Murray A. Potter

Breeding latitude drives individual schedules in a trans-hemispheric migrant bird

Despite clear benefits of optimal arrival time on breeding grounds, migration schedules may vary with an individual birds innate quality, non-breeding habitat or breeding destination. Here, we show that for the bar-tailed godwit (Limosa lapponica baueri), a shorebird that makes the longest known non-stop migratory flights of any bird, timing of migration for individual birds from a non-breeding site in New Zealand was strongly correlated with their specific breeding latitudes in Alaska, USA, a 16,000-18,000 km journey away. Furthermore, this variation carried over even to the southbound return migration, 6 months later, with birds returning to New Zealand in approximately the same order in which they departed. These tightly scheduled movements on a global scale suggest endogenously controlled routines, with breeding site as the primary driver of temporal variation throughout the annual cycle.

Corticosterone responses in birds: Individual variation and repeatability in Adelie penguins (Pygoscelis adeliae) and other species, and the use of power analysis to determine sample sizes

Plasma corticosterone concentrations increase when birds experience a stressor, and in this study we quantified variation in corticosterone responses for the first time in a species of free-living bird. Adelie penguins (Pygoscelisadeliae) nesting at Cape Bird on Ross Island in Antarctica were sampled on three occasions. Penguins with relatively low or high corticosterone responses on the first occasion had consistently low or high responses, as previously found for great tits and chickens. A model for birds is proposed in which birds with low corticosterone responses and proactive personalities are likely to be more successful (have greater fitness) in constant or predictable conditions, whilst birds with reactive personalities and high corticosterone responses will be more successful in changing or unpredictable conditions. There is thus no linear relationship between the size of a corticosterone response and fitness. Whilst the absolute magnitude of corticosterone responses varies markedly across species of birds, coefficients of variation are similar. Individual corticosterone responses are generally repeatable, with significant statistical repeatabilities for 30 min corticosterone concentrations and integrated corticosterone concentrations in the Adelie penguin, great tit and chicken. Coefficients of variation in corticosterone responses between birds and power analyses were used to provide a rule of thumb for determining differences between groups of birds in mean corticosterone concentrations to enable statistical analyses to have acceptable levels of statistical power for given sample sizes. It is suggested that power analyses and this rule of thumb be adopted in future investigations of corticosterone responses in birds.

The relative importance of olfaction and remote touch in prey detection by North Island brown kiwis

Birds that forage by probing in sand, soil or mud substrates must often use senses other than vision to find their prey. Kiwis (Apterygidae) are nocturnal probing birds inhabiting forested areas in New Zealand. Their visual sense is reduced, but they have a highly developed sense of smell, a bill tip organ similar to that found in Scolopacidae shorebirds, which may be used to detect vibrotactile cues produced by burrowing prey (remote touch), and prominent ear openings. We designed a foraging experiment presenting mealworm prey to eight captive North Island brown kiwis, Apteryx mantelli, under a variety of trial conditions to discover whether they were using hearing, olfaction, remote touch or direct touch (chance alone), singly or together, to find prey. Kiwis were most efficient at finding prey using olfaction alone or in combination with other cues, but switched to locating prey with lower efficiency using remote touch, in the absence of olfactory cues. They did not appear to use auditory cues for foraging. The ability to switch between sensory modalities depending on the quality of the cues available has been documented before in other groups of birds (including thrushes (Turdidae) and sandpipers (Scolopacidae)) and would be of great advantage to wild kiwis foraging under a wide range of environmental conditions.

Absolute consistency: Individual versus population variation in annual-cycle schedules of a long-distance migrant bird

Flexibility in scheduling varies throughout an organism’s annual cycle, reflecting relative temporal constraints and fitness consequences among life-history stages. Time-selection can act at different scales, either by limiting the range of alternative strategies in the population, or by increasing the precision of individual performance. We tracked individual bar-tailed godwits Limosa lapponica baueri for two full years (including direct observation during non-breeding seasons in New Zealand and geolocator tracking of round-trip migrations to Alaska) to present a full annual-cycle view of molt, breeding, and migration schedules. At both population and individual scales, temporal variation was greater in post-breeding than pre-breeding stages, and greater in molts than in movements, but schedules did not tighten across successive stages of migration toward the breeding grounds. In general, individual godwits were quite consistent in timing of events throughout the year, and repeatability of pre-breeding movements was particularly high (r = 0.82–0.92). However, we demonstrate that r values misrepresent absolute consistency by confounding inter- and intra-individual variation; the biological significance of r values can only be understood when these are considered separately. By doing so, we show that some stages have considerable tolerance for alternative strategies within the population, whereas scheduling of northbound migratory movements was similar for all individuals. How time-selection simultaneously shapes both individual and population variation is central to understanding and predicting adaptive phenological responses to environmental change.

Rodent and predator population dynamics in an eruptive system

A computer model of the population dynamics of introduced house mice (Mus musculus L.), ship rats (Rattus rattus L.) and stoats (Mustela erminea L.) in New Zealand forest was constructed, to test the relative importance of food availability and predation in shaping observed small-mammal population dynamics. Ship rats and mice are the two common rodent species present in most New Zealand forests, and exhibit eruptive population dynamics. Stoats are the only common mammalian predator, and undergo large density fluctuations following periodic rodent eruptions. A number of outputs and predictions from the model were developed. The model highlights the overall importance of variation in food availability in determining the timing and amplitude of rodent population eruptions. It indicates that predators can not prevent a prey–species eruption, primarily due to differences in reproductive biology. Predation however, can delay the start of the prey-population increase during the eruption. The role of predators in limiting the peak prey-population size will depend on the size of the energy input. In a full-scale eruption following maximal tree seeding, predators cannot significantly truncate peak prey-population size. Predators should be able to significantly hasten the rate of decline in the prey populations, although the strength of predator limitation will depend on the severity of food limitation and cold-induced mortality over the same period. Predators can limit prey populations during the post-crash low phase. As with the crash phase, the strength of predator limitation in the low phase will depend on the severity of food limitation and natural mortality. The model highlights gaps in current knowledge of predator and prey species biology and ecology. The model highlights key areas where further field study should provide a better understanding of the factors driving small-mammal communities in New Zealand.

Corticosterone Responses to Capture and Restraint in Emperor and Adelie Penguins in Antarctica

Abstract Birds respond to capture, handling and restraint with increased secretion of corticosterone, a glucocorticoid hormone that helps birds adjust to stressful situations. Hoods are reported to calm birds, but possible effects of hoods on corticosterone responses have not been reported for any bird. Corticosterone responses to restraint in Adelie penguins held by their legs with their head covered by a hood were markedly lower than responses of penguins restrained in a mesh bag inside a cardboard box (corticosterone at 30 min 15.69±1.72 cf. 28.32±2.75 ng/ml). The birds restrained by the two methods were sampled at the same location but in different years, so the differences in corticosterone responses cannot unequivocally be ascribed to an effect of hoods to reduce corticosterone responses. Corticosterone responses have been measured in some penguins, but not in the largest, the emperor penguin (Aptenodytes forsteri). The relationship between body mass and corticosterone responses to capture and restraint in penguins was examined in emperor penguins captured on sea ice in McMurdo Sound and Adelie penguins (Pygoscelis adeliae) captured at Cape Bird, Ross Island, Antarctica. Total integrated corticosterone responses were higher in the emperor than the Adelie penguins, but corrected integrated corticosterone responses, which represent the increase in corticosterone from initial concentrations and hence the corticosterone response to restraint, were the same. The results for the emperor and Adelie penguins, together with data from other penguin species, suggest that there is no relationship between the size of corticosterone responses and body mass in penguins.

Bill Morphology of Ibises Suggests a Remote-Tactile Sensory System for Prey Detection

ABSTRACT. Birds that forage by probing must often use senses other than vision to find their prey. Remote touch is a sense based on the interception of vibrations produced by moving prey in the substrate or on the evaluation of pressure patterns produced by hard-shelled sessile prey. In probing birds, this system is mediated by an organ made up of clusters of mechanoreceptors housed within pits in the bone of the bill-tips. This bill-tip organ was first described in probing shorebirds (Scolopacidae), and more recently in kiwi (Apterygidae). Here, we describe this bill-tip organ in a third family of probing birds, the ibises (Threskiornithidae). We examined the bill morphology of 11 species of ibis from 8 genera. We found bill-tip organs in species in a wide range of habitat types, from predominantly terrestrial to predominantly aquatic, which suggests that ibises may use remote touch when foraging both in water and in granular substrates. Our data imply a link between bill-tip morphology and habitat use—a pattern that we believe warrants further investigation.

Understanding nuptial gift size in bush-crickets: an analysis of the genus Poecilimon (Tettigoniidae: Orthoptera)

Abstract During mating, male insects of certain species transfer a costly nuptial gift, a large spermatophore, which is eaten by the female as sperm transfer into her. The spermatophore components (the sperm-free spermatophylax and the sperm ampulla) vary greatly in size between species, and have a direct influence on male fitness. Studies of the relationship between spermatophore size variation and male fitness have concentrated on associations between evolutionary changes in spermatophylax size and either ampulla size or sperm number. Two main hypotheses have been put forward to explain the function of the spermatophylax: the ejaculate-protection hypothesis and the paternal investment hypothesis. A strong correlation between the spermatophylax and ampulla or sperm number suggests an ejaculate-protection function because it protects the ampulla from being removed prematurely. However, comparative support comes mainly from disparate bush-cricket species (Tettigoniidae), that vary greatly in relatedness and diet. Furthermore, data are often from animals reared under laboratory conditions. Our study describes the significance of size variation in bush-cricket nuptial gifts, with an analysis from field populations of 33 species within the genus Poecilimon. Poecilimon share similar diets and the variation in spermatophore size within the genus approximates family-wide variation, so confounding influences from diet and relatedness are, to a certain extent, controlled. Previous support for the ejaculate-protection hypothesis is almost universal, so we expected to find similar results. However, unlike previous studies, there was no relationship between body mass and each of the three spermatophore components when body mass was accounted for, or between spermatophylax mass and sperm number. We also found only a weak relationship between ampulla mass and sperm number, suggesting that caution is needed when using ampulla size to predict sperm number or sperm number to predict ejaculate size. In support of the ejaculate-protection hypothesis we found a positive relationship between spermatophylax size and ampulla mass. While our results support the ejaculate-protection hypothesis, they are not inconsistent with the paternal investment hypothesis.

The importance of Yalu Jiang coastal wetland in the north Yellow Sea to Bar-tailed Godwits Limosa lapponica and Great Knots Calidris tenuirostris during northward migration

Summary Bar-tailed Godwits Limosa lapponica and Great Knots Calidris tenuirostris are long-distance migratory shorebirds with declining numbers in the East Asian-Australasian Flyway. One of the most important staging sites for these two species during northward migration is Yalu Jiang coastal wetland in the north Yellow Sea. Historical counts have been limited to once a year and conducted at different periods; these yield inadequate data for population monitoring. We estimated the numbers of Bar-tailed Godwits and Great Knots and described their migration phenology during northward migration from 2010 to 2012 at the Yalu Jiang coastal wetland, using a combination of periodic area-wide counts over the migration period and a modelling approach that estimates passage times and total numbers of birds transiting. The mean arrival date for L. l. baueri godwits was 29 March and mean departure date was 8 May. Corresponding dates were 11 April and 15 May for L. l. menzbieri godwits and 7 April and 14 May for Great Knots. We estimated that an annual average of over 68,000 Bar-tailed Godwits and 44,000 Great Knots used the area on northward migration from 2010-2012. Our results indicate that the Yalu Jiang coastal wetland supports on average at least 42% of the flyways northward-migrating L. l. baueri godwits, 19% of L. l. menzbieri godwits, and 22% of the Great Knots. Comparisons with historical counts conducted during peak migration periods indicate a 13% decline in Bar-tailed Godwits since 2004 and an 18% decline in Great Knots since 1999. Our results confirm that the study area remains the most important northward migration staging site for Bar-tailed Godwits and indicate that it has become the most important northward migration staging site for Great Knots along the flyway.

Plasma levels of sex steroids in the North Island brown kiwi (Apteryx australis mantelli) in relation to time of year and stages of breeding

North Island brown kiwi (Apteryx australis mantelli) have a seasonal pattern of egg laying with a peak in mid to late winter. This study is the first description of changes in plasma steroid concentrations during the annual reproductive cycle of this species. Blood samples were collected at intervals over a 2 1/2-year period from a population of kiwi at Tangiteroria, Northland, New Zealand. Male kiwi had annual cycles of plasma levels of testosterone and estradiol. Mean testosterone levels were low (less than 0.18 ng/ml) during February to April, rose in May to a broad peak lasting 4 months (maximum levels 1.90 +/- 0.76 ng/ml), declined in September, and reached low levels in November to January. With respect to the breeding cycle, testosterone levels were low in the nonbreeding period, rose to high levels over 2 to 4 months before egg laying, then declined steadily toward the start of incubation. Plasma testosterone levels were very low in brooding males. Mean estradiol levels in males showed a pattern similar to testosterone levels, except that the rise to peak levels (1750 +/- 680 pg/ml) started in April. In female kiwi mean testosterone levels were low (less than 0.10 ng/ml) throughout the year. There was an annual cycle of mean estradiol levels in females which in timing and amplitude was similar to the male cycle. Estradiol levels in relation to stages of the breeding cycle in females were basal in the nonbreeding period, increased over a 3-month period before egg laying, declined in the 2 weeks before laying, and were low thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)