The Energy Benefits of the Pantograph Wing Mechanism in Flapping Flight: Case Study of a Gull

Bird wings generally contain a 4-bar pantograph mechanism in the forearm that enables the wrist joint to be actuated from the elbow joint thus reducing the number of wing muscles and hence reducing the wing inertia and inertial drag. In this paper we develop a theoretical model of inertial power for flapping flight to estimate the advantage of the 4-bar pantograph mechanism by comparing the inertial power required for the case where wrist muscles are present in the forearm with the case where wrist muscles are not present in the forearm. It is difficult to predict how wrist muscles would look when there is no pantograph mechanism. Therefore a lower bound and upper bound case are defined. The lower bound case involves redistributing the elbow muscles with no increase in wing mass. The upper bound case involves replicating the biceps-triceps muscles near the wrist joint. At minimum power speed the model estimates that the 4-bar pantograph mechanism reduces the inertial power for the gull from between 6.1%-12.3% and reduces the overall power by 0.6%-1.2%. When account is taken of the tight margins involved in the design of a flying vehicle, the energy savings produced by the pantograph mechanism are significant. A ring-billed gull was chosen for the case study and an adult specimen was obtained to gather morphometric data. Lessons for the design of flapping micro air vehicles are discussed

A Technique for Evaluating Observer Efficiency in Raptor Migration Counts

A technique is described for sampling sections of the sky individually during a raptor migration count to obtain an unbiased estimate of the true number of raptors passing. This allows an estimate to be made of the efficiency of raptor detection by an observer counting at the same location and time. Practical and statistical issues are addressed that must be understood for efficient use of the technique

Morphometric Variation as an Indicator of Genetic Interactions between Black-capped and Carolina Chickadees at a Contact Zone in the Appalachian Mountains

We studied hybridization and introgression between Black-capped (Poecile atricapillus) and Carolina (P. carolinensis) chickadees along two transects in the Appalachians using four genetic markers and multivariate analysis of morphology. Genetic data revealed that at least 58% of the birds in the center of each transect were of mixed ancestry and that recombinant genotypes predominated among hybrids, demonstrating that hybridization is frequent and that many hybrids are fertile. Genetic clines generally were steep and coincident in position, but introgression was evident well beyond the range interface. Introgression was higher at the one autosomal locus surveyed than in mitochondrial DNA or in two sexlinked markers, suggesting that the hybrid zone is a conduit for gene flow between the two forms at some loci. On a broad scale, morphometric variation was concordant with genetic variation. Clines in morphological variation based on principal components (PC) scores were steep and coincident with genetic clines. Also, a strong correlation within a population between PC scores and an individual\u27s genetic makeup suggested that a large amount of morphological variation was genetically determined. However, morphological analysis indicated that hybrids were uncommon on one transect, whereas genetic data clearly showed that they were common on both. In addition, patterns of morphological variation were equivocal regarding introgression across the hybrid zone. Thus, genetic data provided a complementary and more detailed assessment of hybridization, largely due to the discrete nature of genetic variation. Genetic markers are useful in understanding hybridization and introgression, but diagnostic markers may underestimate average gene flow if selection against hybrids maintains steep clines at diagnostic loci. To gain a clearer picture of the genome-wide effects of hybridization. A much larger number of loci must be assayed, including non-diagnostic ones

Reproductive Isolation and Cryptic Introgression in a Sky Island Enclave of Appalachian Birds

Reproductive isolation is central to the speciation process, and cases where the strength of reproductive isolation varies geographically can inform our understanding of speciation mechanisms. Although generally treated as separate species, Black-capped chickadees (Poecile atricapillus) and Carolina chickadees (P. carolinensis) hybridize and undergo genetic introgression in many areas where they come into contact across the eastern United States and in the northern Appalachian Mountains. The Great Smoky Mountains harbor the last large breeding population of atricapillus in the southern Appalachians, isolated from the species’ main range by nearly 200 km. This population is believed to be reproductively isolated from local carolinensis due to an unusual, behaviorally mediated elevational range gap, which forms during the breeding season and may function as an incipient reproductive isolating mechanism. We examined the effectiveness of this putative isolating mechanism by looking for genetic introgression from carolinensis in Great Smoky Mountain atricapillus. We characterized this population and parental controls genetically using hundreds of amplified fragment length polymorphism (AFLP) loci as well as mitochondrial DNA (mtDNA) sequence data from cytochrome-b. Great Smoky Mountain atricapillus have experienced nuclear genetic introgression from carolinensis, but at much lower levels than other populations near the hybrid zone to the north. No mitochondrial introgression was detected, in contrast to northern contact areas. Thus, the seasonal elevational range gap appears to have been effective in reducing gene flow between these closely related taxa

The Dynamics of Vocal, Morphological and Molecular Interaction between Hybridizing Black-Capped and Carolina Chickadees

Previous investigation of genetic interactions between black-capped and Carolina chickadees (Parus atricapillus and P. carolinensis) has been hindered by their morphological similarity, and by a paucity of differentiated genetic markers distinguishing them. Nine fixed or strongly differentiated restriction fragment length polymorphism (RFLP) markers were developed, and one strongly differentiated allozyme locus was detected. These markers were used in conjunction with one fixed allozyme marker and three fixed RFLP markers previously available for these birds to examine interactions along their contact zone at three locations. A principal component analysis of mass, wing length and tail length revealed minimal morphological intermediacy at the contact zone in Virginia, in contrast with more extensive intermediacy at the contact zone in West Virginia, despite high levels of hybridization at both locations. This reflects the unreliable nature of these morphometric characters in reflecting genetic interactions occurring along this hybrid zone, due to the poor morphometric resolution of P. atricapillus and E. carolinensis. Principal component and discriminant analysis of eight frequency and note duration variables showed songs of intermediate nature to be present only at the contact zone in Missouri, while bilingual singing was widespread both in Missouri and West Virginia, but limited in Virginia. The proportion of hybrids detected by the diagnostic genetic markers was high at all three of these regions, demonstrating that like morphology, use of song is unreliable in assessing genetic interactions between E. atricapillus and P. carolinensis. Heterospecific song learning between these chickadees is a potential explanation for this result. Introgression of mitochondrial DNA across the hybrid zone was limited relative to autosomal introgression at all three locations. This observation is consistent with the potential operation of Haldane\u27s rule in F\sb1 hybrids. Introgression of sex-linked markers was likewise limited, suggesting that epistatic interactions involving sex-linked genes contribute to reproductive isolation between these chickadees. In contrast, introgression at autosomal loci appears to be more substantial overall, reflecting the semipermeable nature of this hybrid zone. A correlation between allele frequency and elevation suggests that ecological factors are also important to this hybrid zone\u27s dynamics

An Assessment of Song Admixture as an Indicator of Hybridization in Black-capped Chickadees (Poecile atricapillus) and Carolina Chickadees (Poecile carolinensis)

Vocal admixture often occurs where differentiated populations or species of birds meet. This may entail song sympatry, bilingually singing birds, and songs with intermediate or atypical characteristics. Different levels of vocal admixture at the range interface between Black-capped Chickadees (Poecile atricapillus) and Carolina Chickadees (P. carolinensis) have been interpreted as indicating that hybridization is frequent at some locations but not others. However, song ontogeny in these birds has a strong nongenetic component, so that inferences regarding hybridization based on vocal admixture require confirmation. We used diagnostic genetic markers and quantitative analyses of song to characterize population samples along two transects of the chickadee contact zone in the Appalachian Mountains. More than 50% of individuals at the range interface were of hybrid ancestry, yet only 20% were observed to be bilingual or to sing atypical songs. Principal component analysis revealed minimal song intermediacy. This result contrasts with an earlier analysis of the hybrid zone in Missouri that found considerable song intermediacy. Re-analysis of the Missouri data confirmed this difference. Correlation between an individual\u27s genetic composition and its song type was weak in Appalachian hybrid populations, and genetic introgression in both forms extended far beyond the limits of vocal admixture. Therefore, song is not a reliable indicator of levels of hybridization or genetic introgression at this contact zone. Varying ecological factors may play a role in producing variable levels of song admixture in different regions of the range interface

Preliminary Survey of Autumn Hawk Migration in the Inner Piedmont of Virginia

A hawkwatch was conducted in September 1997-1999 in the Inner Piedmont of Virginia near Lynchburg, to assess the magnitude and species composition of the flight relative to the Blue Ridge. The flight density in the Piedmont averaged one-third to one-half that of two nearby Blue Ridge lookouts, but among years ranged from onefifth to two-thirds that of those two ridge lookouts. The species composition of the Inner Piedmont flight was similar to that on the Blue Ridge, with Broad-winged Hawks (Buteo platypterus) making up over 95% of the September flight. A close-site study in 1998 suggested that the Broad-winged Hawk flight is greater over Lynchburg than to the immediate southeast. Hawk migration studies in this area certainly warrant further attention