Moult Patterns Research Articles

Molt patterns, aging, and sexing criteria for ten temperate Neotropic bird species: an important resource for bird monitoring programs

Molt patterns, aging, and sexing criteria for ten temperate Neotropic bird species: an important resource for bird monitoring programs

Using generalised additive models to visualise the annual cycle of primary feather moult patterns

Moult is a vital but energy-demanding event in a bird's phenological cycle. Primary moult is the shedding of old feathers and the regeneration of new flight feathers to maintain efficient functioning of these critical structures. Life history events, such as moult, breeding and migration, are typically separated from one another temporally because of the costs associated with moult Thus, extrapolation of other life-history events is possible from an understanding of the primary moult schedule in species for which data are easier to collect This study aimed to explore the primary moult patterns of nine nectarivorous species (seven Sunbirds and two Sugarbirds) using data extracted from the South African Bird Ringing Unit (SAFRING) database. Logistic generalised additive models (GAMs) were fitted to active/inactive moult observations to explore annual primary moult patterns. Breeding patterns based on the presence of brood patches in females were also analysed using GAMs for species with sufficient data. The GAMs illustrated the annual patterns well, with the probability of moult having clear peaks and troughs, allowing intuitive understanding of annual life-history patterns, such as the probability of breeding. Generally, GAMs hold potential to be used as a supplementary tool to study the timing of primary moult GAMs appear especially useful for species with no well-defined annual moult period.

Colony attendance and moult pattern of Cory's Shearwaters (Calonectris borealis) differing in breeding status and age

Migratory birds must fit three costly life‐history events within the annual cycle, reproduction, moult and migration, to minimize their overlap and maximize survival and breeding success. However, some seabirds, such as Cory's Shearwater Calonectris borealis, overlap body moult and breeding, with flight feather renewal occurring in late chick‐rearing. In contrast, the moult patterns of non‐breeding adult (sabbatical) and immature Cory's Shearwaters, which also attend the colony during the breeding season, remain poorly understood. Furthermore, the potential implications of life‐stage and breeding status trade‐offs on moult status and colony attendance in non‐breeders has rarely been investigated. Surveying different areas within one colony between June and September 2013 and 2014, we studied the age and breeding status composition of birds attending the breeding colony and scored moult of their body (breast and upper‐neck), wing and tail feathers. We found that in addition to breeders (n = 165), 57.6% of the birds (n = 389) attending the colony were 4‐ to 10‐year‐old immatures (n = 132) and adult sabbatical shearwaters (n = 92). Sabbaticals and 8‐ to 10‐year‐old immatures (n = 28) were present at the colony during incubation, whereas only three sabbatical birds and no 8‐ to 10‐year‐old immatures were captured in late chick‐rearing. Conversely, 4‐ to 7‐year‐old immatures arrived later in the season but were still present in late chick‐rearing. Sabbatical and 8‐ to 10‐year‐old immatures were moulting body feathers at the same time as adult breeders, whereas, among 4‐ to 7‐year‐old immatures, older birds moulted earlier than younger birds. A larger proportion of sabbatical birds were replacing tail feathers compared with adult breeders. However, there was no evidence that sabbaticals or 8‐ to 10‐year‐old immatures differed in wing moult from adult breeders until August. Overall, our study shows that colony attendance by non‐breeding adults and immatures is widespread in this population. The synchronous moult schedule of flight and body feathers across age groups at different life‐history stages may suggest that this aspect of moult is controlled by environmental conditions.

Pattern and intensity of moult in White-capped/Shy Albatrosses Thalassarche steadi/cauta

Albatrosses typically only replace a subset of flight feathers each annual moult cycle. We scored the moult of 662 White-capped/Shy Albatrosses Thalassarche steadi/cauta, using birds that had been killed by longline fisheries off South Africa. Most adults and immatures alternated replacing the outer primaries (phase 1) and inner primaries (phase 2), but there was considerable variation among adults, with 0–10 primaries replaced each moult cycle. Birds in phase 1 moult replaced fewer primaries than birds in phase 2, but the proportion by mass was similar. Adults replaced more primaries than immatures as there was a disproportionate number of adults in phase 2 moult (82%), which might indicate that most adults off South Africa are in their first year after a successful breeding attempt, but a similar bias occurred among beached birds from New Zealand and Australia. The outer primaries were usually replaced outwards from P8, but the replacement sequence was more variable among the inner primaries. Secondary moult overlapped with primary moult, but not all secondaries were moulted each year. Adults had more active moult centres and replaced more secondaries at once than immatures. Tail moult started after primary moult, with 1–11 feathers growing from 1–6 active centres. Some birds replaced their rectrices in pairs, with often 2 or 3 pairs moulting at once, but others replaced alternate feathers or almost all rectrices at once. A few birds exhibited intense wing moult, but the norm was to replace only 1 or 2 primaries and 1–6 secondaries at once. Age- and sex-related differences in moult intensity presumably result from different time constraints. Adult White-capped/Shy Albatrosses take a year off between successful breeding attempts, allowing time for a more protracted moult. However, we cannot explain the intense moult in some immatures. Our findings support recent studies showing that albatross flight feather moult patterns are more varied than previously reported.

A quantitative assessment of ontogeny and molting in a Cambrian radiodont and the evolution of arthropod development

AbstractRadiodonta is a clade of stem euarthropods of central importance to our understanding of the evolution of this phylum. Radiodonts include some of the largest early Paleozoic animals; however, little is known about their ontogeny. We present an analysis of molting patterns and ontogeny in the radiodont Stanleycaris based on 265 exceptionally preserved specimens from the mid-Cambrian (Wuliuan) Burgess Shale. Ranging in size from 10 to 83 mm, they constitute the most extensive radiodont ontogenetic series known. Using a novel morphospace approach, we show that putative carcasses and exuviae can be quantitatively distinguished by the particular suites of structures preserved and their modes of preservation. We propose that Stanleycaris, and probably other radiodonts, molted via a suture near the anterior of the trunk. Similar anterior molting strategies, with a suture located at the head–trunk boundary, are shared with some Cambrian euarthropods and are potentially ancestral. Allometric analyses suggest that as Stanleycaris body size increased, the head sclerite and neck became relatively broader, while the trunk and flaps became slightly longer. The eyes developed precociously, indicating an important role of visual processing in juveniles. Finally, we find evidence for an initial anamorphic developmental phase, where segment number increased at least from 11 or 12 up to 17, followed by an epimorphic phase, in which growth continued without segment addition. This is consistent with the hypothesis that finite postembryonic segment addition (hemianamorphosis) is ancestral for arthropods and refines the timing of the origin of this important developmental mode.

Plumage dimorphism and moult patterns of weaverbirds – a review

The colourful plumages of weaverbirds (family Ploceidae, with 118 species recognised) provide a well-known and in part iconic showcase of sexual selection, with widespread sexual dimorphism (93 species) as well as seasonal dimorphism (62 species). The tremendous diversity in both the type and degree of plumage dimorphism is poorly known, which calls for a better and extended understanding of the highly variable moult patterns in this group. Here, we lay a foundation for this by reviewing and discussing what is known of the timings and patterns of moult in the Ploceidae. The extent of post-juvenile moult is poorly known in weavers: it is known to be complete in 10 species, partial in two species, and either complete or partial in six species. However, it is likely that there is more variation than previously thought. Weavers typically have a complete moult after breeding, and before breeding a partial prenuptial moult, restoring the male (and, in some species, female) breeding plumage; this usually involves only body feathering, one exception being the Seychelles Fody Foudia sechellarum, which has a complete prenuptial moult. We compiled primary moult data based on the proportion of feather mass grown, for 11 weaver species, three of which are newly reported on. Timing of primary moult is discussed in relation to sex, location and annual timing. The duration of primary moult varies widely between and within species, from 46 days (1.5 months) in a widowbird to 215 days (7 months) in an arid species. Weavers in arid regions have longer moult durations than weavers in other regions. Examples of the overlap of primary moult and breeding are presented.

How molting locusts avoid cannibalism

Abstract Group living has various benefits, but it also carries costs, such as risk of cannibalism. Molting is a vulnerable period of being cannibalized in juvenile arthropods, but how gregarious arthropods avoid this threat is poorly understood. Here, we examined how actively migrating gregarious nymphs of desert locust, Schistocerca gregaria, avoid cannibalism during molting, in the Sahara Desert of Mauritania. In the field, gregarious nymphs cyclically march and feed on grass during the day. Our field observations found that marching behavior helped separating pre-molting and cannibalistic non-molting nymphs. Cannibalistic non-molting nymphs marched away from roost plants, leaving sedentary pre-molting nymphs behind, creating cannibal-free spaces. Some non-molting nymphs reached a pre-molting state after daytime marching, thus both pre- and non-molting nymphs roosted on same plants at night. However, pre-molting nymphs moved away from conspecifics prior to molting. Starvation experiments confirmed that food-satiation decreased cannibalistic necrophagy. Physiological surveys of diel feeding and molting patterns revealed that nymphs molted at times when conspecifics were food-satiated rather than hungry. Hence, our results indicate that behavioral and physiological traits of gregarious locusts could function to spatiotemporally separate molting locusts from cannibalistic conspecifics, thus reducing molting-associated cannibalism. This is the first report of migration-dependent molting synchrony as a mechanism reducing costs of aggregation in gregarious arthropods.

Many Central American hummingbirds can be aged and sexed by molt patterns and bill corrugations

Many Central American hummingbirds can be aged and sexed by molt patterns and bill corrugations

A new biologging approach reveals unique flightless molt strategies of Atlantic puffins.

Animal-borne telemetry devices provide essential insights into the life-history strategies of far-ranging species and allow us to understand how they interact with their environment. Many species in the seabird family Alcidae undergo a synchronous molt of all primary flight feathers during the non-breeding season, making them flightless and more susceptible to environmental stressors, including severe storms and prey shortages. However, the timing and location of molt remain largely unknown, with most information coming from studies on birds killed by storms or shot by hunters for food. Using light-level geolocators with saltwater immersion loggers, we develop a method for determining flightless periods in the context of the annual cycle. Four Atlantic puffins (Fratercula arctica) were equipped with geolocator/immersion loggers on each leg to attempt to overcome issues of leg tucking in plumage while sitting on the water, which confounds the interpretation of logger data. Light-level and saltwater immersion time-series data were combined to correct for this issue. This approach was adapted and applied to 40 puffins equipped with the standard practice deployments of geolocators on one leg only. Flightless periods consistent with molt were identified in the dual-equipped birds, whereas molt identification in single-equipped birds was less effective and definitive and should be treated with caution. Within the dual-equipped sample, we present evidence for two flightless molt periods per non-breeding season in two puffins that undertook more extensive migrations (>2000 km) and were flightless for up to 77 days in a single non-breeding season. A biannual flight feather molt is highly unusual among non-passerine birds and may be unique to birds that undergo catastrophic molt, i.e., become flightless when molting. Although our conclusions are based on a small sample, we have established a freely available methodological framework for future investigation of the molt patterns of this and other seabird species.

Split moult: a response to time constraints during the main moult period

Split moult is a relatively rare adaptation to cope with time constraints in the annual cycle, although less rare than previously thought. This moult pattern mainly occurs among long‐distance migrants but also among some northern species wintering in the northern or temperate zones. Hedenström et al. rejected the conclusion of Kiat and Izhaki that split moult is a time constraint strategy; instead, they advocated the view that it is an endogenously controlled strategy. They based their conclusion on the first winter secondaries moult by juvenile birds and on the post‐breeding moult sequence. In contrast, we argue that Hedenström et al.'s conclusions are flawed, probably due to their focus on only one species (Barred Warbler Curruca nisoria). Our results suggest that there are no indications of the uniqueness of the secondaries moult by juvenile birds in relation to other species which have no split moult. We thus suggest that split moult is not initiated during the birds' first winter. In addition, there is no difference in moult sequence, although decoupling between two feather tracts occurs (primaries and secondaries), which is a common mechanism among many passerines that perform a partial or incomplete moult. We therefore argue that split moult is an adaptive strategy driven largely by the actual time constraints the birds experience, as already experimentally proven.

Molt patterns, aging criteria, and molt-breeding seasonality of 8 native forest birds from the Island of Hawai‘i

‘O ka nui o ka ‘ikepili no ke ‘ano a me ka manawa o ka hānau keiki ‘ana a me ka māunu ‘ana o nā manu, ua loa‘a mai ke kālailai ‘ana i nā manu o nā ‘āina kemepale. ‘O nā manu kopikala, he ‘oko‘a loa ko lākou pō‘aiapuni ola. Ma ka hala ‘ana o nā makahiki he mau miliona, ua liliuewe mai he mau lāhulu manu ‘āpa‘akuma ma Hawai‘i pae ‘āina nei, he ‘āina kopikala i loa‘a ‘ole nā kau kemepale. Ua kālailai māua i ka ‘ikepili mai nā atikala he nui ma waena o ka makahiki 1994 a i ka makahiki 2020. He mau ‘atikala kālailai ia i nā pō‘aiapuni ola o nā manu o kekahi mau ‘āina ‘oko‘a i mea e kālai ai i ke ‘ano o ka māunu ‘ana o nā manu, a i mea ho‘i e ho‘okahua ai i nā kūlana pa‘a e maopopo i ke keka a me ka nui makahiki o nā manu ma ke ‘ano kūmau o ka ‘ōnaehana WRP. He ‘ōnaehana ka WRP e hō‘oia ai i ke ‘ano o ka wā māunu a me ke kūlana makahiki o nā manu kopikala. Eia ho‘i, ua wehewehe māua i ka pō‘aiapuni o ka wā māunu, a me ka pō‘aiapuni o ka hānau keiki ‘ana o nā manu i kālai ‘ia. Ua helu ho‘i māua i ka ‘oko‘a o nā manu kāne a me nā manu wahine o ‘ewalu mau lāhulu manu Hawai‘i ma ke ‘ano o ka waiho‘olu‘u o ka hulu a me nā ‘oko‘a ‘ē a‘e o ke kino. Ua hō‘oia māua i ke kūpono o ka WRP i ‘ōnaehana hō‘oia kūlana makahiki ma kona ‘ano he ki‘ina hana e hō‘oia ai i ke kūlana makahiki o nā manu nahele o ka mokupuni ‘o Hawai‘i. Ua wae‘ano nō māua i nā manu a pau o nā lāhulu ‘ewalu i kālai ‘ia ma ke ‘ano o ka hulu a me ke ‘ano o ka māunu ‘ana; ‘o ia mau ‘ano o ka hulu, he hulu kuapo‘i, hulu ‘ōpiopio, a he hulu makua. Eia ho‘i, he ‘elua mau ‘ano hulu makua ‘ana ko ‘elua o nā lāhulu manu. Ua ‘oko‘a nā lāhulu manu ‘ewalu a pau mai ke ‘ano o nā manu kemepale i ka ‘oi lō‘ihi o ko lākou mau wā hānau keiki a me ko lākou mau wā māunu. He ka‘awale na‘e ia mau wā kekahi mai kekahi, no ka ho‘oluhi nui paha i ke kino o ka manu. Kaulapa iki nā wā hānau keiki a me nā wā māunu o kekahi mau manu o ia mau lāhulu, ‘a‘ole na‘e i nui loa nā manu e hana pēlā. He ‘elua wale ho‘i mau lāhulu i ‘oi nui ia kaulapa ‘ana ma ‘umi pakeneka a ‘oi o nā manu i hopu ‘ia. He kōkua nui ka ‘oi maika‘i o nā ki‘ina hana hō‘oia keka a me nā ki‘ina hana hō‘oia kūlana makahiki i ka hō‘oia‘i‘o i ka ‘ikepili i ‘ohi‘ohi ‘ia ma nā kālailai ho‘okolo manu. He ko‘iko‘i ia ‘ikepili e maopopo ai kākou i ka liliuwelo o nā lāhulu manu i ko lākou mau wahi pono‘ī.

Molt patterns and age and sex determination criteria for selected landbirds in an urban area of the Peruvian Central Coast

Despite molting is an important and expensive activity in the life cycle of birds, this process is poorly known for neotropical species and even less so for species inhabiting urban zones. We studied molt patterns, aging and sexing criteria, and morphometrics for seven common resident species in an urban area of ​​Lima city, Peru. All species evidenced complete prebasic molts. Partial to eccentric incomplete preformative molts were evidenced for six species (Camptostoma obsoletum, Pyrocephalus rubinus, Catamenia analis, Poospiza hispaniolensis, Coereba flaveola, and Thraupis episcopus); whereas Columbina cruziana exhibited a complete molt. All thraupid species exhibited partial prealternate molts. Preformative and prebasic molts were recorded mostly during the dry season, and the few records of prealternate molts might suggest its occurrence soon after the wet season. Our species also exhibited low molt synchrony, with some of them (C. cruziana, P. rubinus, and C. flaveola) exhibiting extensive molt periods likely explained by its potential to reproduce throughout the year and/or the existence of suspended/ protracted molts. Morphometric analysis evidenced significant differences according to sex for C. cruziana, P. rubinus, and C. analis, with the wing chord being the most common characteristic for distinguishing between sexes. Our study covers an important gap in the knowledge of the natural history of urban birds and provides information to test hypotheses of molt pattern variation on species with widespread distribution throughout the Americas.

Does the Urban Environment Act as a Filter on the Individual Quality of Birds?

Phenotypic divergences of birds are common between urban and natural habitats and can result from different selective pressures between habitats or maladaptation to the city. No uniform patterns were observed, especially concerning markers of bird health, such as, for example, telomere length. Telomeres are involved in maintaining genome integrity and naturally shorten with age, but environmental stressors can accelerate their attrition. Thus, telomere length can be an indicator of individual quality. Some studies showed that urban breeders had longer telomeres than forest individuals. Two hypotheses can explain this result: (1) urban breeders are younger than forests breeders, and (2) cities act as a filter on individuals and only high-quality birds can successfully reproduce. In this context, we compared the age category (molting pattern) and morphological and physiological characteristics of urban and forest Great Tits before and during breeding. No differences in age or body condition were observed. However, urban breeders were smaller and had shorter telomeres than birds captured in winter. Urban birds had longer telomeres than forest birds, only in winter. These results highlight that urban habitats potentially favor smaller birds. However, the decrease in telomere length between winter and reproduction only in the city suggest a higher cost of reproduction in the city compared to the forest.

Characteristics of Hunter Harvested Montezuma Quail Wings and Implications for Molt Phenology

We obtained 1,899 hunter-harvested Montezuma quail (Cyrtonyx montezumae) wings from southeastern Arizona, USA, from the 2008–2009 hunting season. We determined age and sex based on plumage characteristics for 98.2% (1,864) of the original sample. One-way analysis of variance (ANOVA) of wing-chord length found differences (P < 0.001) based on sex, but not age, with mean (± standard error) male wing chord (113.76 ± 0.15 mm) longer than mean female wing chord (111.03 ± 0.13 mm). Mean male and female wing-chord lengths from our study population were 6.8% and 7.7% shorter, respectively, than previously reported in the literature. We additionally calculated a complete prebasic molt cycle of 177 days based on previously reported preformative molt patterns. The primary benefits of our results are: 1) a more accurate sex-based wing-chord length based on a large sample size, 2) a method to back-calculate molt onset dates for hunter harvested after hatch year Montezuma quail, and 3) a potential means to model the influence of precipitation on population dynamics of Montezuma quail.

Clarification of molt strategies in three Empidonax flycatchers

We studied plumages and molt patterns of Yellow-bellied (Empidonax flaviventris), Least (E. minimus), and Alder (E. alnorum) flycatchers, primarily on the breeding grounds but with additional data from wintering grounds and a migration stopover site, in order to clarify our knowledge of molt strategies in these species. We determined that these 3 species have a similar overall molt strategy: (1) a partial-to-incomplete preformative molt begun on the breeding grounds, suspended over migration, and completed on the wintering grounds; (2) a limited-to-partial first prealternate molt on the wintering grounds that can overlap the final stages of the preformative molt; (3) a complete definitive prebasic molt begun on summer grounds and completed on wintering grounds; and (4) a limited-to-partial definitive prealternate molt that may overlap with the final stages of the prebasic molt. Our study clarifies previous terminologies and allows these molts to be interpreted in an evolutionary framework. We suggest that observed differences in molt extents among species may be linked to differences in wintering latitude and habitat. The broadleaf forest preferred by Yellow-bellied Flycatcher likely retains insect biomass later into the winter season than the scrub habitat preferred by Least Flycatcher, and this may promote more extensive preformative feather replacement in that species. The much more extensive preformative molt of Alder Flycatcher may be due to its wintering farther south, where there is greater annual solar exposure, perhaps resulting in higher rates of feather degradation. Our data also suggest that the extent of prealternate molt in these species may vary with proximate factors on the winter grounds affecting individuals, rather than body condition at the beginning of winter.

Population and reproductive structure in the endangered and highly endemic freshwater crab Aegla concepcionensis (Decapoda:Pleocyemata:Aeglidae) from Chile

AbstractPopulation and reproductive information of highly endemic species allow us to understand their underlying conservation problems. Aegla concepcionensis is restricted to a small and intervened Chilean basin, and its conservation status has varied from extinct in nature to endangered. We characterized their life history measuring population, morphological and environmental variables during an annual cycle capturing individuals with a catch and release method based on electroshocking. Although the maximum water temperature was related to the recruitment, it can be physiologically risky for the remaining macroinvertebrate community. The relationship between abundance and narrow pH variations indicates a condition of unstable equilibrium given the environmental deterioration by deforestation. Sex ratio was predominantly male biased during copulatory activity, and sexually dimorphic body size distributions supported the hypothesis of greater natural selection in females and sexual selection in males. The period of ovigerous females was comparatively restricted, late and consistent with an efficient ecophysiological strategy of reproductive investment. Patterns of pubertal moult, onset of morphometric maturity, absence of morphological differentiation in both sexes suggested that A. concepcionensis tends to maximize reproductive performance favouring the recovery of their relict populations.

PREFORMATIVE MOLT EXTENT AND AGING AND SEXING CRITERIA FOR EIGHT HUMMINGBIRD SPECIES IN SOUTHEASTERN PERU

Little attention has been paid to molt and age criteria in hummingbirds despite the importance of molt and age to numerous behavioral and ecological questions. We examined age-based molt patterns and bill corrugations in eight species of lowland Amazonian hummingbirds. Molt strategies and rates of bill smoothing were similar to those of more well-studied North American species, with all species showing partial preformative molts (replacing only body feathers and some wing coverts and retaining all remiges and rectrices), and bill corrugations reducing to less than 10% of bill length in all species during the first annual cycle. Several species showed evidence of delayed maturation in males in regard to plumage characteristics or bill coloration.

Seasonally divided moult in the Barred Warbler (Sylvia nisoria) is an endogenously controlled strategy

The seasonal timing of moult in migratory birds is an adaptation to cope with time constraints in the annual cycle. Kiat and Izhaki analysed moult patterns in Palaearctic passerines and rejected the proposition that seasonally divided moult is an endogenously controlled strategy. Instead, they advocated the view that it occurs due to a flexible and opportunistic timing of moult. In contrast, we argue that Kiat and Izhaki’s analysis is flawed and that they overlooked several important facts about moult in the Barred Warbler Sylvia nisoria and other species showing seasonally divided moult. These include the facts that juveniles replace a few secondaries already in their first winter, and that the moult sequences of primaries and secondaries are decoupled compared with the typical passerine complete moult sequence. We argue that seasonally divided moult is an adaptive strategy that is largely under endogenous control.

Atypical primary molt patterns in greater sage-grouse: implications for age classification

Age-specific patterns of primary molt facilitate age classification of native North American upland gamebirds, a critical step in understanding their ecology, behavior, life history, population dynamics and harvest. However, deviations from typical molt patterns can create confusing plumages that complicate age classification. We examined data from live-captured greater sage-grouse Centrocercus urophasianus across seven studies in five U.S. states and wings from harvested birds in Oregon and Colorado for evidence of atypical primary molt. We documented atypical replacement through primary nine during preformative molt, atypical retention of juvenile primary 10 during second prebasic molt, and atypical retention of basic outer primaries during definitive prebasic molt. Atypical primary molts were observed more often in live-captured females (3.2%, n = 561) than males (0.8%, n = 494). Many individuals with atypical primary patterns, especially females, are difficult or impossible to reliably age by plumage or morphology and may bias research and harvest data.

Urban links to molt schedule, body condition and carotenoid‐based coloration in the house finch Haemorhous mexicanus

Animals in urban environments are exposed to novel conditions, such as habitat and dietary alterations, and night‐time light pollution, that can shift the timing and expression of life‐history traits. Birds are popular urban‐ecological study subjects, and in these feathered animals regular plumage molt is a critical process for maintenance of feather quality and their associated functions (e.g. thermoregulation, aerodynamics and communicative coloration). We hypothesized that environmental changes associated with urbanization might affect the timing and progression of molt. As molt is energetically and nutritionally costly, we also tested whether putative urban–rural molt differences might be explained by indirect effects of urban environments on aspects of health (i.e. body condition, sexually selected plumage color). We tracked body molt intensity during molt onset, peak and completion in both sexes of urban and rural house finches Haemorhous mexicanus, and related this to body condition and sexually selected carotenoid‐based plumage coloration. We found that urban birds began molting earlier, peaked at a lower molt intensity and ended molt later than rural conspecifics. We also find that both body condition and plumage hue in males explain variation in body molt intensity differently for urban and rural populations at various points during the molting period. Overall, we demonstrate that songbird molt patterns and the development of carotenoid‐based sexual ornaments can be altered in urban environments, and that rapid urbanization may have broader implications for molt dynamics, annual life‐history traits and sexual selection.