Least Tern Research Articles

Breeding of marine birds on Farwa Island, western Libya

The Libyan coast is characterised by many wetlands that are used as stopover routes for many migratory marine birds. They provide food, shelter and nesting grounds for many avifauna during their migration from their home to wintering grounds. Farwa Island, which is located at the furthermost western part of Libya, is considered to be one of the most important coastal wetlands in Libya. It has unique diverse habitats of extensive tidal areas and mudflats and an accumulation of Posidonia oceanica on the northern part of the island and at Ras-Attalgha, beside the plant cover of the island itself. These conditions provide good nesting grounds for some species such as Sterna albifrons and Sterna hirundo. This study was conducted during January–December 1999, June 2001 and May 2004 on migratory and resident marine birds that inhabit the western part of Farwa Island and Ras-Attalgha. It recorded the breeding of Sterna caspia for the first time in Libya and some behavioural indicators as evidence of breeding of Charadrius alexandrinus and Tringa totanus in this area as well. Human activities — especially fishing, traffic from fishing boats and tourism — are considered to be major disturbance factors that may have a negative impact on successful breeding of birds that utilise the diverse habitats of this area.

폐그물 방치에 의한 육추기의 쇠제비갈매기(Sterna albifrons) 사망

Abandoned fishing nets served Little Tern(Sterna albifrons) chicks as cover on a sandy island on Ganwol Lake, Hongsung-gun, Chungcheongnam-do, Korea. Chicks were incidently caught in <TEX>$2.5cm{\times}2.5cm$</TEX> mesh sized nets and died of dehydration and exhaustion. Three adults died when they were caught by abandoned fishing net during parental care period in <TEX>$2.5cm{\times}2.5cm$</TEX> mesh sized nets. Whereas <TEX>$0.7cm{\times}0.7cm$</TEX> mesh sized nets did not affect the chicks' or adults' survival. Overlapped nets with several layers were more dangerous for chicks than were spread nets with a single layer. Dead chicks and adults were found to have been entangled by wing and neck. In this study, wing and nape(head+bill) of dead chicks were longer than those of live chicks. To improve the survival rate of Little Tern chicks at Ganwol Lake, abandoned fishing nets must be removed before the breeding season.

Assessment of Exposure Risk of Polychlorinated Biphenyls to Interior Least Terns (Sterna antillarum)

Assessment of Exposure Risk of Polychlorinated Biphenyls to Interior Least Terns (Sterna antillarum)

Signage reduces the impact of human disturbance on little tern nesting success in Portugal

This study evaluated the influence of human disturbance in nesting success of little tern ( Sterna albifrons) and its interaction with the intrinsic seasonal variation in the birds’ breeding biology. During 2003–2005 we studied little tern nesting ecology in southern Portugal in two different types of habitat: their natural habitat (sandy beaches) and a man-made habitat (salinas). In both habitat types, annual variations were found in the distribution of nest initiation over the breeding season and in the size of the clutches. The percentage of nests producing hatched chicks varied between 26.7% and 66.4% in different years and habitats. The main causes of hatching failure varied between years and habitats, but predation, flooding and human activities were very common. No consistent differences in breeding parameters or nesting success were found between habitats. On sandy beaches, the effect of protective measures (warning signs and wardening) on nesting success, together with differences between years and within each breeding season, were assessed using a logistic regression model. The presence/absence of protective measures was the most important predictor of nesting success, with birds being up to 34 times more likely to succeed with protective measures. Seasonal declines were found for clutch size and egg volume, and season was also an important predictor of nesting success, with nests more likely to succeed earlier in the season. Hence, earlier breeders will be those that benefit more from protective measures, suggesting that conservation efforts for little tern can be maximised if concentrated earlier in the season.

Roof-top Selection by Least Terns in Pinellas County, Florida

Abstract Primarily due to loss and disturbance of their open beach habitat, Least Tern (Sterna antillarum) nesting colonies often occur on flat or gently sloped gravel rooftops throughout the Southeastern United States. Currently, these rooftops are being converted to a new substrate, unsuitable for Least Tern nesting, because of changes in state building codes. The purpose of this study was to determine which rooftops Least Terns are currently selecting to help develop man-made structures for nesting and determine where these structures should be placed. From 1998-2003 in Pinellas County, Florida, all previously occupied Least Tern rooftops were surveyed to see if they had a colony and new colonies were located. In 2003, there were 36 rooftops with colonies and 34 unoccupied rooftops that had been previously occupied sometime from 1998-2002 but still had gravel rooftops. In addition, 36 gravel rooftops that had no record of supporting a Least Tern colony were randomly selected. At each building distance ...

CALIFORNIA LEAST TERN CHICK PREDATION BY GREATER ROADRUNNER

We present the first documented account of adult greater roadrunner (Geococcyx californianus) feeding on California least tern chicks (Sterna antillarum browni). This predation event occurred at a designated nesting site within Batiquitos Lagoon, San Diego County, California, in 1996. We hypothesize that the concentrated foraging efforts by the roadrunner were an opportunistic response to a localized abundance of favorable prey items, which warrants an increased awareness at other least tern nesting sites situated in close proximity to greater roadrunner habitat.

Impact of wind turbines on birds in Zeebrugge (Belgium)

We studied the impact of a wind farm (line of 25 small to medium sized turbines) on birds at the eastern port breakwater in Zeebrugge, Belgium, with special attention to the nearby breeding colony of Common Tern Sterna hirundo, Sandwich Tern Sterna sandvicensis and Little Tern Sterna albifrons. With the data of found collision fatalities under the wind turbines, and the correction factors for available search area, search efficiency and scavenging, we calculated that during the breeding seasons in 2004 and 2005, about 168 resp. 161 terns collided with the wind turbines located on the eastern port breakwater close to the breeding colony, mainly Common Terns and Sandwich Terns. The mean number of terns killed in 2004 and 2005 was 6.7 per turbine per year for the whole wind farm, and 11.2 resp. 10.8 per turbine per year for the line of 14 turbines on the sea-directed breakwater close to the breeding colony. The mean number of collision fatalities when including other species (mainly gulls) in 2004 and 2005 was 20.9 resp. 19.1 per turbine per year for the whole wind farm and 34.3 resp. 27.6 per turbine per year for 14 turbines on the sea-directed breakwater. The collision probability for Common Terns crossing the line of wind turbines amounted 0.110–0.118% for flights at rotor height and 0.007–0.030% for all flights. For Sandwich Tern this probability was 0.046–0.088% for flights at rotor height and 0.005–0.006% for all flights. The breeding terns were almost not disturbed by the wind turbines, but the relative large number of tern fatalities was determined as a significant negative impact on the breeding colony at the eastern port breakwater (additional mortality of 3.0–4.4% for Common Tern, 1.8–6.7% for Little Tern and 0.6–0.7% for Sandwich Tern). We recommend that there should be precautionary avoidance of constructing wind turbines close to any important breeding colony of terns or gulls, nor should artificial breeding sites be constructed near wind turbines, especially not within the frequent foraging flight paths.

Waterbirds (other than Laridae) nesting in the middle section of Laguna Cuyutlán, Colima, México

Laguna de Cuyutlán, in the state of Colima, Mexico, is the only large coastal wetland in a span of roughly 1150 km. Despite this, the study of its birds has been largely neglected. Between 2003 and 2006 we assessed the waterbirds nesting in the middle portion of Laguna Cuyutlán, a large tropical coastal lagoon, through field visits. We documented the nesting of 15 species of non-Laridae waterbirds: Neotropic Cormorant (Phalacrocorax brasilianus), Tricolored Egret (Egretta tricolor), Snowy Egret (Egretta thula), Little Blue Heron (Egretta caerulea), Great Egret (Ardea alba), Cattle Egret (Bubulcus ibis), Black-crowned Night-heron (Nycticorax nycticorax), Yellow-crowned Night-heron (Nyctanassa violacea), Green Heron (Butorides virescens), Roseate Spoonbill (Platalea ajaja), White Ibis (Eudocimus albus), Black-bellied Whistling-duck (Dendrocygna autumnalis), Clapper Rail (Rallus longirostris), Snowy Plover (Charadrius alexandrinus), and Black-necked Stilt (Himantopus mexicanus). These add to six species of Laridae known to nest in that area: Laughing Gulls (Larus atricilla), Royal Terns (Thalasseus maximus), Gull-billed Terns (Gelochelidon nilotica), Forster's Terns (S. forsteri), Least Terns (Sternula antillarum), and Black Skimmer (Rynchops niger), and to at least 57 species using it during the non-breeding season. With such bird assemblages, Laguna Cuyutlán is an important site for waterbirds, which should be given conservation status.

Failure of Methiocarb to Produce Conditioned Taste Aversion in Carrion Crows Consuming Little Tern Eggs

Abstract An experimental procedure was set up to test if Carrion Crow (Corvus corone) predation on Little Tern (Sterna albifrons) eggs could be decreased by conditioned taste aversion. The experiment started with a control period, during which 30 artificial Little Tern nests were maintained with quail eggs for 6 days at two study sites. The rate of egg predation was assessed through daily visits and observations of crow behavior. During the treatment period (following 6 days), 15 nests were supplied with eggs pre-treated with methiocarb, an ill-inducing compound, while the other 15 nests were maintained with non-treated eggs. The treatment period was extended by a further period of eight days, during which only treated eggs were deployed at 15 nests. Carrion Crows did not develop any aversive response to the eggs. All treated and untreated eggs were taken by crows from the nests and broken in less than 24 h after delivery. However, treated eggs were apparently not consumed by crows, which suggests that th...

A control taste aversion experiment on predators of roseate tern (Sterna dougallii) eggs

European starlings (Sturnus vulgaris) are responsible for high rates of egg predation at one of the main colonies of the endangered roseate tern (Sterna dougallii) in the Azores archipelago. Control taste aversion has been effective in controlling raven predation in a colony of California least tern (Sterna antillarum browni), but there is little quantitative information about its efficacy on other species of predators taking eggs. We conducted a control taste aversion experiment on yellow-legged gulls (Larus michahellis) and European starlings eating eggs of terns in a mixed colony of common (Sterna hirundo) and roseate terns in the Azores. We treated quail (Coturnix coturnix) eggs with methiocarb and deployed them in artificial nests in the tern colony. On the first experiment, conducted before the terns laid eggs, predation rates on quail eggs by yellow-legged gulls showed significant and rapid decrease after deployment of treated eggs. During the second experiment, after the terns had started laying, results were mixed. Although predation rates by European starlings on treated quail eggs decreased, predation rates on tern eggs did not. We conclude that control taste aversion using methiocarb-treated eggs is likely to reduce depredation by gulls but not starlings because of the need to pre-train the birds and the tendency of starlings to be attracted by the movement of adults, not the presence of nests.

Intercolony and Annual Differences in the Diet and Feeding Ecology of Little Tern Adults and Chicks in Portugal

Abstract We used pellets and prey dropped near nests to study the diet and feeding ecology of Little Tern (Sterna albifrons) adults and chicks in northern and southern Portugal during 2000–2004. We compared diets among study areas, years, and birds breeding in two main habitat types: sandy beaches and salinas (man-made salt-pans). We also sampled prey fish in one study area and used published data from another area to examine whether the diet of Little Tern adults and chicks corresponded with the abundance of prey found in primary foraging habitats. Adult Little Terns fed mainly on sand-smelts (Atherina spp.) and gobies (Pomatoschistus spp.), which were the most abundant fish species in our estuarine and lagoon study areas. Despite some differences among colonies we did not find clear differences in adult diets among study areas and habitat types. Little Tern chicks also ate primarily Atherina spp., but their diet was more diverse than that of the adults, and characterized by a significantly higher proportion of prey with a high energetic value such as sardines (Sardina pilchardus), garfish (Belone belone), and killifish (Fundulus spp.). Chick diets differed significantly between habitat types, which may be a consequence of the limited foraging range of adult breeding birds. Both adult and chick diets matched the abundance of the main prey in our study areas, confirming the opportunistic foraging character of this species. We suggest that annual variation in prey availability may be the most important factor explaining annual variation in adult diets.

Radio telemetry as a tool for impact assessment of wind farms: the case of Little Terns Sterna albifrons at Scroby Sands, Norfolk, UK

Many seabirds travel widely to exploit variably distributed prey resources, utilizing even profitable patches only briefly as prey become available. Assessing the relative importance of areas occupied by wind farms relies on sufficient survey effort to increase the probability of detection and later assessment to an acceptable level. Conventional techniques suffer from high sampling costs and infrequent sampling of patches within larger areas. Remote techniques, which continuously sample habitat, may offer a solution although sufficient coverage may be difficult to achieve. In this paper, we outline experiences of the use of radio telemetry on LittleTerns Sterna albifrons at their most important UK breeding site, the Great Yarmouth North Denes Special Protection Area (SPA), in relation to a 30 turbine offshore wind farm on Scroby Sands, which encroaches to 2 km from the North Denes colony. Little Terns had not been radio‐tagged previously in the UK, and the technical difficulties of tagging and subsequently following a small (55 g) diving seabird limited data collection. However, comparative data from 2 years (2003 and 2004), in which the abundance of the terns’ preferred prey varied greatly, revealed striking differences in activity and foraging patterns, which changed the perception of the scope of the birds. With an active nest, birds occupied a range of &lt; 6.3 km2 with a range span of up to 4.6 km. In comparison, failed birds ranged widely, occupying ranges up to 52 km2 and travelling up to 27 km in a single foraging bout. As birds were recorded from 2 to 3 km offshore, the wind farm is within range of birds from the breeding colony at North Denes, although only a small proportion of foraging time was spent at such distance in the years of study. The potential value of radio (and satellite) telemetry in illustrating habitat use, perhaps to set precautionary distance limits for wind farms as well as defining actual use of particular areas including for collision risk assessment is discussed.

Influence of environmental factors and energetic value of food on Little Tern Sterna albifrons chick growth and food delivery

Capsule Chick diet and early growth parameters differed between birds breeding on natural (sandy beaches) and alternative (salinas) habitats. Aims To describe diet and growth of Little Tern chicks, to examine the influence of tide and wind speed on food delivered to chicks in southern Portugal, and to determine whether diet and early chick growth parameters differed between birds breeding in natural (sandy beaches) and man-made alternative (salinas) habitats. Methods Nests were marked and visited regularly. Chicks were ringed and weighed at hatching. Between 12 and 14 nests were enclosed by a fence in order to measure and weigh chicks every day. Prey items delivered to fenced chicks were observed daily from hides, in different tidal periods and wind speed conditions. Prey items dropped in the colonies were collected. Foraging efficiency of adults was evaluated in relation to tide and wind speed. Fresh prey items were collected to determine their energetic content using a calorimeter. Results A chicks grew faster than B chicks, but both attained the same weight, tarsus-length and wing-length at 19 days old; C chicks attained the same values at day 21. There were significant differences in early growth parameters. A and B chicks grew faster on sandy beaches than on salinas. The main prey items were Atherina spp., Fundulus sp. and shrimps in salinas and Sardina pilchardus, Atherina spp. and Belone belone on sandy beaches. There was no correlation between ingestion rate and chick age, but mean length of prey ingested by chicks increased significantly with age. Conclusion Tide and wind speed influenced both size and type of prey delivered to chicks. Parents met the increasing energy demands of the growing chicks by adjusting prey size rather than prey delivery frequency. Differences in chick growth between salinas and sandy beaches could be related to both parental quality and diet. The presence of a high energy-content euryhaline fish species in the salinas, together with more sheltered conditions and no tidal influences, may be important in explaining the use of salinas by Little Terns.

Genetic Variation among Subspecies of Least Tern (Sterna antillarum): Implications for Conservation

DNA sequence variation from two nuclear introns and part of the mitochondrial cytochrome-b gene were used to evaluate population structure among three subspecies of Least Tern that nest in the United States (California [Sterna antillarum browni], Interior [S. a. athalassos], Eastern [S. a. antillarum]). Sequence variation was highest for nuclear intron XI (Gadp) within the glyceraldehyde-3-phosphate dehydrogenase gene. The second nuclear intron was fixed for the same allele in all subspecies. Fixation indices, FST and MST, for Gadp indicated genetic divergence between California and Interior subspecies. Estimates of nuclear gene flow were <4 individuals/generation, except between the Interior and Eastern subspecies (4 individuals/generation). Genetic indices for mitochondrial DNA did not differ among subspecies, and gene flows (reflecting female dispersal) ranged from 10 to 83 individuals/generation. Reservations are expressed about the validity of the current subspecific divisions and further research is required, including their taxonomic relationship to the Little Tern (Sterna albifrons).

INTERCOLONY AND ANNUAL DIFFERENCES IN THE DIET AND FEEDING ECOLOGY OF LITTLE TERN ADULTS AND CHICKS IN PORTUGAL

Abstract We used pellets and prey dropped near nests to study the diet and feeding ecology of Little Tern (Sterna albifrons) adults and chicks in northern and southern Portugal during 2000–2004. We compared diets among study areas, years, and birds breeding in two main habitat types: sandy beaches and salinas (man-made salt-pans). We also sampled prey fish in one study area and used published data from another area to examine whether the diet of Little Tern adults and chicks corresponded with the abundance of prey found in primary foraging habitats. Adult Little Terns fed mainly on sand-smelts (Atherina spp.) and gobies (Pomatoschistus spp.), which were the most abundant fish species in our estuarine and lagoon study areas. Despite some differences among colonies we did not find clear differences in adult diets among study areas and habitat types. Little Tern chicks also ate primarily Atherina spp., but their diet was more diverse than that of the adults, and characterized by a significantly higher propor...

Identification of Nest Predators at a Least Tern Colony in Southwestern Indiana

Abstract Nest predators commonly limit productivity of Least Tern (Sterna antillarum) breeding colonies in both natural and artificial habitats. In 2003 and 2004 we used remote still cameras aimed at model nests and remote video cameras aimed at occupied Least Tern nests to identify predators of Least Terns breeding at Gibson Lake, an artificial breeding area in southwestern Indiana, USA. At the primary breeding site, a narrow gravel dike that bisects Gibson Lake (center dike), Ring-billed Gulls (Larus delawarensis) were responsible for 100% and 75% of known predation events on model nests in 2003 and 2004, respectively. Throughout the 2004 breeding season, the proportion of model nests disturbed by Ring-billed Gulls on the center dike was strongly correlated with their numbers roosting on the center dike. We recorded predation by Ring-billed Gulls on six Least Tern chicks and two eggs in 2004 with remote video cameras. Our evaluation of the predator community at Gibson Lake strongly implicated Ring-bille...

Colony specific variation in the use of a moulting site in the migratory little tern Sterna albifrons

Individual‐based data on little terns Sterna albifrons at a post‐breeding moulting area were used to investigate the spatial extent at which this site attract birds. Combining information collected on young terns, ringed at the natal colonies, with that on birds captured a few months later at the moulting site, we estimated a survival/movement parameter for each age‐by‐colony combination. This parameter is the product between the survival probability and the probability to visit the moulting site. The distance between the natal colony and the moulting site negatively influenced the probability of reaching the site in yearlings. Having corrected for the distance from the moulting area, colony characteristics explained only about 10% of the spatial variation in the survival/movement parameter of juveniles. In older birds that had visited the site at least once in their life, neither the colony nor the distance affected the survival/movement parameter significantly. The average annual adult survival/movement probability was 0.90. Juvenile survival between June and September was 0.60. Overall results suggest that the moulting area could act as a ‘population funnel’ within a system of moult migration that involves birds breeding up to 500 km away. However, other unknown moulting site must exist within this area that could be important for the conservation of the species.

Distribution and Abundance of Breeding Birds in Boston Harbor

We surveyed birds during May and June, 2001–2003, on 26 islands and 1 mainland location in Boston Harbor, MA. We detected 136 species, 67 of which were suspected of breeding. Abundant breeding seabirds included Double-crested Cormorants (Phalacrocorax auritus), Herring Gulls (Larus argentatus), and Great Black-backed Gulls (Larus marinus). We found 73 Common Eider (Somateria mollissima) nests on Calf, Green, Middle Brewster, and Outer Brewster Islands in 2003, making Boston Harbor one of the largest, southernmost nesting areas for this species on the western Atlantic Ocean. We surveyed 7 wading bird colonies composed of Black-crowned Night-Heron (Nycticorax nycticorax), Great Egret (Ardea alba), Snowy Egret (Egretta thula), Glossy Ibis (Plegadis falcinellus), and Little Blue Heron (Egretta caerulea). We found a colony of Least Terns (Sterna antillarum), a state-listed species, on Rainsford Island. We estimated that 49 species of landbirds nested on Boston Harbor islands, but most islands had few species (mean = 9.8 [± 2.2 (SE)] species per island), presumably because many islands were small and dominated by non-native second-growth forests. The most widespread species were Yellow Warbler (Dendroica petechia), Song Sparrow (Melospiza melodia), and Red-winged Blackbird (Agelaius phoeniceus). We also detected over 50 species of migratory birds which did not nest on islands in the Harbor, including many species of shorebirds and warblers.

Fish Abundance and the 1995 Nesting Season of the Least Tern at Bahía de San Jorge, Northern Gulf of California, México

Abstract During 1995, the relationship between the nesting chronology of the Least Tern (Sterna antillarum) and the near-shore abundance of fish was examined at La Purinera, Sonora, the site of one of the largest known Least Tern colonies in northwest Mexico. Fish abundance was measured adjacent to the shoreline during early mornings using a beach seine net, and the sampling periods corresponded to different phases of the Least Tern’s annual cycle. During this year, the nesting season (April to July) coincided with peak prey fish abundance, and peak hatching of tern eggs (early July) coincided with the greatest abundance of fish of adequate size for chicks. Departure of the terns from the area coincided with a marked reduction in suitable food in September. Collections of fish dropped and left uneaten by Least Terns in the colony contained five species, which were also present in the fish samples obtained with the beach seine net. The observations on foraging adult Least Terns and the collections of fish ...

EFFICACY OF USING RADIO TRANSMITTERS TO MONITOR LEAST TERN CHICKS

Little is known about Least Tern ( Sterna antillarum) chicks from the time they leave the nest until fledging because they are highly mobile and cryptically colored. We evaluated the efficacy of using radio- telemetry to monitor Interior Least Tern (S. a. athalassos) chicks at Salt Plains National Wildlife Refuge, Oklahoma. In 1999, we attached radio transmitters to 26 Least Tern chicks and tracked them for 2-17 days. No adults abandoned their chicks after transmitters were attached. Transmitters did not appear to alter growth rates of transmittered chicks (P 5 0.36) or prevent feather growth, although dermal irritation was observed on one chick. However, without frequent reattachment, transmitters generally did not remain on chicks ,1 week old for more than 2 days because of feather growth and transmitter removal, presumably by adult terns. Although the presence of transmitters did not adversely affect Least Tern chicks, future assessments should investigate nonintrusive methods to improve retention of transmitters on young chicks and reduce the number of times that chicks need to be handled. Received 27 May 2004, accepted 30 December 2004.