Tern Colony Research Articles

Fluctuating Breeding of Arctic Terns (Sterna paradisaea) in Arctic and High-Arctic Colonies in Greenland

Abstract. Arctic Terns show large variations in colony attendance between breeding seasons, making comparable counts of colony size complex and population status estimates difficult. Here, three areas in two regions of Greenland were surveyed in consecutive breeding seasons between 2002 and 2009. Between-year variation in population size in the small and mid-sized Arctic Tern colonies in West Greenland was considerable (mean CV of individual colonies 117.5%, CV of total 49.6%). In the largest colony in Greenland, Kitsissunnguit, overall colony size showed minor variations (CV 14.6%), but variation in numbers was pronounced at the sub-colony level (mean CV 47.4%). When combining the surveyed colonies in West Greenland, the total population size varied little (CV 6.7%) and less than expected if colonies fluctuated independently (P = 0.023), indicating that local movements between the colonies took place and annual variation was linked to local rather than to large-scale phenomena. In Northeast Greenland, co...

Recovery of Coded Wire Tags at a Caspian Tern Colony in San Francisco Bay: A Technique to Evaluate Impacts of Avian Predation on Juvenile Salmonids

AbstractWe recovered coded wire tags (CWTs) from a colony of Caspian terns Hydroprogne caspia on Brooks Island in San Francisco Bay, California, to evaluate predation on juvenile salmonids originating from the Sacramento and San Joaquin rivers. Subsamples of colony substrate representing 11.7% of the nesting habitat used by the terns yielded 2,079 salmonid CWTs from fish released and subsequently consumed by terns in 2008. The estimated number of CWTs deposited on the entire tern colony was 40,143 (ranging from 26,763 to 80,288), once adjustments were made to account for tag loss and the total amount of nesting habitat used by terns. Tags ingested by terns and then egested on the colony were undamaged, and the tags’ complete numeric codes were still identifiable. The CWTs found on the tern colony indicated that hatchery Chinook salmon Oncorhynchus tshawytscha trucked to and released in San Pablo Bay were significantly more likely to be consumed by Caspian terns than Chinook salmon that migrated in‐river to the bay; 99.7% of all tags recovered were from bay‐released Chinook salmon. Of the CWTs recovered on the tern colony, 98.0% were from fall‐run Chinook salmon, indicating a higher susceptibility to tern predation than for the spring run type. None of the approximately 518,000 wild Chinook salmon that were coded‐wire‐tagged and released in the basin were recovered on the tern colony, suggesting that the impacts on wild, U.S. Endangered Species Act–listed Chinook salmon populations were minimal in 2008. Overall, we estimate that 0.3% of the approximately 12.3 million coded‐wire‐tagged Chinook salmon released in the basin in 2008 were subsequently consumed by Caspian terns from the Brooks Island colony. These results indicate that CWTs implanted in juvenile salmon can be recovered from a piscivorous waterbird colony and used to evaluate smolt losses for runs that are tagged.Received January 25, 2010; accepted December 13, 2010

Long Term Decline of a Common Tern (Sterna hirundo) Population Nesting in Salt Marshes in Venice Lagoon, Italy

Each year between 1989 and 2008, I monitored Common Tern colonies in the lagoon of Venice (Italy). This population nests only on salt marsh islets, which are subjected to flooding during high tides. The number of breeding pairs decreased significantly from 832 to 109, with an average rate of decrease of −10.1%. Overall, 188 colonies were found, ranging from two to 583 pairs; median colony size was 57 pairs, and it decreased significantly. The mean turnover rate was high at 41.5%, and it ranged each year between 7.7% and 60%. The observed trends could be attributed to the increase in mean sea level that occurred over the last 20 years (0.5 cm/yr). In the May–June period, the number of days with high tides leading to a complete flooding of the breeding site increased. Between 1989 and 1998 there was on average 4.4 days with floodings. This increased to 8.4 days between 1999 and 2008. Therefore, sea level rise could be a major contributor to declining Common Tern populations in the lagoon of Venice.

Roseate Terns Sterna dougallii successfully rearing a young Sandwich Tern S. sandvicensis

Isle aux Dames in the Bay of Morlaix, northern Brittany (48°41’N 3°53’W), holds one of the largest mixed tern colonies in France, with Sandwich Terns Sterna sandvicensis, Roseate Terns S. dougallii and Common Terns S. hirundo, and this island has been the main French Roseate Tern colony since the 1980s (Cadiou et al. 2004; Le Nevé 2005). Annual surveys are conducted to obtain data on breeding numbers and productivity. In 2007 the census of the colony was carried out on 12 June by a team of eight experienced and inexperienced people. Different teams covered different areas of the colony, counting nests, using different colour of small paper marks put inside to avoid double-counting, and reporting nest-contents.

Aggression by adult South American Terns toward conspecific chicks

Infanticide and nonfatal aggression by adults toward unfamiliar chicks have been widely reported in colonial birds, and can be an important cause of chick mortality. We studied intraspecific aggression by adults toward chicks at a South American Tern (Sterna hirundinacea) colony in Patagonia, Argentina, during 2005 to characterize this behavior, evaluate its relationship with nesting density, chick age and microhabitat characteristics, and assess its effect on breeding success. Of 111 chicks in the study area, 45% were attacked at least once. Chicks older than 9 d posthatching were more likely to be attacked than younger chicks, and unattended chicks were more likely to be attacked than guarded chicks (88 vs. 12%). Chicks were also attacked more often when in their own territories (76% of cases), but were less likely to be attacked in territories with more vegetation cover and high-quality shelters (i.e., vegetation with characteristics that prevented adults from reaching chicks). The number of aggression events was not related to nest density. At least 8% of the chicks in our study area died as a result of adult intraspecific aggression. Our results indicate that intraspecific aggression by adult South American Terns toward chicks is relatively common in the Punta Loma colony and should not be underestimated as a factor affecting their breeding success.

Distribution and abundance of nesting common and Caspian terns on the North American Great Lakes, 1976 to 1999

Canadian and US federal wildlife agencies completed three surveys (1976–1980, 1989–1991, and 1997–2000) to census colonial waterbirds breeding on the Great Lakes. We here summarize and comment on nest numbers and colony site distribution of common terns ( Sterna hirundo) and Caspian terns ( Hydroprogne caspia). Common terns are in serious trouble on the Great Lakes. Numbers declined with substantial losses in nests (− 19.1%) and colony sites (− 23.2%) between the first and third censuses. An increase in numbers at US sites (+ 26.6%) did not compensate for losses (− 33.1%) at Canadian sites. Caspian terns increased in nest numbers (+ 65.9%) and colony sites (+ 50.0%) over the same period. The increase at US sites (136.5%) was greater than at Canadian sites (11.5%). Most (70.7%, n = 186) common tern sites had nests during only one census; 17 sites (6.5%) had nests during all censuses. In contrast, 9 of 33 (27.2%) Caspian tern sites had nests during all censuses and contained a majority of nests (50–82%) in each census. Pairs of both species nested on natural substrates across the Great Lakes. Common terns nested mostly on artificial (human-constructed) substrates on the lower Great Lakes. We identify site characteristics that may have contributed to long-term (three census) occupancy by common terns (small size, artificial substrates, absence of ring-billed gulls) and Caspian terns (natural substrates on large, remote islands). We suggest an urgent need for protection and conservation of common tern colonies and identify specific priority sites for implementation of management protocols.

Are European starlings breeding in the Azores archipelago genetically distinct from birds breeding in mainland Europe?

The European starling (Sturnus vulgaris) has recently been found to eat eggs of the endangered roseate tern (Sterna dougallii) in the Azores. Azorean starlings are considered an endemic subspecies (S. vulgaris granti), so we investigated how much genetic divergence has accumulated between the Azores and other European populations in order to assess whether lethal control measures might be possible, as previous experiments have found that taste aversion is not likely to be successful. For this purpose, we sequenced a region of the protein-coding mitochondrial gene ND2 for samples from six different populations. Of the 1,026 base pairs sequenced, 19 (1.7%) were variable and formed 15 different haplotypes. The Azores had high and significant genetic differentiation from all the other populations studied. Haplotype diversity was high in the mainland populations studied, ranging from 0.767 to 0.900, but there was no variation among the Azores samples, which were collected from a geographically broad region. Given the lack of genetic variability in the Azores birds and their abundance throughout the archipelago, lethal control on a local basis and as part of an integrated control plan can be seen as a reasonable measure to protect tern colonies.

Ross's Gulls (<i>Rhodostethia rosea</i>) Breeding in Greenland: A Review, with Special Emphasis on Records from 1979 to 2007

This review summarizes breeding records of Ross’s gull in Greenland with special emphasis on the period between 1979 and 2007. The review comprises both previously published records (including some published only in Danish) and unpublished reports and breeding records from 2004 and 2006. The majority of the Greenland breeding records fall into two geographically isolated areas that differ in habitat and climate: the Disko Bay area in West Greenland and the Northeast Water Polynya in Northeast Greenland. Despite the fact that antagonistic interactions with arctic terns are common, Ross’s gulls show a nest site preference for the edge of tern colonies, suggesting breeding association between these species. A general increase in breeding records in Greenland since 1978 is most likely the result of increased ornithological effort. Successful breeding has not yet been confirmed, and a Ross’s gull fledgling remains to be seen in Greenland. The Greenland breeding records suggest an opportunistic strategy in choice of breeding site among vagrant and possibly first-time breeders.

Nesting Ecology of Red-Breasted Mergansers in a Common Tern Colony in Eastern New Brunswick

Nest-site selection and nest success for Red-breasted Mergansers (Mergus serrator) breeding on a barrier island complex (Tern Islands) with >10,000 Common Terns (Sterna hirundo) in eastern New Brunswick, Canada, were studied in 2005 and 2006. Concealment was the most important feature for nest placement as 153 of 156 nests were in dense stands of Marram Grass (Ammophila breviligulata), and overhead concealment, vegetation density and vegetation height were all greater at nests than at random locations. Apparent success for all nests was 57% and was similar between years. Few nests were depredated (N = 3), but abandonment was responsible for 95% of nest losses and was most common early in the season. Nest success was <45% for nests initiated before 25 May but >75% for nests initiated after 10 June. Nest abandonment was influenced by intraspecific nest parasitism and investigator activity. Red-breasted Mergansers selected nest sites adaptively on Tern Islands because: 1) nests were more concealed than random sites; 2) avian predation at nests in the Common Tern colony was lower than at nests on nearby islands without terns; 3) nests were not exposed to mammalian predators; and 4) nest success and nest densities were high.

Chick Survival, Fledgling Residency and Evaluation of Methods for Estimating Fledging Success in Least Terns

Fledgling counts are often used to estimate fledgling production or calculate an index of chick survival (i.e., fledging success) in the Least Tern (Sterna antillarum). Timing of counts is critical because numbers of fledglings present may be influenced by temporal patterns in fledgling departures from colonies and post-fledging mortality. The objectives of the present study were to measure chick survival and fledgling residence time (FRT) at three Least Tern colonies in Maine and examine the accuracy of single or multiple counts of fledglings for estimating fledgling production and fledging success. Chicks were color-banded at age zero to one d in 2002-2003 to estimate chick survival using mark-resighting methods and to examine relationships between fledging date and FRT. Colony sites were searched for banded chicks and fledglings every one to three d from just prior to fledging until their disappearance from the vicinity of nesting areas at three colonies. Data on numbers of banded fledglings known alive on each survey date were used to simulate single or periodic counts of banded fledglings for the purpose of comparing estimates of fledgling production and success based on count methods with known values. Chick survival estimates were 0.73, 0.74, and 0.14 for the three colonies. Fledgling residence times decreased relative to fledging date at all colonies, and the trend for maximum values of FRT, which may be an indicator of the maximum time to departure, varied from approximately 30 d in mid-July to 15 d in early to mid-August. The highest one-d counts of fledglings underestimated fledgling production by 21-30% for the two sites with high chick survival. Methods based on multiple counts also tended to underestimate fledgling production. Fledgling residency patterns limit the utility of count methods for estimating fledgling production and fledging success.

Spatial variability of seabird distribution associated with environmental factors: a case study of marine Important Bird Areas in the Azores

Abstract Amorim, P., Figueiredo, M., Machete, M., Morato, T., Martins, A., and Serrão Santos, R. 2009. Spatial variability of seabird distribution associated with environmental factors: a case study of marine Important Bird Areas in the Azores. – ICES Journal of Marine Science, 66: 29–40. The spatial structure and distribution at sea of Cory's shearwaters (Calonectris diomedea borealis), common terns (Sterna hirundo), and roseate terns (Sterna dougallii) were analysed in the Azores for various environmental factors: sea surface temperature, chlorophyll a concentration, distance to fronts, wind, distance to island shore or tern colonies, distance to seamounts, seabed slope, and depth. Data on seabird sightings were collected by observers on board fishing vessels, 2002–2006. Generalized linear modelling (GLM) explained 43 and 11% of the abundance variability for terns (both species pooled) and Cory's shearwaters, respectively. Variability in seabird abundance was mainly explained by month, wind, distance to shore and/or tern colonies, and distance to seamounts. Variogram modelling indicated that species distribution presented a small-scale spatial structure (i.e. low autocorrelation). Cory's shearwater predictive distribution maps showed widespread distribution patterns of abundance, despite occurring at a greater intensity around the islands and around some seamounts, which are areas of fishery interest. Conversely, terns were essentially concentrated near the shore. The establishment of marine important bird areas should be encouraged close to seabird colonies and around some seamount areas.

Diet of Nestling Black-crowned Night-herons in a Mixed Species Colony: Implications for Tern Conservation

Boluses were collected from Black-crowned Night-heron (Nycticorax nycticorax) nestlings in 1992 to examine the impact of night-heron predation on a restored tern colony. Boluses (n = 101) were collected from 18 nests. Fish remains occurred in 89% of nests, sand shrimp (Crangon septemspinosa) in 50%, birds in 28%, and amphibians in 16% of nests sampled; mammalian, eel, squid, and marine invertebrate remains were also noted. Regurgitated bird remains were found in five nests and included four species, Common Terns (Sterna hirundo), Common Eiders (Somateria mollissima), Gulls (Larus sp.), and the legs of an unknown wading bird. Nestling night-herons from three nests were fed tern chicks, but 92% of tern chicks known to have been eaten were fed to nestling Black-crowned Night-herons in one nest. No tern chicks fledged in 1992 and night-herons were observed in the tern colony on multiple occasions. This study suggests that individual night-herons will specialize on waterbird prey. The subsequent removal of a specialist night-heron predator resulted in improved tern productivity.

Impact of common tern colonies upon the zooplankton in Rybinsk Reservoir shallow waters

The comparison of the zooplankton communities developing in the semiprotected shallow waters of Rybinsk Reservoir under the impact of common tern (Sterna hirundo Linnaeus) colonies with communities in sheltered overgrowing habitats situated apart from colonies, has reveled some peculiar features of the former: higher biomass, prevalence of cladocerans, lower share of rotifers, and decrease in species diversity.

Population Trend, Colony Size and Distribution of Little Terns in the Lagoon of Venice (Italy) between 1989 and 2003

Between 1989 and 2003 colonies of Little Terns (Sterna albifrons) occurring in the lagoon of Venice (55,000 ha; Italy) have been surveyed. Each year the number of breeding pairs ranged between 31 (in 1997) and 611 (in 1995), with a yearly mean of 205 (SD = ±163). An overall stability in breeding numbers was observed, with an increase from 1989 to 1995 and a decrease afterwards. 34 sites were used; 13 (38%) were saltmarsh islets, twelve (35%) dredge islands, four (12%) beaches and the remaining five (15%) artificial beaches. Colony size median ranged between 25 and 15 pairs, with no differences among site typology. Sites used each year ranged between one and twelve, with a mean of 4.7 ± 3.0 sites. Turn over rate was high, 60%, and it did not vary significantly among colony sites type. Larger colonies were not more stable than smaller ones. Despite historically breeding at both beaches and saltmarshes, over the 15 years of study a shift in colony sites from beaches to saltmarshes and from these to dredge islands has been documented. Dredge islands, taken as a whole, were over the last years the most important breeding site in the entire lagoon.

Effects of Predation and Food Provisioning on Black Tern Chick Survival

We placed predator exclosures around 31 Black Tern (Chlidonias niger) nests in Maine in 2001–2002 to measure growth and survival of chicks. Fifty-four percent of exclosed nests that hatched young were depredated in 2001 and four exclosed nests were abandoned prior to hatch. We modified our exclosure design in 2002 and only one nest (7%) was depredated and no nests were abandoned prior to hatch. Kaplan-Meier estimates of chick survival in the absence of predation were 0.87 to 18 days in 2001 and 0.90 to 15 days in 2002. Mass ratios among first, second, and third-hatched chicks indicated that size hierarchies were present in broods near time of brood completion, but linear growth rates and asymptotic mass were not affected by hatch order in 2- or 3-chick broods. Predation was the primary determinant of chick survival in Black Tern colonies studied and food availability was not limiting chick growth. Predator exclosures did not prevent all depredation, but our exclosure design was effective at protecting and retaining chicks until fledgling age at 70% of nests; the majority of adults readily accepted predator exclosures.

Colony habitat selection by Little Terns Sternula albifrons in East Anglia: implications for coastal management

Little Terns Sternula albifrons are unusual among UK seabirds in that a large proportion of the population breed on mainland beaches in East Anglia. Relative sea-level rise means that such habitats are under threat in this region, and so we quantified colony habitat selection of beach nesting Little Terns in order to inform habitat restoration and creation initiatives. Random 1 km sections of beach were selected and the presence or absence of a Little Tern colony within each was related to physical (substrate type, height and width), biotic (vegetation cover, predator activity) and anthropogenic (disturbance) characteristics using logistic regression models. Little Terns positively selected for beaches with vegetation cover and negatively for those with high disturbance levels. They showed no selection according to width and height or Red Fox Vulpes vulpes presence, even though these are likely to affect flood and predation risk respectively. Red Foxes were found to be widespread on beaches irrespective of tern colony presence, and so movement of tern colonies will not always result in predator avoidance. Little Tern habitat creation needs to be integrated into coastal management plans in order to safeguard their population from the combined threats of relative sea-level rise, predation and disturbance.

ASSESSMENT OF EXPOSURE RISK OF POLYCHLORINATED BIPHENYLS TO INTERIOR LEAST TERNS (STERNA ANTILLARUM)

Risk of polychlorinated biphenyl (PCB) exposure and effects were assessed for a colony of federally endangered interior least terns (Sterna antillarum) nesting on the Bitter Lake National Wildlife Refuge (NM, USA). The colony feeds from an area on the Refuge (Hunter Marsh/Oxbow Complex) wherein fish with elevated concentrations of total PCBs have been documented. Concentrations of total PCBs in whole fish averaged 0.94 mg/kg with a maximum concentration of 2.77 mg/kg, wet weight. Estimated daily PCB intake rates by adult birds throughout their 180-d breeding season ranged from <0.01 mg/kg/d to 0.98 mg/ kg/d, yielding hazard quotients that ranged from 0.01 to 21.68. Polychlorinated biphenyls pose a moderate risk to the colony of interior least terns that breed at the Bitter Lake National Wildlife Refuge, but the exposure rate is not likely to threaten their overall breeding success.

Survival of Interior Least Tern Chicks Hatched on Gravel-covered Roofs in North Texas

Understanding how Interior Least Tern (Sternula antillarum athalassos) chicks hatched on rooftops interact with their environment is essential in the conservation of roof nesting colonies. We observed a colony of terns nesting on gravel roofs in Denton County, Texas, in 2003 and 2004. We used focal sampling to examine how chicks behave in relation to surface temperatures and in the presence of predators. We also placed two types of structures, artificial plants and wooden teepees, on the roofs to determine whether chicks would use them for shade or for protection from predators. As surface temperature increased, chicks increased time spent under cover (whether a man-made structure or being brooded) and decreased intraspecific interactions (ducking while an adult flew over, attacking or being attacked by other terns, submissive behaviors, and posturing). As chicks matured shade use decreased and body maintenance (preening and scratching) increased. When adults were mobbing potential predators over the colony, chicks ceased body maintenance, flight muscle preparation (stretching wings or flapping wings), and intraspecific interaction. Most chicks either fell prostrate where they stood when mobbing began or ran away from the predator. The use of structures by chicks did not change in the presence or absence of potential predators. Of the two experimental structures, only artificial plants were used more than expected. Overall, chicks hatched on roofs survive high surface temperatures by relocating to shade and survive predation by running or using camouflage. Artificial plants may be important for providing shade but not for providing protection against predators.

CORRELATIONS BETWEEN AGE, PHENOTYPE, AND INDIVIDUAL CONTRIBUTION TO POPULATION GROWTH IN COMMON TERNS

There have been numerous reports of changes in phenology, which are frequently attributed to environmental change. Age-dependent change in phenotypic traits, fledgling production, and the timing of events in the life cycle is also widespread. This means that changes in the age structure of a population could generate changes in phenology, which may be incorrectly attributed to environmental change or microevolution. Here, estimates of selection for arrival date, arrival mass, and laying date are compared when age is and is not corrected for. This is achieved using long-term individual-based data collected from a breeding colony of Common Terns (Sterna hirundo) and a novel fitness measure: individual contributions to population growth. The failure to correct for age generated deceptive estimates of selection in eight out of nine comparisons. In six out of nine comparisons, the direction of selection differed between age-corrected and uncorrected estimates. Persistent individual differences were detected: individuals remained within the same part of the phenotype distribution throughout life. The age-corrected estimates of selection were weak and explained little variation in fitness, suggesting that arrival date, arrival mass, and laying date are not under intense selection in this population. These results also demonstrate the importance of correcting for age when identifying factors associated with changes in seabird phenology.

Status of Tern Colonies in the Honduras Bay Islands

In the first comprehensive survey of tern colonies in the Honduras Bay Islands, 46 cays were surveyed in 2005 and 2006 and three species of terns were observed nesting in colonies on ten individual cays. Apparent colony turnover was high between years for Least (Sternula antillarum) and Roseate (Sterna dougallii) Terns, from 71% to 100%, respectively. The first nest records of Bridled Tern (Onychoprion anaethetus) for Honduras are documented.