Yoram Yom-Tov

INTRASPECIFIC NEST PARASITISM IN BIRDS

(1) The incidence of intraspecific nest parasitism in birds is reviewed. This phenomenon can be identified by various methods, ranging from biochemical examination of protein and enzyme polymorphisms to observations on the sequence of appearance of eggs in the nest as well as on the shape and colour of the eggs. The phenomenon has been reported for at least 53 species (Table I), mostly among precocial birds.

Global warming and body mass decline in Israeli passerine birds

Global warming may affect the physiology, distributions, phenology and adaptations of plants and animals. In Israel, minimum summer temperatures increased by an average of 0.26°C per decade during the second half of the 20th century. Bergmanns rule predicts that, in warm–blooded animals, races from warm regions are smaller than races from cold regions. Numerous studies have reported general correlations between body mass in fossil animals and independently established palaeoclimatic changes from various parts of the world in accordance with this rule. Using museum specimens, I tested the prediction that the body mass and tarsus length of five resident passerine species in Israel declined between 1950 and 1999. The body mass of four species (the graceful warbler Prinia gracilis, the house sparrow Passer domesticus, the yellow-vented bulbul Pycnonotus xanthopygos and the Sardinian warbler Sylvia melanocephala, but not of the crested lark Galerida cristata) declined significantly during this period. Tarsus length also declined significantly during this period for two species (the graceful warbler and the house sparrow). Body condition (body mass–to–tarsus length ratio) decreased in the Sardinian warbler, the yellow–vented bulbul and the crested lark. It is suggested that the above declines in body mass and tarsus length are due to global warming and also in accordance with Bergmanns rule. The above explanation does not exclude the possibility that other factors, such as a decrease in food availability, contributed to the decline in body mass.These declines may have serious implications for community structure and competition among bird species and may affect the survival of small passerines.

Geographic variation in body size: the effects of ambient temperature and precipitation

Latitudinal trends in body size have been explained as a response to temperature- or water-related factors, which are predictors of primary production. We used the first principal component calculated from three body parameters (weight, body length and the greatest length of the skull) of a sample of mammals from Israel and Sinai to determine those species that vary in size geographically, and whether such variation is related to annual rainfall, average minimum January temperature and average maximum August temperature. We used a conservative approach to discern the effects of precipitation and temperature by applying sequential regression. Variable priorities were assigned according to their bivariate correlation with body size, except for rainfall and its interactions that entered into the model last. Eleven species (Acomys cahirinus, Apodemus mystacinus, Canis lupus, Crocidura suaveolens, Gerbillus dasyurus, Hyaena hyaena, Lepus capensis, Meles meles, Meriones tristrami, Rousettus aegyptius and Vulpes vulpes) of the 17 species examined varied in size geographically. In five of them, rainfall was positively related to body size, while in one species it was negatively related to it. Contrary to the prediction of Bergmann’s rule, mean minimum January temperature was positively related to body size in five species and negatively related to body size in two species (C. suaveolens and G. dasyurus). As predicted by Bergmann’s rule, maximum June temperature was negatively related to body size in three species, and positively so in one (L. capensis). Primary production, particularly in desert and semi-desert areas, is determined mainly by precipitation. The above results indicate that, in our sample, primary production has an important effect on body size of several species of mammals. This is evident from the considerable proportion of the variability in body size explained by rain. However, low ambient temperatures may slow down and even inhibit photosynthesis. Hence, the observed positive relationships between average minimum January temperature and body size in four of the six species influenced by rain further support this conclusion.

A winter feeding experiment on an island Song Sparrow population

SummarySupplemental food, in the form of millet seed, was provided to half of an island Song Sparrow population during the 1978–1979 winter to test if winter food influenced: (1) overwinter survival; (2) winter wights; (3) breeding density in 1979 and (4) 1979 breeding performance.Territorial males were most dominant at feeders and may have restricted access of young to feeders. Young females were most subordinate at feeders. Adult survival was not affected by supplementary food, but young survival was higher than in 6 previous years and young seen to visit feeders may have survived better than young not seen at feeders. Young females were more variable in weight on the unfed half of the island than on the fed end. The breeding population increased by 38% from 1978 to 1979, but it is not known how much of this increase resulted from food addition. Pairs of birds with feeders on their territories began to lay 25 days earlier in 1979 than control pairs, but delayed longer than controls before a second breeding attempt. One-year old females began to lay significantly later than adults on the control area, but not on the fed area. Other measures of breeding performance were not affected by supplemental food. Winter food may be more important and male territorial behaviour less important than previously supposed in limiting numbers in the Mandarte Island Song Sparrow population.

Differential germination of two closely related species of Solanum in response to bird ingestion

This study evaluated the effect which ingestion of seeds of Solanum nigrum and S. luteum by bulbuls (Pycnonotus xanthopygos) and blackbirds (Turdus merula) had on their germination, and tried to reveal the ecological implications of such endozoochory. Those closely related plant species are often sympatrical but whereas S. nigrum is a noxious weed invariably associated with human disturbed habitats, S. luteum may also occur in natural plant associations. Our data indicated that germination of seeds of S. nigrum was not affected by ingestion by either bulbuls or blackbirds. On the contrary, germination of the seeds of S. luteum was significantly (p < 0.01) improved by their ingestion by either bird species. Comparative scanning electron micrographs of the seeds showed that seed coat sculpture of S. nigrum was not affected by ingestion. In contrast, in ingested seeds of S. luteum, the sculpture of the seed coat was abraded compared with the uningested seeds; here, also, in the seeds ingested by the bulbuls, the intracellular contents disappeared, and in most of those ingested by blackbirds, there was destruction of the cell wall as well. Assumedly abrasion of the seed coat sculpture of S. luteum increases the seed coat permeability and consequently germination. It would seem that germination and dispersal of this more arid species which grows in unstable habitats is mediated largely by birds, whereas the germination of S. nigrum seeds is not affected by avian ingestion; for this weed, birds serve only as dispersal agents.

Recent spatial and temporal changes in body size of terrestrial vertebrates: probable causes and pitfalls.

Geographical and temporal variations in body size are common phenomena among organisms and may evolve within a few years. We argue that body size acts much like a barometer, fluctuating in parallel with changes in the relevant key predictor(s), and that geographical and temporal changes in body size are actually manifestations of the same drivers. Frequently, the principal predictors of body size are food availability during the period of growth and ambient temperature, which often affects food availability. Food availability depends on net primary productivity that, in turn, is determined by climate and weather (mainly temperature and precipitation), and these depend mainly on solar radiation and other solar activities. When the above predictors are related to latitude the changes have often been interpreted as conforming to Bergmanns rule, but in many cases such interpretations should be viewed with caution due to the interrelationships among various environmental predictors. Recent temporal changes in body size have often been related to global warming. However, in many cases the above key predictors are not related to either latitude and/or year, and it is the task of the researcher to determine which particular environmental predictor is the one that determines food availability and, in turn, body size. The chance of discerning a significant change in body size depends to a large extent on sample size (specimens/year). The most recent changes in body size are probably phenotypic, but there are some cases in which they are partly genetic.

THE EVOLUTION OF PARENTAL CARE IN BIRDS

The data on which this work is based were accumulated mainly from the existing literature. A substantial amount of data on body weight, egg weight, clutch size and incubation length was first gathered by Heinroth (1922). His list contained 436 bird species, on the majority of which he has all the above data. In addition to that, Heinroth added information on egg characteristics, mainly yolk content of 57 of the above 436 species. In a series of short papers published in 1929-1930, Harms (1929/30) gave such data on 14 bird species, some of which had already been mentioned by Heinroth. Data on the yolk and albumin weights of nine species were given by Asmundson et al. (1943). Thirteen species were listed by Romanoff and Romanoff (1949), and 24 species of Anatidae (some of which were mentioned by the former authors) by Lack (1968). We gathered such data on 37 species (Appendix 1), mainly from Aberdeenshire, Scotland, and the Tel-Aviv University Research Zoo. In order to complete the information needed for this work and not given by the above authors, we referred to various works on fauna or specific systematic groups (Ali and Ripley, 1968-1974; Delacour, 1954-1964; Dementiev et al., 1967; Harrison, 1975; Heinzel et al., 1972; Macworth Praed and Grant, 1953; Merom, 1960; Schonwetter, 1960-1972; Witherby et al., 1938-1941), where we found evoludata on female body weight, egg weight,

Ecological character displacement in Saharo-Arabian Vulpes: outfoxing Bergmann's rule

The red fox, a widely distributed Holarctic carnivore, exhibits a temperature- and latitude-correlated size gradient in the Palaearctic region, but little change of size in the southern part of its range, in the Saharo-Arabian region, where it is sympatric with a smaller congener, Ruppells sand fox. The slope of the regression of red fox lower carnassial length against mean ambient temperature in the Saharo-Arabian region is very slight, and differs significantly from the slope in the allopatric zone. This deviation suggests ecological character displacement in the red fox in sympatry with its smaller congener. This hypothesis is enhanced by the existence of constant size ratios (1.18-1.21) between lower carnassial lengths of these two foxes throughout the Saharo-Arabian region, notwithstanding regional fluctuations in overall size. Moreover, in Israel, where the still smaller Blanfords fox exists, the ratios between the means for both lower carnassial length and condylo-basal length of the three sympatric species are remarkably constant. Condylo-basal length and canine diameter ratios between the red fox and Ruppells sand fox in the different localities studied, while displaying the same general pattern, are considerably less regular than ratios of lower carnassial lengths. We suggest that the length of the carnassials relates directly to the feeding habits of these species, and is therefore the suitable morphological character to use when studying ecological character displacement in this group. The length and shape of the skull is influenced by other functions, as well as by autecological factors. Correlating the size of the red fox with various latitude correlated variables (e.g., ambient temperature) should be accompanied by investigation of its size relationship with congeners.

Clutch size in passerines of southern South America

Clutch size of the passerines of southern South America was studied by comparing data taken from the literature for 331 species (177 genera), which breed in Chile, Argentina, Uruguay, and southern Brazil. Mean overall clutch size was 2.98 eggs, appreciably smaller than clutch size of passerines at similar latitudes in the northern hemisphere. There was a highly significant difference between mean clutch size of the two sub-orders represented in the study area, with the Deutero-Oscines having on average smaller clutches (2.73) than the Oscines (3.32). This difference between the two sub-orders was maintained in each of the five zoogeographical regions of the study area. There were also significant differences in clutch size between the five main zoogeographical regions: overall mean clutch size was smallest in the Amazonian region (2.67) and largest in the Chaco (3.29). DeuteroOscines eggs were proportionally larger than those of Oscines (14% and 11% of body mass, respectively). There was no correlation between clutch size and body mass, nor was clutch size related to either nest type or migration. There is no evidence for latitudinal gradient in clutch size in the area studied.

DIFFERENTIAL USE OF THERMAL CONVECTION BY SOARING BIRDS OVER CENTRAL ISRAEL

Abstract Maximum altitudes of soaring migration for White Pelicans (Pelecanus onocrotalus), White Storks (Ciconia ciconia), Lesser Spotted Eagles (Aquila pomarina), and Honey Buzzards (Pernis apivorus) were measured in central west Israel and compared to the upper boundary of thermal convection and thermal intensity as predicted by the convection model ALPTHERM. The model predictions of upper boundary of convection explained at least 20% of the variance in maximum altitudes of migration for each species studied. Each species used thermal convection differently. White Pelicans, with the largest wing loading, used 54% of the thermal boundary layer, as calculated by dividing the maximum flight altitude by the modeled thermal depth. White Storks and Lesser Spotted Eagles used 69% and 65%, respectively; Honey Buzzards, with the lowest wing loading, used 95% of the thermal boundary layer. Mean lift rate of convection had a stronger effect on maximum altitudes of flight or the proportion of the thermal boundary layer used by Lesser Spotted Eagles and Honey Buzzards, than it did on storks and pelicans. Honey Buzzards, which combine flapping with soaring flight, were not confined to the thermal boundary layer. Changes in migration altitudes within a species and differential use of thermal convection between species were related to a combination of upper boundary of thermal convection, average lift rate, migratory behavior, wing loading, topography, and additional local meteorological conditions. Uso Diferencial de la Convección Térmica por Aves que Realizan Vuelos Planeados Elevados Sobre Israel Central Resumen. Se midieron las alturas máximas de planeo elevado durante la migración al oeste de Israel central para Pelecanus onocrotalus, Ciconia ciconia, Aquila pomarina y Pernis apivorus, y se compararon con el límite superior de la convección y la intensidad térmica predicho por el modelo de convección ALPTHERM. Las predicciones del límite superior de convección del modelo explicaron al menos el 20% de la varianza en alturas máximas de migración para cada especie estudiada. Cada especie utilizó la convección térmica de una forma diferente. Pelecanus onocrotalus, la especie con la mayor carga alar, utilizó el 54% de la capa térmica límite, lo que se calculó dividiendo la altura máxima de vuelo por la profundidad térmica modelada. Ciconia ciconia y A. pomarina usaron el 69% y 65% de la capa térmica límite, respectivamente; P. apivorus, la especie con menor carga alar, utilizó el 95%. La tasa promedio de fuerza ascensional de convección tuvo un efecto más marcado en las alturas máximas de vuelo o la proporción de la capa térmica utilizada en A. pomarina y P. apivorus que en P. onocrotalus y C. ciconia. Pernis apivorus, que combina el aleteo con el vuelo planeado, no estuvo confinada a la capa térmica límite. Los cambios en las alturas de migración dentro de una especie y el uso diferencial de la convección térmica entre especies estuvieron relacionados con una combinación del límite superior de la convección térmica, la tasa promedio de fuerza ascensional, el comportamiento migratorio, la carga alar, la topografía y condiciones meteorológicas locales adicionales.