Eric A. VanderWerf

Breeding biology and territoriality of the Hawaii creeper

The Hawaii Creeper (Oreomystis mana) is an endangered honeycreeper restricted to high-elevation forests on the island of Hawaii. I found eight Hawaii Creeper nests at Hakalau Forest National Wildlife Refuge from 1991-1997. Three nests fledged one or two chicks each, one failed because of bad weather, and two were abandoned after kleptoparasitism of nest material by other bird species. Females did most nest construction and all incubation and brooding. Both sexes fed the nestlings by regurgitation, with the male making 57% of feedings. The male fed the female during incubation and brooding. At two nests construction took 11-15 days and the incubation period was 13 days. At one nest the clutch size was two and the nestling period was 18 days. Mean nest tree height and diameter were 21.7 ± 2.9 m and 54.9 ± 23.6 cm, respectively, and mean nest height was 12.0 ± 4.3 m. Four nests were in cavities and four were open. One pair built an open and a cavity nest in the same season. During the breeding season males defended a small type-B territory with a radius around the nest of 15-20 m. Home ranges were larger in the nonbreeding season (11.9 ± 7.7 ha) than in the breeding season (4.5 ± 0.2 ha) and overlapped extensively.

Population trends of Mariana Crow Corvus kubaryi on Rota, Commonwealth of the Northern Mariana Islands

Endemic to the islands of Guam and Rota in the Mariana Islands, Mariana Crow Corvus kubaryi is the only corvid in Micronesia. Currently, it survives on Guam only because of translocation of individuals from Rota (1999–2003). Island-wide surveys in 1982 and 1995 on Rota yielded population estimates of 1,348 and 592 respectively, indicating a 56% decrease in only 13 years. A sharp decline in the only viable Mariana Crow population has serious implications for conservation efforts on Rota and for efforts to re-establish the Guam population. However, the validity of the apparent decline has been debated among scientists and government management agencies. We augmented the 1982 and 1995 island-wide VCP surveys with (1) an additional island-wide survey conducted in 1998, and (2) roadside surveys conducted during 1991–1993 and again during 1999–2002. We also outline historical changes in Rota’s limestone forest based on aerial photographs and historical information. Data from all surveys indicate a significant decline in the Mariana Crow population. Declines occurred especially along the north-central coast and in the area east of the airport known as As Dudo in the 1990s, but the data indicate an island-wide decline over the entire span of the surveys. Introduced predators, human persecution, and habitat loss and degradation by anthropogenic and natural causes have all contributed to the decline. Long-term preservation of this species will require effective brown treesnake Boiga irregularis control, habitat protection, continued monitoring and research, and increased public education and awareness of Rota’s rare and endangered species.

Collapsing avian community on a Hawaiian island

Climate change and disease are linked to the rapid decline of native birds on the Hawaiian island of Kaua‘i. The viability of many species has been jeopardized by numerous negative factors over the centuries, but climate change is predicted to accelerate and increase the pressure of many of these threats, leading to extinctions. The Hawaiian honeycreepers, famous for their spectacular adaptive radiation, are predicted to experience negative responses to climate change, given their susceptibility to introduced disease, the strong linkage of disease distribution to climatic conditions, and their current distribution. We document the rapid collapse of the native avifauna on the island of Kaua‘i that corresponds to changes in climate and disease prevalence. Although multiple factors may be pressuring the community, we suggest that a tipping point has been crossed in which temperatures in forest habitats at high elevations have reached a threshold that facilitates the development of avian malaria and its vector throughout these species’ ranges. Continued incursion of invasive weeds and non-native avian competitors may be facilitated by climate change and could also contribute to declines. If current rates of decline continue, we predict multiple extinctions in the coming decades. Kaua‘i represents an early warning for the forest bird communities on the Maui and Hawai‘i islands, as well as other species around the world that are trapped within a climatic space that is rapidly disappearing.

TWO-YEAR DELAY IN PLUMAGE MATURATION OF MALE AND FEMALE 'ELEPAIO

Abstract I studied molt and plumage in the ‘Elepaio (Chasiempis sandwichensis), a monarch flycatcher endemic to the Hawaiian Islands, at Hakalau Forest National Wildlife Refuge on the island of Hawai‘i from 1994–1997. I captured birds in mist nets, examined them for molt, measured their plumage color with Munsell color chips, and followed them for several years to document plumage changes. Male and female Hawai‘i ‘Elepaio exhibited three distinct post-juvenal plumages, first basic, second basic, and definitive basic, and thus have a two-year delay in plumage maturation. ‘Elepaio have a single annual molt, so there are no alternate plumages. The first prebasic molt is partial, but all subsequent molts are complete. The first basic plumage is juvenile-like and sexually monochromatic. The second basic and definitive basic plumages are sexually dimorphic in throat color. In each sex the second basic plumage resembles definitive plumage. Age-related plumage changes include increases in the whiteness, number, and length of contrasting tips to feathers on the throat, rump, wing coverts, and tail. Subadults do not molt fewer body feathers than adults and produce many feathers that are not adult in coloration, indicating the subadult plumages are not caused by a molt constraint. Appearance of the subadult plumages is consistent in some respects with juvenile mimicry, but the subadult plumages are unlikely to function in sexual mimicry. Desfase de Dos Años en la Maduración del Plumaje del Macho y la Hembra de Chasiempis sandwichensis Resumen. Entre 1994–1997 estudié la muda y el plumaje de Chasiempis sandwichensis, un monarca atrapamoscas endémico de las Islas de Hawai, en el Refugio Forestal Nacional de Vida Silvestre Hakalau en la Isla de Hawai‘i. Capturé aves empleando redes de niebla, las examiné para establecer la muda, medí el color de sus plumajes con fichas de colores Munsell, y las seguí durante varios años para documentar cambios en el plumaje. El macho y la hembra de C. sandwichensis exhibieron tres plumajes post-juveniles diferentes, básico primero, básico segundo, y básico definitivo, mostrando así un desfasaje de dos años en la maduración del plumaje. La primera muda pre-básica es parcial, pero todas las mudas subsecuentes son completas. El primer plumaje básico se asemeja al del juvenil y es similar para ambos sexos. El segundo plumaje básico y el básico definitivo presentan dimorfismo sexual en el color de la garganta. En ambos sexos el color del plumaje básico se asemeja al del plumaje definitivo. Los cambios en el plumaje relacionados a la edad incluyen un incremento en blancura, número, y largo de la punta contrastada de las plumas de la garganta, rabadilla, cubiertas alares y cola. Los subadultos no mudan menos plumas corporales que los adultos y producen muchas plumas que no son como la de los adultos en coloración, indicando que el plumaje de los subadultos no responde a una limitante de la muda. La apariencia del plumaje de subadultos es consistente en cierto sentido con la imitación de juveniles, pero el plumaje de subadultos es improbable que funcione como imitación sexual.

Survival estimates of wild and captive-bred released Puaiohi, an endangered Hawaiian thrush

ABSTRACT Estimating and monitoring adult and juvenile survival are vital to understanding population status, informing recovery planning for endangered species, and quantifying the success of management. We used mark–recapture models to estimate apparent annual survival of the Puaiohi (Myadestes palmeri), an endangered thrush endemic to the Hawaiian island of Kauai, from 2005 to 2011. Our sample included 87 wild birds and 123 captive-bred birds that were released at various ages. Survival was higher for wild adult males (0.71 ± 0.09) than for wild adult females (0.46 ± 0.12). Survival of wild juveniles (0.23 ± 0.06) was lower than that of wild adults of both sexes, indicating that recruitment may limit population growth. Captive-bred birds released when <1 yr old had survival (0.26 ± 0.21) comparable with that of wild juveniles, but captive-bred birds released at 1–3 yr old had very low survival (0.05 ± 0.06). Only 8 of 123 (7%) captive birds were seen again after release. Two wild birds resighted five years after marking are the oldest known individuals, being at least six years of age. Malarial infection did not affect survival of wild Puaiohi, unlike many Hawaiian forest birds. The difference between adult male and adult female survival is consistent with rat (Rattus spp.) predation of females on the nest as a major source of mortality. As such, attempting to reduce nest predation by controlling rats may be the best available management option. Releasing captive-bred birds has had little effect on the wild population in recent years.

Adaptive value of same-sex pairing in Laysan albatross

Same-sex pairing is widespread among animals but is difficult to explain in an evolutionary context because it does not result in reproduction, and thus same-sex behaviour often is viewed as maladaptive. Here, we compare survival, fecundity and transition probabilities of female Laysan albatross in different pair types, and we show how female–female pairing could be an adaptive alternative mating strategy, albeit one that resulted in lower fitness than male–female pairing. Females in same-sex pairs produced 80% fewer chicks, had lower survival and skipped breeding more often than those in male–female pairs. Females in same-sex pairs that raised a chick sometimes acquired a male mate in the following year, but females in failed same-sex pairs never did, suggesting that males exert sexual selection by assessing female quality and relegating low-quality females into same-sex pairs. Sexual selection by males in a monomorphic, non-ornamented species is rare and suggests that reconsideration is needed of the circumstances in which alternative reproductive behaviour evolves. Given the lack of males and obligate biparental care in this species, this research demonstrates how same-sex pairing was better than not breeding and highlights how it could be an adaptive strategy under certain demographic conditions.

Juvenile survival, recruitment, population size, and effects of avian pox virus in Laysan Albatross (Phoebastria immutabilis) on Oahu, Hawaii, USA

ABSTRACT Understanding population dynamics and determining conservation priorities in long-lived species with delayed breeding often is hampered by lack of information about younger age classes. Obtaining accurate estimates of juvenile survival and recruitment can be difficult because young individuals are infrequently observed. We used mark–recapture models to estimate age-specific survival, recruitment, population size, and encounter probability of Laysan Albatrosses (Phoebastria immutabilis) using a 14-yr dataset from Oahu, Hawaii, USA. We also measured the long-term effect of avian pox virus (Poxvirus avium) on the survival and recruitment of albatrosses infected as nestlings. Survival of juvenile albatrosses during the first year after fledging was 0.757 ± 0.042. We were able to estimate juvenile survival, the first such estimate in any long-lived seabird, because our high search effort revealed that some birds began visiting the natal colony at the age of 1 yr. The survival of prebreeders increased rapidly and reached a value in the second year (0.973 ± 0.008) that was similar to the survival of breeding adults (0.973 ± 0.017). The average age of first return to the natal colony was 4.24 ± 0.11 yr. The average age at first breeding was 8.44 ± 0.15 yr, with recruitment probability peaking at ages 9–10 yr and a single bird being recruited into the breeding population at the age of 4 yr. Pox virus decreased survival in the first year by 4%–13% and decreased recruitment probability up to age 12 by 4%–26%, depending on the severity of infection. The total size of the Laysan Albatross population on Oahu in 2015 was 555 birds, consisting of 270 active breeders, 231 prebreeders, and 54 birds that likely skipped breeding that year. The number of prebreeders constituted an average of 44% of the total population. These demographic estimates will be useful for population modeling exercises involving various threat and management scenarios, and for examining environmental factors that influence demography.

Data loggers in artificial eggs reveal that egg-turning behavior varies on multiple ecological scales in seabirds

ABSTRACT In most avian species, egg-turning behavior during incubation is vital for proper embryonic development and hatching success. However, changes in turning behaviors are rarely studied across different temporal scales (e.g., day–night or across incubation phases), though the timing of incubation behaviors affects reproductive success. We used data loggers encapsulated in artificial eggs to measure turning rates and angle changes of eggs in Western Gull (Larus occidentalis) and Laysan Albatross (Phoebastria immutabilis) nests. We examined diurnal and daily cycles in egg-turning behaviors across early, middle, and late incubation phases. Our results indicate that (1) egg-turning behaviors remain similar throughout incubation, resulting in a consistent environment for developing chicks; (2) egg-turning rates and angle changes vary according to diurnal cycles and day length in each species; and (3) egg-turning rates, but not angle changes, were similar between species. Egg-turning behaviors may vary among species according to seasonality and geography, and using consistent methodologies to measure egg turning will further clarify the role of egg turning in avian life history and ecology.