Megan D Gall

Georgia State University, Atlanta, Georgia, United States

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Publications (13)24.59 Total impact

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    ABSTRACT: Many species of songbirds exhibit dramatic seasonal variation in song output. Recent evidence suggests that seasonal changes in auditory processing are coincident with seasonal variation in vocal output. Here, we show, for the first time, that frequency selectivity and temporal resolution of the songbird auditory periphery change seasonally and in a sex-specific manner. Male and female house sparrows (Passer domesticus) did not differ in their frequency sensitivity during the non-breeding season, nor did they differ in their temporal resolution. By contrast, female house sparrows showed enhanced frequency selectivity during the breeding season, which was matched by a concomitant reduction of temporal resolution. However, males failed to show seasonal plasticity in either of these auditory properties. We discuss potential mechanisms generating these seasonal patterns and the implications of sex-specific seasonal changes in auditory processing for vocal communication.
    Proceedings of the Royal Society B: Biological Sciences 01/2013; 280(1751):20122296. · 5.68 Impact Factor
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    ABSTRACT: We studied how age affects selection of foraging microhabitats, foraging behaviors, and rates of vigilance in the black phoebe (Sayornis nigricans). Juveniles generally perched higher in trees than adults and in areas with higher intensity of light, which may increase the difficulty of visually tracking prey. Juveniles allocated more effort to visual searching prior to a foraging attempt and flew farther than adults to capture a prey item. When at rest on a perch, juveniles monitored the environment more slowly than adults, suggesting lower levels of vigilance. In general, our results suggest that differences between ages in foraging behavior of visually guided predators may be influenced by intensity of ambient light in their foraging territories. Estudiamos como la edad afecta la selección de microhábitats de forrajeo, el comportamiento de forrajeo, y las tasas de vigilancia del mosquero negro (Sayornis nigricans). Los juveniles se hallaron en perchas más altas en los árboles que los adultos y en áreas con mayor intensidad de luz, lo que puede aumentar la dificultad de rastrear visualmente a la presa. Los juveniles asignaron un esfuerzo mayor a la búsqueda visual de presa antes de un intento de depredación y se desplazaron una distancia mayor para capturar a las presas que los adultos. Cuando descansaron en una percha, los juveniles monitorearon el entorno más lentamente que los adultos, lo que sugiere niveles menores de vigilancia. En general, nuestros resultados sugieren que las diferencias de edad en el comportamiento de alimentación de predadores visuales están influenciadas por la intensidad de luz en sus territorios de forrajeo.
    The Southwestern Naturalist 01/2013; 58(1):41-49. · 0.28 Impact Factor
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    ABSTRACT: The ability of a receiver to detect a signal is a product of the signal characteristics at the sender, habitat-specific degradation of the signal, and properties of the receiver's sensory system. Active space describes the maximum distance at which a receiver with a given sensory system can detect a signal in a given habitat. Here the effect of habitat structure and urbanization on brown-headed cowbird (Molothrus ater) perched song active space was explored. The active space of the cowbird song was affected by both habitat type and level of urbanization. High frequency (4 to 6 kHz) portions of song resulted in the maximum active space. Surprisingly, the active space was the largest in open urban environments. The hard surfaces found in open urban areas (e.g., sidewalks, buildings) may provide a sound channel that enhances song propagation. When the introductory phrase and final phrase were analyzed separately, the active space of the introductory phrase was found to decrease in open urban environments but the active space of the final phrase increased in open urban environments. This suggests that different portions of the vocalization may be differentially influenced by habitat and level of urbanization.
    The Journal of the Acoustical Society of America 12/2012; 132(6):4053-62. · 1.65 Impact Factor
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    ABSTRACT: The sender-receiver matching hypothesis predicts that species-specific features of vocalizations will be reflected in species-specific auditory processing. This hypothesis has most often been invoked to explain correlations between vocal frequency ranges and the frequency range of auditory sensitivity; however, it could apply to other structural features, such as the rise time of stimuli. We explored this hypothesis in five songbird species that vary in the rise times and frequency range of their vocalizations. We recorded auditory evoked potentials (AEPs) to onset and sustained portions of stimuli that varied in both frequency and rise time. AEPs are gross potentials generated in the auditory nerve and brainstem and measured from the scalp. We found that species with shorter rise times in their vocalizations had greater amplitude and shorter latency onset AEPs than species with longer rise times. We also found that species with lower frequency and/or more tonal vocalizations had stronger sustained AEPs that follow the sound pressure changes in the stimulus (i.e. frequency following responses) than species with higher frequency and/or less tonal vocalizations. This is the first study in songbirds to show that acoustic features such as rise time and tonality are reflected in peripheral auditory processing.
    Journal of Experimental Biology 08/2012; 215(Pt 21):3742-51. · 3.24 Impact Factor
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    ABSTRACT: Studies of auditory temporal resolution in birds have traditionally examined processing capabilities by assessing behavioral discrimination of sounds varying in temporal structure. Here, temporal resolution of the brown-headed cowbird (Molothrus ater) was measured using two auditory evoked potential (AEP)-based methods: auditory brainstem responses (ABRs) to paired clicks and envelope following responses (EFRs) to amplitude-modulated tones. The basic patterns observed in cowbirds were similar to those found in other songbird species, suggesting similar temporal processing capabilities. The amplitude of the ABR to the second click was less than that of the first click at inter-click intervals less than 10 ms, and decreased to 30% at an interval of 1 ms. EFR amplitude was generally greatest at modulation frequencies from 335 to 635 Hz and decreased at higher and lower modulation frequencies. Compared to data from terrestrial mammals these results support recent behavioral findings of enhanced temporal resolution in birds. General agreement between these AEP results and behaviorally based studies suggests that AEPs can provide a useful assessment of temporal resolution in wild bird species.
    Journal of Comparative Physiology 01/2012; 198(1):61-8. · 1.86 Impact Factor
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    ABSTRACT: Physical tradeoffs may in some cases constrain the evolution of sensory systems. The peripheral auditory system, for example, performs a spectral decomposition of sound that should result in a tradeoff between frequency resolution and temporal resolution. We assessed temporal resolution in three songbird species using auditory brainstem responses to paired click stimuli. Temporal resolution was greater in house sparrows (Passer domesticus) than Carolina chickadees (Poecile carolinensis) and white-breasted nuthatches (Sitta carolinensis), as predicted based on previous observations of broader auditory filters (lower frequency resolution) in house sparrows. Furthermore, within chickadees, individuals with broader auditory filters had greater temporal resolution. In contrast to predictions however, temporal resolution was similar between chickadees and nuthatches despite broader auditory filters in chickadees. These results and the results of a model simulation exploring the effect of broadened auditory filter bandwidth on temporal resolution in the auditory periphery strongly suggest that frequency resolution constrains temporal resolution in songbirds. Furthermore, our results suggest that songbirds have greater temporal resolution than some mammals, in agreement with recent behavioral studies. Species differences in temporal resolution may reflect adaptations for efficient processing of species-specific vocalizations, while individual differences within species may reflect experience-based developmental plasticity or hormonal effects.
    Journal of Comparative Physiology 01/2011; 197(4):351-9. · 1.86 Impact Factor
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    ABSTRACT: Predator–prey interactions are regulated by the ability of individuals to detect, and then approach or avoid, each other. In visually guided organisms, the prevalent view is that predators have large binocular visual fields and high acuity, whereas prey have wide lateral areas and low acuity, which could affect vigilance behaviour. We characterized the configuration of the visual system (visual fields, retinal topography, visual acuity) and vigilance behaviour (head movement rate) of two ground-foraging avian prey (white-crowned sparrow, Zonotrichia leucophrys, California towhee, Pipilo crissalis) with laterally placed eyes. We found that the binocular field of both species (45°) was actually wider than those of some of their avian predators. Both species also had a single retinal specialization (high ganglion cell density area) located in the centro-temporal sector of the retina, which projected into the lateral and frontal part of the head. Wide binocular fields may increase binocular contrast to detect and visually guide the bill towards prey items. Both species had wider lateral visual fields and faster head movement rates than some of their predators, probably to enhance detection and visual tracking of predators. California towhees made faster sideways movements of the head than did white-crowned sparrows, probably to cover visual space more quickly with their retinal specialization because of the comparatively lower spatial resolution of their retinal periphery. Alternatively, California towhees might move their heads more rapidly to monitor for potential risks (e.g. competitors, predators), as they rely mostly on personal information because of their degree of territoriality. Our findings suggest that the visual system and vigilance behaviour of these two avian prey species combine traits to enhance predator detection through large visual coverage and fast head movements, but also to enhance food detection at close range through enhanced binocular vision.
    Animal Behaviour. 01/2011;
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    ABSTRACT: Brown-headed cowbirds, Molothrus ater, and red-winged blackbirds, Agelaius phoeniceus, are frequently used as model systems for communication and vocal learning; however, relatively little is known about their auditory processing. Although auditory space and acoustic signal space are assumed to coevolve, it is less clear when, or even if, sex differences are expected in auditory processing. Here we explored frequency-specific auditory responses using auditory brainstem responses (ABRs). We generated sex-specific audiograms using two methods: visual detection and cross-correlation. We also measured the amplitude and latency of ABRs to stimuli over a range of frequencies (0.5–6 kHz) and intensities (8–72 dB sound pressure level). Thresholds generated by both methods were good predictors of behavioural thresholds in the best frequency range (2–4 kHz). The visual detection method resulted in a slightly better correspondence with behavioural thresholds than the cross-correlation method above and below best frequencies. We found no significant differences between red-winged blackbird and brown-headed cowbird ABR thresholds; however, overall, females had lower thresholds than males. Sex differences were larger than species differences for ABR amplitude, while latency differences were greater between species than between sexes. Taken together our results suggest that despite high-frequency vocal elements, brown-headed cowbirds do not have enhanced high-frequency auditory sensitivity when measured with auditory evoked potentials. Moreover, we show that females have greater auditory sensitivity than males, which is generally not seen in other passerine species.
    Animal Behaviour. 01/2011;
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    ABSTRACT: Mutations in the Drosophila variable nurse cells (vnc) gene result in female sterility and oogenesis defects, including egg chambers with too many or too few nurse cells. We show that vnc corresponds to Arrest Defective1 (Ard1) and encodes the catalytic subunit of NatA, the major N-terminal acetyl-transferase complex. While N-terminal acetylation is one of the most prevalent covalent protein modifications in eukaryotes, analysis of its role in development has been challenging since mutants that compromise NatA activity have not been described in any multicellular animal. Our data show that reduced ARD1 levels result in pleiotropic oogenesis defects including abnormal cyst encapsulation, desynchronized cystocyte division, disrupted nurse cell chromosome dispersion, and abnormal chorion patterning, consistent with the wide range of predicted NatA substrates. Furthermore, we find that loss of Ard1 affects cell survival/proliferation and is lethal for the animal, providing the first demonstration that this modification is essential in higher eukaryotes.
    Developmental Dynamics 09/2010; 239(11):2813-27. · 2.59 Impact Factor
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    Megan D Gall, Jeffrey R Lucas
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    ABSTRACT: Receiver sensory abilities can be influenced by a number of factors, including habitat, phylogeny and the selective pressure to acquire information about conspecifics or heterospecifics. It has been hypothesized that brood-parasitic brown-headed cowbird (Molothrus ater) females may locate or determine the quality of potential hosts by eavesdropping on their sexual signals. This is expected to produce different sex-specific pressures on the auditory system to detect conspecific and heterospecific acoustic signals. Here, we examined auditory filter shape and efficiency, which influence the ability to resolve spectral and temporal information, in males and females at center frequencies of 2, 3 and 4 kHz. We found that overall, cowbirds had relatively wide filters (lsmean +/- SE: 619.8 +/- 41.6 Hz). Moreover, females had narrower filters (females: 491.4 +/- 66.8, males: 713.8 +/- 67.3 Hz) and greater filter efficiency (females: 59.0 +/- 2.0, males: 69.8 +/- 1.9 dB) than males. Our results suggest that the filters of female cowbirds may allow them to extract spectral information from heterospecific vocalizations. The broader auditory filters of males may reflect limited spectral energy in conspecific vocalizations in this frequency range, and hence, weaker selection for high resolution of frequency in the range of 2-4 kHz.
    Journal of Comparative Physiology 08/2010; 196(8):559-67. · 1.86 Impact Factor
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    ABSTRACT: Foraging mode influences the dominant sensory modality used by a forager and likely the strategies of information gathering used in foraging and anti-predator contexts. We assessed three components of visual information gathering in a sit-and-wait avian predator, the black phoebe (Sayornis nigricans): configuration of the visual field, degree of eye movement, and scanning behavior through head-movement rates. We found that black phoebes have larger lateral visual fields than similarly sized ground-foraging passerines, as well as relatively narrower binocular and blind areas. Black phoebes moved their eyes, but eye movement amplitude was relatively smaller than in other passerines. Black phoebes may compensate for eye movement constraints with head movements. The rate of head movements increased before attacking prey in comparison to non-foraging contexts and before movements between perches. These findings suggest that black phoebes use their lateral visual fields, likely subtended by areas of high acuity in the retina, to track prey items in a three-dimensional space through active head movements. These head movements may increase depth perception, motion detection and tracking. Studying information gathering through head movement changes, rather than body posture changes (head-up, head-down) as generally presented in the literature, may allow us to better understand the mechanisms of information gathering from a comparative perspective.
    Journal of Comparative Physiology 11/2009; 196(1):15-22. · 1.86 Impact Factor
  • Megan D. Gall
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    ABSTRACT: Para los depredadores de tipo posa y espera, un factor clave que influencia las decisiones de forrajeo es la habilidad para detectar y perseguir a las presas, lo cual deberĺa variar con relación a las propiedades fĺsicas y lumĺnicas del ambiente. Evaluamos como los cambios en la disponibilidad fĺsica y visual de las presas alteró la selección de perchas y la búsqueda visual (tasa de movimiento de la cabeza y longitud del ataque) en Sayornis nigricans, un depredador de tipo posa y espera. Mediante observaciones, estudiamos individuos en áreas de forrajeo que variaron en los factores ecológicos de interés a lo largo de un ambiente urbanizado. S. nigricans seleccionó perchas con alta cobertura de árboles y pastos y con baja intensidad de luz, lo cual podrĺa aumentar el acceso a las presas y reducir el riesgo de depredación. La búsqueda visual de presas disminuyó a medida que la cobertura de pastos aumentó y que la cobertura de árboles disminuyó, probablemente debido a una menor obstrucción fĺsica y visual. La búsqueda visual aumentó con la intensidad de luz, probablemente como resultado del efecto del resplandor, pero el contraste cromático no ejerció una influencia significativa. Sugerimos que para S. nigricans en áreas urbanizadas, el acceso fĺsico a las presas puede estar regulado por la disponibilidad de sotobosque abierto y de acceso visual con buena iluminación, más que por el contraste de la presa contra el ambiente de fondo.
    The Condor 02/2009; · 1.37 Impact Factor
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    ABSTRACT: In birds, differences in the extent and position of the binocular visual field reflect adaptations to varying foraging strategies, and the extent of the lateral portion of the field may reflect anti-predator strategies. The goal of this study was to describe and compare the visual fields of two ground-foraging passerines, House Finch Carpodacus mexicanus and House Sparrow Passer domesticus. We found that both species have a binocular field type that is associated with the accurate control of bill position when pecking. Both species have eye movements of relatively large amplitude, which can produce substantial variations in the configuration of the binocular fields. We propose that in these ground foragers, their relatively wide binocular fields could function to increase foraging efficiency by locating multiple rather than single food items prior to pecking events. The lateral fields of both species are wide enough to facilitate the detection of predators or conspecifics while head-down foraging. This suggests that foraging and scanning are not mutually exclusive activities in these species, as previously assumed. Furthermore, we found some slight, but significant, differences between species: House Sparrow binocular fields are both wider and vertically taller, and the blind area is wider than in House Finches. These differences may be related to variations in the degree of eye movements and position of the orbits in the skull.
    Ibis 09/2008; 150(4):779 - 787. · 2.36 Impact Factor

Publication Stats

69 Citations
24.59 Total Impact Points

Institutions

  • 2012–2013
    • Georgia State University
      • Neuroscience Institute
      Atlanta, Georgia, United States
  • 2009–2013
    • Purdue University
      • • Department of Biological Sciences
      • • Department of Speech, Language and Hearing Sciences
      West Lafayette, IN, United States
  • 2008–2009
    • California State University, Long Beach
      • Department of Biological Sciences
      Long Beach, CA, United States