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North Falmouth, MA, United States

Nisbet I.C.T.,I. C. T. Nisbet and Company | Wingate D.B.,P.O. Box CR 86 | Szczys P.,Eastern Connecticut State University

A small, isolated population of Common Terns (10-30 pairs) has bred at Bermuda since at least the 1920s. In September 2003, a hurricane eliminated all the adult males; only females returned in 2004 and these paired together and laid clutches of threeseven infertile eggs. The breeding population was re-established in 2005-06 by four adult males that had been too young to breed in 2003-04. These males paired with females that were probably young and bred with high success (mean 2.6 fledged chicks/pair) through 2009. Two males apparently each mated with two females to form productive trios. The old females continued to pair together and lay infertile eggs, even though males were raising chicks on the same islets. Consequently, the effective population size at the 'bottleneck' was only four males and four females. Although the population is now increasing rapidly, it remains critically endangered. Source

Arnold J.M.,Pennsylvania State University | Nisbet I.C.T.,I. C. T. Nisbet and Company | Oswald S.A.,Pennsylvania State University
Journal of Animal Ecology

Post-natal growth is an important life-history trait and can be a sensitive indicator of ecological stress. For over 50 years, monotonic (never-decreasing) growth has been viewed as the predominant trajectory of post-natal mass change in most animal species, notably among birds. However, prevailing analytical approaches and energetic constraints may limit detection of non-monotonic (or multiphasic), determinate growth patterns, such as mass recession in birds (weight loss prior to fledging, preceded by overshooting adult mass), which is currently believed to be restricted to few taxa. Energetic surplus and shortfall are widespread conditions that can directly influence the degree of mass overshooting and recession. Thus, we hypothesize that in many species, prevailing energetic constraints force mass change away from a fundamental non-monotonic trajectory to instead follow a monotonic curve. We observed highly non-monotonic, mass change trajectories (overshooting adult mass by up to almost 20%) among common tern Sterna hirundo chicks, a well-studied species long-established as growing monotonically. We quantified the prevalence and magnitude of non-monotonic mass change prior to fledging for 313 common tern chicks that successfully fledged from two discrete populations in multiple years. We used a new approach for analysing non-monotonic curves to examine differences in mass change trajectories between populations under contrasting abiotic (freshwater vs. saltwater) and biotic stresses (low rates of food provisioning). Some degree of mass recession occurred in 73% of all study chicks. Overshooting adult mass followed by extensive mass recession was most prevalent at our freshwater colony, being detected among 34-38% of chicks annually. Non-monotonic trajectories were less marked in populations experiencing ecological stress and among lower quality individuals. Chicks that were provisioned at higher rates were more likely to both overshoot adult mass and experience subsequent mass recession. Our results in common terns provide strong support for the hypothesis that non-monotonic trajectories are the fundamental pattern of mass change but are constrained to be monotonic under energetic shortfall. This justifies future tests of the generality of this hypothesis across a broad range of taxa. We also demonstrate a recent analytical tool that prevents routine fitting of monotonic curves without prior investigation of non-monotonic trends. © 2016 British Ecological Society. Source

Heidinger B.J.,University of Glasgow | Chastel O.,CNRS Chize Center for Biological Studies | Nisbet I.C.T.,I. C. T. Nisbet and Company | Ketterson E.D.,Indiana University Bloomington
Functional Ecology

Reproductive success often increases with age; however the mechanisms underlying this commonly observed pattern are poorly understood. One mechanism that may be important is a set of physiological responses (the stress response) that allows organisms to evade and cope with stressors, but often inhibits reproduction. If older parents respond less strongly to stressors than younger parents, this age-related difference in the stress response may contribute to the higher reproductive success that often characterizes older parents. Typically the stress response is measured as an increase in plasma glucocorticoid (CORT) concentration, and we have previously reported that stress-induced CORT levels decline with age in the common tern (Sterna hirundo). Another hormone, prolactin (PRL), has been reported to decrease in response to stressors in breeding birds and is often positively associated with parental behaviour. We predicted that like the CORT stress response, the PRL stress response would also be suppressed with age. To test this prediction, we captured known-age, incubating common terns ranging in age from 3 to 29 years and measured stress-induced changes in PRL and CORT levels within the same individuals. We found that PRL levels decreased less rapidly in response to capture and restraint stress in older than in younger parents. In these same birds, we also found that stress-induced maximum CORT levels decreased with age, which is consistent with what we have previously reported for this species. Measures of PRL and CORT were not, however, correlated within individuals. Taken together, these results support the hypothesis that modulations of both the PRL and CORT stress response are flexible hormonal mechanisms that help to account for the increase in reproductive success that occurs with age. © 2010 The Authors. Journal compilation © 2010 British Ecological Society. Source

Oswald S.A.,Pennsylvania State University | Nisbet I.C.T.,I. C. T. Nisbet and Company | Chiaradia A.,Phillip Island Nature Parks | Arnold J.M.,Pennsylvania State University
Methods in Ecology and Evolution

1. Nonlinear, parametric curve-fitting provides a framework for understanding diverse ecological and evolutionary trends (e.g. growth patterns and seasonal cycles). Currently, parametric curve-fitting requires a priori assumptions of curve trajectories, restricting their use for exploratory analyses. Furthermore, use of analytical techniques [nonlinear least-squares (NLS) and nonlinear mixed-effects models] for complex parametric curves requires efficient choice of starting parameters. 2. We illustrate the new R package FlexParamCurve that automates curve selection and provides tools to analyse nonmonotonic curve data in NLS and nonlinear mixed-effects models. Examples include empirical and simulated data sets for the growth of seabird chicks. 3. By automating curve selection and parameterization during curve-fitting, FlexParamCurve extends current possibilities for parametric analysis in ecological and evolutionary studies. Video. Video © 2012 The Authors. Methods in Ecology and Evolution © 2012 British Ecological Society. Source

Hatch J.J.,University of Massachusetts Boston | Nisbet I.C.T.,I. C. T. Nisbet and Company

Manipulation of clutch size during incubation has been used in a number of studies to investigate life-history costs of incubation. We increased or decreased clutches of Common Terns Sterna hirundo during incubation and measured subsequent chick growth and productivity. Our results provide little support for the hypothesis that costs of incubation in Common Terns are substantially affected by the number of eggs incubated. © 2010 The Authors. Journal compilation © 2010 British Ornithologists' Union. Source

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