John T. Darby

Carotenoid-derived ornaments reflect parental quality in male and female yellow-eyed penguins (Megadyptes antipodes)

The handicap principle suggests that ornamental traits that function as honest signals in mate selection must be costly to be effective. We evaluated in the sexually monochromatic yellow-eyed penguin (Megadyptes antipodes) whether the carotenoid-derived plumage and eye coloration predicts parental quality and whether males and females within pairs mate assortatively in relation to these carotenoid-derived ornaments. In addition, we investigated whether age or body condition was related to the coloration of the ornamental traits. In yellow-eyed penguins, parental quality of males and females was predicted by eye and head plumage coloration. Even when we controlled for gender- and age-specific differences, eye and head plumage coloration reflected honestly parental quality. Males and females mated assortatively in relation to these ornamental traits. While age influenced coloration of both the eye and head plumage, body condition was related only to the saturation of plumage coloration. These results provide evidence that the carotenoid-derived ornaments in yellow-eyed penguins reflect the parental abilities of birds and, therefore, may be costly signals. Potentially, female and male yellow-eyed penguins could use eye and plumage coloration as an indirect cue in assessing age and quality of individual birds during mate choice. This is only the second study to examine plumage coloration in relation to sexual selection in penguins, while conspicuous ornamental traits in other species of penguin beg the question whether they also play a role in sexual selection.

Bycatch of yellow-eyed penguins (Megadyptes antipodes) in gillnets in New Zealand waters 1979–1997

Between 1979 and 1997, autopsies of 185 yellow-eyed penguins were conducted as part of a long-term study of their population biology. Twenty-one penguins known to have been drowned in gillnets were used to compile a set of physical features and injuries characteristic of death by gillnet entanglement. A further 21 birds whose cause of death was initially unknown showed features consistent with death by gillnet entanglement. Fishers reported a further 30 gillnet entanglements to government agencies. Considering the rarity of this species on the South Island of New Zealand, gillnet entanglement is interpreted to be a significant threat to South Island populations.

The Use of Morphometric Measurements to Sex Yellow-eyed Penguins

Abstract The Yellow-eyed Penguin (Megadyptes antipodes) is monomorphic but exhibits subtle sexual morphometric dimorphism. Information on the sexes of these birds is needed for informed management of the species and the construction of accurate population models. Using DNA analysis and Discriminant Function Analysis on head and foot measurements, we tested whether adults and fledglings of Yellow-eyed Penguin can be sexed using morphometry. We found that head and foot measurements can be used to correctly sex up to 93% of adults. Using only foot length, 88% of fledglings can be sexed accurately. As age until fledging was found to have an effect on morphometric variables, sexing should be conducted as synchronized as possible when chicks are over 90 days of age. We recommend that error rates inherent in sexing fledglings be taken into account when publishing sex-ratio data and subsequent analyses, particularly when age of fledglings could not be determined. The use of whole-skull measurements for sexing may be useful in other species in which bill measurements between the sexes are only slightly dimorphic or contains large degrees of overlap.

Investigation of interacting effects of female age, laying dates, and egg size in Yellow-eyed Penguins (Megadyptes antipodes)

Abstract Increased experience with age may allow long-lived seabirds to forage more efficiently and ultimately to invest more into reproduction. In many seabirds, egg size increases with female age, but declines with laying date. Declines in laying date might be due either to quality of individual females or females may adjust their egg size in response to poorer conditions typically found late in the season. We investigated the influence of female age, date of laying, and annual variation on egg size in Yellow-eyed Penguins (Megadyptes antipodes). Further, we tested whether there was an effect of individual females or female age on date of laying. Whereas female age influenced egg volume, mass, and width, laying date had no effect on egg size or mass in Yellow-eyed Penguins. Laying dates differed significantly among females but were not affected by their ages. These results indicate that in Yellow-eyed Penguins, some individual females lay consistently early or late, regardless of age, but that egg size generally increases with age.

Effects of artificial social stimuli on the reproductive schedule and hormone levels of yellow-eyed penguins (Megadyptes antipodes)

The effects of social stimuli on avian reproductive behaviors such as breeding schedules and courtship behaviors are well known due to numerous field studies. However, studies that have simultaneously examined the effects of social stimuli on reproductive behavior and the mediating endocrine mechanisms have been largely restricted to captive populations, which may not be representative of free-living populations. This study, conducted over two breeding seasons, aimed to simultaneously measure the effects of experimentally increasing auditory stimuli on the breeding schedule and endocrinology (levels of total androgen, estradiol, progesterone and prolactin) on free-living yellow-eyed penguins (Megadyptes antipodes). The yellow-eyed penguin is the least colonial of all penguins, nesting far apart from each other under dense vegetation, and, therefore, is presumed to experience much lower levels of social stimuli than other penguins. Egg laying was significantly more synchronous and tended to be earlier when birds were exposed to playbacks of the calls of conspecifics in 1 year of the study. We also found that levels of total androgen and estradiol of males in 1 year, and prolactin in another year, were proportionally higher among treated birds compared control birds that received no artificial auditory stimuli. These results show that even among supposedly solitary nesters, social stimuli could still play a role in influencing reproductive behavior and physiology. For the first time in free-living seabirds, we have demonstrated that behavioral responses to increased social stimuli are associated with hormonal changes.

MATE AND TERRITORY RETENTION IN YELLOW-EYED PENGUINS

Abstract Using nest and banding data collected from 1991 to 2002, we investigated mate and territory retention rates of Yellow-eyed Penguins (Megadyptes antipodes), and the effects of reproductive success. Annual mate retention rate was 63%, and territory retention for males and females were 52% and 46% respectively. The majority of pair dissolutions were due to death of a partner, with only 6% of bonds ending in separation. Previous reproductive success was a good predictor of mate or territory retention as pairs that failed to fledge a single chick were significantly more likely to separate or move their territories than those that were successful at fledging chicks. Reproductive success of birds that changed their mates or moved territories was not higher than those that retained their mates or territories. However, birds that moved territories were less likely to have reduced fledging success relative to their previous breeding attempt. Birds that did not retain their mates, particularly males, were significantly more likely to skip breeding for at least one year. This suggests that the costs of mate or territory changes are not accrued at the end of the breeding attempt (as reflected by the number of fledged chicks), but are associated with the costs of pair formation and establishment of territories at the beginning of the breeding season. Retención de Parejas y Territorios en Pingüinos Megadyptes antipodes Resumen. Investigamos las tasas de retención de parejas y de territorios por parte de pingüinos Megadyptes antipodes y el efecto del éxito reproductivo sobre estas tasas con base en datos de nidificación y anillamiento recolectados entre 1991 y 2002. La tasa anual de retención de parejas fue del 63% y las de retención de territorios del 52% y 46% para machos y hembras, respectivamente. La mayoría de las disoluciones de parejas se debieron a la muerte de una de las aves y sólo el 6% de las parejas terminaron separándose. El éxito reproductivo previo predijo acertadamente la retención de compañeros y de territorios, ya que las parejas que no lograron emplumar ningún pichón tuvieron una probablilidad de disolverse o de cambiar de territorio significativamente mayor que las que criaron exitosamente. El éxito reproductivo de las aves que cambiaron de pareja o de territorio no fue mayor que el de aquellas que no lo hicieron. Sin embargo, los individuos que cambiaron de territorio fueron más propensos a presentar un éxito de emplumamiento reducido con respecto a su intento reproductivo previo. Las aves que no retuvieron sus parejas, particularmente los machos, presentaron una probabilidad mayor de no reproducirse durante al menos un año. Esto sugiere que los costos que implica cambiar de pareja o de territorio no se hacen evidentes al final del intento reproductivo (como lo indica el número de volantones producidos), sino que están asociados con los costos de la formación de parejas y el establecimiento de territorios al comienzo de la época reproductiva.

Investigations into climate influence on population dynamics of yellow‐eyed penguins Megadyptes antipodes

Abstract Since 1980, the yellow‐eyed penguin Megadyptes antipodes has had three seasons of poor breeding success or low adult survival. Causes for poor seasons are not identified but could be related to climate ‐ in particular, the El Niño‐Southern Oscillation event, which affects ocean currents and climate over the penguins’ range. We carried out an exploratory analysis to determine whether fluctuations in penguin population variables were correlated with fluctuations in climate variables. Population variables across breeding areas showed consistently strong correlations with rainfall and sea surface temperature. We modelled changes in climate variables and penguin population variables to test whether the effect could be explained as a chance correlation. Investigations using these models indicated that the observed relationship was unlikely to have been due to chance. The models also suggested that fledge‐ling success increased in seasons that were slightly cooler and wetter than average. Modelling studies were also carried out on a historical dataset of penguin population variables in the 1930s. It was found that the population tended to increase in seasons that were warmer and drier than average. Average temperatures have risen and average precipitation levels have become highly variable in the study area during this time. Therefore, long term climate change in general, rather than the El Niño‐Southern Oscillation events in particular, could be among the underlying causes of gradual decline in yellow‐eyed penguin numbers.

Survival and breeding of yellow-eyed penguins (Megadyptes antipodes), at two locations on Otago Peninsula, South Island, New Zealand, 1991-96

Abstract Two breeding locations of the endangered yellow‐eyed penguin (Megadyptes antipodes), were monitored for six seasons between 1991 and 1996 to assess breeding success, breeding frequency, and survival parameters. Breeding success was inversely related to the total number of nests, suggesting that an influx of inexperienced breeders decreases the average breeding success. The proportions of males not breeding at either location in a season ranged from 0 to 13%, and 0 and 23% for females. Between 75 and 92% of breeders were recorded breeding in two consecutive seasons, while between 0 and 6% of breeders skipped one season and 9% of females (but no males) skipped two consecutive seasons. Annual survival averaged 90% for both breeding locations for four seasons (males 93%, females 90%).

Activity budget for breeding yellow-eyed penguins

Abstract Instantaneous scan sampling was used to determine time allocation for various breeding activities of the yellow-eyed penguin (Megadyptes antipodes), from pre-egg phase to post-guard phase. Breeding commences with the pre-egg phase, characterised by the presence of birds ashore during the day. Males are more active at this time, spending more time in an upright posture, preening, or displaying from the nest bowl. Females appear to follow an energy conserving strategy during egg deposition. Two eggs are laid, 3–5 days apart, with fully-prone incubation commencing after the laying of the second egg. Delayed onset of prone incubation is possibly because of low levels of egg predation and the temperate breeding climate. Incubation is shared by both sexes and, energetically speaking, is a period of hiatus; both birds gain weight during this time. Synchronous hatching caused by delayed incubation results in equal-sized siblings. Chick feeding is shared equally by both adults. The period of chick care is...

Quantifying climate change impacts emphasises the importance of managing regional threats in the endangered Yellow-eyed penguin

Climate change is a global issue with effects that are difficult to manage at a regional scale. Yet more often than not climate factors are just some of multiple stressors affecting species on a population level. Non-climatic factors—especially those of anthropogenic origins—may play equally important roles with regard to impacts on species and are often more feasible to address. Here we assess the influence of climate change on population trends of the endangered Yellow-eyed penguin (Megadyptes antipodes) over the last 30 years, using a Bayesian model. Sea surface temperature (SST) proved to be the dominating factor influencing survival of both adult birds and fledglings. Increasing SST since the mid-1990s was accompanied by a reduction in survival rates and population decline. The population model showed that 33% of the variation in population numbers could be explained by SST alone, significantly increasing pressure on the penguin population. Consequently, the population becomes less resilient to non-climate related impacts, such as fisheries interactions, habitat degradation and human disturbance. However, the extent of the contribution of these factors to declining population trends is extremely difficult to assess principally due to the absence of quantifiable data, creating a discussion bias towards climate variables, and effectively distracting from non-climate factors that can be managed on a regional scale to ensure the viability of the population.