Glenn A. Proudfoot’s research while affiliated with Vassar College and other places

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Publications (21)


Sample point variation in gastrointestinal bacteria of migrating Northern Saw-whet Owls (Aegolius acadicus) of eastern North America
  • Article

March 2022

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24 Reads

The Wilson Journal of Ornithology

Fiona M. Hart

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Glenn A. Proudfoot

We characterize bacteria of the gastrointestinal tract of 28 Northern Saw-whet Owls (Aegolius acadicus) netted on the Mohonk Preserve near New Paltz, New York, during autumn of 2017. We used selective culture media to determine the presence and assess the point infection level of Escherichia coli, Pseudomonas aeruginosa, Salmonella spp., and Staphylococcus aureus in the buccal, cloaca, feces, and pellets of Northern Saw-whet Owls. We tested for associations between bacteria type, sample point location, and infection levels and then assessed the influence of bacterial infection on the health of owls using multivariate analysis of mass/wing chord body condition index estimates and heterophil to lymphocyte ratios. All Northern Saw-whet Owls tested positive for at least one type of bacteria. We found an inverse relationship between the number of bacteria types detected per individual and the percentage of Northern Saw-whet Owls affected, with 46.43%, 32.14%, and 3.57% of individuals showing presence of 2, 3, and 4 types of bacteria, respectively. Multivariate analysis revealed a significantly heightened presence of S. aureus in the buccal cavity, and Spearman's rho analysis revealed positive correlations between site colonization levels and bacterial species levels. We found no significant relationship between bacterial load and mass/wing chord body condition indexes or heterophil to lymphocyte ratios. We did, however, find a positive relationship between heterophil to lymphocyte ratios and Leucocytozoon infections. Providing baseline information of common microflora can help future research recognize potentially harmful gastrointestinal pathogens. Therein, as the first study to characterize bacteria of the Northern Saw-whet Owl, this research adds to the information portfolio of the species and may benefit future research efforts.


Effects of Frequency on the Directional Auditory Sensitivity of Northern Saw-Whet Owls (Aegolius acadicus)

November 2021

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35 Reads

Brain Behavior and Evolution

Many animals use sound as a medium for detecting or locating potential prey items or predation threats. Northern saw-whet owls ( Aegolius acadicus ) are particularly interesting in this regard, as they primarily rely on sound for hunting in darkness, but are also subject to predation pressure from larger raptors. We hypothesized that these opposing tasks should favor sensitivity to low-frequency sounds arriving from many locations (potential predators) and high-frequency sounds below the animal (ground-dwelling prey items). Furthermore, based on the morphology of the saw-whet owl skull and the head-related transfer functions of related species, we expected that the magnitude of changes in sensitivity across spatial locations would be greater for higher frequencies than low frequencies (i.e., more “directional” at high frequencies). We used auditory-evoked potentials to investigate the frequency-specific directional sensitivity of Northern saw-whet owls to acoustic signals. We found some support for our hypothesis, with smaller-magnitude changes in sensitivity across spatial locations at lower frequencies and larger-magnitude changes at higher frequencies. In general, owls were most sensitive to sounds originating in front of and above their heads, but at 8 kHz there was also an area of high sensitivity below the animals. Our results suggest that the directional hearing of saw-whet owls should allow for both predator and prey detection.


Account and Utilization of Blood Lipid Profiles: Lipid Levels Predicted Hemosporidian Infection in Migrating Northern Saw-Whet Owls of Eastern North America

March 2021

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19 Reads

Journal of Parasitology

Noting lipidomic changes following the parasitism of migrating birds, the metabolic needs of which are primarily fueled by lipids, can deepen our understanding of host-parasite interactions. We identified lipids of migrating Northern saw-whet owls (Aegolius acadicus) using collision-induced dissociation mass spectrometry, compared the lipidomic signatures of hemoparasite-infected and noninfected individuals, and performed cross-validation analyses to reveal associations between parasite infection and lipid levels. We found significantly lower levels of lipid classes phosphatidic acid (PA), phosphatidylglycerol (PG), phosphatidylinositol (PI), phosphatidylserine (PS), phosphatidylethanolamine (PE), phosphatidylcholine (PC), and sphingomyelin (SM) in infected Northern saw-whet owls than in the noninfected individuals. Conversely, we found higher levels for certain lysoPS and lysoPE species, and variable lipid level changes for free fatty acid (FFA) species. Reporting lipidomic changes observed between hemosporidian-infected and noninfected Northern saw-whet owls can strengthen our understanding of the mechanisms governing parasite proliferation in this species. Furthermore, our analysis indicated that lipidomic signatures are better predictors of parasite infection than the log-adjusted mass/wing chord body index, a metric commonly used to assess the influence of hemosporidia infection on the health of birds. Establishing a lipidomic profile for Northern saw-whet owls that provides baseline lipid levels during fall migration may assist future studies assessing causes of reductions in breeding brought about from subtle differences in behaviors such as delayed migration.


Hearing in 3D: Directional Auditory Sensitivity of Northern Saw-Whet Owls (Aegolius acadicus)

May 2020

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93 Reads

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7 Citations

Integrative and Comparative Biology

Northern saw-whet owls (Aegolius acadicus) are nocturnal predators that are able to acoustically localize prey with great accuracy; an ability that is attributed to their unique asymmetrical ear structure. While a great deal of research has focused on open loop sound localization prior to flight in owls (primarily barn owls), directional sensitivity of the ears may also be important in locating moving prey on the wing. Furthermore, directionally sensitive ears may also reduce the effects of masking noise, either from the owls' wings during flight or environmental noise (e.g. wind, leaf rustling, etc.), by enhancing spatial segregation of target sounds and noise sources. Here, we investigated auditory processing of Northern saw-whet owls in three-dimensional space using auditory evoked potentials (AEPs). We simultaneously evoked auditory responses in two channels (right and left ear) with broadband clicks from a sound source that could be manipulated in space. Responses were evoked from 66 spatial locations, separated by 30° increments in both azimuth and elevation. We found that Northern saw-whet owls had increased sensitivity to sound sources directly in front of and above their beaks and decreased sensitivity to sound sources below and behind their heads. The spatial region of highest sensitivity extends from the lower beak to the crown of the head and 30° left or right of the median plane, dropping off beyond those margins. Directional sensitivity is undoubtedly useful during foraging and predator evasion, and may also reduce the effect of masking noise from the wings during flight due to the spatial segregation of the noise and targets of interest.


Fig. 2 a Neighbor-joining phenogram based on pairwise comparisons of average nucleotide differences. Abbreviations for localities are the same as those provided in Table 1. Group 1 (pink), Group 2 (blue), Group 3 (brown), Newfoundland (Grey). b Haplotype network with numbers corresponding to haplotypes described in Table 1. Cross marks represent single mutations, and the dark dot represents an unknown haplotype
Mitochondrial DNA variation of the ruffed grouse (Bonasa umbellus)
  • Article
  • Full-text available

September 2019

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133 Reads

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3 Citations

BMC Research Notes

Objective: The ruffed grouse, Bonasa umbellus, is broadly distributed across North America and displays considerable taxonomic diversity. Except for a genetic study of some western populations of ruffed grouse, nothing is known about genetic variation in other regions of Canada and the United States. Our objective is to examine patterns of mitochondrial DNA (mtDNA) variation in the ruffed grouse across western, central, and eastern parts of its distribution. We compare patterns of mtDNA variation to those characterized by morphology and ecology. Additionally, we evaluate the demographic history of the species based on mitochondrial haplotype diversity. Results: Patterns of mtDNA variation revealed geographic subdivision, with populations of ruffed grouse subdivided into 3 to 4 genetically distinct groups. This subdivision partially coincided with the ranges of described subspecies. Behavioral traits prohibiting long-distance movement and barriers to dispersal in response to physiography and unsuitable habitat help explain these patterns of subdivision. Historically, the ruffed grouse probably experienced a population expansion, possibly in response to changes during the Pleistocene.

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Effects of presentation rate and onset time on auditory brainstem responses in Northern saw-whet owls ( Aegolius acadicus )

April 2019

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69 Reads

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5 Citations

The Journal of the Acoustical Society of America

Monitoring auditory brainstem responses (ABRs) is a common method of assessing auditory processing in non-model species. Although ABRs are widely used to compare auditory abilities across taxa, the extent to which different features of acoustic stimuli affect the ABR is largely unknown in most non-mammalian species. The authors investigated the effects of varying presentation rate and onset time to determine how different features of acoustic stimuli influence the ABR in Northern saw-whet owls (Aegolius acadicus), a species known for their unique auditory adaptations and hunting abilities. At presentation rates ranging from 21.1 to 51.1 s⁻¹, there were no differences in the size or synchrony of ABRs, suggesting that stimuli can be presented at a relatively rapid rate to maximize the number of observations recorded for analysis. While increasing onset time was associated with a decrement in response size and synchrony, tonebursts with 1 ms onset times produced overgeneralized neural responses as a result of spectral splatter. This suggests that 2 to 3 ms onset times may balance the trade-off between response synchrony and frequency specificity when comparing relative neural recruitment across frequencies. These findings highlight the importance of considering stimulus parameters when interpreting ABR data.


Table 1 . Results of mixed effects stepwise logistic regression analysis of host age and average annual temperature at northern saw-whet owl breeding grounds and the likelihood of single or mixed genera infections and parasitism by Plasmodium or Leucocytozoon, with year as a random effect.
Figure 2. Average annual temperature (a), total annual precipitation (b), and total days with > 2.54 cm of snow depth (c) determined from data provided by NOAA weather stations located within the proposed northern saw-whet owl breeding grounds established from stable isotope analysis (Warne et al. 2015).
Figure 3. Number and percentage of Haemospordian infections in northern saw-whet owls (n = 1253) captured at the Mohonk Preserve near New Paltz, NY from 2006 to 2016, arranged by infection type. L = Leucocytozoon; P = Plasmodium; LL = two different Leucocytozoon lineages; LP = Leucocytozoon and Plasmodium; LH = Leucocytozoon and Haemoproteus; LLLH = mixed Leucocytozoon and Haemoproteus infection (quadruple infection); U = uninfected.
Figure 4. Number and percentage of Haemospordian infections in northern saw-whet owls (n = 1253) captured at the Mohonk Preserve near New Paltz, NY from 2006 to 2016, arranged by haemosporidian lineage. Blue = Leucocytozoon; red = Plasmodium; yellow = Haemoproteus. Other Leucocytozoon lineages include BUVIR04, AEFUN02, BNOW04, STOCC13, STOCC03, and sequences that were either < 525 bp and/or contained < 100% matched bp to a sequence in the MalAvi database. Other Plasmodium lineages include BT7, SW5, CATUST05, RWB01, BAEBIC02, and sequences that were < 477 bp and/or contained < 100% matched bp to a sequence in the MalAvi database.
Haemosporidian prevalence in Northern saw‐whet owls (Aegolius acadicus) is predicted by host age and average annual temperature at breeding grounds

September 2018

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340 Reads

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14 Citations

Monica L. Carlson

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Glenn A. Proudfoot

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Kaya Gentile

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[...]

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Understanding factors that determine haemosporidian prevalence is critical in predicting how parasite and avian host populations will respond to environmental change. Here, we used molecular screening of blood samples from migrating Northern saw‐whet owls (Aegolius acadicus) in eastern North America to characterize haemosporidian infections and examine parasite prevalence with respect to abundance of migrants, timing of migration, climatic conditions at the breeding grounds, and avian host age. We identified three haemosporidian genera (Leucocytozoon, Plasmodium, and Haemoproteus) and discovered a new lineage of Leucocytozoon that is thus far specific to the Northern saw‐whet owl. We found no significant relationship between parasite prevalence and Northern saw‐whet owl abundance or timing of migration. After‐hatch‐year birds were significantly more likely to be parasitized by Leucocytozoon than hatch‐year birds, whereas prevalence of Plasmodium was higher in hatch‐year birds. Of the three climatic variables analyzed at owl breeding grounds (temperature, precipitation, and snowpack days), lower average annual temperatures significantly increased the chance of a bird being parasitized by Leucocytozoon; no significant temperature‐dependent relationship was found for Plasmodium. This study contributes to our general understanding of the relationship between parasite prevalence and host density, host age, resource abundance, and abiotic factors such as temperature and precipitation. This article is protected by copyright. All rights reserved.


Frequency sensitivity in Northern saw-whet owls (Aegolius acadicus)

February 2018

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1,581 Reads

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21 Citations

Journal of Comparative Physiology A

Northern saw-whet owls (Aegolius acadicus) are known for their unique asymmetrical ear structure and ability to localize prey acoustically, yet few attempts have been made to explore the auditory capabilities of this species. In this study, we evoked auditory brainstem responses (ABRs) with tonebursts to assess three main hypotheses regarding the evolution of auditory sensitivity: sender-receiver matching, ecological constraints, and phylogenetic/morphological constraints. We found that ABR amplitude increased with increasing stimulus level, which is consistent with results in other avian species. ABR amplitudes, latencies, and thresholds indicate that the hearing range of Northern saw-whet owls extends from 0.7 to 8.6 kHz, with an extended frequency range of best sensitivity between 1.6 and 7.1 kHz. Sensitivity fell off rapidly above and below these frequencies. The average audiogram was structurally similar to those found in other species of owls, suggesting that phylogeny or morphology may be constraining the frequency range of auditory sensitivity. However, ABR thresholds were 10–25 dB lower than those of Eastern screech-owls (Megascops asio), with thresholds below 0 dB SPL in some individuals. The lowest thresholds were at frequencies not found in the vocalizations of Northern saw-whet owls, suggesting ecological constraints rather than conspecific vocalizations are driving absolute sensitivity.


Figure 1: A diversity of biomarkers derived from numerous integrative fields can be assayed on blood and feathers (or other keratinaceous tissues) collected from the same individual. By applying these assays to the same tissues, differing time periods (days, weeks to seasons) can be examined, and a more comprehensive assessment can be developed for the state and health of animals, as well as how a host of ecological factors affects them. Note that the order in which the fields are presented is random, but the positive trend of each shape suggests the increasing depth of information that can be gained through multiple assays applied to the same tissues.
Figure 2: Geostatistical isoscape estimates for the origin of Northern saw-whet owls that were netted and banded in the Hudson Valley of New York. Estimates are based upon δ2Hydrogen analysis of feathers of hatch-year owls. IsoMAP Project: Isoscapes Modeling, Analysis, and Prediction (version 1.0). Available at: http://isomap.org.
Figure 3: Relationship between corticosterone levels in the feathers of Northern saw-whet owls and the date of capture (A), δ2Hydrogen values (B), and plasma CORT levels (C). The triangle symbols are for adult owls, and the circles are for hatch-year owls; note that only the hatch-year owls are presented in plot B because of uncertainty in δ2Hydrogen values for adults.
Figure 4: Plasma CORT levels of adult (triangles) and hatch-year (circles) Northern saw-whet owls in relationship to blood parasite loads. The triangle symbols are for adult owls, and the circles are for hatch-year owls.
Biomarkers of animal health: Integrating nutritional ecology, endocrine ecophysiology, ecoimmunology, and geospatial ecology

February 2015

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199 Reads

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23 Citations

Diverse biomarkers including stable isotope, hormonal, and ecoimmunological assays are powerful tools to assess animal condition. However, an integrative approach is necessary to provide the context essential to understanding how biomarkers reveal animal health in varied ecological conditions. A barrier to such integration is a general lack of awareness of how shared extraction methods from across fields can provide material from the same animal tissues for diverse biomarker assays. In addition, the use of shared methods for extracting differing tissue fractions can also provide biomarkers for how animal health varies across time. Specifically, no study has explicitly illustrated the depth and breadth of spacial and temporal information that can be derived from coupled biomarker assessments on two easily collected tissues: blood and feathers or hair. This study used integrated measures of glucocorticoids, stable isotopes, and parasite loads in the feathers and blood of fall-migrating Northern saw-whet owls (Aegolius acadicus) to illustrate the wealth of knowledge about animal health and ecology across both time and space. In feathers, we assayed deuterium (δD) isotope and corticosterone (CORT) profiles, while in blood we measured CORT and blood parasite levels. We found that while earlier migrating owls had elevated CORT levels relative to later migrating birds, there was also a disassociation between plasma and feather CORT, and blood parasite loads. These results demonstrate how these tissues integrate time periods from weeks to seasons and reflect energetic demands during differing life stages. Taken together, these findings illustrate the potential for integrating diverse biomarkers to assess interactions between environmental factors and animal health across varied time periods without the necessity of continually recapturing and tracking individuals. Combining biomarkers from diverse research fields into an integrated framework hold great promise for advancing our understanding of environmental effects on animal health.


FIG. 1. Parasite genera present in Northern Saw-whet Owls (10003 magnification): A) Haemoproteus (arrow); B) Leucocytozoon; C) Microfilaria; D) Plasmodium (arrow); E) Trypanosoma; F) Unknown cell intrusion (arrow).  
TABLE 1 . Prevalence proportion of haematozoa infected Northern Saw-whet Owls captured on the Mohonk Preserve in Ulster County, New York from 1 October to 2 December 2011.
Results of general linear models used to assess the relationships between body condition (dependent variable) of Northern Saw-whet Owls and infection status (fixed factor) of haematozoa genera. Owls were captured on the Mohonk Preserve in Ulster County, New York from 1 October to 2 December 2011.
Prevalence of haematozoa in migrating Northern Saw-Whet Owls (Aegolius acadicus) of eastern North America

December 2014

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206 Reads

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7 Citations

The Wilson Journal of Ornithology

We examined blood smears from 139 Northern Saw-whet Owls (Aegolius acadicus) to ascertain the prevalence of haematozoa in this species during fall migration in eastern North America. Owls were captured with mist nets on the Mohonk Preserve near New Paltz, New York from 1 October to 2 December 2011. We examined blood smears under an optical microscope at 200× and 1000× magnification, and observed four genera of haematozoa, Haemoproteus, Leucocytozoon, Plasmodium, and Trypanosoma, in addition to a genus or genera of microfilarial nematodes, unidentifiable by morphology. We found haematozoa in blood smears from both male and female Northern Saw-whet Owls and in both age groups sampled, i.e., hatching year and after hatching year. Leucocytozoon was the most common parasite, with an overall prevalence of 49.6%. Prevalence of Haemoproteus, microfilaria, Plasmodium, and Trypanosoma was 5.0%, 5.0%, 10.0%, and 2.9% respectively, and overall occurrence of infection was 64%. We found no difference in body condition of individuals compared by age, infection status, or intensity of infection. To our knowledge, this is the first record of Plasmodium in Northern Saw-whet Owls, and the first study to document five genera of haematozoa in Northern Saw-whet Owls during fall migration. Revealing new host–parasite information, this study contributes to the information portfolio of Northern Saw-whet Owls and, thus, may influence future research.


Citations (17)


... 5(b) and 8(c)]. Similar vertical differences have been observed in other species adept at acoustically localizing prey, such as owls and bats, which can enhance sound localization in the vertical plane (Coles and Guppy, 1988;Jen and Chen, 1988;Fuzessery, 1996;De Koning et al., 2020). More importantly, our findings highlighted the significant role of the air sinuses in enhancing asymmetric sound reception (Fig. 8). ...

Reference:

Role of air sinuses in sound reception of the Yangtze finless porpoise: A numerical study
Hearing in 3D: Directional Auditory Sensitivity of Northern Saw-Whet Owls (Aegolius acadicus)
  • Citing Article
  • May 2020

Integrative and Comparative Biology

... mountains) might prove informative in reconstructing the history of this species. Another example, the Ruffed Grouse Bonasa umbellus, showed multiple genetically different groups based on mtDNA CR sequences in its distribution range in North America (Honeycutt et al. 2019, Jensen et al. 2019. Jensen et al. (2019) indicated that dispersal resistance is the most important factor in shaping population structure in of this species. ...

Mitochondrial DNA variation of the ruffed grouse (Bonasa umbellus)

BMC Research Notes

... In at least one clade (Clade F, M. atricapilla) we found clinal variation in body mass, which increases from lower to higher latitudes, mirroring Bergmann´s rule (Bergmann 1847). Latitudinal clines in size and plumage are also known for other screech-owls, such as M. asio and M. kennicottii (Proudfoot et al. 2007). ...

Mitochondrial DNA Variation and Phylogeography of the Eastern and Western Screech-Owls
  • Citing Article
  • August 2007

Ornithological Applications

... The following is an example of a protocol used in the clinical practice to obtain BAEP recordings: click stimulus, condensation polarity, stimulus intensity of 80 dB HL, a rate of 27.7 stimuli/s and a bandpass filter of 100 Hz to 3,000 Hz. 9 The stimulation rates can be applied in different ways, and the rate of 27.7 stimuli/s is one of the most used in audiology services. 1,10 The presentation of higher rates of stimuli per second enables the collection of a greater number of responses in a given period of time, promoting a shorter testing time; however, the collected recordings are subject to changes related to wave morphology. 11 These changes are important and must be considered to standardize data and define protocols for the clinical practice. ...

Effects of presentation rate and onset time on auditory brainstem responses in Northern saw-whet owls ( Aegolius acadicus )
  • Citing Article
  • April 2019

The Journal of the Acoustical Society of America

... DNA was extracted from the blood samples using the Qiagen DNeasy 96 Blood & Tissue Kit (Qiagen, Germantown, MD, USA) protocol. Each sample was screened for avian haemosporidian parasites of the genera Plasmodium, Haemoproteus (including the subgenus Parahaemoproteus) and Leucocytozoon using a standard cytochrome b (cytb) barcoding approach following Carlson et al. (2018). The resulting consensus sequences were used to identify unique haemosporidian cytb haplotypes, which we refer to as 'genetic lineages' following the standard in avian haemosporidian research (Bensch et al., 2009). ...

Haemosporidian prevalence in Northern saw‐whet owls (Aegolius acadicus) is predicted by host age and average annual temperature at breeding grounds

... We used two methods to determine ABR thresholds. First, we used a visual detection method to estimate ABR thresholds for each subject at each stimulus frequency (Brittan-Powell et al. 2002;Schrode et al. 2014;Beatini et al. 2018). For each frequency, we plotted the average AEP in order of descending stimulus level and operationally defined the ABR threshold as the level 2.5 dB (one-half step) below the lowest stimulus level at which an ABR was observed (Fig. 2a). ...

Frequency sensitivity in Northern saw-whet owls (Aegolius acadicus)

Journal of Comparative Physiology A

... Explicit quantification of immune tradeoffs, such as those experienced by short-versus long-distance migrants, would also be informative. Little consensus exists on the impacts of haemosporidian parasites on the condition and survival of their avian hosts, with some studies finding no significant effects on body condition (Young and Proudfoot 2014) or fitness (Bensch et al. 2007), while some instead find positive effects on fitness (Zylberberg et al. 2015). The lack of a negative relationship between body condition and haemosporidian infection observed here suggests that robins are tolerant to these parasites, a possibility that merits further study given the ubiquitous nature of this bird across North America. ...

Prevalence of haematozoa in migrating Northern Saw-Whet Owls (Aegolius acadicus) of eastern North America

The Wilson Journal of Ornithology

... Compared to the depth and breadth of knowledge on reproductive physiology in domestic species, knowledge of wildlife reproductive endocrinology is less well-developed, particularly with respect to molecular mechanisms [42]. However, as research labs identify new biomarkers of reproductive status [43][44][45][46], it is expected that the wildlife biology field will catch up. For application to the study of wildlife reproductive health, useful biomarkers must: 1) have a characterized relationship with the process of interest (i.e. ...

Biomarkers of animal health: Integrating nutritional ecology, endocrine ecophysiology, ecoimmunology, and geospatial ecology

... To date fewer than half of these have been described (298 spp.), but even this represents a three-fold increase over the past decade. As relationships and taxonomic limits have slowly improved, we have carved off and revised a number of subgroups/genera (Caterino et al. 2012(Caterino et al. , 2013Caterino and Tishechkin 2013a, b, 2014, 2016, 2019. However, the fauna remains a complicated one, containing many small, similar-looking species with relatively few distinguishing features. ...

A New Genus and Species of North American Exosternini Associated with Cavity-Nesting Owls and a Reassignment of Phelister simoni Lewis (Coleoptera: Histeridae: Histerinae)
  • Citing Article
  • December 2013

The Coleopterists Bulletin

... [Traducció n del equipo editorial] Migration patterns of Northern Saw-whet Owls (Aegolius acadicus; hereafter saw-whet owls) have been a focus of study across North America in recent decades , Priestley et al. 2010, Beckett and Proudfoot 2011, De Ruyck et al. 2012, Frye 2012, Confer et al. 2014). In particular, many aspects about the timing (Holroyd and Woods 1975), magnitude , demographics (Beckett and Proudfoot 2012), and irruptive tendencies (Whalen and Watts 2002, Cheveau et al. 2004, Brittain et al. 2009) of this species are now better understood, primarily through the contributions of participants in Project Owlnet, a continentwide monitoring network of banding stations focused on banding saw-whet owls during spring and autumn migrations (Huy 2004). ...

Sex-Specific Migration Trends of Northern Saw-Whet Owls in Eastern North America
  • Citing Article
  • March 2012

Journal of Raptor Research