Native Bird Populations Research Articles

Evolutionary Theories of Aging: Confirmation of a Fundamental Prediction, with Implications for the Genetic Basis and Evolution of Life Span

Evolutionary considerations predict that rate of aging should vary in direct relation to the mortality rate of presenescent young adults (extrinsic mortality rate) independently of differences in physiology, such as rate of metabolism. This prediction emerges from theory irrespective of the particular genetic mechanisms responsible for variation in aging. Yet this critical relationship has not been confirmed in comparative studies of natural populations. In the present analysis, rate of aging is estimated by the rate of increase in mortality rate (mx) with age (x). Comparisons between natural and captive populations of birds suggest that the Weibull model (mx = m0 + alphaxbeta) provides a better description of aging than the Gompertz model (mx = m0esigmax). Rate of aging is quantified by the parameter omega (dimension: 1/time), which is calculated from the Weibull parameters alpha and beta (omega = alpha1/(beta+1)). In this analysis, rate of aging in birds and mammals is directly related to extrinsic mortality (estimated by the initial mortality rate, m0) independently of taxonomic group and of variation in body size and, by implication, metabolic rate. When time is expressed in years, rate of senescence is related to initial mortality rate by omega = 0.294m0(0.367). This result implies that natural selection in response to variation among taxa in m0 has resulted in the evolutionary modification of factors that influence the rate of aging in natural populations. The potential strength of selection on factors that could further reduce rate of aging is indicated by the proportion of deaths due to aging-related causes. Although species with low initial mortality rates also exhibit reduced rates of increase in mortality rate with age (i.e., delayed senescence), the relatively high proportion of aging-related deaths in such species suggests that further evolutionary responses leading to long life are severely constrained. This argues against mutation accumulation and antagonistic pleiotropy as genetic mechanisms underlying senescence and suggests, instead, that rate of aging represents a balance between wear and tear, on the one hand, and genetically controlled mechanisms of prevention and repair, on the other. Evidently, remedies for extreme physiological deterioration in old age either are not within the range of genetic variation or are too costly to be favored by selection.

Genetic variation and causes of genotype-environment interaction in the body size of blue tit (Parus caeruleus).

In several studies of natural populations of birds, the heritability of body size estimated by parent-offspring regression has been lower when offspring have developed in poor feeding regimens than when they developed in good feeding regimens. This has led to the suggestion that adaptation under poor regimens may be constrained by lack of genetic variation. We examined the influence of environmental conditions on expression of genetic variation in body size of nestling blue tits (Parus caeruleus) by raising full sibs in artificially reduced and enlarged broods, corresponding to good and poor feeding regimens, respectively. Individuals grown in the poor regimen attained smaller body size than their sibs grown in the good regimen. However, there was among-family variation in response to the treatments--i.e., genotype-environment interactions (GEIs). Partitioning the GEI variance into contributions attributable to (1) differences in the among-family genetic variance between the treatments and (2) imperfect correlation of genotypic values across treatments identified the latter as the main cause of the GEI. Parent-offspring regressions were not significantly different when offspring were reared in the good environment (h2 = 0.75) vs. when they were reared in the poor environment (h2 = 0.63). Thus, there was little evidence that genetic variance in body size was lower under the poor conditions than under the good conditions. These results do not support the view that the genetic potential for adaptation to poor feeding conditions is less than that for adaptation to good conditions, but they do suggest that different genotypes may be favored under the different conditions.

MHC variation in birds and reptiles.

The major histocompatibility complex (MHC) has been studied in a multitude of mammals by now, but much less is known about its organisation and variation in other vertebrate species. The mammalian MHC is organised as a single gene cluster, but recent studies on birds suggest that this paradigm of MHC organisation has to be supplemented. The domestic chicken thus possesses two separate gene clusters which both contain MHC class I and class II B genes, and we have shown that the ring-necked pheasant Phasianus colchicus also has two unlinked clusters of class II B genes. We are studying the effect of the MHC on mate choice, survival and reproductive success in natural populations of birds and reptiles. For this reason, we are developing DNA techniques to determine the animals' MHC genotype. The amplification of the hypervariable exon 3 of the class I gene from songbirds and reptiles has provided us with species specific probes that can be used in Southern blot analysis. The first results indicate very extensive variation in all studied species, that is starlings Sturnus vulgaris, great reed warblers Acrocephalus arundinaceus and water pythons Liasis fuscus. The restriction fragment length polymorphism (RFLP) analysis also suggests that the number of MHC genes is significantly larger in these species than in pheasants and domestic chickens.

Target Specificity of Foxoff Baits at Belair National Park.

Red Foxes (Vulpes vulpes) pose a significant threat to small native mammals in Australia (Saunders et al. 1995) and may restrict the recovery of some populations of native mammals and birds (Norman, Cullen and Dann 1992; Augee, Smith and Rose 1996; Priddel and Wheeler 1996; Seebeck and Booth 1996; Smith and Quin 1996). In the Adelaide area V. vulpes are wide- spread in the hills. They are often reported near houses and are a nuisance because of their predation on backyard poultry. Within Belair National Park, an area of 840 ha located in the Adelaide hills about 8 km from the City Centre, foxes are a potential danger to small native mammals, such as the Southern Brown Bandicoot (lsoodon obesulus).There is a small population of I. obesulus in Belair National Park, (Regel et al. 1996) of which 62 individuals from an area of about 30 ha were recently marked with microchips. A fox baiting program with Foxoff® in autumn 1996 in Belair National Park saw the uptake of 97 poisoned baits, with two fox carcasses located.

Secondary poisoning of mustelids in a New Zealand Nothofagus forest

Eleven radio‐tagged stoats (Mustela erminea) and one weasel (M. nivalis) died of secondary poisoning following Talon 20 PTM (20 ppm brodifacoum) poisoning operations which killed mice (Mus musculus), ship rats (Rattus rattus) and probably brushtail possums (Trichosurus vulpecula) in a New Zealand beech (Nothofagus) forest. This poisoning method could be an especially useful way of restoring New Zealand native bird populations because it kills several predator species in one operation. Potential unwanted side‐effects must be researched before its routine use. This research also demonstrates the potential hazards of second‐generation anticoagulant rodenticides to conservation of rodent predators in Europe.

Heritability of head size in the common gull Larus canus in relation to environmental conditions during offspring growth

We studied the heritability of head length in a common gull (Larus canus) population breeding in western Estonia. Heritability estimates obtained from offspring-parent regressions were moderate to high and significantly different from zero. Head size might hence respond evolutionarily to phenotypic selection. Offspring-mother and offspring-father regressions yielded similar heritability estimates. This indicated that size-related maternal or paternal effects were absent or weak. Heritability and additive genetic variance estimates obtained from offspring-parent regressions and full-sib analyses were higher when offspring had grown up under good environmental conditions than under poor environmental conditions. Such a pattern has previously been found in some other studies of birds. This suggests that genotype-environment interactions might be frequent within the range of conditions experienced by natural bird populations.

Heritability of head size in the common gull Larus canus in relation to environmental conditions during offspring growth

We studied the heritability of head length in a common gull (Larus canus) population breeding in western Estonia. Heritability estimates obtained from offspring-parent regressions were moderate to high and significantly different from zero. Head size might hence respond evolutionarily to phenotypic selection. Offspring-mother and offspring-father regressions yielded similar heritability estimates. This indicated that size-related maternal or paternal effects were absent or weak. Heritability and additive genetic variance estimates obtained from offspring-parent regressions and full-sib analyses were higher when offspring had grown up under good environmental conditions than under poor environmental conditions. Such a pattern has previously been found in some other studies of birds. This suggests that genotype-environment interactions might be frequent within the range of conditions experienced by natural bird populations.

DNA fingerprinting of captive breeding pairs of lesser white-fronted geese (Anser erythropus) with unknown pedigrees

For a number of decades, the lesser white-fronted goose (Anser erythropus) has been almost-absent from the Fennoscandian fauna and has a current population size of only about 60 breeding pairs, with fewer than 10 pairs in Sweden. During the period 1981-1991 more than 200 young have been reintroduced in northern Sweden. However, the origin and possible relatedness of lesser white-fronted individuals were unknown when the breeding program started. We have used DNA fingerprinting to assess the similarity of 18 individuals, i.e., the entire captive population used for breeding in 1991 and about 60% of the captive population used in 1981-1991. Minisatellite probe 33.15 provided an index for an average similarity of 0.39 between the mates of the 12 breeding pairs used for producing offspring for reintroduction. This is a higher similarity than in natural populations of birds in general but lower than in populations that have passed through serious population bottlenecks. Individuals originating from different breeders are more dissimilar than those from the same breeder. However, the close relationships (similarity, 0.5-0.6) found in a group of five individuals from different breeders show that selecting individuals from different breeding groups is not sufficient to prevent mating between closely related individuals.

Temporal Stability and Microgeographic Homogeneity of Heritability Estimates in a Natural Bird Population

Temporal stability and microgeographic homogeneity of heritability estimates in a natural bird population

A PCR test for avian malaria in Hawaiian birds

The decline of native Hawaiian forest birds since European contact is attributed to factors ranging from habitat destruction to interactions with introduced species. Remaining populations of Hawaiian honeycreepers (Fringillidae: Drepanidinae) are most abundant and diverse in high elevation refuges above the normal range of disease-carrying mosquitoes. Challenge experiments suggest that honeycreepers are highly susceptible to avian malaria (Plasmodium sp.) but resistance exists in some species. In order to detect low levels of malarial infection and quantify prevalence of Plasmodium in high elevation natural populations of Hawaiian birds, a polymerase chain reaction (PCR) based diagnostic test was developed that identifies rRNA genes of Plasmodium in avian blood samples. Quantitative competitive PCR (QC-PCR) experiments indicate that the detection limit of our test is an order of magnitude greater than that reported for human malaria DNA blot tests. Compared with standard histological methods, the PCR test detected a higher prevalence of diseased birds at mid-elevations. Malaria was detected in three species of native birds living in a high elevation wildlife refuge on the island of Hawaii and in four species from Maui. Our results show that avian malaria is more widespread in Hawaiian forests than previously thought, a finding that has important conservation implications for these threatened species.

Introduced Swedish Canada geese (Branta canadensis) have low levels of genetic variation as revealed by DNA fingerprinting

AbstractThe Swedish, Finnish and Norwegian population of Canada geese (Branta canadensis), now amounting to some 30–50 000 birds, was founded by only five individuals. We used DNA fingerprinting to assess the level of genetic variability in minisatellite loci of Swedish Canada geese from two northern areas. For comparison, we estimated the minisatellite variability in lesser white‐fronted geese (Anser erythropus), barnacle geese (Branta leucopsis) and a reintroduced stock of Canadian giant Canada geese (Branta canadensis maxima).The mean similarity between Swedish Canada geese was 0.76 ± 0.15, which is higher than recorded for any other natural bird population. The high similarity implies that a fourfold increase of homozygosity has taken place in this population. The probable cause for the loss of variation is the low number of birds originally introduced and a history of repeated translocations, leading to a sequence of founder events. As a consequence of the high similarity, it has not been possible to use DNA fingerprinting for determination of parenthood in the population studied.

Heritability of migratory activity in a natural bird population

The presence of additive genetic variation is a prerequisite for changes in migratory behaviour through selection. Previous work with the blackcap, Sylvia atricapilla, has shown that the urge to migrate and the migratory direction are under genetic control. Here we examine whether migratory activity in this species has a significant additive genetic component, with the aim of predicting micro-evolutionary changes in migratory distance. Migratory activity was recorded in 280 southern German blackcaps from 69 families. We calculated heritabilities by parent-offspring regressions and by full-sibling correlations. Heritability estimates obtained by different methods were significantly different from zero and in good agreement with each other (h$^{2}$ = 0.37-0.46). This suggests that in the expression of migratory activity maternal and dominance effects are negligible. The high amount of phenotypic and additive genetic variation found for migratory activity in this population could lead to rapid evolutionary changes of migratory habits. Under moderate selection intensities and environmental conditions similar to those presented in this study, the southern German blackcap population could evolve into a short-distance migrant in 10-20 generations.

Foster parent experiment reveals no genotype-environment correlation in the external morphology of Ficedula albicollis, the collared flycatcher

Heritabilities of quantitative traits have recently been estimated in several natural populations of birds. The predictive value of these estimates is based on the assumption that heritability estimates are not inflated by an environmental correlation between parent and offspring. We here show with a foster experiment that heritability estimates of seven morphological traits in the collared flycatcher are not inflated as a result of a genotype-environment correlation. Surprisingly, there was a negative foster parent-offspring relation in a poor environment. It is suggested that large foster parents have more difficulties raising offspring under poor environmental conditions than do small foster parents. Our experiment also provides evidence for a heritable basis of phenotypic variation in feather traits and that the morphology of the collared flycatcher could respond rapidly to selection.

Conservation of Habitats for Shrubsteppe Birds

Extending over a year, all the birds that could be detected were counted on two transects which together sampled an area of 1.39 km2. Only 37 species were recorded during 82 surveys. Total bird density during the spring (March–June) was 43.0 birds/km2, and the density for the entire year was 26.7 birds/km2. The characteristic nesting birds were Western Meadowlark, Sage Sparrow, Burrowing Owl, Mourning Dove, Horned Lark, Long-billed Curlew, Lark Sparrow, and Loggerhead Shrike. Western Meadow-larks and Sage Sparrows were the most abundant nesting birds, having an average density of 11.2 and 7.8 birds/km2, respectively. Seasonal distribution of birds varied with species, but most species were present only from March to September.Sixty-three per cent of the habitat surveyed was dominated by Big Sagebrush, 26% was dominated by Cheatgrass, and the remaining 11% was dominated by Spiny Hopsage. Big Sagebrush habitat supported a greater total bird density than the Cheatgrass or Hopsage habitats. Sage Sparrows were closely associated with Sagebrush habitats, while Western Meadowlarks showed no strong habitat affinities.Extensive habitat modifications induced by more than a century of agriculture and livestock grazing have greatly depleted native Shrubsteppe habitat in the Columbia Basin. Over the past 40 years, the Hanford Site has served as a refugium for Shrubsteppe habitat that supports populations of native Shrubsteppe birds. The concept of the Hanford Site as a refugium for native Shrubsteppe habitat and Shrubsteppe nesting birds is favourably discussed.

Borrelia burgdorferi in Ixodes dammini (Acari: Ixodidae) feeding on birds in Lyme, Connecticut, U.S.A.

Passerine birds were captured in Japanese mist nets in Lyme, Connecticut, during 1990 and 1991 to collect larval and nymphal Ixodes dammini and to identify potential bird reservoirs for Borrelia burgdorferi, the etiologic agent for Lyme borreliosis. Of the 3291 birds captured and recaptured (32%), 503 in 35 species were parasitized by I. dammini. Ninety-eight of the recaptured birds had ticks attached. Borrelia burgdorferi was detected by indirect immunofluorescence staining in 72 (4.7%) of 1518 larvae and in 114 (23.3%) of 490 nymphs tested. Prevalence of infected larvae was comparatively greater for specimens removed from veeries (21.4%, n = 140 tested), Carolina wrens (15.5%, n = 84), hooded warblers (8.9%, n = 79), and house wrens (8.6%, n = 58). Based on the presence of infected larval ticks on birds, members of these 4 host species have the greatest potential for being reservoirs of B. burgdorferi. Relatively lower percentages of infected larvae (0.3–6.7%) were recorded for 8 other bird species. June through mid-August is a suitable time to isolate B. burgdorferi from natural populations of birds or ticks feeding on avian hosts.

Was disease involved in the decimation of Guam's avifauna?

Between 1982 and 1986, 402 (290 live, 112 dead) exotic, migrant or native resident birds on Guam were surveyed for disease-causing agents to determine the role of disease in the decline of native forest bird populations on Guam. Traumatic injury, primarily from collisions with motor vehicles and predation, was the most prevalent (46%) cause of death. Thirty-eight percent of the carcasses examined were in poor body condition largely as a result of inadequate nutrition in captive native birds and poultry and adipose exhaustion in errant migrants. A variety of commensal or opportunistic bacteria, including Salmonella spp., were cultured from 220 birds, and nothing remarkable was found in 15 fecal samples. Lastly, no haematozoans, the suspected cause for the decline of the Hawaiian avifauna, were observed in blood slides examined from 260 birds. Based on the results of the survey and other lines of evidence presented in the discussion, we concluded there were no data implicating disease in the decline of Guam's avifauna.

Color bands function as secondary sexual traits in male red-winged blackbirds

We present the first experiment to assess band color effects in a natural bird population. 38 territorial male red-winged blackbirds (Agelaius phoeniceus) were randomly assigned to 1 of 2 banding treatments. They received either all red bands (to match their epaulets) or all black bands (controls). Over half the red-banded males lost their territories while all black-banded males retained their territories. Red and black-banded males did not differ morphologically. However, among red-banded males, those that lost their territories had larger epaulets and were in poorer condition than those retaining their territories. Red-banded males suffered much higher intrusion rates, particularly by neighbors, than black-banded males. We propose that red color bands exaggerated the males' natural aggressive signal beyond the point where the signal was reliable. Our results suggest that signal reliability is maintained by regular testing, particularly of those males most likely to be signalling dishonestly.

Genetic Variation and Differentiation in the Spotted Owl (Strix occidentalis)

-We used starch-gel electrophoresis to investigate genetic variability at 23 loci in 107 individuals from seven populations of the Spotted Owl (Strix occidentalis). These populations sample all three currently recognized subspecies. No genetic variation was found in six populations from Oregon and California. Average heterozygosity in owls from New Mexico was 0.022. The low level of genetic variability will make it more difficult to monitor the genetics of this threatened species; the paucity of variation is possibly due to a small overall effective population size or bottlenecks in the past. At one locus there was a major allelic frequency difference between the Pacific Coast populations (S. o. caurina and S. o. occidentalis) and the allopatric taxon (S. o. lucida) found in New Mexico; our estimate of FST is 0.55. We believe the two allopatric populations have long been isolated, and it is probable that they represent two species. The data do not help elucidate the subspecific status of S. o. caurina. Received 11 December 1989, accepted 11 May 1990. OVER the last two decades, evolutionary and systematic biologists have devoted a major effort to assessing the extent of genetic variation within, and differentiation among, populations (Lewontin 1985, 1986). This has been true of many disciplines, including ornithology (for recent reviews, see Avise and Aquadro 1982, Avise 1983, Barrowclough 1983, Corbin 1983, Barrowclough et al. 1985, Barrowclough and Johnson 1988). These results have allowed biologists to make inferences about the evolutionary history of a species and, perhaps, to generalize about evolutionary processes (e.g. Lewontin 1974). In addition, these studies provide systematists with data, independent of classical morphology and phenotypes, to assess biogeographic and taxonomic patterns (e.g. Barrowclough 1985). Conservation biologists now realize that such data permit monitoring threatened populations for evidence of genetic deterioration (Lande and Barrowclough 1987) as well as identifying evolutionary and taxonomic units for conservation (e.g. Ryder 1986a, b). The recent report on genetic variation in the endangered New Zealand Kakapo (Strigops habroptilus; Triggs et al. 1989) is an example. One North American species that is the subject of much concern among conservationists, foresters, and wildlife biologists is the Spotted Owl, Strix occidentalis (e.g. Gutierrez and Carey 1985, Dawson et al. 1987, U.S. Dep. Agric. For. Serv. 1988). We report on an electrophoretic examination of genetic variation within and among populations of the Spotted Owl over much of its range. This study adds to the small, but growing, body of reports on the extent of genetic variation and differentiation in natural populations of birds; it also provides a survey of the population genetics of a species of particular environmental concern.

Suppression of fruit production of the endemic forest tree,Elaeocarpus dentatus, by introduced marsupial brushtail possums,Trichosurus vulpecula

Abstract Fruit production by the endemic hardwood tree Elaeocarpus dentatus (hinau) was measured during 1981–88 on two study areas about 3 km apart in the Orongorongo Valley, Wellington, using collecting funnels and trays placed under the crowns of the trees. Fruit production differed significantly between study areas, years and individual trees. Buds, flowers, and fruits of hinau were browsed by the introduced marsupial brushtail possum, Trichosurus vulpecula. When possums were eradicated from one of the study areas hinau fruit production increased significantly. As possums recolonised the study area over the next 2–3 years, fruit production declined to former levels. Such effects of possums on fruit production of native trees and shrubs are likely to have serious consequences for native bird populations, and forest dynamics.

Selenium teratogenesis in natural populations of aquatic birds in Central California

The frequency and types of malformations are described that were encountered during the spring of 1983 in a natural population of aquatic birds exposed to agricultural drainwater ponds and food items containing high concentrations of selenium in central California. A total of 347 nests of aquatic birds containing 1,681 eggs was selected for study at Kesterson Reservoir located in the Kesterson National Wildlife Refuge (NWR), Merced County, California. Embryos collected during incubation or from eggs that failed to hatch were examined to determine the age at death and presence of malformations. Embryonic death was generally high; approximately 17–60% of the nests of different species contained at least one dead embryo. The incidence of malformed embryos was also high; approximately 22–65% of the nests where at least two embryos were examined contained abnormal embryos. American coots (Fulica americana) and black-necked stilts (Himantopus mexicanus) experienced the highest incidence of malformed embryos. For all species, the average percentage of eggs containing dead or live abnormal embryos was 16.1 whereas the average percentage containing live abnormal embryos was 10.7. Multiple gross malformations of the eyes, brain, and feet were often present. Brain defects included hydrocephaly and exencephaly. Eye defects included both unilateral and bilateral anophthalmia and microphthalmia. Eye and foot defects with ectrodactyly and swollen joints were the most common in coots. Beak defects also occurred frequently and most often included incomplete development of the lower beak of ducks (Anas spp.) and stilts. Wing and leg defects were most prevalent in stilts and ducks, with ectromelia and amelia most prevalent in stilts. Other malformations occurring at lower frequencies included enlarged hearts with thin ventricular walls, liver hypopiasia, and gastroschisis. Based upon simultaneous examination of a control population of aquatic birds of the same species and published studies, the incidences of embryonic mortality and deformities were 9–30 times greater than expected. The role of the form of selenium responsible for teratogenesis in laboratory studies is discussed.