André A. Dhondt

Anticipatory reproduction and population growth in seed predators.

Mast seeding, the intermittent, synchronous production of large seed crops by a population of plants, is a well-known example of resource pulses that create lagged responses in successive trophic levels of ecological communities. These lags arise because seed predators are thought capable of increasing reproduction and population size only after the resource pulse is available for consumption. The resulting satiation of predators is a widely cited explanation for the evolution of masting. Our study shows that both American and Eurasian tree squirrels anticipate resource pulses and increase reproductive output before a masting event, thereby increasing population size in synchrony with the resource pulse and eliminating the population lag thought to be universal in resource pulse systems.

Male quality, reproduction, and survival in the great tit (Parus major)

SummaryThree possible measures of male quality (social dominance, song, and size), reproduction, and survival were studied in a single population of great tits. Winter dominance position on a feeder was related to strophe length (number of phrases per strophe), inversely related to positive drift (decrease of the singing rate of the phrases in a strophe), but not related to song repertoire size. Neither winter dominance position nor song were related to size (wing length, tarso-metatarsus length, weight).Singing capacity was not correlated with individual reproductive success in a single breeding season, using a rather limited data set. However, “better” singers (males which sing longer strophes, show less positive drift, and have larger song repertoires) survived better and had a higher individual lifetime reproductive success (on the basis of a males recruited offspring of all breeding seasons). Our results show that there exist measurable differences whereby birds that are dominant in winter sing “better”, survive longer, and produce more surviving offspring during their life time. We suggest that differences in male quality are the common cause (direct and indirect) of all these effects.

Spacing behaviour of red squirrels, Sciurus vulgaris: variation between habitats and the sexes

Abstract Home range size, range use and range overlap of adult male and female red squirrels in a coniferous and a deciduous woodland were studied using radio-telemetry. Hypotheses, concerning (1) resource predictability and territorial behaviour, and (2) sex-related and habitat-related differences in spacing strategies were tested. In both habitats males had larger home ranges than females. Range size varied seasonally, tending to increase in April–June and to decrease in winter. Both males and females had intensively used core-areas (70% of all locations) that were much smaller than their total range. Dominant males had larger ranges than subordinates, and male body weight was positively correlated with home range size. For females, range size was inversely correlated with food abundance (coniferous area) or local density (deciduous area). Core-area overlap within a sex was smaller than that between sexes. Dominant females defended exlusive core-area overlap within a sex was smaller than that between sexes. Dominant females defended exclusive core-areas against other females, while subordinates behaved as floaters or settled on the edges of the ranges of dominant females. In the deciduous woodland squirrels had larger home ranges, used significantly larger and more strongly overlapping core-areas and were more tolerant of conspecifics than in the coniferous woodland. The results support the hypotheses that (1) the predictability in time and space of food resources, and (2) sexual differences in key resources used to increase reproductive success in mammals with promiscuous or polygynous mating systems, cause differences in spacing behaviour between habitat types and between adult males and females.

Density-dependent clutch size caused by habitat heterogeneity

In some studies but not in others the average clutch size decreases with density. We propose that density-dependent fecundity occurs because, as density increases, proportionally more poor-quality sites (with small clutches) are occupied, and not because the clutch size in all territories decreases. This mechanism will only cause density dependence if the habitat is heterogeneous at the scale of the home range or territory of an individual. Density-dependent fecundity will be found in some populations but not in others because of differences in the scale of habitat heterogeneity

EPIDEMIC MYCOPLASMAL CONJUNCTIVITIS IN HOUSE FINCHES FROM EASTERN NORTH AMERICA

In the winter of 1993–94, house finches (Carpodacus mexicanus) with severe conjunctivitis (later shown to be caused by Mycoplasma gallisepticum) were first observed in suburban Washington D.C. (USA) and adjacent states. Using a large network of volunteer observers in eastern North America, we were able to track the monthly prevalence of the disease between November 1994 and March 1997. Using the information on 24,864 monthly data forms, we describe the very rapid spread of the conjunctivitis epidemic through the eastern house finch population. The epidemic first expanded mainly north, probably carried along by house finches on their return migration, then mainly toward the southeast, and later west. By March 1997, conjunctivitis had been reported from most of the eastern range of the house finch. The prevalence of the disease seemed to fluctuate seasonally with increases in the fall, probably as a result of dispersing juveniles. House finch numbers decreased throughout winter in areas with cold winters and high conjunctivitis prevalence, suggesting significant mortality associated with the disease.

Mate guarding and copulation behaviour in monogamous and polygynous blue tits: do males follow a best-of-a bad-job strategy?

This study investigates the importance of mate guarding for males and females in the facultatively polygynous blue tit Parus caeruleus. We present observational data in combination with a paternity analysis using DNA fingerprinting to show that (1) male blue tits guard their mate, since they stay closer to their mate, initiate fewer flights and follow their mate more often during the females presumed fertile period; (2) polygynous males do not suffer more from lost paternity despite lower mate guarding; (3) in monogamous pairs there is either no relation or a positive relation (depending upon the variable measured) between measures of mate guarding intensity and the proportion of extra-pair young in the nest; and (4) monogamous males that are more often followed by their fertile female suffered less from lost paternity. We conclude that, despite mate guarding, paternity seems to be largely under female control and unattractive males guarding their mate are making the best of a bad situation. Experimental evidence is provided showing that when males were temporarily removed from their territory, their mate suffered from increased harassment from neighbouring males that intruded in the territory and tried to copulate with the female. Almost all of these copulation attempts were unsuccessful because females refused to copulate. We conclude that mate guarding may be beneficial for females because harassment by neigbouring males is prevented.

The anti-exhaustion hypothesis: a new hypothesis to explain song performance and song switching in the great tit

Abstract This paper describes the results of a detailed analysis of 52 song bouts, recorded from 22 great tits, Parus major , during the dawn chorus. A song bout consists of a number of song bursts (called strophes) separated by periods of silence. High quality males, as measured by average strophe length, sang their bouts with a higher percentage performance time (i.e. the percentage of time spent singing in a bout), but the average number of strophes per bout was not related to male quality. In 31 of 52 bouts there was a systematic decrease in the percentage performance time throughout the bout. This was mainly caused by a prolongation of the pauses between the strophes, and sometimes by a shortening of the strophes. Both high and low quality males sang bouts with and without this decrease in the percentage performance time. Bouts that started with longer strophes and/or shorter inter-strophe pauses showed on average a more rapid decrease in the percentage performance time, and contained fewer strophes, than bouts that started with shorter strophes and/or longer inter-strophe pauses. After switching to another song type the males again used longer strophes and/or shorter inter-strophe pauses. An ‘anti-exhaustion’ hypothesis is proposed and discussed. This hypothesis gives a mainly causal explanation for the existence of song switching and song repertoires in passerine birds.

Space use and dispersal of red squirrels in fragmented habitats

Eurasian red squirrels Sciurus vulgaris in fragmented woodlands had a similar spacing pattern as in large woodlands: females had intrasexual exclusive core-areas, while core-areas of males overlapped extensively with core-areas of other males and with core-areas of females. However, in fragmented woodlands, home ranges (site B) and core-areas (both study sites) were smaller than in large deciduous woodlands. Hence, space use and home range size in habitat fragments are strongly influenced by size and structure of the woodlots and, in case of small woodland patches, by the presence of connecting treerows. Juveniles had very small home ranges prior to dispersal, but home range size increased after the dispersal period

Genetic Similarity, Inbreeding and Hatching Failure in Blue Tits: Are Unhatched Eggs Infertile?

We use data from a long-term population study in combination with DNA fingerprint data to study the frequency of inbreeding and its effects on reproductive parameters in a blue tit population. Close inbreeding was very rare in this population. The proportion of unhatched eggs in a clutch was related to the degree of genetic similarity between the parents as determined by multilocus DNA fingerprinting. Data from blue and great tit populations studied over 15 years show that about 25—30% of blue tit and 20 % of great tit nests contained at least one unhatched egg. The number or proportion of unhatched eggs in the nest was highly repeatable for pairs breeding in different years, but not for individual males or females. Unhatched eggs, therefore, were unlikely to result from functional infertility. The hypothesis that female blue tits engage in extra-pair copulations as insurance against their mate’s infertility can thus be discarded. Because the genetic similarity between the female and the extra-pair male was not lower than that between the female and her social partner, our data do not support the hypothesis that females engage in extra-pair copulations to reduce inbreeding depression.

Seasonality and wildlife disease: how seasonal birth, aggregation and variation in immunity affect the dynamics of Mycoplasma gallisepticum in house finches

We examine the role of host seasonal breeding, host seasonal social aggregation and partial immunity in affecting wildlife disease dynamics, focusing on the dynamics of house finch conjunctivitis (Mycoplasma gallisepticum (MG) in Carpodacus mexicanus). This case study of an unmanaged emerging infectious disease provides useful insight into the important role of seasonal factors in driving ongoing disease dynamics. Seasonal breeding can force recurrent epidemics through the input of fresh susceptibles, which will clearly affect a wide variety of wildlife disease dynamics. Seasonal patterns of social aggregation and foraging behaviour could change transmission dynamics. We use latitudinal variation in the timing of breeding, and social systems to model seasonal dynamics of house finch conjunctivitis across eastern North America. We quantify the patterns of seasonal breeding, and social aggregation across a latitudinal gradient in the eastern range of the house finch, supplemented with known field and laboratory information on immunity to MG in finches. We then examine the interactions of these factors in a theoretical model of disease dynamics. We find that both forms of seasonality could explain the dynamics of the house finch–MG system, and that these factors could have important effects on the dynamics of wildlife diseases generally. In particular, while either alone is sufficient to create recurrent cycles of prevalence in a population with an endemic disease, both are required to produce the specific semi–annual pattern of disease prevalence seen in the house finch conjunctivitis system.