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IBIS  |  Volume 158  |  Issue 2  |  April 2016

The latest issue of IBIS features 16 full papers and two short communications, plus our usual extensive book review section. Here are some of the many highlights.

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A review of survival estimates for raptors and owls 
Ian Newton, Michael J. McGrady & Madan K. Oli
Raptors and owls comprise a model group in the study of population dynamics and lifetime reproductive success. A key demographic in such studies, and one that is difficult to estimate accurately in the field, is annual survival. In the first review of its kind, leading raptor ecologist Ian Newton and colleagues provide an overview of the various methods used to estimate the survival rates of raptors and owls and the strengths and weaknesses of each. They then pull together a large number of published estimates of survival in this group of species in order to identify the main underlying patterns. This analysis reveals that there is a significant tendency for annual adult survival to increase with body weight, that there is a lower survival in the first or pre-breeding years of life than in subsequent years, that there is a lack of obvious or consistent differences in survival between the sexes, where these could be distinguished; and that in the few species for which enough data were available, there was evidence of a decline in annual survival rates in the later years of life. This review is set to be a seminal reference on this important topic for many years to come.

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Carry-over effects provide linkages across the annual cycle of a Neotropical migratory bird, the Louisiana Waterthrush Parkesia motacilla 
Steven C. Latta, Sonia Cabezas, Danilo A. Mejia, Maria M. Paulino, Hodali Almonte, Cassandra M. Miller-Butterworth & Gary R. Bortolotti 
Population models of migratory birds have sought to include impacts from events across the full annual cycle; what happens on the breeding grounds can affect a bird’s survival or behaviour on the wintering grounds and vice versa. Previous work has shown that events occurring in winter result in some individuals arriving on the breeding grounds earlier or in better physical condition than others, thereby affecting reproductive success (carry-over effects). However, evidence for carry-over effects from breeding to wintering grounds has been shown less often. In a remarkable study of Louisiana Waterthrushes breeding in North America and wintering in the Dominican Republic, Steve Latta and colleagues find that birds with lower levels of the stress hormone corticosterone in their feathers, indicating lower stress levels on the breeding grounds where the feathers were grown, occupied better winter territories and were in better body condition than birds with higher stress hormone levels. These birds were also more likely to survive to return the following year. Together these data suggest a carry-over effect from the breeding grounds to the wintering grounds that is further extended to annual return rates. Very few other studies have linked conditions during the previous breeding season with latent effects during the subsequent overwintering period or with annual survival.

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Pre-breeding survival of Roseate Terns Sterna dougallii varies with sex, hatching order and hatching date
Ian C. T. Nisbet, David Monticelli, Jeffrey A. Spendelow & Patricia Szczys
In most bird species, and particularly in threatened populations, males tend to outnumber females. However, female-biased sex ratios are found in many species of gulls and terns, and in these species males can be the limiting resource because biparental care is required for successful reproduction. In a long-term study of Roseate Terns in Massachusetts, USA, Ian Nisbet and colleagues find that pre- breeding survival (from fledging to age 3 years) was lower in males than in females, but only among B-chicks (second in hatching order). Pre-breeding survival also declined with hatching date. The proportion of females in this cohort increased from 54.6% at hatching to 56.2% at fledging and to an estimated 58.0 % among survivors at age three years. This was more than sufficient to explain the degree of skew in the sex ratio of the adult population.

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First report of “mining” as a feeding behaviour among Australian manna-feeding birds 
Samuel B. Case & Amanda B. Edworthy
The Forty-spotted Pardalote Pardalotus quadragintus is an endangered songbird endemic to the forests of Tasmania, Australia, where it forages almost exclusively in the foliage of White (or Manna) Gums. Now Samuel Case and Amanda Edworthy explain this rare dependence of a bird on a single tree species, showing that the pardalote is in fact a manna ‘miner’ that uses a specially adapted bill to pierce leaf stalks and collect the manna (plant sap rich in nutrients) that is exuded; this is by far the most important item in their chicks’ diet. Case and Edworthy used a model pardalote bill to try to stimulate manna production from other tree species, without success. Although many species feed opportunistically on manna, this is the first record of an Australian bird actually ‘mining’ it. The results reveal the conservation importance of White Gums to this globally threatened bird.


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Advances in avian tracking methods

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