Divergent rectrix moult: the implications and conditions of moult sequence

Wing and tail morphology strongly affect flight performance which may consequently decline during feather moult due to the creation of feather gaps in the flight‐surface. Hence, the size and shape of moult‐related gaps may directly affect flight capacity. Here, I examined the divergent rectrix moult sequence compared to the more common distal moult sequence. In the divergent moult, the focus of rectrix moult is shifted from the tail centre (R₁; rectrices numbered distally from mid‐tail outward) to another rectrix (R₂ or R₃), and then rectrices are moulted bidirectionally, towards the tail centre and outwards. The result of this moult sequence is the splitting of the tail gap into multiple smaller gaps. Using a large moult database including 5669 individuals of 47 Western Palaearctic passerine species, I found evidence of divergent moult sequence for only seven species. Using comparative and experimental approaches, I found that the divergent rectrix sequence is correlated with higher moult speed and lower aerodynamic cost. Furthermore, the divergent rectrix sequence is more common among adults than juveniles. This work focused on the feather moult sequence – a seldom studied aspect of the avian life‐history. I propose that moult‐related aerodynamic costs may be an important evolutionary factor not only in moult speed, but also in moult sequence.     

Ontogeny of sexual dimorphism in the Long-tailed Manakin Chiroxiphia linearis: long maturation of display trait morphology

Males of dimorphic species often show ornaments that are thought to have evolved through female choice or/and male–male competition. The sexual differentiation of similar morphologies occurs during ontogeny, resulting in differential sex and age-specific selection. The Long-tailed Manakin is a dimorphic species with a highly skewed mating system, the males of which delay plumage maturation over 3 to 4 years. We describe ontogenetic changes in feather morphology in this species through sexual maturity. Males showed a significant increase in length of the central rectrices with age, hence their degree of sexual dimorphism increased from zero in 1-year-old males to 189.5% in adults. In contrast, male tail length decreased with age. Wing length did not vary significantly with age, but females had relatively longer wings than males. Wing loading was greater in females and decreased with age in males. In adults, rectrix length was positively correlated with testis volume, supporting the hypothesis that secondary sexual characters can signal the condition of primary sexual characters. Rectrix length showed positive allometry with body size in males less than 4 years old, whereas older males showed negative allometry and females showed isometry. Wing area and wing loading shifted from negative to positive allometry in males of 2 to 3 years of age. Changes in male morphology during ontogeny in the Long-tailed Manakin appeared to be associated with their specific display behaviours. Age-related changes in allometric growth of rectrices in the Long-tailed Manakin suggested that young males invest disproportionately more in the length of this trait relative to their body size. This investment could act as a signal of competitive ability to move status position in their orderly queue.     

Adventitious feather replacement favours a more rapid regeneration of primaries over rectrices in two passerine bird species

There is increasing evidence of adaptive preferential investment during moult in those feather tracts that are more advantageous for fitness. In this study, we assessed whether, after the manual removal of two functionally different flight feathers (one primary and one rectrix), birds from two common passerine species (Eurasian Blackcap Sylvia atricapilla and European Robin Erithacus rubecula) favoured the regeneration of primary (supposedly the most functionally important feathers) over rectrix feathers. Our results did not show differences between replaced primary and rectrix feathers in their final length, but demonstrated that the gap left by the loss of the primary feather was filled earlier, suggesting that a rapid repair of the most essential feather tracts is also evolutionarily advantageous during the adventitious replacement of plumage.     

Temporal and spatial patterns of flight and body feather molt of Bank,Barn, and Cliff swallows in North and South America

Molt is energetically demanding and various molt strategies (i.e., molt series, duration, intensity, timing, and location) have evolved to reduce the negative fitness consequences of this process. As such, molt varies considerably among species. Identifying where and when specific feathers are molted is also crucial to inform species‐specific studies using stable isotope markers to assign individuals to geographical regions where they molt. Using museum specimens, we examined the molt of three species of migratory swallows in the Americas: Bank Swallows (Riparia riparia), Barn Swallows (Hirundo rustica), and Cliff Swallows (Petrochelidon pyrrhonota). All three species have one primary and two secondary molt series. Bank and Cliff swallows had one rectrix molt series, and Barn Swallows molted the outer rectrix (R6) separately from the inner five rectrices (R1‐5). All three species have a relatively long flight feather molt duration (i.e., 140–183 days) and low molt intensity. Barn Swallows initiated flight feather molt in the fall, about 2 months later than Bank and Cliff swallows. Barn Swallows likely delay molt because of constraints associated with double brooding. For all three species, molt started with the primaries and inner secondaries and was closely followed by the rectrices and, finally, the outer secondaries. For those that began and then interrupted molt either in breeding areas or during fall migration, the first feathers molted were predominantly S8 and P1. All three species underwent body molt throughout the year, but most individuals molted their body plumage in wintering areas. We recommend that the most appropriate feathers for stable isotope research examining migratory connectivity and habitat use are either R2‐R4 or S2‐S4.     

Sex determination of Red-tailed Hawks (Buteo jamaicensis calurus) using DNA analysis and morphometrics

ABSTRACT.   Currently, the sex of Red-tailed hawks ( Buteo jamaicensis ) cannot be determined by in-hand methods. Males and females do not differ in plumage and overlap in size. We collected feather samples and morphological measurements from migrating birds at four sites in the western United States. Sex was determined for individual birds using sex-specific DNA markers and polymerase chain reaction was used to identify these DNA markers. Using discriminant function analysis, we created equations for determining the sex of Red-tailed Hawks using in-hand measurements based on the DNA-determined sexes. We formed two equations, one for adults that was 98% accurate, and one for hatch-year birds that was 97% accurate. The ability to determine the sex of western Red-tailed Hawks using morphological measurements will be useful to investigators examining possible intra- or intersexual differences.     

Body condition and feather molt of a migratory shorebird during the non‐breeding season

Migratory shorebirds have some of the highest fat loads among birds, especially species which migrate long distances. The upland sandpiper Bartramia longicauda makes long‐distance migrations twice a year, but variation in body condition or timing of feather molt during the non‐breeding season has not been studied. Molt is an important part of the annual cycle of migratory birds because feather condition determines flight performance during migration, and long‐distance movements are energetically costly. However, variation in body condition during molt has been poorly studied. The objective of our field study was to examine the timing and patterns of feather molt of a long distance migratory shorebird during the non‐breeding season and test for relationships with body size, fat depots, mass, and sex. Field work was conducted at four ranches in the Northern Campos of Uruguay (Paysandú and Salto Departments). We captured and marked 62 sandpipers in a 2‐month period (Nov–Jan) during four non‐breeding seasons (2008–2012). Sex was determined by genetic analyses of blood samples taken at capture. Molt was measured in captured birds using rank scores based on published standards. Body mass and tarsus length measurements showed female‐biased sexual size dimorphism with males smaller than females. Size‐corrected body mass (body condition) showed a U‐shaped relationship with the day of the season, indicating that birds arrived at non‐breeding grounds in relatively good condition. Arriving in good body condition at non‐breeding grounds is probably important because of the energetic demands due to physiological adjustments after migration and the costs of feather molt.     

Age, growth and reproduction of the black scorpionfish, Scorpaena porcus (Pisces, Scorpaenidae), on the Black Sea coast of Turkey

Age, growth and reproduction of the black scorpionfish, Scorpaena porcus were studied in specimens from the coast of the Sinop Peninsula (Black Sea) between March 2002 and April 2003 in order to characterize these population parameters in comparison to specimens from populations of nearby regions. A total of 1086 specimens was captured by beam trawl at the depths between 0 and 30 m. The total number of females (510) was significantly higher than that of males (373). Total length of males and females ranged between 5.7 and 23.6 cm, and 4.9 and 31.7 cm, respectively. The length–weight relationship showed a positive allometric growth. Females grew faster and reached a larger size at age than males ( L _∞ = 111.9 cm, K  = 0.035 year⁻¹, φ' = 2.64 for females, and L _∞ = 74.6 cm, K  = 0.054 year⁻¹, φ' = 2.49 for males). The age range estimated was up to 8 years for females and 5 years for males. Reproduction likely occurs between June and September. Sex ratio varied greatly with season, perhaps indicating different seasonal migratory patterns in adults of different sex. An inverse correlation between gonadosomatic index (GSI) and hepatosomatic index (HSI) was evident during the reproduction seasons. The mean size at first sexual maturity was 17.5 cm TL for females, and 16.7 cm TL for males.     

Viability selection on prey morphology by a generalist predator

Prey use their locomotory capacity to escape predators, and there should thus be strong viability selection on locomotory morphology of prey. We compared feather morphology of wood pigeons Columba palumbus killed by goshawks Accipiter gentilis with that of survivors to quantify directional and quadratic selection on primary and rectrix feathers. The goshawk is mainly a predator attacking by surprise, leaving wood pigeons with an ability to accelerate fast at a selective advantage. There was directional selection for light primary feathers with a narrow calamus. In addition, there was directional selection for increased area of rectrices. These patterns of natural selection were confirmed in multivariate analyses of selection that showed selection for light primary feathers with a large area and narrow calamus and for a large area of rectrix feathers. These results provide evidence of selection on different aspects of feather morphology directly related to flight performance and thus escape ability from predators.     

The scaling of primary flight feather length and mass in relation to wing shape, function and habitat

The mass and length of each primary flight feather was measured in 120 species of birds (347 individuals) representing 37 families and 15 orders. The scaling relationship between mass and length was determined using the mass of each primary as a proportion of total primary feather mass for that individual and, similarly, length as a proportion of total length. This eliminated errors due to intra- and interspecific differences in absolute size. In every species there was a highly significant constant scaling relationship (log mass/log length) for all of the primary feathers proximal to the feather that formed the wing tip. This relationship was allometric and varied between 1.80 in Rooks Corvus frugilegus and 4.87 in Winter Wrens Troglodytes troglodytes . The mean scaling relationship for 120 species was 2.41 ± 0.42 sd, which was significantly less ( P  < 0.0001) than isometry (i.e. 3.00). In most species (117 of 120) the primary feather forming the wing tip and all feathers distal to it had a different scaling relationship, and had a greater mass than expected from their length. The greater relative mass of the outer primaries may reflect a protective role against physical abrasion, or an aerodynamic role in that each of these feathers provides a leading edge to the wing. Thus, there were two scaling relationships that pivoted about the feather forming the wing tip, resulting in a characteristic 'signature' for each species. Scaling relationships can be related to flight characteristics and habitat, rather than to phylogeny. Closely related species often had widely varying scaling relationships. In general, species exploiting dense vegetation had greater scaling relationships than more aerial species. However, species with a high scaling relationship did not have a greater mean feather mass, so the increased relative mass of the distal primaries was at the expense of proximal primary feather mass.     

A comparative study of aerodynamic function and flexural stiffness of outer tail feathers in birds

To transmit aerodynamic forces to the body, tail feathers should be stiff to resist lift forces with minimum deformation. Because aerodynamic theory predicts that such feathers do not produce lift forces beyond the point of the maximum continuum width of the tail, species with deeply forked tails should not require stiff outer rectrices distal to that point. I tested this prediction by comparing the relative thickness of the outer rectrix rachis between species with deeply forked tails to those with triangular or shallowly forked tails. Eleven pairs of closely related species belonging to families Fregatidae, Phalacrocoracidae, Accipitridae, Sternidae, Caprimulgidae, Trochilidae, Coraciidae, Tyrannidae, Cotingidae, and Hirundinidae were compared. All but one of the phylogenetically independent comparisons showed that the species with triangular or shallowly forked tails have higher relative rachis thickness than their deeply forked relatives. In addition, nine out of eleven of the species with deeply forked tails showed a proportionately greater increase in relative rachis thickness from distal to proximal parts of the feather. In contrast, triangular and shallowly forked tails showed an approximately linear relation between relative rachis thickness and relative rachis length. These results considered together are consistent with the idea that the distal part of outer rectrix rachis in species with deeply forked tails has not been selected to resist lift forces and may be adaptively reduced to attenuate the costs of a hypertrophied ornament.     

SOME INTERESTING RHODESIAN RECORDS—IV

Austin, G. T. 1979. Pattern and timing of moult in penduline tits (Anthoscopus). Ostrich 49:168-173.

Moult was examined in species of Anthoscopus. Second and subsequent prebasic moults were complete. Primary and rectrix moult was typical of passerines, but secondary moult was some what irregular. Moult was largely non-overlapping with breeding, although some body moult was noted during the breeding season. In southern Africa there was some regional variation in timing of moult. First year birds moulted after adults had largely completed feather replacement. This first prebasic moult was incomplete.     

Identification of Lanius species and subspecies using tandem repeats in the mitochondrial DNA control region

The number of tandem repeats in the mitochondrial control region were used to differentiate the Red-backed Shrike Lanius collurio , Woodchat Shrike Lanius senator , Great Grey Shrike (subspecies Lanius excubitor excubitor ) and the Southern Grey Shrike (subspecies L. meridionalis meridionalis , L. m. koenigi, L. m. pallidirostris and L. m. aucheri ). The Red-backed and Woodchat Shrikes lacked repeats whereas the Great Grey and Southern Grey had two, three and 2 + 3 repeats. A subspecies of Southern Grey ( L. m. koenigi ) had 2 + 3 + 4 repeats. These findings are discussed in terms of the taxonomy of the Lanius genus, especially with respect to the Great Grey and Southern Grey Shrikes.     

The timing, duration and pattern of moult and its relationship to breeding in a population of the European Greenfinch Carduelis chloris

Moult was studied in 1 year among Greenfinches trapped in a garden in east‐central England. Over the period June–December 2003, 333 captures of 179 individual adults provided information on breeding condition, moult, body weight, sex and age (yearling or older adult, equivalent to birds in their second or later calendar years, respectively). About 95% of all birds (sex and age groups combined) started primary feather moult from 2 July to 14 August, and finished from 10 October to 22 November. The mean date of moult onset in the population as a whole was 24 July. On average, males began 8 days before females, and yearlings began 6 days before older birds. The mean duration of moult was 100 days, whether the figure was calculated for the population as a whole or just for the 36 individual birds that were caught more than once during moult. However, moult rate was slightly slower, and moult duration slightly longer, in yearlings than in older adults of both sexes. No evidence was found for any systematic relationship between moult onset date and rate (duration). Breeding and moult overlapped by up to 5 weeks or more in individual birds, and some birds probably started to moult as early as the incubation stage of their last clutch of the season. The cloacal protuberance (taken as indicative of breeding condition) had regressed in all males by the time the fifth primary was shed, and the brood patch had regressed and re‐feathered in all females by the time the fourth primary was shed. The bulk of feather replacement in the secondary, tail and body tracts occurred in the second half of primary moult, and after cloacal protuberances and brood patches were completely regressed. In all birds examined near the end of primary moult the secondaries were still growing, and would have continued growth for up to another 19 days or more, extending the end of the moulting season into December. Body mass during moult was affected significantly by sex and age, as well as by time of day, amount of food in gullet, reproductive condition and date. No firm evidence emerged that body mass was affected by moult stage, after allowing for effects of date and other variables (although there was a non‐significant negative relationship between moult stage and body mass in males). In the population as a whole, the breeding season (from first egg‐laying to independence of last young) was spread over 21 weeks and moult over 24 weeks. With an overlap between the two events at the population level of up to 9 weeks, the two processes together took up to 36 weeks, some 69% of the year.     

Adult dispersal of Ostrinia nubilalis Hübner (Lepidoptera: Crambidae) and its implications for resistance management in Bt-maize

Abstract:  Dispersal of European corn borer, Ostrinia nubilalis Hübner was examined by release and recapture of the dye marked adults and by capture of the feral adults in and around the large 50 ha center pivot irrigated fields of Bacillus thuringiensis (Bt) maize. Pheromone and black light traps were used to catch the adults. In 1999, 15 094 marked males and 7993 marked females were released, and in 2001, 13 942 marked males and 9977 marked females were released. In 1999, maximum mean recapture beyond the release point was 1.95 and 1.67% for males and females, but in 2001, the recapture rate was 9.97 and 4.37% for males and females. Few males (3.8%) and females (2.07%) were recaptured in neighbourhood maize fields. An exponential decay function explained recapture of marked adults across the dispersal distance. More than 90% of marked adults were recaptured within 300 m of the release point. Large numbers of feral adults were captured throughout the study fields. Feral adult dispersal could be fitted to a linear model. Virgin females (20% marked and 8% feral) were captured throughout the study fields. The recapture of marked insects suggests that the dispersal was limited. However, capture of feral adults throughout Bt-maize fields indicate that the actual dispersal may be more extensive than indicated by recapture of marked adults. Potential refuge sources for the feral adults were 587–1387 m from the edge of the study fields. It is not clear if the dispersal recorded in this study is extensive enough to support the current resistance management strategy for corn borers. There appears to be some dispersal of corn borers from the non-transgenic 'refuge' fields into the transgenic fields that allows some genetic mixing of the two populations.     

Does fluctuating asymmetry constitute a sensitive biomarker of nutritional stress in house sparrows (Passer domesticus)?

Small random deviations from left–right symmetry in bilateral traits, termed fluctuating asymmetry (FA), are theoretically predicted to increase with environmental stress and believed to constitute a potential biomarker in conservation. However, reported relationships between FA and stress are generally weak and variable among organisms, traits and stresses. Here we test if, and to what extent, FA increases with nutritional stress, estimated from independent feather growth measurements, in free-ranging house sparrows (Passer domesticus). Ptilochronological feather marks showed significant heterogeneity among study plots, indicating that house sparrow populations were exposed to variable levels of nutritional stress during development. However, individuals from more stressed populations did not show increased levels of fluctuating asymmetry in tarsus or rectrix length, nor was there evidence for significant between-trait concordance in FA at the individual or the population level. Lack of support for FA in tarsus and rectrix length as estimator of nutritional stress in house sparrows may indicate that developmental instability is insensitive to nutritional stress in this species, poorly reflected in patterns of fluctuating asymmetry due to ecological or statistical reasons, or highly context-specific. Such uncertainty continues to hamper the use of FA as a biomarker tool in conservation planning.     

Subtle,pervasive genetic correlation between the sexes in the evolution of dimorphic hummingbird tail ornaments*

Male hummingbirds have repeatedly evolved sexually dimorphic tails that they use as ornaments during courtship. We examine how male ornament evolution is reflected in female morphology. Lande's two-step model of the evolution of dimorphism predicts that γ (the genetic correlation between the sexes) causes trait elaboration to first evolve quickly in both sexes, then dimorphism evolves more slowly. On the hummingbird phylogeny, tail length does not fit this two-step model; although hummingbirds repeatedly evolved ornamental, elongated tails, dimorphism evolves on the same phylogenetic branch as elongation, implying that γ quickly evolves to be low over phylogenetic timescales. Male “bee” hummingbirds have evolved diverse rectrix shapes that they use to produce sound. Female morphologies exhibit subtle, pervasive correlations with male morphology. No female-adaptive hypotheses explain these correlations, since females do not also make sounds with their tail. Subtle shape similarity has arisen through the genetic correlation with males, and is subject to intralocus sexual conflict. Intralocus sexual conflict may produce increased phenotypic variation of female ornaments. Other evolutionary constraints on tail morphology include a developmental correlation between neighboring tail-feathers, biasing tail elaboration to occur most often at the ends of the feather tract (rectrix 5 or 1) and not the middle.     

Moult in the Loggerhead Shrike Lanius ludovicianus is influenced by sex,latitude and migration

We investigated moult strategies in Loggerhead Shrikes by examining first prebasic or preformative moult patterns and by assessing the general location where individual feathers were grown using stable hydrogen isotope (δ²H) analysis. We tested the relative importance of factors known to impact moult timing and pattern, including age, sex, body size, food availability and migration. Migratory Shrikes showed evidence of suspended moult, in which feathers are moulted on both the breeding and the non‐breeding grounds with a suspension of moult during migration. Extent of moult was best explained by sex, longitude, migratory behaviour and breeding‐ground latitude. Male Hatch Year (HY) Shrikes replaced more feathers on the breeding grounds prior to migration than did HY females and moulted more extensively on the breeding grounds than did females. Non‐migratory HY Shrikes underwent a more extensive preformative moult than migratory HY Shrikes. Individuals in more southerly migratory populations moulted more extensively on the breeding grounds than did those breeding further north. Our data also indicate that individuals in the northeastern populations moulted more extensively on the breeding grounds than did those in the north and southwest. Our study underlines the complex structure and variation in moult possible within species, revealing surprising levels of differentiation between sexes and age cohorts, linked to environmental factors on the breeding grounds. Our study highlights the utility of an intrinsic marker, specifically δ²H analysis, to test hypotheses regarding the evolutionary and ecological forces driving moult. Although the methodology has not commonly been applied to this area of research, our results indicate that it can provide unprecedented insight into inter‐ and intra‐specific adaptive response to constraints, whereby individuals maximize fitness.     

Do melanin-based tail patterns predict individual quality and sex in Lesser Grey Shrikes Lanius minor ?

In many bird species, males display colourful, usually carotenoid or structurally based plumage ornaments. On the other hand, there are many bird species and entire avian genera that are achromatic, i.e. with predominantly white, grey and black plumage colours. Achromatic plumage is a typical feature in many shrikes for example. In this study, we examine the importance of an achromatic plumage pattern, namely, the black tail spots on the two outermost tail feathers (T6 and T5) of Lesser Grey Shrikes (LGS) for sex discrimination and as an indicator of individual quality. Our results suggest that the black tail patterns, especially spots on T5, are important for sex discrimination, but only in combination with other melanin-based or morphological features. The presence of black tail spots on T5 is also an indicator of male age. However, there is no indication that presence, size and asymmetry of these black spots are indicators of individual quality of both sexes in the terms of breeding performances.     

Using stable isotopes to investigate the dietary trophic level of fledgling songbirds

ABSTRACT Use of early successional habitat by mature forest birds during the postfledging period is well documented, but reasons for this habitat shift remain elusive. Although forest‐breeding songbirds are primarily insectivorous during the nestling and early fledgling periods due to high protein requirements, older fledglings may adopt a heavily frugivorous diet. Our objectives were to use stable isotopes to examine the dietary trophic level of juveniles of three species of mature forest songbirds to determine if juvenile songbirds heavily consume fruit resources during the postfledging period and to evaluate a possible link between diet and energetic condition. We collected the outer right rectrix and several body feathers from 34 Wood Thrushes (Hylocichla mustelina), 34 Ovenbirds (Seiurus aurocapilla), and 35 Scarlet Tanagers (Piranga olivacea) captured in regenerating clearcuts in southeastern Ohio in 2005 and 2006. We also collected fruit and arthropod samples from each clearcut. Isotopic values of body feathers were significantly higher (more enriched) than those of rectrices in all cases except values of δ¹³C for Ovenbirds where we found no difference between body and rectrix feathers. These results suggest that juvenile songbirds did not undergo a strong shift to frugivory during the postfledging period, and arthropods were the primary source of protein during the period when rectrix and body feathers were growing. In addition, the energetic condition of birds was not related to the isotopic signature of feathers. Although our results are inconsistent with the hypothesis that juveniles move into regenerating clearcuts enabling them to shift to a primarily frugivorous diet during the postfledging period, they may consume fruit for nonprotein requirements, such as lipids and carbohydrates.     

Patterns of rectrix rachis modification in pintails and the evolution of sexually selected traits

In order to transmit aerodynamic forces to the rest of the body, tail feathers need to be stiff to resist lift forces with minimum deformation. Because delta-wing theory predicts that such feathers do not produce lift forces beyond the point of the maximum continuum width of the tail, species with pintails should not require stiff central rectrices distal to that point. We tested this prediction by comparing the relative thickness of the central rectrix rachis in taxa with pintails and triangular tails. Fourteen pairs of closely related species or species groups belonging to the families Phaethontidae, Phalacrocoracidae, Anatidae, Stercorariidae, Psittacidae, Trochilidae, Alcedinidae, Momotidae, Meropidae, Bucerotidae, Tyrannidae, Pipridae and Nectariniidae were compared. Twelve of the phylogenetically independent comparisons showed that the taxa with triangular tails have higher relative rachis thickness (RRT) than their pintailed relatives just behind the point of the maximum continuum width of the tail. In contrast, two taxa with pintails showed proportionately higher RRT than their triangular-tailed relatives. Triangular tails showed an approximately linear relationship between RRT and relative rachis length, which contrasts with a proportionately greater increase in RRT from distal to proximal parts of the feather in 12 pintailed taxa. These results show that in most of the pintailed taxa studied the distal part of the central rectrix rachis has not been selected to resist lift forces and may be adaptively reduced to attenuate the costs of a hypertrophied ornament. However, the presence of distally reinforced rachices in Eumomota superciliosa and Colonia colonus suggests that a different explanation may be required to account for the design of pintail structure in other taxa.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 86 , 477–485.