Brian G. Palestis

Common Tern (Sterna hirundo) chicks are highly mobile, as they are semi-precocial. However, they generally stay in the territories near their nests until soon after fledging. In the salt marsh-breeding population in Barnegat Bay, New Jersey, USA, Common Tern chicks were recorded far from their nests before fledging. Movements from the nest were quantified at two islands in Barnegat Bay. For the first 1-3 days, chicks stayed very close to the nest. By 4 to 6 days of age, no chicks were within the nest cup, but they typically remained nearby, at a median distance of 0.45 m from the nest. From 1 to 3 weeks of age, median distance from the nest steadily increased from about 1 to 4 m. Among those chicks older than 3 weeks, the median distance away from the nest was 6.45 m, and none were found closer than 1.75 m. Common Tern chicks older than one week were usually not present in their territories, despite continuing to rely on their parents for care. The contrast between this and previous studies of the Common Tern may relate to habitat differences.

Common Tern Sterna hirundo populations have declined in the southern portion of their breeding range along the Atlantic coast of the United States. The Barnegat Bay (New Jersey, USA) population has been declining, with sea-level rise increasing the frequency of flooding of salt marsh islands believed to be a contributory factor. Productivity is typically very poor, relative to studies undertaken elsewhere, and a previous analysis suggested permanent emigration of breeding adults out of Barnegat Bay. At Pettit Island, a long-term study site in the bay, the number of ringed chicks recaptured as adults was extremely low, even when accounting for mortality prior to fledging. Of 1,314 chicks ringed at Pettit Island from 2006 to 2014, only 23 were recaptured as adults at Pettit from 2010 to 2017 (1.8%, or 3.9% of presumed fledglings). Correcting for the proportion of adults captured, recruitment by four years of age was estimated at 8.1 to 9.3% of fledglings, or 3.5 to 4.0% of all chicks. Recruits comprise a small percentage of breeders in the colony. Of 34 adults captured in 2016, 10 were previously ringed and only three of these had been ringed as chicks (8.8% of total, 30% of ringed birds). It is unlikely that the small number of returns at Pettit Island simply reflects natal dispersal within the bay, because no terns ringed as chicks at Pettit Island were recaptured as young breeders at other colonies. Whether poor recruitment reflects low postfledging or subadult survival, or emigration out of the population is unknown.

Fluctuating asymmetry (FA), random deviation from perfect bilateral symmetry, is an indicator of developmental stability. Examining the ontogeny of FA can illustrate whether symmetry is actively maintained as the organism grows or breaks down as perturbations accumulate with age. Previous studies of changes in human FA with age have been cross-sectional studies and give conflicting results. We analyzed data from a longitudinal study of bodily FA in Jamaicans, using a composite index of seven paired traits. In addition, 288 children (ages 5–12) were first measured in 1996, and many were re-measured in 2002 and 2006 (maximum age = 22 years). Both within-individual longitudinal comparisons and between-individual comparisons across age groups demonstrate changes in FA with age. In males and females, FA increased until around age 13, but the pattern of change differed between the sexes. In males, FA increased rapidly approaching adolescence and then slightly declined into early adulthood. The increase in female FA was more gradual and then leveled off. The patterns observed likely reflect accumulation of developmental errors over time, rapid physical changes during puberty (especially in boys), and then regulation of symmetry when transitioning into adulthood. Although most changes in symmetry over time probably reflect random processes, the magnitude and direction of asymmetry in an individual at one point in time tended to be positively (though weakly) related to asymmetry in later years, pointing to underlying differences among individuals in developmental stability.

The population of Common Terns (Sterna hirundo) in Barnegat Bay, New Jersey, USA, has recently experienced poor productivity with complete or near-complete breeding failure at multiple colonies, and the number of breeding pairs has declined. Adult Common Terns were captured and banded at Pettit Island from 2010 through 2014 and at four additional islands from 2011 through 2014. Although the number of breeding pairs on Pettit Island decreased and reproductive success was generally poor, this colony was more productive than the other colonies. Data from the other colonies were too sparse to treat each site separately, and the analysis is instead based on two “locations”: Pettit Island and all other sites. Apparent survival and movement probabilities were estimated using multistate capture-recapture modeling based on recaptures combined with resighting of color-banded Common Terns. The two best supported models included location, transience, and presence or absence of color bands as variables and produced very similar parameter estimates. Adult survival at Pettit Island was estimated at approximately 0.88, which is within the range of previous estimates for Common Terns. Survival estimates for the other sites had high uncertainty but appeared to be very low, at approximately 0.71. There was no evidence that apparent survival changed across time (2010–2012 compared to 2012–2014). Movement probabilities suggest a frequency of breeding dispersal within Barnegat Bay above 6%. Detection probabilities were much higher for color-marked birds than for those with metal bands only. Low apparent survival and decreases in the number of adults probably reflect permanent emigration out of the study area. The most likely cause of this decline in the Barnegat Bay population is frequent flooding due to sea level rise and severe storms.

Behavioral research has long had an important role in the conservation of terns (Aves: Sternidae). Habitat management and restoration of breeding colony sites depends on knowledge of the cues used to select colony and nest sites. For example, conspecific attraction with playback and decoys is commonly used to bring terns to suitable colony sites and habitat modification is often used to increase the availability of suitable nest sites. Tern colonies are interconnected by dispersal, and a metapopulation approach is needed for effective management. Population dynamics are therefore affected by behaviors that influence the frequency of movement among colony sites: site fidelity, natal and breeding dispersal, and group adherence. The monogamous breeding system of terns should keep effective population size similar to census population size, but variation in sex ratios (likely resulting from sex differences in behavior) and in parental quality can result in a smaller than expected effective population size. In addition to the behavior of terns, knowledge of the behavior of predators on terns contributes to management plans, because predator behavior can sometimes be manipulated and predation is often performed by only a few specialized individuals. Other examples of links between tern behavior and conservation are also briefly reviewed, such as behavioral toxicology research and studies of behavioral responses to human disturbance and manmade structures. More work is needed on the behavior of migratory terns at staging sites, stopover sites and wintering grounds, and on the behavior of less well-studied species and species in less well-studied geographic regions [Current Zoology 60 (4): 500–514, 2014].

Feather sampling is often assumed to be harmless, but this assumption has not been tested. From 2008–2012, we recorded the behavior of 340 Common Tern (Sterna hirundo) chicks following the removal of a pinch of body feathers. Only 11.2% of these chicks ran after sampling and 69.4% showed no visible reaction to sampling. The probability of a chick running away increased with age. We therefore recommend that sampling be conducted as soon as possible after juvenal feathers emerge. There was evidence for individual differences in behavior: approximately 71% of chicks that ran after feather sampling also ran away when re-encountered on later dates, while other chicks rarely did so. We found no evidence that removal of feather samples increased chick mortality, supporting the assumption that this technique is minimally invasive, but small differences in mortality rates would have been difficult to detect.

Ethanol (EtOH) often has stimulatory effects at low doses and inhibitory effects at high doses, affecting behavior and physiology of many organisms in a non-linear manner suggestive of hormesis. Zebrafish ( Danio rerio) shoaling was studied in adult fish exposed to one of five different EtOH concentrations (v/v): 0.0% control, 0.125%, 0.25%, 0.5%, and 1.0%. Digital photographs of groups of four fish were taken every 2 min, with each trial lasting a total of 12 min. The median nearest neighbor distance and shoal area were calculated for each photograph. Exposure to 1.0% EtOH inhibited shoaling. In contrast, as predicted from hormesis, shoaling was significantly tighter (as measured by nearest neighbor distance) at low concentrations (0.125%, 0.25%) compared to the control, and a J-shaped dose-response curve was present. A similar pattern occurred for shoal area, but in this case the only statistically significant differences were between the high concentration and all others.