In species with bi-parental care, individuals must partition energy between parental effort and mating effort. Typically, female songbirds invest more than males in reproductive activities such as egg-laying and incubation, but males invest more in secondary sexual traits used in attracting mates. Animals that breed more than once within a season must also allocate time and energy between first and subsequent breeding attempts and between current and future breeding seasons. To investigate strategies of reproductive investment by males and females and the consequences of such strategies, we manipulated the size of broods of Eastern Bluebirds Sialia sialis. Pairs with enlarged first broods were less likely to produce a second clutch or took longer to initiate one than pairs with reduced broods. After rearing enlarged broods, females were less likely than males to survive to the following year. Although plumage coloration is a sexually selected trait in Eastern Bluebirds that is influenced by nutritional stress, we did not detect an effect of brood-size manipulation on female coloration. Past research, however, demonstrates that, in males, plumage colour is negatively affected by increasing brood size. We suggest that there are sex-specific strategies of reproductive investment in Eastern Bluebirds, and that researchers should incorporate measures of residual reproductive value in studies of life-history evolution.
Nine hundred and sixty-eight bird species, covering all orders, were studied in search of distinctive ultraviolet reflections. All species in the following orders were completely surveyed: Struthioniformes, Tinamiformes, Craciformes, Turniciformes, Galbuliformes, Upupiformes, Coliiformes, Apodiformes and Musophagiformes. The coloured plumage regions in particular exhibited high proportions of UV-reflecting feathers. Bird orders with species which are believed to possess VS (violet-sensitive) cone types mostly had their UV maxima between 380 and 399 nm while orders with species which are assumed to have UVS (ultraviolet-sensitive) cone types contained significantly species which had their UV maxima between 300 and 379 nm. With an emphasis on non-passerine birds the present study provides evidence that birds of many more groups may see UV light than have been studied to date. Ecological aspects related to UV reflection and perception, as well as sexual dimorphism visible only in the UV, are discussed.
Further experiments confirm our recently reported findings that Adelie Penguins Pygoscelis adeliae, transported from rookeries on the coasts of Antarctica to remote release points, consistently select a departure direction to the N.N.E. with respect to their home meridian. New releases were made at the South Pole where sun altitude is constant and in the offshore pack ice where the initial N.N.E. departure direction led the birds directly away from their home.
Birds imported from the Mirnyy coast, 85° of longitude to the west of Cape Crozier selected a departure direction to the N.W. After being held in an open pen at the new position for three weeks, however, Mirnyy birds revised their orientation to match the N.N.E. departures of a comparably held group of Crozier birds.
Juvenile penguins taken from creches and from the beach at Cape Crozier selected the same departure direction as adults.
Several lines of evidence suggest that the mechanism used in initial direction selection may be different from that used in course maintenance.
The consistent northward or outward departure orientation is discussed in terms of escape to offshore feeding grounds. The easterly component of this orientation is discussed in terms of compensation for a westward drift imposed on outward-moving birds by coastal currents. A circadian rhythm in phase with conditions at the longitude of the home rookery is regarded as serving to guide a displaced bird back to its home coast. A circadian rhythm reset to the solar cycle of a new longitude is regarded as serving to guide a displaced bird to the nearest coast.
The return of displaced birds to their home rookery, after initial orientation in other directions, emphasizes the fact that the departure response observed in these studies is only one part of a complex navigational mechanism, which guides the Adelie Penguin through its seasonal migrations.
Phylogenetic analysis of 11 genera of Corvidae has been undertaken using a sequence of 925 bp of the cytochrome b gene of the mtDNA. Both maximum-parsimony and maximum-likelihood analyses were performed, and different weighting schemes have been used according to the saturation observed in the data (mostly at the third codon position). The cytochrome b data provide good evidence for the monophyly of the Corvidae, including the Piapiac Ptilostomus afer in spite of its aberrant morphology. In all analyses, the choughs are the first lineage emerging in the family; this result conflicts with the traditional chough-crow group, as well as the hypothesis of the ancestral position of the jays. The monophyly of the American jays is well supported by the molecular data, unlike the Palearctic jays, which are not closely related. The other intergeneric relationships are not strongly supported by bootstrap proportions, and are not congruent in all different weightings and methods, except for groups of species of the same or very closely related genera.
Offspring sex ratios in wild bird populations, and the extent to which they vary from the equality expected by random genotypic sex determination, have received much recent attention. Adult sex ratios (ASRs) in wild birds, on the other hand, remain very poorly described, and many of the questions about them posed by Ernst Mayr in 1939 remain unanswered. This review assesses population-level sex ratio patterns in wild bird populations, with an emphasis on the ASR. A quantitative assessment of over 200 published estimates of ASR, covering species from a wide range of taxa, regions and habitats, supported Mayr's assertion that skewed ASRs are common in wild bird populations. On average, males outnumbered females by around 33%, and 65% of published estimates differed significantly from equality. In contrast, population-level estimates of offspring sex ratio in birds did not generally differ from equality, and mean ASR across a range of wild mammal species was strongly female-skewed. ASR distortion in birds was significantly more severe in populations of globally threatened species than in non-threatened species, a previously undescribed pattern that has profound implications for their monitoring and conservation. Higher female mortality, rather than skewed offspring sex ratio, is the main driver of male-skewed ASRs in birds, and the causes and implications of this are reviewed. While estimates of ASR in wild bird populations may be subject to a number of biases, which are discussed, there is currently no quantitative evidence that an ASR of one male to one female represents the norm in birds. A better understanding and reporting of ASRs in wild bird populations could contribute greatly to our understanding of population processes and could contribute much to theoretical and applied research and conservation.
Perusal of Brisson's ‘Ornithologie’, Pierre Poivre's autobiography and this traveller's publications induced the writer to concern himself with the type localities of Brisson's new Oriental birds. Those accepted by previous authors proved to be wrong in a number of cases. On the strength of the actual type localities the current names of some well-known birds will have to be changed. The following names are affected: —
Eurystomus orientalis (L.), Eclectus pectoralis (St. Müller), Saxicola borbonensis W. Sclater, Lalage nigra (Forster), Ducula aenea (L.), Cinnyris asiatica (Latham), Pelargopsis capemis (L.) and Psittacula krameri echo (Newton).
The longest available bag record of Grey Partridges Perdix perdix in Great Britain (1793–1993) reveals a collapse of stocks after 1952 despite considerable annual variation. The annual fluctuations were attributable largely to annual variations in chick survival rate. The Game Conservancy Trust's National Game Census revealed that chick survival rates averaged 49% before the introduction of herbicides and 32% once their use became widespread. On a study area in Sussex, where spring density declined from around 21 pairs per km2 in 1968 to under four pairs per km2 in 1993, annual chick survival rates averaged 28% with no demonstrable trend. The annual over-winter “survival” rates in the area improved during 1968–1993, whereas brood production rates declined. Simulation modelling showed that a reduction in chick survival rate from 49% to 32% had little effect on spring stocks as long as nest predation was controlled but that stocks collapsed when nest predation control was relaxed. The effect of such a change in chick survival rate on population status was investigated by reference to 36 other studies in the literature. Amongst 20 studied populations which were stable, adjusting mean chick survival rates downwards produced demographic parameters characteristic of declining populations in all but two cases. Conversely, adjusting chick survival rates upwards for 16 declining populations made all but two stable. Diagnosing and remedying the causes of population change require a testable understanding of density-dependent factors and compensatory processes, best approached by a combination of monitoring, modelling and management.
In the year 1819 His Imperial Majesty Alexander Pavlovich, Emperor of Russia, despatched an expedition to explore high southern latitudes, with the special object of proceeding as far as possible towards the South Pole. This expedition was led by Captain Thaddeus von Bellingshausen, who had under his command the corvette ‘Vostok’ and the sloop ‘Mirnyi’