Bart Kempenaers

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

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.

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.

The use of a breeding synchrony index

People who study mating systems or behavioural aspects of sperm competition in birds are aware of the importance of breeding synchrony in a population. Birkhead and Moller (1992) summarize some ideas on how breeding synchrony, by affecting the operational sex ratio, may have an influence on for example copulation behaviour and mate guarding. In general, the idea is that the more synchronous the population is, the fewer options males have to attract extra mates and become polygynous (see also Oring 1982) or to engage in extra-pair copulations. If we want to understand the effect of breeding synchrony when comparing behaviour between both species and populations of the same species, we need a measure of synchrony for the population under study. Many researchers have these necessary data, but they are rarely presented in their papers. Bj6rklund and Westman (1986) developed a breeding synchrony index, which takes into account differences in population size and duration of the fertile period. However, their index suffers from a minor error in the formula. By presenting here the correct index formula, I hope that people will be encouraged to use it, so that more data on breeding synchrony become available and that these data can be more easily compared. The correct formula for the synchrony index (SI) is:

Polygyny in the blue tit: intra- and inter-sexual conflicts

The occurrence and importance of intra- and inter-sexual conflicts were studied in a blue tit,Parus caeruleus, population with a high level of polygyny. Males could increase their chances of becoming polygynous by actively attracting extra females or by displaying towards visiting floater females. Polygynous males allocated their parental care in relation to the hatching interval between the two broods. If the hatching interval was small, males divided their effort between the primary and the secondary nest. If the hatching interval was large, males fed only the nestlings of the primary female. Primary females that had to share male help did not fledge fewer young, but survived less well. Primary females tried to prevent or delay the settlement of secondary females by behaving aggressively towards all intruder females and by guarding their mates. Secondary females fledged more young if they received more help, that is, if the hatching interval was small, but there was no effect on female survival. Secondary females tried to settle early during the breeding season despite severe aggression of primary females. Secondary females needed less time for nest building and incubation and laid a smaller clutch, which increased the probability of hatching their young early relative to the primary brood. It is concluded that sexual conflicts play an important role in shaping the mating system of the blue tit and that parental care is the key factor in these conflicts.

Intraspecific brood parasitism in two tit Parus species: occurrence and responses to experimental parasitism

In many bird species females parasitize the parental investment of other pairs by laying eggs in their nests. Such intraspecific brood parasitism is considered rare among altricial birds, but this may result from methodological difficulties in detecting and quantifying this behaviour. In this study, we investigated first whether intraspecific brood parasitism occurs in Blue Tits Parus caeruleus and Great Tits P. major, using a combination of frequent nest inspections, DNA profiling and a survey of the literature. No evidence for parasitism was found. Next, we investigated whether the absence of brood parasitism could be explained by efficient anti-parasite strategies of the hosts. We experimentally parasitized 75 Blue Tit and 51 Great Tit nests before and during egg-laying. We found no evidence for rejection of the parasitic eggs. Thus the absence of brood parasitism is not a product of undetected parasitism. Although intense female-female aggression may deter females that try to lay eggs in other nests, we suggest that in both species intraspecific brood parasitism has not evolved because females do not benefit from laying eggs in the nests of others.

A case of polyandry in the blue tit: extra-pair behaviour results in extra male help

Anderson, D. J., Sievert, P. R., Andrews-Labenski, J. and Ricklefs, R. E. 1991. A miniature activity recorder for plunge-diving seabirds. Auk 108: 257-263. Birt-Friesen, V. L., Montevecchi, W. A., Cairns, D. K. and Macko, S. A. 1989. Activity-specific metabolic rates of free-living northern gannets and other seabirds. Ecology 70: 357-367. Cairns, D. K., Bredin, K. A., Birt, V. L. and Montevecchi, W. A.1987. Electronic activity recorders for aquatic wildlife. J. Wildl. Manage. 51: 395-399. Jouventin P. and Weimerskirch, H. 1990. Satellite tracking of Wandering Albatrosses. Nature 343: 746-748. Mohus, I. 1987. A storing telemetry-transmitter for recording bird activity. Ornis Scand. 18: 227-230. Prince, P. A. and Francis, M. D. 1984. Activity budgets of foraging Grey-headed Albatrosses. Condor 86: 297-300. , Wood, A. G., Barton, T. and Croxall, J. P. 1992. Satellite tracking of Wandering Albatrosses (Diomedea exulans) in the South Atlantic. Antarct. Sci. 4: 31-36. Tickell, W. L. N. 1968. The biology of the great albatrosses, Diomedea exulans and Diomedea epomophora. Antarct. Res. Ser. 12: 1-68. Trivelpiece, W. Z., Bengtson, J. L., Trivelpiece, S. G. and Volkman, N. J. 1986. Foraging behaviour of Gentoo and Chinstrap penguins as determined by new radiotelemetry techniques. Auk 103: 777-781. Wanless, S., Harris, M. P. and Morris, J. A. 1991. Foraging range and feeding locations of Shags Phalacrocorax aristotelis during chick rearing. Ibis 133: 30-36. Wilson, R. P., Grant, W. S. and Duffy, D. C. 1986, Recording devices on free-ranging marine animals: does measurement affect foraging performance? Ecology 67: 1091-1093.

Identification of hypervariable single locus minisatellite DNA probes in the blue tit Parus caeruleus

We report the isolation of a set of hypervariable minisatellite DNA sequences from a blue tit Parus caeruleus genomic DNA library. In our strategy, we cloned a minisatellite‐rich DNA fraction into a charomid vector. The resulting cosmid library was screened with the two minisatellite DNA probes 33.6 and 33.15 for recombinants containing a minisatellite DNA insert. A total of 233 positive clones were isolated. Of 37 clones that have been analysed, nine gave polymorphic signals and can be used as single locus probes (SLPs). Four of the SLPs were investigated in more detail. The number of alleles, the heterozygosity and the mutation rate were estimated. Linkage analysis revealed that two of these loci were linked. The SLPs are of value to studies of the mating system and reproductive success in the blue tit, and may also be useful in population genetic studies.

The genetic structure of Parus caeruleus (blue tit) populations as revealed by minisatellite single locus probes

The genetic structure of three blue tit (Parus caeruleus) populations near Antwerp in Belgium was determined with the use of three hypervariable minisatellite DNA single locus probes. The degree of genetic variability within and among populations, deviations from Hardy-Weinberg equilibrium and population differentiation were estimated to determine whether these DNA regions are informative for studying population processes in birds. All populations were significantly differentiated. In one population, consisting of several subpopulations in discrete wood-lots, a slight heterozygote deficit (Wahlund effect) was observed. More detailed information concerning the population structure was found using Wrights F-statistics. Gene flow between all populations was high. Furthermore, Neis genetic distance showed a slight increase with increase of geographical distance between populations, despite their close proximity.