Broadening Our Approaches to Studying Dispersal in Raptors

Dispersal is a behavioral process having consequences for individual fitness and population dynamics. Recent advances in technology have spawned new theoretical examinations and empirical studies of the dispersal process in birds, providing opportunities for examining how this information may be applied to studies of the dispersal process in raptors. Many raptors are the focus of conservation efforts; thus, reliable data on all aspects of a species\u27 population dynamics, including dispersal distances, movement rates, and mortality rates of dispersers, are required for population viability analyses that are increasingly used to inform management. Here, we address emerging issues and novel approaches used in the study of avian dispersal, and provide suggestions to consider when developing and implementing studies of dispersal in raptors. Clarifying study objectives is essential for selection of an appropriate methodology and sample size needed to obtain accurate estimates of movement distances and rates. Identifying an appropriate study-area size will allow investigators to avoid underestimating population connectivity and important population parameters. Because nomadic individuals of some species use temporary settling areas or home ranges before breeding, identification of these areas is critical for conservation efforts focusing on habitats other than breeding sites. Study designs for investigating raptor dispersal also should include analysis of environmental and social factors influencing dispersal, to improve our understanding of condition-dependent dispersal strategies. Finally, we propose a terminology for use in describing the variety of movements associated with dispersal behavior in raptors, and we suggest this terminology could be used consistently to facilitate comparisons among studies

Broadening Our Approaches to Studying Dispersal in Raptors

Dispersal is a behavioral process having consequences for individual fitness and population dynamics. Recent advances in technology have spawned new theoretical examinations and empirical studies of the dispersal process in birds, providing opportunities for examining how this information may be applied to studies of the dispersal process in raptors. Many raptors are the focus of conservation efforts; thus, reliable data on all aspects of a species\u27 population dynamics, including dispersal distances, movement rates, and mortality rates of dispersers, are required for population viability analyses that are increasingly used to inform management. Here, we address emerging issues and novel approaches used in the study of avian dispersal, and provide suggestions to consider when developing and implementing studies of dispersal in raptors. Clarifying study objectives is essential for selection of an appropriate methodology and sample size needed to obtain accurate estimates of movement distances and rates. Identifying an appropriate study-area size will allow investigators to avoid underestimating population connectivity and important population parameters. Because nomadic individuals of some species use temporary settling areas or home ranges before breeding, identification of these areas is critical for conservation efforts focusing on habitats other than breeding sites. Study designs for investigating raptor dispersal also should include analysis of environmental and social factors influencing dispersal, to improve our understanding of condition-dependent dispersal strategies. Finally, we propose a terminology for use in describing the variety of movements associated with dispersal behavior in raptors, and we suggest this terminology could be used consistently to facilitate comparisons among studies

Potential factors influencing nest defense in diurnal North American raptors

Nesting habitat, predator type, and level of reproductive effort influence nest defense behaviors in many bird species, yet no study has examined these or other possible factors influencing nest defense in a cross-species comparison for raptors. Using data from the literature, we grouped the nest defense behaviors of 19 diurnal North American raptors into four categories based on a gradient of aggressiveness. For each species, we identified the cover types where nesting occurred, accessibility of nest location, assessed two indices of reproductive effort, and examined associations between these factors and nest-defense behavior. We also we examined responses by raptor species to different predator types including diurnal avian, nocturnal avian, mammalian (not human), and human. Most raptor species with high reproductive effort exhibited very aggressive nest defense. Most raptor species nesting in open cover types and species with accessible nests showed aggressive nest defense. While many raptors react aggressively toward diurnal and nocturnal avian predators, they exhibit less aggressive defense against potential human predators. Results from this study suggest that a variety of factors may influence nest-defense strategies used by diurnal raptors. However, more work is needed on the relative influence of these factors (including predation risk) and variation in raptor nest defense strategies before general patterns can be elucidated

Evolution of Communal Roosting: A Social Refuge-Territory Prospecting Hypothesis

© 2018 The Raptor Research Foundation, Inc. Avian communal roosts provide insight into evolution and serve as focal points for conservation. Nonbreeding Crested Caracaras (Caracara cheriway; hereafter caracaras) use communal roosts, but evolutionary implications have not been explored. Though nonbreeding caracaras are nonmigratory, the scientific literature fails to explain seasonal differences in their movement and survival concurrent with seasonal consistency in their habitat and social ecology. In the Social Refuge-Territory Prospecting hypothesis we propose, socially subordinate nonbreeding caracaras precluded from breeding by habitat limitation use communal roosts as social refuges to avoid aggression from dominant territory holders during nonbreeding seasons, and engage in territory prospecting during breeding seasons. Communal roosts thus become central places from which to forage not for food, but for a breeding territory. Because foraging gains are stored as remembered information, competition costs resulting from public information are preempted. For the Social Refuge-Territory Prospecting hypothesis to be valid, two criteria need to be met. First, communal roost use needs to be higher during nonbreeding seasons. Second, a measure of fitness needs to be used to evaluate the hypothesis as an evolutionarily stable strategy. To meet these criteria, in this study we report that numbers of nonbreeding caracaras using a communal roost in Florida are higher during nonbreeding seasons (mean = 111.8 individuals/night) than during breeding seasons (mean = 60.7 individuals/night) as counted from August 2006-April 2009 (n = 407 counts). We also compare differential survival by season from previous work to demonstrate that by limiting exploratory movements to times when prospecting is most informative, nonbreeding caracaras balance maximizing survival against the likelihood of securing a breeding territory. Our hypothesis provides a unifying explanation for otherwise unexplained paradoxes in the ecology of nonbreeding caracaras, and may be useful in guiding conservation and expanding our understanding of the ecology of other communally roosting birds

Environmental Correlates of Nesting Success in Red-Shouldered Hawks

We evaluated the influence of weather on reproduction of the Red-shouldered Hawk (Buteo lineatus) in an agricultural landscape in south-central Florida where we found relatively high densities of successfully nesting hawks. We used a generalized linear modeling approach within an information-theoretic framework to examine the influence of total rainfall, rainfall frequency, and temperature on the timing of nesting, nesting success, and productivity of hawks during 1995-2000. The best models indicated an influence of rainfall frequency and laying period on hawk reproduction. During years with less frequent rainfall in the summer and fall months prior to the beginning of the breeding season, fewer pairs attempted to nest, and hawks nested later and had smaller clutch sizes and lower productivity. Hawks that nested later in the breeding season had lower hatching success and lower overall nest success. Although Red-shouldered Hawks are generally reported to inhabit forested landscapes throughout their range, a common feature seems to be a dependence on wetlands and riparian habitat for foraging. We propose that the proportion of wetlands throughout the landscape is a unique aspect of south-central Florida that may allow for persistence of unusually high numbers of hawks

Environmental Correlates of Breeding in the Crested Caracara (Caracara cheriway)

We evaluated the influence of weather on reproduction of the Crested Caracara (Caracara cheriway) in an agricultural landscape in south-central Florida. We used a mixed logistic-regression modeling approach within an information-theoretic framework to examine the influence of total rainfall, rainfall frequency, and temperature on the number of breeding pairs, timing of breeding, nest success, and productivity of Crested Caracaras during 1994–2000. The best models indicated an influence of rainfall frequency and laying period on reproduction. More individuals nested and more pairs nested earlier during years with more frequent rainfall in late summer and early fall. Pairs that nested later in each breeding season had smaller clutches, lower nest success and productivity, and higher probability of nest failure. More frequent rainfall during early spring months that are usually characterized by water deficit (March–May), more frequent rainfall during the fall drawdown period (September–November), and a shorter winter dry period showed some association with higher probability of brood reduction and lower nest success. The proportion of nests that failed was higher in wet years, when total rainfall during the breeding season (September–April) was \u3e10% above the 20-year average. Rainfall may influence reproduction in Crested Caracaras indirectly through food resources. As total rainfall increased during February–April, when most pairs are feeding nestlings or dependent fledglings, the proportion of drawdown-dependent species (those that become available as rainfall decreases and wetlands become isolated and shallow) in the diet of Crested Caracaras declined, which may indicate reduced availability of foraging habitat for this primarily terrestrial raptor

Identification of Regulatory Phosphorylation Sites in a Cell Volume– and Ste20 Kinase–dependent ClC Anion Channel

Changes in phosphorylation regulate the activity of various ClC anion transport proteins. However, the physiological context under which such regulation occurs and the signaling cascades that mediate phosphorylation are poorly understood. We have exploited the genetic model organism Caenorhabditis elegans to characterize ClC regulatory mechanisms and signaling networks. CLH-3b is a ClC anion channel that is expressed in the worm oocyte and excretory cell. Channel activation occurs in response to oocyte meiotic maturation and swelling via serine/threonine dephosphorylation mediated by the type I phosphatases GLC-7α and GLC-7β. A Ste20 kinase, germinal center kinase (GCK)-3, binds to the cytoplasmic C terminus of CLH-3b and inhibits channel activity in a phosphorylation-dependent manner. Analysis of hyperpolarization-induced activation kinetics suggests that phosphorylation may inhibit the ClC fast gating mechanism. GCK-3 is an ortholog of mammalian SPAK and OSR1, kinases that bind to, phosphorylate, and regulate the cell volume–dependent activity of mammalian cation-Cl− cotransporters. Using mass spectrometry and patch clamp electrophysiology, we demonstrate here that CLH-3b is a target of regulatory phosphorylation. Concomitant phosphorylation of S742 and S747, which are located 70 and 75 amino acids downstream from the GCK-3 binding site, are required for kinase-mediated channel inhibition. In contrast, swelling-induced channel activation occurs with dephosphorylation of S747 alone. Replacement of both S742 and S747 with glutamate gives rise to kinase- and swelling-insensitive channels that exhibit activity and biophysical properties similar to those of wild-type CLH-3b inhibited by GCK-3. Our studies provide novel insights into ClC regulation and mechanisms of cell volume signaling, and provide the foundation for studies aimed at defining how conformational changes in the cytoplasmic C terminus alter ClC gating and function in response to intracellular signaling events

Invertebrate Diet of Breeding and Nonbreeding Crested Caracaras (Caracara cheriway) in Florida

We compared the invertebrate component of the diet of breeding and nonbreeding northern Crested Caracaras (Caracara cheriway) during the breeding season, January through April, in Florida, using pellet analysis. Pellets from breeding adults were collected at active nests and pellets of nonbreeding caracaras were collected from beneath a communal roost. During the breeding season, breeding and nonbreeding caracaras consumed invertebrate prey from a minimum of 61 genera and a total of 33 families from eight orders. Nonbreedingcaracaras consumed greater total numbers of invertebrates, more different prey types, and a greater diversity of invertebrates than did breeding caracaras. Pellets of nonbreeding caracaras contained more invertebrates per pellet, and carrion insects occurred more frequently in pellets of nonbreeding caracaras. Our findings suggest hypotheses regarding the possible role of intraspecific competition in the use of particular habitats and food resources by breeding and nonbreeding caracaras in Florida. Breeding pairs of caracaras are highly territorial and primarily feed nestlings larger-sized vertebrate prey, and field observations indicated that territorial adults can exclude young (nonbreeding) birds from their breeding areas; thus, diet differences may reflect social structure within this population. If pairs of breeding adults exclude conspecifics from important food resources or foraging habitats, nonbreeders may hunt arthropods or rely on carrion by necessity, especially if nonbreeders occur in suboptimal habitat in which other prey are less available

The Grizzly, April 2, 1982

PA Special Olympics This Weekend • Room Selection Continues • Student Publications Staffs Chosen • Parents Day Plans Offer Variety of Talents • USGA Notes • Letters to the Editor • Dean of College Accepting Nominations for Lindback Award • Class Elections Next Week • News Briefs: Hooters Concert Tickets Now Available; Friends of Library Book Sale; Senior Women Invited to Parents Day Reception; Photography in Space Topic of Final Forum; Scholarship Offered for Students of Hellenic Descent • Food Day: A Chance to Share the Wealth • New Library Survey Conducted • Alumna Presents DuPont Grant • Students Direct Comedy Series • Duet Takes First in Talent Show • F&M Tops Track Team • W\u27s Tennis Drops Warm-up • Division 1 West Chester a Little Too Strong • MAC Champs Back • Harvard Slips by Lady Bears • Batsmen Split Twin Bill • Softball Team Takes Two Out of Threehttps://digitalcommons.ursinus.edu/grizzlynews/1077/thumbnail.jp