

impedes the formulation of effective management 

and conservation strategies to reverse population 

declines (DeSante 1992). Furthermore, if deficiencies 

in survivorship are revealed, management strategies 

may need to address habitats on both breeding and 

non-breeding grounds, as well as along migratory 

pathways. One technique that helps inform 

management strategies is the biochemical analysis of 

isotopes and genetic markers, from the sampling of 

individual feathers from live birds (Smith et al. 2003, 

Pérez and Hobson 2006; Appendix). 

Determining demographic parameters and 

effectively sampling feathers to reveal connectivity 

between breeding and wintering grounds requires 

detailed knowledge of molt patterns and age 

determination criteria for the target species, in the 

hand. For example, productivity, survivorship, and 

territory acquisition may all be age-dependent, 

with first-year birds showing different patterns and 

responses than older birds. In many cases it may 

be possible to sample both a feather grown on the 

breeding grounds and one grown on the wintering 

grounds from a single individual, but knowledge of 

age-specific molt patterns, as well as an ability to 

recognize different feather generations, is needed 

to accomplish such a task. While some information 

on molt and aging criteria exists for grassland 

passerine species (Pyle 1997a), these species have 

been rarely captured during mark-recapture studies 

(Jones et al. 2007) and this information thus needs 

refining. There is a need for additional resources to 

assist field workers in determining molt patterns 

and age in captured individuals. 

Our objective is to describe molt and aging criteria 

for four grassland passerine species with the aid 

of digital photographs taken in the field. We hope 

that this document will be useful for researchers 

studying grassland species through capture and 

banding of live individuals on either the breeding or 

the wintering grounds. We present a general section 

on molt and aging techniques, followed by specific 

accounts for the four species treated: Sprague’s 

Pipits, Grasshopper and Baird sparrows, and 

Chestnut-collared Longspur. We also provide a brief 

protocol on collecting feather samples (Appendix). 

Molt and Aging by Molt Limits

Molt and plumage terminology used here follow 

Humphrey and Parkes (1959) as modified by Howell 

et al. (2003), and age terminology follows the 

calendar-based system presented by Pyle (1997a). 

Preformative and prebasic molts.--Passerines 

typically undergo a preformative molt (referred to 

as “first prebasic molt” in Pyle 1997a) in their first 

summer and fall, and a complete prebasic molt in 

July to October following breeding (Figure 1). For 

migratory species these molts can occur on the 

breeding grounds, on molting grounds away from 

breeding or wintering grounds, or on the wintering 

grounds; or, they can begin on breeding or molting 

grounds, suspend for migration, and complete on 

wintering grounds (Pyle 1997a). Which of these 

strategies is undertaken can vary both among 

species and among individuals of the same species 

(Figure 1). In Sprague’s Pipits, the location(s) where 

the preformative and prebasic molts occur have yet 

to be determined. 

The preformative molt undergone by first-cycle, 

hatching year/second year (hereafter “HY/SY”), 

passerines in July through September (Howell et al. 

2003; Figure 1) shows substantial inter- and intraspecific variation in both extent (varying from partial 

Introduction

Introduction
2 Molt and Aging Criteria for Four North American Grassland Passerines

to complete) and in location of occurrence (Pyle 

1997a). In some species (including Grasshopper 

Sparrows) the preformative molt is typically 

complete, and thereafter it becomes difficult or 

impossible to separate HY/SY from older after 

hatching year/after second year (hereafter “AHY/

ASY”) individuals by plumage-related criteria. In 

most passerine species; however, this molt is partial 

or incomplete. HY/SYs can be separated from 

AHY/ASYs throughout the year by the presence of 

“molt limits” (see below for details) within feather 

tracts (Figure 2; Pyle 1997a, 1997b; Froehlich 

2003), particularly those of the wing (Figure 2), 

and sometimes among the rectrices (tail feathers). 

Some passerines, particularly those that inhabit 

sunny or harsh environments, can also replace outer 

primaries during what is known as an eccentric 

preformative molt (Pyle 1997a, 1997b; see Figure 

6). Although undocumented in the four species 

treated here, it appears that at least some Sprague’s 

Pipits may undergo such a molt (see species account 

below). 

Prealternate molt.-- Prealternate molts typically 

occur before spring migration on wintering grounds 

(February to April). All four species treated here 

are reported to have limited or partial prealternate 

molts (Figure 1; but see the Grasshopper Sparrow 

Figure 1. Molt patterns among four species of grassland passerines during the first and definitive molt cycles. 

Solid bars indicate complete molts and dashed bars indicate incomplete, limited, or partial molts. Locations 

of where molts occur are indicated above the bars: BG = breeding grounds; WG = wintering grounds.

Figure 2. Tracts of the wing for identification of molt 

limits in grassland passerines. The primary covert 

tract is emphasized because it is often the best 

tract to use to separate SYs from ASYs in spring. 

Primaries are numbered distally and secondaries are 

numbered proximally, reflecting the order in which 

they molt (except for the tertials, which molt before 

other secondaries). Note that the “tertials” are 

usually considered a subset of the secondaries, s7-s9. 

Illustration: Steve N.G. Howell
 3

and Chestnut-collared Longspur accounts). This 

can result in up to two generations of feathers (basic 

and alternate) in ASYs and up to three generations 

(juvenal, formative, and alternate) in SYs (see 

Sprague’s Pipits and Grasshopper Sparrows species 

accounts, below). Alternate feathers are typically 

worn only for three to five months and can be poorly 

constructed and “looser”, as in juvenal feathers. 

In grassland species, these alternate feathers also 

typically occur in more exposed areas, such as 

among scapulars, inner and/or central wing coverts, 

tertials, and central rectrices. The prealternate molt 

is seldom more complete than the preformative molt. 

The use of molt limits, as in fall and winter birds 

(Figures 3 and 4), continues to be a reliable method 

of aging, once alternate feathers are recognized 

(Figure 5). The recognition of alternate feathers is 

also a crucial step in determining which feathers to 

sample for connectivity studies.

Molt limits.-- Molt limits are visual differences in 

feather color, shape, amount of wear, and quality 

within and between feather tracts due to differing 

feather generations resulting from partial molts. 

Molt limits occur most frequently and are easiest 

to identify among feather tracts of the wing. In 

October-March, HY/SYs of species that have 

incomplete preformative molts will show molt limits 

among the lesser, median, and greater coverts 

(Figure 3A-D); between the secondary coverts and 

the primary coverts (Figures 3E and 4); and/or 

among the tertials and inner secondaries (Figure 

3D-E). Some individuals, particularly those with 

more extensive wing molts (Figure 3D-E), may also 

replace the two central rectrices. Replaced feathers 

are formative whereas retained feathers, including 

most or all primaries, secondaries, and rectrices, are 

juvenal feathers developed at the natal site. Thus, 

through February on the wintering grounds, look for 

molt limits in the patterns of Figures 3A-E, 4, and 

5 on HY/SYs, and look for uniform basic feathers as 

in Figure 3F on HY/SY Grasshopper Sparrows and 

AHY/ASYs of all four species treated here. 

Juvenal feathers are typically of poorer quality 

than formative or basic feathers, and because of 

this are increasingly (through time) affected by 

feather wear. This is especially true of grassland 

species, where feathers of the upperparts and wing 

are typically exposed to more sunlight and abrading 

vegetation than woodland species. Juvenal wing 

coverts and tertials can often be recognized by their 

paler coloration and frayed tips, especially when in 

direct contrast with formative feathers (Froehlich 

2003). Juvenal flight feathers, particularly the outer 

primaries and rectrices, can wear more rapidly, 

resulting in a thinner shape and more frayed tips, 

especially in the spring and early summer. In 

Introduction

Figure 3. Indication of molt limits within the wings of grassland passerines. Darker feathers indicate those 

replaced during the preformative (or prealternate) molt. A-E indicate limits resulting from varying extents 

of these molts. F represents uniform feather tracts following a complete molt. Illustration: Steve N.G. 

Howell.
4 Molt and Aging Criteria for Four North American Grassland Passerines

Sprague’s Pipits, Baird’s Sparrows, and Chestnutcollared Longspurs, the presence of contrasts 

between juvenal and formative feathers, and the 

shape of the outer primaries and rectrices, are useful 

means of aging birds in winter and early spring 

(Pyle 1997a, 1997b). 

The ability to recognize feather generations on 

breeding and wintering birds is essential both 

for accurate aging of birds in the hand, and for 

assessing where in the annual cycle (e.g., on the 

breeding or wintering grounds) sampled feathers 

were developed using stable isotopes (Appendix; see 

Pérez and Hobson 2006) or other means. 

The following species accounts give details of molt 

and aging, accompanied by digital images, of each 

of the four species treated in this report. Live 

individuals of the four species were photographed 

by SLJ and JMR in 2004-2006 during a long-term 

banding study at Bowdoin National Wildlife Refuge 

in Phillips Co., north-central Montana (Dieni and 

Jones 2003, Jones et al. 2007). Individuals were lured 

into 30 or 36-mm mesh mist nets using tape playback 

recordings of conspecific song (Jones et al. 2007). 

Study skins housed at the California Academy of 

Sciences, San Francisco, California, and the Museum 

of Vertebrate Zoology, Berkeley, California, were 

examined by PP.

Figure 4. A common molt-limit pattern found in 

certain SY passerines, including Baird's Sparrows. 

Darker feathers are formative and paler feathers 

are juvenal. Illustration: Steve N.G. Howell

Figure 5. Juvenal (white), formative (stippled), 

and alternate (dark) feathers following the firstprealternate molt in certain passerines. Illustration: 

Steve N.G. Howell

Figure 6. Eccentric molt pattern among the primaries 

and secondaries. Note the replaced formative outer 

primaries and inner secondaries contrasting with a 

block of juvenal feathers in the center of the wing. 

Sprague’s Pipits may show this pattern. Illustration: 

Steve N.G. Howell
 5

Species Accounts

Species Accounts

Baird’s Sparrow. Photo: Bob Gress©
6 Molt and Aging Criteria for Four North American Grassland Passerines

Molt.--Our knowledge of molts in this species is 

rudimentary, based almost entirely on examination 

of a small (n = 15) number of specimens (Pyle 1997a, 

1997b). Thus, banding and feather-sampling studies 

will continue to be extremely useful in confirming, 

updating, or correcting available information. 

In HYs (hatching year), the preformative molt 

reportedly occurs from August-October and is 

partial to incomplete (Figure 1A). Where this molt 

occurs (on the breeding, molting, or wintering 

grounds) in Sprague’s Pipits is unknown; isotopic 

analysis (Appendix) would be useful in determining 

this (see below).

The preformative molt typically includes most or 

all body feathers, 5-10 greater coverts, and usually 

(in 80%; n = 15) 1-4 tertials/inner secondaries (Pyle 

1997a, 1997b). For HY/SYs in formative plumage 

(September-March), molt limits will occur among the 

median and greater coverts, between the greater and 

primary coverts, and/or among the tertials (Figures 

3B-E, 7, and 8). No rectrices are reported to be 

replaced during the preformative molt but study is 

needed to confirm this (see below). 

It appears that at least three SY individuals captured 

in Montana in June 2006 may have undergone 

eccentric preformative molts, replacing four outer 

primaries and the tertials (Figure 8). Species that 

undergo eccentric preformative primary molts 

typically also replace all rectrices and at least two 

of these individuals appeared to have had done so 

(see below). Another possibility, however, may be 

that birds showing this pattern are ASYs that had 

suspended molt for migration after replacing the 

inner five primaries, but it seems more likely that 

this was an eccentric molt on an SY, as found in many 

other passerines (Pyle 1997b). 

Eccentric molts have not been previously reported 

for Sprague’s Pipits but could occur based on 

the species’ exposed habitat preferences, where 

feathers degrade quickly from bleaching and/or 

abrasion (Pyle 1997a). Lark Bunting (Calamospiza 

melanocorys), a species with similar migration 

patterns and habitat requirements, also has an 

eccentric molt pattern (2-5 outer primaries replaced) 

and renews all rectrices during the preformative 

molt (Pyle 1997a) so it might not be an unexpected 

pattern in the unstudied Sprague’s Pipit. 

In AHYs, the prebasic molt occurs from AugustSeptember and is complete (Figure 1A). As with 

the preformative molt, the location where this molt 

occurs has yet to be determined. Because this molt is 

complete, AHY/ASYs in basic plumage (SeptemberMarch) will not show molt limits (Figure 3F), 

although it is possible that a suspension of molt for 

migration may simulate a molt limit (see Figure 8). 

The first and subsequent prealternate molts are 

limited to partial, and occur in March and April 

on the wintering grounds (Figure 1A). The first 

prealternate molt in SYs usually (75%; n = 15) 

includes 1-3 inner greater coverts, 1-3 tertials, and 

sometimes (25%; n = 15) 1-2 central rectrices (Pyle 

1997b). In the wing it is less extensive than the 

preformative molt so, by ignoring alternate feathers, 

molt limits between juvenal and formative feathers 

will still be useful in identifying SYs in April through 

August (Figure 5). In ASYs the prealternate molt 

may average more extensive, including 3-5 inner 

or medial greater coverts, 2-3 tertials, and (more 

often than in SYs) 1-2 central rectrices. Thus, ASYs 

in March-August may show molt limits resembling 

Figure 3C-D, but with 2-3 tertials replaced. 

Age Determination.--In September-March, HY/

SY Sprague’s Pipits will show molt limits among 

the greater coverts and/or tertials (Figures 3B-E). 

Replaced formative coverts will be noticeably darker 

and fresher looking than retained juvenal coverts 

(Figures 7, 8, and 9). It appears that some SYs may 

also have replaced the outer primaries in eccentric 

sequence during their preformative molt (Figure 

6) and thus show molt limits between the outer and 

inner primaries (Figures 8 and 9). It is probable that 

these primaries may not have been replaced until 

October and November on the wintering grounds 

but more study is needed to determine this. AHY/

ASYs in September-March, by contrast, should 

show uniformly basic secondary coverts and tertials 

(Figure 3F). The greater coverts may contrast 

slightly in color with the primary coverts but these 

feather tracts will appear uniform in feather quality 

(see Baird’s Sparrows species account below). On 

HY/SYs, the primary coverts are juvenal feathers 

and will appear tapered and worn as compared with 

the broader, less worn basic primary coverts of AHY/

ASYs (Figure 7). In addition, juvenal rectrices will 

be narrower and more pointed in HY/SYs than in 

AHY/ASYs (Figure 10); however, individuals with 

adult-like rectrices should be checked carefully for 

eccentric molt patterns (Figure 8). These individuals 

may replace all rectrices with formative feathers 

that resemble basic feathers (Figure 11). 

In spring (February-June), both SYs and ASYs may 

show molt limits resulting from prealternate molts, 

but some formative feathers usually remain on SYs, 

allowing the continued use of molt limits to age these 

(Figures 5, 7, 9, 11, and 12). Eccentric molt patterns 

among the primaries would continue to indicate 

SY (Figures 6 and 8). Otherwise, the shape and the 

condition of the primary coverts (Figure 7) may be 

the best method of separating SYs from ASYs. Some 

individuals may also retain juvenal rectrices (Figures 

10 and 12) which would be of continued use in aging; 

however, individuals with adult-like rectrices may be 

SYs that had replaced them during the preformative 

molt (see Figure 11) and, thus, ASYs should not be 

aged by rectrix shape alone. 

Sprague’s Pipit (Anthus spragueii) 
 7

Figure 7. Specimens of HY and ASY Sprague’s 

Pipit (collected in Texas) demonstrating molt 

limits between formative and juvenal feathers 

(HY) and alternate and basic feathers (ASY). Note 

that the juvenal primary coverts on HYs are more 

tapered and worn than the basic primary coverts on 

ASYs. The difference becomes more obvious when 

comparing SYs with ASYs in spring. Photo: Peter 

Pyle

Figure 8. Apparent SY Sprague’s Pipit (from 

Montana) showing eccentric preformative molt 

patterns. Note that the outer four primaries appear 

fresher, darker, and with darker shafts than the 

inner five primaries. The three tertials also appear to 

have been replaced during the preformative and/or 

prealternate molts, as would be typical in individuals 

replacing the outer four primaries. The left wing 

showed the same patterns of replacement. Based on 

images of the tail, it is difficult to determine whether 

or not the rectrices were replaced during the 

preformative molt. Photo: Janet M. Ruth

Figure 9. Feather generations among wing feathers 

in an apparent SY Sprague’s Pipit, captured in 

Montana in June. J = juvenal, F = formative, and 

A = alternate feather; red indicates good feathers 

to sample for connectivity studies. Photo: Janet M. 

Ruth

Figure 10. Rectrix shape and condition by age in 

Sprague’s Pipit specimens (collected in Texas). 

Note that by spring the juvenal outer rectrix shown 

above will become even more worn and frayed 

in comparison to the basic outer rectrix. Juvenal 

rectrices might be replaced during the preformative 

molt but at what frequency is unknown (see Figures 

11 and 12). Photo: Peter Pyle

Species Accounts
8 Molt and Aging Criteria for Four North American Grassland Passerines

Feather Sampling for Biochemical Analysis.--As 

alluded to above, much can still be learned about 

molt in Sprague’s Pipits based on biochemical 

analysis. At any time of year, juvenal feathers can be 

recognized in the wing (and at least sometimes the 

rectrices) and sampled to determine the location or 

latitude of the natal site. Perhaps the best strategy 

would be to sample some barbs from the base of the 

innermost primary, which will always be a juvenal 

feather on SYs. For ASYs this feather should 

indicate where the prebasic molt commenced, either 

on the breeding grounds, the wintering grounds, 

or perhaps at a molting stopover site. On HY/SYs 

showing eccentric patterns it would also be useful 

to sample barbs from the first replaced primary 

(e.g., p6 in the individuals in Figures 8 and 9). 

This should indicate where this eccentric portion 

of the preformative molt occurred, most likely on 

the wintering grounds or at a stopover location. 

Sampling of both an inner and an outer primary in 

ASYs could also reveal whether or not the prebasic 

molt was suspended for migration (Pérez and 

Hobson 2006). 

In spring, look also for different generations of 

wing coverts (e.g., Figure 5; the ASY in Figure 

7) and tertials on both SYs and ASYs. It would 

probably be easiest to sample from tertials and 

inner secondaries, as varying numbers of tertials 

are usually replaced during preformative and 

prealternate molts (Figures 8 and 9), and in some 

individuals up to two or even three generations of 

feathers may be present in these tracts. In Figure 9, 

for example, signals from the natal site (s1-s5), the 

location of the preformative molt (s6, s7 and s9), and 

the location of the prealternate molt (s8) might all be 

detected by taking barb samples from secondaries 

of the right wing. On ASYs, the locations of both the 

prebasic and the prealternate molts may similarly 

be detected by sampling basic and alternate feathers 

among the tertials. Signals from two to three 

locations might also be detected by taking a sample 

from a central rectrix (often replaced during the 

prealternate molt) along with samples from one or 

more other, more distal rectrices (Figure 12). 

We recommend taking samples from several feathers 

among the primaries, greater coverts, secondaries, 

tertials, and rectrices, to gain a better understanding 

of how extensive each molt is and where it occurs. 

Even within tracts, it is possible that different 

feathers have been replaced at different locations 

within the same molt. We would recommend taking 

samples from p1 (Figure 2) and an outer primary in 

fall and winter, as well as from the greater coverts 

and/or inner secondaries and tertials in spring.

Figures 11 & 12. Rectrices in two apparent SY Sprague’s Pipits captured for banding in Montana in June. 

Both of these individuals showed apparent eccentric patterns in the wings. Many passerines with eccentric 

patterns replace all rectrices during the preformative molt but more study is needed (e.g., through 

biochemical analysis) to determine rectrix-replacement patterns in this species. Photos: Janet M. Ruth
Species Accounts 9

Grasshopper Sparrow. Photo: Bob Gress©
10 Molt and Aging Criteria for Four North American Grassland Passerines

Molt.--In HY Grasshopper Sparrows, the 

preformative molt occurs from July to November 

and is usually complete (Figure 1C). Pyle (1997a) 

indicates that occasional HY/SYs may retain some 

medial juvenal secondaries during the preformative 

molt but this appears to be a rare occurrence. 

This molt can take place on the breeding grounds, 

wintering grounds, or both, being suspended for 

migration. As in Baird’s Sparrows (see below), the 

tertials and inner greater coverts are naturally 

blacker, representing “pseudolimits” (Pyle 1997a: 

207-208; Figure 13). Thus, although it may appear 

that there are molt limits, most to all HY/SYs should 

have uniformly formative feathers following the 

preformative molt. 

In AHY Grasshopper Sparrows, the prebasic molt 

occurs from July - September and is complete 

(Figure 1C). It reportedly occurs primarily on the 

breeding grounds but this should be confirmed with 

biochemical analysis. Grasshopper Sparrows may 

undergo unusual breeding and migration strategies, 

and some birds (at least) may show variable molt 

patterns with relation to migration (Vickery 1996). 

Because this molt is complete, AHY/ASYs in basic 

plumage (September to March) will not show 

molt limits (Figure 3F), and will thus be similar 

in appearance to HY/SYs (Figure 13). However, 

occasional HY/SYs (perhaps 20-30%, n = 40) may 

retain juvenal secondaries among s4-s6 during the 

preformative molt (Pyle 1997a; Figure 14). Pyle 

(1997a) also reports that some birds may undergo 

a prealternate molt of some body feathers but this 

report also needs to be confirmed, perhaps through 

biochemical analysis. Such a limited prealternate 

molt might include feathers of the head and upper 

back (Figures 13 and 15).

Age Determination.--Because both the 

preformative and the prebasic molts are complete 

in most Grasshopper Sparrows it is not possible 

to age most individuals to HY/SY once the skulls 

undergo complete ossification in October through 

February, although those HY/SYs that retain 

secondaries among s4-s6 may be recognized to age 

by molt limits within this tract (see Figure 14). 

Another area to look for retained juvenal feathers 

in Grasshopper Sparrows is among the underwing 

coverts. For example, during the preformative molt 

many blackbirds replace all feathers except for the 

primary and some greater coverts on the underwing 

(Pyle 1997a) and it is possible that other species may 

show this feather-retention pattern as well. Look 

for paler and more worn juvenal underwing coverts 

contrasting with darker and more glossy replaced 

coverts (see Figure 323 in Pyle 1997a). 

In some species, formative feathers can show 

retained characteristics of juvenal plumage. For a 

species like Grasshopper Sparrows, which can have 

a complete preformative molt, it would be useful 

to document what juvenal feathers look like on 

juvenile birds in summer and early fall, and to see 

if formative-plumaged birds in winter and spring 

may retain some of these juvenal characteristics. 

Otherwise, biochemical analysis might provide clues 

to aging, since the preformative molt can occur 

on the wintering grounds and the prebasic molt is 

supposed to occur on the breeding grounds (see 

below).

Feather Sampling for Biochemical Analysis.--It 

is likely that more can be learned about molt and 

aging of Grasshopper Sparrows through biochemical 

analysis than for any of the other three species 

covered in this report. It is known that some HYs 

migrate in juvenal or partial juvenal plumage, 

indicating that some feathers can be replaced on 

the wintering grounds or on molting grounds (Pyle 

1997a). Thus, samples from p1, p9, the tertials 

(s7-s9), and s6 will help us determine where these 

feathers were replaced. Likewise, the outer and 

central rectrices might be good feathers to sample. 

If any feathers appear to have been replaced 

adventitiously (e.g., Figure 16), it would be good to 

compare them with adjacent feathers that have not 

been replaced. Finally, search for newer-looking 

feathers among the scapulars and/or in the back 

(Figures 13 and 15) that might represent alternate 

feathers. Sampling these (along with adjacent, more 

worn feathers) would not only help confirm the 

presence and extent of a prealternate molt, it might 

also help determine both wintering and molting 

grounds for the same individual. 

Grasshopper Sparrow (Ammodramus savannarum) 
 11

Figure 13. Grasshopper Sparrow captured for 

banding in Montana. Note that all wing feathers 

appear to be uniform in quality, part of a single 

generation of either formative or basic feathers. 

The darker tertials and proximal greater coverts 

represent pseudolimits rather than replaced 

feathers of a newer generation. Some of the 

scapulars may represent alternate feathers. Photo: 

Janet M. Ruth

Figure 14. Grasshopper Sparrow captured for 

banding in Montana in June. Note the more worn 

secondaries (especially s2-s6) perhaps representing 

retained juvenal feathers. Photo: Janet M. Ruth

Figure 15. Grasshopper Sparrow captured for 

banding in Montana in June. Look for darker and 

fresher feathers among the back and scapulars 

that could represent alternate feathers replaced 

on the wintering grounds. It would be of interest to 

compare the biochemical signals from these feathers 

with those of older, adjacent feathers. Photo: Janet 

M. Ruth

Figure 16. Rectrices of a Grasshopper Sparrow 

captured for banding in Montana in June. The 

central rectrices were likely replaced due to accident 

rather than molt. It would be of interest to sample 

one of these, along with one of the other rectrices, to 

compare locations of development. Photo: Janet M. 

Ruth

Species Accounts
12 Molt and Aging Criteria for Four North American Grassland Passerines

Molt.--In HY Baird’s Sparrows, the preformative 

molt occurs from July - November and is partial 

(Figure 1B). According to the literature (e.g., Pyle 

1997a) this molt can take place on the breeding 

grounds, the wintering grounds, or both, being 

suspended for migration. The preformative molt 

typically includes most or all contour feathers 

and all secondary coverts but no primary coverts, 

primaries, or secondaries. Thus, molt limits (Figure 

4) result from the preformative molt. Pyle (1997a, 

1997b) reports that 2-3 tertials are also typically 

replaced during the preformative molt, but this 

should be confirmed based on biochemical analysis. 

The tertials (and inner greater coverts) are naturally 

blacker in this species, resulting in “pseudolimits” 

(Figures 18 and 19; Pyle 1997a: 207-208), and thus, 

it can be difficult to assess whether or not these 

feathers had been replaced during preformative 

and/or prealternate molts. The central rectrices are 

also replaced often during the preformative molt 

(Figure 20). In AHYs the prebasic molt occurs from 

August - November and is complete (Figure 1B). 

It reportedly occurs primarily on the wintering 

grounds but this should also be confirmed with 

biochemical analysis. Because this molt is complete, 

AHY/ASYs in basic plumage (September-March) 

will not show molt limits (Figure 3F).

The first and subsequent prealternate molts in 

Baird’s Sparrows are partial, and occur in FebruaryApril on the wintering grounds (Figure 1B). 

Although molt limits among the greater coverts 

will occur in about half of birds in spring, the limit 

between the formative outer greater coverts and 

juvenal primary coverts will be present in all SYs 

(Figures 17 and 18).The first and subsequent 

prealternate molts are similar in extent sometimes 

including 1-5 inner greater coverts and 1-3 tertials 

(30-50% of individuals), and occasionally including 

1-2 central rectrices (~17% of individuals; n = 26). 

When no wing feathers are renewed, scapulars 

adjacent to the wing often have been replaced and 

can be recognized as fresher feathers (Figures 18 

and 19). ASYs will have no limit in this area (Figure 

19). 

Age Determination.--The best way to age Baird’s 

Sparrows throughout the year is by the presence 

or absence of a molt limit between the greater 

coverts and the primary coverts (Figures 4, 17 and 

18). Juvenal primary coverts in HY/SYs, especially 

toward the outer portion of the wing, are typically 

frayed, narrow, and pale brown. These contrast 

with the darker and fresher, replaced, formative 

greater coverts (Figures 17 and 18). In AHY/ASYs 

the primary coverts are darker, broader and fresher 

(Figures 17 and 19) and do not contrast in quality 

with the greater coverts (Figure 19). This difference 

is not affected by the prealternate molt and is thus 

valid for aging Baird’s Sparrows throughout the 

year. 

Other useful criteria include the shape and 

condition of the primaries (Figures 18 and 19) 

and the rectrices (Figures 20 and 21). By using a 

combination of all of these criteria it will be possible 

to age most or all birds encountered on the breeding 

grounds. 

Feather Sampling for Biochemical Analysis.--As 

with Sprague’s Pipits, it should be possible to obtain 

feather samples representing breeding, molting, 

and wintering sites from Baird’s Sparrows, often 

from the same individual. On HY/SYs in both winter 

and summer, feathers developed on the breeding 

site include the primaries, secondaries, and outer 

rectrices, possibly excepting the tertials in a few 

individuals. As the preformative molt can occur 

on breeding grounds, wintering grounds, or both, 

it will be of interest to sample multiple formative 

feathers, to try and establish the locations of both of 

these grounds and perhaps additional molting areas. 

Feathers molted earlier in the preformative molt 

include those of the crown and upper back, whereas 

later molted feathers include the scapulars, tertials 

(if replaced), and central rectrices (if replaced). The 

wing coverts are typically replaced all at once, and 

it would be interesting to know where this occurred, 

so taking a formative greater covert (toward the 

outside of the tract) would also be of value. On 

AHY/ASYs sampled on the wintering grounds, all 

feathers may produce winter-ground signals but it 

would be interesting to see if some birds may begin 

the prebasic molt on the breeding grounds, and 

this might be established by taking a sample from 

the innermost primary, or feathers of the crown 

and back. In addition, it is possible (but unlikely for 

this species) that birds may interrupt migration to 

molt somewhere north of the wintering grounds, 

in which case these or other feather samples may 

provide this information. In spring, winter signals 

should be obtained from alternate feathers among 

greater coverts (Figure 17 and 22), tertials (Figure 

22), scapulars (Figures 18, 19, and 22), and central 

rectrices (Figures 20 and 21). 

Baird’s Sparrow (Ammodramus bairdii)
 13

Figure 17. Specimens of SY and ASY Baird’s 

Sparrows (collected in Arizona) demonstrating the 

molt limit between the formative greater coverts 

and juvenal primary coverts in the SY, lacking in the 

ASY. Note the difference in quality of the primary 

coverts, and that both individuals had replaced 2-3 

inner greater coverts during the prealternate molt. 

Photo: Peter Pyle

Figure 18. SY Baird’s Sparrow in Montana in June 

showing molt limits in the wing. Note that the 

replaced formative greater coverts appear fresher 

and of better quality than the retained juvenal 

primary coverts (compare with Figure 19). Note 

also that the lesser alula appears to be replaced 

formative whereas the greater alula appears to 

be retained juvenal. Due to possible pseudolimits 

among tertials, it is difficult to tell whether or not 

they were replaced at the preformative molt. The 

juvenal outer primary is also narrow at the tip. This 

individual appears not to have replaced any tertials 

or greater coverts during the prealternate molt (the 

darker inner coverts resulting from pseudolimits) 

but appears to have newer alternate scapulars that 

can be used for feather sampling. Photo: Janet M. 

Ruth

Figure 19. ASY Baird’s Sparrow in Montana in June 

showing uniformly basic feathers in the wing. In 

contrast to the SY in Figure 18, note the darker and 

higher-quality primary coverts, not contrasting as 

markedly with the greater coverts, which are slightly 

darker in color (naturally) than the primary coverts 

but uniform in wear and quality. The outer primaries 

are also broader and fresher at the tips. No greater 

coverts or tertials appear to have been replaced 

during the prealternate molt but note at least two 

replaced scapulars near the joint of the wing. Photo: 

Janet M. Ruth

Figure 20. Shape and condition of the rectrices in 

Baird’s Sparrows captured for banding in Montana 

in June. Note that the SY appears to have replaced 

the central rectrices during the preformative and/or 

prealternate molt and that the ASY has replaced the 

right central rectrix during the prealternate molt. 

Photos: Janet M. Ruth

Species Accounts
14 Molt and Aging Criteria for Four North American Grassland Passerines

Figure 21. Shape and condition of the outer rectrices 

in SY and ASY Baird’s Sparrows collected in 

Arizona. Some individuals show intermediate 

conditions that would be unreliable to use for aging. 

Note that the central rectrices appear to have been 

replaced during preformative and/or prealternate 

molts (see Figure 20). Photo: Peter Pyle

Figure 22. SY Baird’s Sparrow in Montana in 

June. Biochemical signals can be obtained for this 

individual’s natal site (juvenal secondaries and 

primaries), wintering site (alternate scapulars, 

tertials, and inner greater coverts), and possibly 

other molting sites (formative greater outer 

coverts). Photo: Janet M. Ruth
Species Accounts 15

Chestnut-collared Longspur. Photo: Bob Gress©
16 Molt and Aging Criteria for Four North American Grassland Passerines

Molt.--In HY Chestnut-collared Longspurs, the 

preformative molt occurs on the breeding grounds 

from July - September and is partial (Figure 1D). 

Compared to the other three species treated here, 

this molt is less complete, typically including body 

feathers but no wing or tail feathers. In AHYs, the 

prebasic molt also occurs in July - September, on or 

near the breeding grounds, and it is complete. Thus, 

neither HY/SY nor AHY/ASY Chestnut-collared 

Longspurs will show molt limits in the wing at any 

time of the year (Figure 23). Pyle (1997a) indicates 

that some individuals may undergo a limited 

prealternate molt of head and breast feathers but a 

recent examination of specimens failed to detect any 

certain alternate feathers on spring and summer 

birds. The colorful black and chestnut feathers 

of males, developed during the preformative or 

prebasic molts, are tipped buff in fall and winter. 

This buff tipping then wears off by spring, unveiling 

the colorful “breeding” formative and basic plumage 

aspect. However, there may also be a few feathers 

replaced on some birds, and it would be important 

to recognize and sample these feathers to obtain a 

signal from winter grounds.

Age Determination.-- Condition of the wing 

coverts and amount of white edging to the inner 

primary coverts should also allow reliable aging of 

most individuals (Figures 23 and 24). Probably the 

most reliable method of aging Chestnut-collared 

Longspurs throughout the year is by the shape of 

the rectrices (Figure 25). Within each sex, AHY/

ASYs will average brighter plumage than HY/SYs 

(e.g., see Figure 23), especially in males during the 

breeding season. Unlike other species, the presence 

or absence of molt limits in the wing will not provide 

a clue to age. 

Feather Sampling for Biochemical Analysis.--

Unlike in the other species treated here, most or all 

feathers will likely yield a signal from the breeding 

grounds. It will thus be of interest to collect feather 

samples from wintering grounds to determine 

breeding or molting localities. Some or all individuals 

may migrate away from their nesting territories to 

undergo the preformative or prebasic molt, and it 

is possible that this difference may be detectable. 

For HY/SYs, sampling from any of the wing or tail 

feathers should yield a natal signal, whereas a body 

feather will yield the location of the preformative 

molt, which may or may not occur exactly on or near 

the natal site. AHY/ASYs will likely have undergone 

the entire prebasic molt in one locality but it may 

not necessarily be on the natal site, and obtaining 

information about this locality through biochemical 

analysis would be of interest. 

On the breeding grounds, it is important to look for 

any newer feathers that may yield a winter signal. 

These may include a few head or breast feathers 

replaced during the prealternate molt or, especially, 

adventitiously replaced wing or tail feathers. Look 

for these adventitiously replaced feathers among the 

tertials, wing coverts, rump feathers, and rectrices, 

feathers that often are lost during stressful 

interactions or while avoiding predators. 

Chestnut-collared Longspur (Calcarius ornatus) 
 17

Figure 23. AHY female Chestnut-collared Longspur 

wing (collected in California) showing uniformly 

basic wing feathers. HY/SYs show uniformly juvenal 

wing feathers throughout the year; thus, molt limits 

in the wing cannot be used for aging Chestnutcollared Longspurs, unlike the other species treated 

here. Note the broad primary coverts and outer 

primary tips and the richly colored tertials and 

greater coverts which, for a female, combine to 

indicate an AHY/ASY (Figure 24). Photo: Peter Pyle

Figure 24. SY female and ASY male Chestnutcollared Longspurs collected on the wintering 

grounds in Arizona. Note the more worn wing 

coverts on the SY, and the lack of white on the inner 

primary coverts; within each sex, ASYs have more 

white than SYs (e.g., compare the SY female here 

with the AHY female in Figure 23). Photo: Peter 

Pyle

Figure 25. Shape and condition of the outer rectrices 

in Chestnut-collared Longspurs (collected in Texas). 

This criterion is reliable throughout the year. Photo: 

Peter Pyle

Species Accounts
18 Molt and Aging Criteria for Four North American Grassland Passerines

Davis, S.K. 2003. Nesting ecology of mixed-grass 

prairie songbirds in southern Saskatchewan. 

Wilson Bulletin 115:119–130.

Davis, S.K. 2004. Area sensitivity in grassland 

passerines: effects of patch size, patch shape, 

and vegetation structure on bird abundance 

and occurrence in southern Saskatchewan. Auk 

121:1130-1145. 

Davis S.K., and S.G. Sealy. 1998. Nesting biology of 

the Baird’s Sparrow in southwestern Manitoba. 

Wilson Bulletin 110:262–270.

DeSante, D.F. 1992. Monitoring avian productivity 

and survivorship (MAPS): a sharp, rather than 

blunt, tool for monitoring and assessing landbird 

populations. Pages 511-521 in D. R. McCullough 

and R.H. Barrett, editors. Wildlife 2001: 

populations. Elsevier Applied Science, London, 

England 

DeSante, D.F. 1995. Suggestions for future 

directions for studies of marked migratory 

landbirds from the perspective of a practitioner 

in population management and conservation. 

Journal of Applied Statistics 22:949-965. 

Dieni, J.S., and S.L. Jones. 2003. Grassland songbird 

nest site selection patterns in north central 

Montana. Wilson Bulletin 115:388-396.

Froehlich, D. 2003. Ageing North American 

landbirds by molt limits and plumage criteria. 

Slate Creek Press, Bolinas, California. 

Howell, S.N.G., C. Corben, P. Pyle, and D. Rogers. 

2003. The first basic problem: a review of molt and 

plumage homologies. Condor 105:635-653. 

Humphrey, P.S., and K.C. Parkes. 1959. An approach 

to the study of molts and plumages. Auk 76:1-31. 

Johnson, D.H., and L.D. Igl. 1997. Changes in 

breeding bird populations in North Dakota: 1997 

to 1992-93. Auk 114:74-92. 

Jones, S.L., and J.S. Dieni. 2007. The relationship 

between predation and nest concealment in 

mixed-grass prairie passerines: an analysis using 

program MARK. Studies in Avian Biology 34:117-

123.

Jones, S.L., J.S. Dieni, M.T. Green, and P.J. Gouse. 

2007. Annual return rates in breeding grassland 

songbirds. Wilson Bulletin of Ornithology 119:89-

94.

Knopf, F.L. 1994. Avian assemblages on altered 

grasslands. Studies in Avian Biology 15:247–257.

Pérez, G., and K.A. Hobson. 2006. Isotopic 

evaluation of interrupted molt in northern 

breeding populations of the Loggerhead Shrike. 

Condor 108:877-886. 

Peterjohn, B.G., and J.R. Sauer. 1999. Population 

status of North American grassland birds from 

the North American Breeding Bird Survey, 1966-

1996. Studies in Avian Biology 19:27-44. 

Pyle, P. 1997a. Identification guide to North 

American birds. Part 1. Slate Creek Press, 

Bolinas, California. 

Pyle, P. 1997b. Molt limits in North American 

passerines. North American Bird Bander 22:49-

90. 

Smith, T. B., P.P. Marra, M.S. Webster, I. Lovette, L. 

Gibbs, and R.T. Holmes. 2003. A call for feather 

sampling. Auk 120:218-221. 

Sauer, J.R., J.E. Hines, and J. Fallon. 2007. The 

North American Breeding Bird Survey, results 

and analysis 1966 - 2006. USGS Patuxent Wildlife 

Research Center, Laurel, Maryland. <http://www.

mbr-pwrc.usgs.gov/bbs/> (7 April 2008).

Vickery, P.D. 1996. Grasshopper Sparrow 

(Ammodramus savannarum). In A. Poole and 

F. Gill, editors. The Birds of North America, No. 

239. Academy of Natural Sciences, Philadelphia, 

Pennsylvania; The American Ornithologists’ 

Union, Washington, D.C.

Literature Cited
 19

Appendix

Appendix

Feather Collection Protocols for Analysis 

(Isotope and DNA)

For DNA analysis it is easiest to take two rectrices 

(tail feathers), which provides enough DNA to 

proceed with genetic analysis, although only one 

is needed for isotopic analysis. In general, we 

recommend taking a central rectrix from one side 

of the tail and an outer rectrix from the other side 

of the tail. This will keep the tail as “balanced” as 

possible while also preserving rectrices that are most 

likely to have been grown at different times of year 

or in different locations, thus resulting in more data 

from the individual based on isotopic analyses. For 

example, the central rectrix may have been grown 

on the breeding grounds followed by suspension 

for migration and replacement of the outer rectrix 

on the wintering grounds, or all rectrices may have 

developed on the breeding grounds and the central 

rectrix replaced again on the wintering grounds 

during a prealternate molt, resulting in signals 

from both breeding and a wintering grounds from 

the same individual. For isotopic analyses it is also 

useful, for the same reason, to take feathers or 

feather samples from other parts of the body. These 

might include juvenal feathers from nestlings; newer, 

alternate back feathers from breeding individuals, or 

samples from the bases of inner and outer primaries, 

which may have grown at different localities (see 

Pérez and Hobson 2006 for examples and methods). 

By knowing molt patterns and bird age it may be 

possible to get feather samples from three locations 

from a single individual.

1) To take a rectrix hold the tail feathers close to the 

base with your fingers and gently pull it out. Please 

take care not to touch the feather (quill) once you 

have pulled out the feather as this is where the DNA 

is tested. Feathers need to be pulled and not cut 

because: a) they will then grow back; b) the DNA is 

found within the skin cells at the base of the feather. 

For back feathers from nestlings, simply and gently 

pluck the feathers. Put feathers from each nestling 

in a separate envelope. For primaries it is best to 

take a section of barbs from the inner web of each 

sampled primary. Primaries are too hard to pull out, 

and taking a small (~ 1cm x 1 cm) section will allow 

the bird to continue flying without hindrance.

2) Insert the feather(s) into a coin envelope. Only use 

one envelope per individual; in some cases it might 

be advisable to use separate envelopes for separate 

feathers or feather generations from the same 

individual and to clearly mark which feathers are in 

each envelope.

3) Write the following information on the outside 

of the envelope. Use pencil or permanent ink (so 

it doesn’t run on the feathers in case the sample 

gets wet). For nestlings, in the comments section 

or on the back, record the other band numbers of 

their siblings; we need to be able to sort out related 

individuals. Remarks should include where the 

feather was sampled and what generation (juvenal, 

formative, basic, alternate) the feather was believed 

to be.

Record:

Species, Sex, Age (if known), Date, Location 

(including the state), and Band Number.

Remarks: include what feather tract sampled; 

relationship to other samples, etc.

4) Store samples in a dry place, in a sealed plastic 

bag; any humidity or water can ruin the sample.
U.S. Department of the Interior

U.S. Fish & Wildlife Service

Route 1, Box 166

Shepherdstown, WV 25443

http://www.fws.gov

September 2008