Bettina Mahler

Bio: Bettina Mahler is an academic researcher from Facultad de Ciencias Exactas y Naturales. The author has contributed to research in topics: Brood parasite & Cowbird. The author has an hindex of 12, co-authored 37 publications receiving 410 citations. Previous affiliations of Bettina Mahler include University of Buenos Aires & National Scientific and Technical Research Council.

Different recognition cues reveal the decision rules used for egg rejection by hosts of a variably mimetic avian brood parasite

Abstract: Brood parasitism imposes several fitness costs on the host species. To reduce these costs, hosts of avian brood parasites have evolved various defenses, of which egg rejection is the most prevalent. In the face of variable host-parasite mimicry and the costs of egg discrimination itself, many hosts reject only some foreign eggs. Here, we experimentally varied the recognition cues to study the underlying cognitive mechanisms used by the Chalk-browed Mockingbird (Mimus saturninus) to reject the white immaculate eggs laid by the parasitic Shiny Cowbird (Molothrus bonariensis). Immaculate eggs are the only parasite eggs rejected by this host, as it accepts all polymorphic, spotted eggs laid by cowbirds. Using a within-breeding pair experimental design, we tested for the salience of spotting, UV reflectance, and brightness in eliciting rejection. We found that the presence of spotting significantly decreased the probability of rejection while increments in brightness significantly increased rejection frequencies. The cognitive rules underlying mockingbird rejection behavior can be explained by a decision-making model which predicts changes in the levels of rejection in direct relation to the number of relevant attributes shared between host and parasite eggs.

Impact of Shiny Cowbird and botfly parasitism on the reproductive success of the globally endangered Yellow Cardinal Gubernatrix cristata

Abstract: Fil: Dominguez, Marisol. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Ecologia, Genetica y Evolucion de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecologia, Genetica y Evolucion de Buenos Aires; Argentina

Partial host fidelity in nest selection by the shiny cowbird (Molothrus bonariensis), a highly generalist avian brood parasite.

Abstract: Obligate avian brood parasites can be host specialists or host generalists. In turn, individual females within generalist brood parasites may themselves be host specialists or generalists. The shiny cowbird Molothrus bonariensis is an extreme generalist, but little is known about individual female host fidelity. We examined variation in mitochondrial control region sequences from cowbird chicks found in nests of four common Argentinean hosts. Haplotype frequency distributions differed among cowbird chicks from nests of these hosts, primarily because eggs laid in nests of house wrens Troglodytes aedon differed genetically from those laid in nests of the other three hosts (chalk-browed mockingbird Mimus saturninus, brown-and-yellow marshbird Pseudoleistes virescens, and rufous-collared sparrow Zonotrichia capensis). These differences in a maternally inherited marker indicate the presence of a nonrandom laying behaviour in the females of this otherwise generalist brood parasite, which may be guided by choice for nest type, as house wrens nest in cavities whereas the other three species are open cup nesters.

Reproductive Success and Nestling Growth of the Baywing Parasitized by Screaming and Shiny Cowbirds

Abstract: We studied the breeding biology of the Baywing (Agelaioides badius), a shared host of Screaming (Molothrus rufoaxillaris) and Shiny (M. bonariensis) cowbirds. We monitored 193 nests from December 2002 to March 2007 in the Province of Buenos Aires, Argentina. Baywings used a wide variety of nesting sites, mainly old nests of furnarids. Their breeding season lasted from late November to February and was closely matched by that of Screaming Cowbirds. The breeding season for Shiny Cowbirds started in late September but overlapped that of Baywings. Frequency and intensity of Screaming Cowbird parasitism were 93% and 5 eggs per parasitized nest, while for Shiny Cowbirds they were 16% and 1.4 eggs. Host clutch size was 4.0 ± 0.1 eggs and did not vary with time of breeding. Weight at hatching and age of maximum growth were similar for host and Screaming Cowbird nestlings. Shiny Cowbird nestlings had higher weight at hatching and lower age of maximum growth than the other two species. Screaming and Shiny ...

Chapter 2 The Evolution of Song in the Phylloscopus Leaf Warblers (Aves: Sylviidae): A Tale of Sexual Selection, Habitat Adaptation, and Morphological Constraints

Abstract: Differences in song between species of birds are often the most reliable criteria by which to identify them. Thus, the study of the evolution of bird song provides biologists with a powerful insight into the nature of speciation processes. Both adaptive and nonadaptive explanations have been proposed to account for the evolution of song differences in birds. In this study, we put several of these hypotheses to a test in the genus Phylloscopus, a species-rich group of Old World leaf warblers in which song is used by males for mate attraction and territory defense. We found that song characteristics contained significant amounts of phylogenetic information, although they were more labile than morphological traits. Song frequency characteristics were more phylogenetically preserved than temporal or song structure traits. Changes in body size between species were correlated with changes in maximum and minimum frequencies and frequency bandwidth: small-bodied species had higher frequencies and wider bandwidths than large-bodied species. Beak shape was not found to limit overall frequency patterns. We used an ecomorphological correlate of habitat use, the tarsus/beak ratio, to test for song adaptation to specific habitat sound transmission characteristics. We found that species with larger tarsus/beak ratio, typically inhabiting broadleaf habitats and understory vegetation, had lower emphasized frequencies in their songs, as expected if songs are adapted to maximize sound transmission. However, this relationship did not held when controlling for common descent. Song complexity, a wide-ranging measurement encompassing temporal and structural sound complexity estimates, was best explained by breeding latitude. We interpret this relationship as a correlate of increased sexual selection by mate choice toward more Northern latitudes. We failed to find a significant role of character displacement in the evolution of song in this group: sympatric pairs of species did not show larger differences in song than allopatric pairs of species. To sum up, superimposing upon large haphazard selection of song themes, selective pressures for higher song elaboration in areas of high sexual selection, and correlative change in song brought about by natural selection of body size, would explain some of the diversity of songs that are found within the genus Phylloscopus.

Declining body size: a third universal response to warming?

Abstract: A recently documented correlate of anthropogenic climate change involves reductions in body size, the nature and scale of the pattern leading to suggestions of a third universal response to climate warming. Because body size affects thermoregulation and energetics, changing body size has implications for resilience in the face of climate change. A review of recent studies shows heterogeneity in the magnitude and direction of size responses, exposing a need for large-scale phylogenetically controlled comparative analyses of temporal size change. Integrative analyses of museum data combined with new theoretical models of size-dependent thermoregulatory and metabolic responses will increase both understanding of the underlying mechanisms and physiological consequences of size shifts and, therefore, the ability to predict the sensitivities of species to climate change.

Threatened Birds of the Americas (the ICBP/IUCN Red Data Book)

Abstract: Editors NJ Collar, LP. Gonzaga, N. , Krabbe, A. Madrano Nieto, L.G. Naranjo, T.A. Parker III and D.C. Wege. Smithsonian Institution Press 1992. Price approx. $75.00 U.S. For anyone with an interest in conservation and/or the field status of the endangered birds of the Americas, this book is a must. Work on the book, which began in 1985, had to be halted in 1988 due to a lack of funding but was resumed after the 500th anniversary of Columbus's voyage of discovery produced some funds from the Spanish government. While seven authors are listed, the "tome" is actually the result of contributions of several hundred individuals. The book replaces the 1978 publication by W.B. King, "Red data book, 2 Aves," and its subsequent 1981 reprint under the title "Endangered birds of the world; the ICBP bird red data book." While King was able to list the endangered birds of the world, the current revision requires four parts to complete the task. Part one dealt with "Threatened birds of Africa and related islands" (Collar and Stuart 1985) and was followed by the current part two dealing with the Americas. The final parts three and four will deal with birds of Europe and Asia, Australasia and the Pacific. Throughout its 1,150 pages, species after species is profiled as to its distribution, population, and threats. Finally, each profile is concluded with those conservation measures that have been taken as well as those proposed. There are 38 psittacidae listed as threatened and an additional 17 listed in the appendix titled nearthreatened. The majority of the birds listed, however, are small insect, nectar or fruit eating birds. While many are colorful, they are genreally poorly represented in captivity. Due to our lack of experience with these "softbilled" birds, the possibility that aviculture will play a major role in their survival seems remote. To compound the misery, there seems to be a veiy small following of individuals and/or organizations dedicated to the survival of these frequently termed "dicky birds." While habitat protection certainly will grasp many from the hands of extinction, some focused species-specific actions are needed. All aviculturists and pet owners with an interest in conservation should have one or more of the volumes of this important text. Augmented with a copy of the National Wildlife Federation's Conservation Directory, individuals and bird clubs should have the resources necessary to join forces in saving the World's birds.e The Diamond Dove (A beautiful dove for both the novice and experienced aviculturist) by Dale R. Thompson Canyon Country, California The Diamond Dove is found throughout most of Australia except for the southeastern coastal regions. This dove is very popular because of its small size (seven inches), low cost and its readiness to breed under most conditions. It gets its name from the many white spots found on its gray wings. There are several mutations with the silver mutation being the most common. Others include the dark-eyed white mutation and the cinnamon mutation. Diamond Doves can be sexed by observing their behavior. Both sexes will coo but only the male can be seen bowing before the female with its tail raised and fanned. The red of the male's eye-ring is larger and brighter than the female's. The female generally is more brownish in coloration with larger and more numerous white spots on her wings. Diamond Doves are considered free breeders. Since these doves can be pugnacious, they are best kept as sing le pairs. If their housing is large enough (4' x 8' x 12' flight), more than one pair can be kept together. But remember that the success rate for rearing young is much poorer in a colony situation than by single pairs. Sometimes they can be quite aggressive to each other. These doves can breed throughout the year, but should be given a rest during the colder winter months. Often eggs or babies are lost due to the cold and the female is more prone to egg binding.

Conservation and the Genetics of Populations

Abstract: Review(s) of: Conservation and the Genetics of Populations, Fred W. Allendorf and Gordon Luikart, 2007, Publisher: Blackwell Publishing No. pages 642 ISBN-13: 9781405121453, ISBN-10: 1405121459, RRP AUD $34.99.

Long-term coevolution between avian brood parasites and their hosts.

Abstract: Coevolutionary theory predicts that the most common long-term outcome of the relationships between brood parasites and their hosts should be coevolutionary cycles based on a dynamic change selecting the currently least-defended host species, given that when well-defended hosts are abandoned, hosts will be selected to decrease their defences as these are usually assumed to be costly. This is assumed to be the case also in brood parasite-host systems. Here I examine the frequency of the three potential long-term outcomes of brood parasite-host coevolution (coevolutionary cycles, lack of rejection, and successful resistance) in 182 host species. The results of simple exploratory comparisons show that coevolutionary cycles are very scarce while the lack of rejection and successful resistance, which are considered evolutionary enigmas, are much more frequent. I discuss these results considering (i) the importance of different host defences at all stages of the breeding cycle, (ii) the role of phenotypic plasticity in long-term coevolution, and (iii) the evolutionary history of host selection. I suggest that in purely antagonistic coevolutionary interactions, such as those involving brood parasites and their hosts, that although cycles will exist during an intermediate phase of the interactions, the arms race will end with the extinction of the host or with the host acquiring successful resistance. As evolutionary time passes, this resistance will force brood parasites to use previously less suitable host species. Furthermore, I present a model that represents the long-term trajectories and outcomes of coevolutionary interactions between brood parasites and their hosts with respect to the evolution of egg-rejection defence. This model suggests that as an increasing number of species acquire successful resistance, other unparasitized host species become more profitable and their parasitism rate and the costs imposed by brood parasitism at the population level will increase, selecting for the evolution of host defences. This means that although acceptance is adaptive when the parasitism rate and the costs of parasitism are very low, this cannot be considered to represent an evolutionary equilibrium, as conventional theory has done to date, because it is not stable.