Jeremy J. Hatch

Age-related changes in efficiency among breeding Common Terns Sterna hirundo: measurement of energy expenditure using doubly-labelled water

We used doubly-labelled water to measure field metabolic rates of breeding Common Terns Sterna hirundo, and hence to investigate differences in reproductive efficiency among birds of different ages. Field metabolic rates, activity patterns, changes in body mass, chick provisioning rates, and chick growth rates were measured for 14 males of known age (6-24 yr) during a 48-h period immediately after hatching of the first chick, when males provide most of the food. Males expended energy at high rates (3.3-6.3 x estimated basal metabolic rates). We found no significant relationship between male age and energy expenditure. Some aspects of male performance (feeding rates and food provisioning rates) were age-related due to changes in efficiency. Efficiency in the use of time and energy was low in the youngest breeding males, increased thereafter to peak at about 12 years of age, but appeared to decline again amongst the oldest breeding males. Changes in body mass and measures of activity were not correlated with energy expenditure and hence were not appropriate measures of reproductive effort.

Characteristics and Performance of Common Terns in Old and Newly-established Colonies

Abstract In 1999, we compared demographic and biological parameters in Common Terns (Sterna hirundo) among three colonies located 10-26 km apart in Buzzards Bay, Massachusetts, USA. The three colony sites differed primarily in size, number of pairs, and length of occupancy by terns: Penikese Island (8 ha, 132 pairs, 3 yr), Ram Island (1.1 ha, 1,900 pairs, 8 yr), Bird Island (0.6 ha, 1,800 pairs, >65 yr). This study compared parental ages and origins, nesting phenology, clutch-size, chick growth rates, productivity, chick diets, feeding rates and foraging trip times among the three colonies. Common Terns breeding at the new colony on Penikese Island were significantly younger (mean age 6.8 yr) and laid later (mean laying date 25 May), had higher productivity (2.2 fledged chicks/pair) and higher chick growth rates than those at the old colony on Bird Island (means 11.7 yr, 20 May, 0.8 chicks/pair, respectively). Feeding rates were highest and foraging trip times for all types of prey were shortest at Penikese Island. Birds at Ram Island were intermediate in all these respects. Although productivity of Common Terns at Bird Island was relatively low during the period in which the other two colonies were established (1992-1999), both breeding adults at Bird Island and chicks raised there have been very slow to move to the other colonies, which were colonized mainly by immigrants from outside the region.

Temporal variation in adult survival rates of Roseate Terns during periods of increasing and declining populations

Abstract We used 19 years of mark-recapture/resighting data collected on 11,020 birds from 1988-2006 at five colony sites in Massachusetts, New York, and Connecticut, USA, to examine temporal variation in the survival rates of adult Roseate Terns (Sterna dougallii) during periods of overall population increase (1988-2000) and decline (2000-2006). Roseate Terns nested at only one colony site in Buzzards Bay, Massachusetts at the start of this period, but two more sites in this area were recolonized as the study progressed. Adult survival rates varied temporally in different ways at the different colony sites, but for the five sites combined they did not differ between the period of overall population increase (0.835 ± 0.006 SE) and the period of population decline (0.835 ± 0.008 SE). As expected based on previous work, adult survival from 1991 to 1992 was lowered as a result of a severe hurricane in August 1991. An oil spill in Buzzards Bay in April 2003 did not appear to result in lower survival of the birds nesting at the sites in this area compared to those nesting at the other two study sites in New York and Connecticut. Temporal variation in other vital rates of this species (such as postfledging survival) needs to be examined to determine the likely cause(s) of the recent population decline.

Hematology and Absence of Hemoparasites in Breeding Common Terns (Sterna hirundo) from Cape Cod, Massachusetts

Abstract In June and July 1995, 98 breeding common terns (Sterna hirundo) were captured, weighed, and bled as a part of ongoing research on the population health and reproductive biology of this species of special concern. Packed cell volume, total and differential white blood cell counts, and blood smears were obtained. Blood smears from 75 terns were examined. No hemoparasites were found. There were some significant differences among hematologic parameters in birds from different islands, and between birds nesting earlier versus later in the season, but there were no significant differences associated with body mass, sex, or age. The absence of hemoparasites in the blood smears of these terns is noteworthy, especially because other studies of seabirds (including Charadriiformes) have revealed low prevalences of hematozoa.

Responses of Known-aged Common Terns to Experimental Shortening of the Wings

Abstract Fourteen male Common Terns (Sterna hirundo) of known age (3-21 yr) were handicapped by shortening their wings early in the incubation period, and were then followed through chick-raising. The study was conducted at Bird Island, Massachusetts, USA, in 1996, a year when chick growth and survival appeared to be limited by food availability. Chick growth and survival were used as indirect measures of allocation of resources to current reproduction. Rates of change of body-mass and feather re-growth (ptilochronology) were used as indirect measures of allocation of resources to self-maintenance. The birds’ mates were studied similarly, but were not handicapped. Experimental birds and pairs were compared to controls matched for laying date and clutch-size. Handicapped males re-grew tail-feathers pulled for ptilochronology significantly more slowly than controls. They and their mates raised significantly more young than controls. Older handicapped males lost more body-mass during chick-raising than their matched controls, whereas younger males lost less. These results conflict with the prediction of life-history theory that long-lived birds faced with increased costs of reproduction should allocate these costs to their offspring rather than to themselves. However, we point out several problems in using handicapping to test such predictions. The assumed effects of handicapping on the cost of flight and on foraging ability have not been verified or measured. Changes in reproductive effort are not measured directly, and the end points that have been investigated are often ambiguous. The assumption that older individuals consistently have lower residual reproductive value than younger individuals may be incorrect if there is selective survival of high-quality individuals within the study population.

Differences in Foraging Performance between Juvenile and Adult Roseate Terns at a Pre-Migratory Staging Area

-Complex foraging skills may be acquired slowly and may therefore improve with age and experience. This note compares foraging proficiency of adult Roseate Terns (Sterna dougallii) to that ofjuveniles aged eight to ten weeks (still being fed by parents) at a pre-migratory staging area located on Nantucket Island, MA, USA. Adults used high plunge dives exclusively, while juveniles used four different dive types. Adults were statistically superior foragers. Juveniles had a lower capture rate (0.27 prey captures/min) and were less successful (0.15 prey captures/ attempt) than adults (0.98 prey captures/min; 0.52 prey captures/attempt). These data are discussed in light of extended parental care in Roseate Terns. Received 29 August 1999, accepted 8 September 1999.

Post-fledging brood and care division in the roseate tern (Sterna dougallii)

Extended post-fledging parental care is an important aspect of parental care in birds, although little studied due to logistic difficulties. Commonly, the brood is split physically (brood division) and/or preferential care is given to a subset of the brood by one parent or the other (care division). Among gulls and tern (Laridae), males and females generally share parental activities during the pre-fledging period, but the allocation of parental care after fledging is little documented. This study examined the behaviour of male and female roseate terns (Sterna dougallii) during the late chick-rearing and early post-fledging periods, and in particular the amount of feeds and the time spent in attendance given to individual chicks/fledglings. Pre-fledging parental care was biparental in all cases. Post-fledging parental care was dependent on the number of fledglings in the brood. Males and females continued biparental care in clutches with one surviving fledgling, while in two-fledgling clutches, males fed the A-fledgling while females fed the B-fledgling. Overall, there was no difference in attendance, only in feeds. This division of care may be influenced by the male only being certain of the paternity of the A-chick but not by chick sex.

Effect of intraspecific interactions on seasonal decline in productivity of Common Terns Sterna hirundo

Capsule Kleptoparasitic activities of older chicks from earlier nests did not contribute to late reproductive declines. Aims To determine whether intraspecific interactions, such as kleptoparasitism and aggression, were experienced more frequently by birds breeding late in the season as a result of exposure to breeders at a more advanced stage. If so, to investigate whether this was the cause of the observed seasonal decline in reproductive parameters observed at Bird Island, where nesting density is high and interactions are more probable. Methods Plots were fenced within the colony, exploiting natural variability in distribution of early and peak breeders to create two treatments: plots with only late-laying terns and those with a mixture of early-, peak- and late-layers. Hatching success, productivity and the growth and survival of chicks were measured for all late-laying pairs. Intraspecific interactions, adult attendance and provisioning of chicks were recorded during 9600 minutes of nest observations made within two periods: a few days after hatching and one week later. Results The frequency of intraspecific interactions was maintained by the kleptoparasitic activities of older chicks within the mixed-laying-date treatment and was significantly lower in plots containing only late breeders with chicks of similar ages (mean 11.0 days). The overall rate was rarely greater than two interactions per nest per hour and there was no corresponding reduction in the growth or survival of chicks from late nests or any change in the provisioning activities of late-breeding adults. Conclusion Increased frequency of intraspecific interactions experienced by late breeders in the presence of early-breeding conspecifics resulted from the kleptoparasitic activities of older chicks but was not sufficient to contribute to the observed seasonal reproductive decline at this dense breeding colony.

Morphometric Sexing of Northwest Atlantic Roseate Terns

Abstract.— A difficulty in the study of monomorphic species is the inability of observers to visually distinguish females from males. Based on a sample of 745 known-sex birds nesting at Bird Island, MA, USA, a discriminant function analysis (DFA) was used to sex Roseate Terns (Sterna dougallii) of the Northwest Atlantic population using morphological measurements. DFA using only the total length of the head (including the bill) correctly identified the sex of approximately 86% of the terns, which increased to 88% if both members of a pair were measured. Including additional measurements increased these percentages slightly, to 87% and 90%, respectively. These levels of accuracy are generally higher than those reported for other species of terns. Because female-female pairs are frequent in this population, one cannot assume that the member of a pair with the larger head is a male, and additional discriminant functions were developed to help separate female-female from male-female pairs.

Piracy at the nest: factors driving kleptoparasitic behaviour of Common Tern Sterna hirundo chicks

Abstract. Stealing of provisioned food items by adult conspecifics (intraspecific kleptoparasitism or piracy) is common among birds, can reduce breeding success and may be one disadvantage of colonial breeding. Theft by chicks from neighbouring broods has rarely been quantified but may have similar reproductive consequences and the factors that influence it require further study. We took advantage of unusually diverse weather during the critical early stages of growth to elucidate the factors driving kleptoparasitic behavior of Common Tern Sterna hirundo chicks. Kleptoparasitism was restricted to misty days when large chicks were fed much smaller fish than on other days, inducing them to steal from neighbouring broods with young chicks. Our study indicates that kleptoparasitism by chicks could be a way to overcome shortfalls in parental provisioning, and may be a net cost of colonial breeding. Our results both provide evidence of a potential mechanism behind food-stealing by chicks and suggest hypotheses for future testing.