SEXUAL SELECTION IN THE MONOGAMOUS BARN SWALLOW (HIRUNDO RUSTICA). I. DETERMINANTS OF TAIL ORNAMENT SIZE

The proportion of phenotypic variance in the length of the sexually selected tail of the monogamous barn swallow Hirundo rustica that is attributable to genetic variance was studied in the field in Denmark during a seven-year period. Tail length was on average 20% greater in males than in females. Tail length correlated with wing length, but not with other morphological traits. Tail length increased with the first molt, but remained constant during subsequent years. Changes in tail length between years, owing to molt were significantly affected by sex and by degree of infection with an haematophagous mite (Ornithonyssus bursa). There were significant differences in sexual size dimorphism between years, apparently as a result of environmental conditions in the African winter quarters during molt. Tail length was a highly repeatable morphological trait, and standardization of tail length for age effects only marginally increased repeatability. Heritability of tail length as estimated from regression of values for sons on those of their fathers was 0.59. This suggests that secondary sexual traits affected by strong directional selection still may show a statistically significant heritability.     

SEXUAL SELECTION IN THE BARN SWALLOW HIRUNDO RUSTICA. III. FEMALE TAIL ORNAMENTS

Male secondary sexual characters are often expressed in females, and the maintenance of the character in females can be due to either direct selection on females favoring the maintenance of the trait, or a correlated response to selection in males. Here I report on determinants of and phenotypic selection on tail length of female barn swallows Hirundo rustica. The homologous trait in males is under strong directional sexual selection. Female tail length was positively associated with several reproductive parameters including total seasonal reproductive success, even when controlling for year and age effects. A change in female tail length from one year to another was often associated with a change in the reproductive parameters correlated with absolute tail length. There was little evidence for an association between female tail length and the duration of the incubation period (only females incubate) and absolute and relative female provisioning rates of offspring, and subsequent size of offspring. Tail length of female barn swallows was positively correlated with that of their mates. Female tail length was a heritable trait as determined from regression of the tail trait of offspring on that of their mother and their father, and there was a positive genetic correlation between the tail trait in males and females. In conclusion, female tail length reliably reflects female reproductive potential, and the trait appears to be under directional selection, which may result in an evolutionary response to selection because of the heritability of the tail trait.     

NOTES ON THE PEARL-BREASTED SWALLOW HIRUNDO DIMIDIATA IN THE SOUTH-WESTERN CAPE

Earlé R. A. &; Herholdt, J. J. 1988. Breeding and moult of the Anteating Chat Myrmecocichla formicivora. Ostrich 59: 155–161.

The general breeding biology and moult of the Anteating Chat Myrmecocichla formicivora was studied in open grassveld over a two-year period. During the winter (July), groups were significantly smaller than during summer (December) (1,81 ± 0,50 versus 2,85 ± 1,35 birds per group). There was a large turnover of individuals in the study area but the total population stayed the same. The breeding season in the study area lasted from September to February but analysis of nest record cards from a larger area gave a breeding season of August-April. Two types of nests were used: 90,6% were burrows in sand banks or other excavations, but 9,4%were in the mud pellet nests of Greater Striped Swallows Hirundo cucullata (n = 53). Consecutive breeding attempts were never made in the same burrow. Clutches consisted of three, four or five eggs ([Xbar] = 3,73 ± 0,67). Incubation lasted 14–14,5-15 days. The nestling period lasted 15–18 days. Fledgling/egg breeding success was 41,8% with 48,2% of all eggs not reaching the hatching stage. Juveniles showed an unequal sex ratio of 0,57 ♂ ♂: 1,0 ♀ ♀ but adults had a nearly equal ratio (0,9 ♂ ♂: 1,0 ♀ ♀). There was a significant positive correlation between the primary moult score and the week of the seven months in which moult was recorded. Juveniles underwent a complete body moult and partial primary moult 3–4 months after fledging.     

CLUTCH SIZE, EGG SIZE, HATCH WEIGHT AND LAYING DATE IN RELATION TO EARLY MORTALITY IN RED GROUSE LAGOPUS LAGOPUS SCOTICUS CHICKS

Clutches of Red Grouse eggs were collected from the wild and subsequent hatching and rearing done in standard conditions in captivity. Variations in chick survival from one clutch to another in the same year were related to differences in hatch weight. Hatch weight was determined only partly by egg size. Weight loss between laying and hatching was related to survival independently of egg size. Variation in this weight loss obscured any simple relationship between egg size and survival, except in eggs laid by captive hens. Intrinsic differences amongst hens caused some variations in laying date, egg size, hatch weight and chick survival. Variations in egg size and hatch weight accounted for less than half the variation in survival; other unmeasured intrinsic factors were also important. Big clutches hatched earlier than small ones. The commonest clutches were of seven and eight eggs, with six and nine frequent. Very big clutches of ten or more eggs were infrequent and chicks from them sometimes survived worse than from smaller clutches. As in other species, the commonest clutch sizes were not the most productive. There was no simple relationship between egg size and clutch size.     

TAXONOMY,DISTRIBUTION, MIGRATION AND MOULT OF THE REDBREASTED SWALLOW HIRUNDO SEMIRUFA

Earlé R. A. & Brooke, R. K. 1989. Taxonomy, distribution, migration and moult of the Redbreasted Swallow Hirundo semirufa. Ostrich: 60:151-158.

There are two well defined races of the Redbreasted Swallow Hirundo semirufa, the nominate and gordoni. H. s. neumanni is a synonym of gordoni. The breeding ranges of the two races do not meet. The Redbreasted Swallow has extended its range south and southeast following the construction of concrete road culverts which provide nest sites, together with bush clearance. The strongly migratory southern populations reach their southern limits by August each ear and depart again mainly in March-April although there are some records for May. Males are significantly larger than females in wing length and the length of the longest rectrix but not in other measurements. Moulting birds were found in each month of the year but the moults of the two races are largely separated in time. Moulting birds were found only between 10S and 10N with the majority close to the equator.     

CLUTCH SIZE AND EGG SIZE IN FREE-LIVING AND PARASITIC COPEPODS: A COMPARATIVE ANALYSIS

The evolution of reproductive strategies and the trade-off between number and size of eggs were investigated in a comparative analysis of free-living and parasitic copepods. Data from 1038 copepod species were used to obtain family averages for 105 families; the phylogenetic relationships among these families include 94 branching events or 94 independent contrasts on which the analysis was based. Transition from a free-living existence to parasitism on invertebrates resulted in small increases in body size. Transition from parasitism on invertebrates to parasitism on fish was associated with greater increases in body size. After controlling for body size, a switch to fish hosts resulted in an increase in the number of eggs produced and a reduction in egg size. Among all contrasts, there was a negative relationship between changes in relative clutch size and changes in relative egg size, suggesting the existence of a trade-off between egg size and numbers. However, opposite changes in these measures of clutch size and egg size were not quite more frequent than expected by chance, therefore indicating that investments into egg numbers are not necessarily made at the expense of egg size, and vice versa. Latitude affected copepod body size, clutch size, and egg size, whereas the effects of freshwater colonization or size of the fish host were not significant. Comparative analyses at either the genus or species levels within given taxa of copepods parasitic on fish provided limited support for a trade-off between clutch size and egg size, but were hampered by the small number of independent phylogenetic contrasts available. From the family-level comparative analysis, it appears that the evolutionary transition from a free life to parasitism on invertebrates, and the transition from parasitism on invertebrates to parasitism on fish, have led to changes in life-history traits in response to the different selective pressures associated with the different modes of life.