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.     

Can rats prey on gull eggs? An experimental approach

Black rat Rattus rattus populations can reach high densities on the Mediterranean islands, as has been the case on the Chafarinas Islands (Western Mediterranean coast) in the last decade. This archipelago holds the second largest breeding population of Audouin's gull Larus audouinii and an important population of yellow-legged gull Larus cachinnans. Circumstantial evidences of rat predation upon Audouin's gull eggs led to conservation concerns about the impact of rat predation on gull productivity. We studied the impact of rats on gull nests experimentally by building artificial nests into the breeding area of yellow-legged gulls. Two kinds of eggs were placed in the artificial nests: manipulated eggs, in which the shell had been previously opened, and intact (unmanipulated) eggs. Rats preyed extensively on opened eggs but only once on intact eggs, apparently due to lack of skills to prey on intact eggs, suggesting that rats do not normally have access to fresh gull eggs. Rats inhabiting breeding areas of gulls can scavenge on broken eggs rolled out of the nest or on eggs with softened shells after nest desertion, but it is unlikely that they prey on natural gull nests guarded by parents. We suggest that introduced black rats on Mediterranean islands can only marginally affect the productivity of gulls owing to egg predation.     

Wie richtet eine Flußseeschwalbenkolonie (Sterna hirundo) ihr Abwehrverhalten auf den Feinddruck durch Silbermöwen (Larus argentatus) ein?

How a Common Tern (Sterna hirundo) Colony Defends itself against Herring Gulls (Larus argentatus) The subject of this study is the anti-predator behaviour of a small common tern colony near a large herring gull colony on the island of Mellum, West Germany (Fig. 1). In 1980 the number of gulls crossing this tern colony increased during the terns' chick-stage (Fig. 4). Observed predation of tern chicks was independent of tide and time of day (3., Fig. 5). The frequency of tern reactions corresponded to the number of herring gull crossings (Fig. 5, Table 1). The terns' responses increased between morning and evening (Fig. 8). Tern up-flights and attacks increased absolutely and as a percentage, with the advance of the breeding season (Fig. 3, 4). They were positively correlated with the observed chick predation and the number of pairs with chicks, most markedly with chicks older than 5 days (Figs. 3, 4; Table 1). This increased defence was maintained by fewer pairs as, by then, many had lost their own broods (Fig. 4). As the breeding season progressed, herring gulls increasingly became the main cause of tern up-flights and the object of the attacks (Figs. 9–11). The up-flights of the whole colony, which occurred frequently and spontaneously during incubation, were observed only rarely after hatching and were almost exclusively a response to herring gulls (Figs. 10, 12). The lower herring gulls flew over the colony, the more frequently common terns flew up or attacked and the more individuals were involved in these responses (Figs. 6, 13, 14). During the breeding period, communal up-flights and attacks by terns increased as a percentage (Figs. 12, 13, 15–17). Group-attacks effected changes in the gulls' flying-routes more often than did individual attacks (Fig. 18). Despite the defence behaviour and its adaptation to the predation pressure, herring gulls often succeeded in robbing chicks. This is why the breeding success of the common tern was poor (< 0.4 chicks/nest). Possible reasons for this are discussed.     

Predation by Kelp Gulls Larus dominicanus at a mixed-species colony of Royal Terns Sterna maxima and Cayenne Terns Sterna eurygnatha in Patagonia

We studied the predator-prey interaction between Kelp Gulls Larus dominicanus and Royal Terns Sterna maxima and Cayenne Terns Sterna eurygnatha at Punta León, Argentina, from 1990 to 1992. Kelp Gulls were the main predator of tern eggs in all 3 years, accounting for 99% of observed predations (n = 454). A total of 99% of predations occurred on peripheral tern nests. Total predation rate on both tern species was highest in 1990 and varied significantly between years, with between 0.01 and 0.03 cases of predation per hour. Predation rates in all years were significantly higher on Cayenne than on Royal Terns probably because the latter were significantly more aggressive towards gulls than were Cayenne Terns. Royal and Cayenne Terns displayed aggressively towards gulls at least once in 64% and 10% of the observation periods, respectively. Defence behaviour, such as attacking and chasing the predator, was used more frequently by Royal than Cayenne Terns (13.2% v 3.6%). Predation on tern eggs was restricted to only a few Kelp Gulls which nested close to the tern colony periphery, and 50% of the eggs that were stolen were taken by only two pairs during 1991 and 47% by three pairs in 1992. This suggests that the current expansion of the Kelp Gull numbers at Punta León might not necessarily result in a proportional increase in predation rate on both tern species. Stealing eggs from the ground was more successful than from the air (77% v 17%). The nesting strategy shown by Royal and Cayenne Terns at Punta León appears to be an important factor which reduced the impact on their breeding success of high potential predation pressure by gulls.     

Effect of brood size and hatching sequence on prefledging mortality of Sandwich terns: why lay two eggs?

The mortality of Sandwich tern Sterna sandvicensis chicks held in enclosures was studied in colonies on Griend, in the Dutch Wadden Sea, from 1992 to 1999, and on Hirsholm, in the Danish Kattegat, in 1997. Survival of chicks until fledging was 73% for chicks hatching from first-laid eggs or single-egg clutches and 59–64% for partially hatched two-egg clutches, whereas 6% of second hatchlings survived until fledging. Less than 2% of all two-chick broods actually fledged two chicks. Because 18% of the two-egg clutches only hatched one egg, 7% of fledglings of two-egg clutches originated from a second-laid egg. In nests where both eggs hatched, the number of chicks was usually reduced soon after hatching. Within five days of hatching more than 50% of the second hatchlings died of starvation or were preyed upon. It seems that overproduction commonly occurs in Sandwich terns and that investment in a surplus egg mainly serves as an insurance mechanism. On Griend and Hirsholm, chick productivity of two-egg clutches was somewhat higher than for one-egg clutches. Undernourishment was an important cause of death, either directly by starvation or by selective predation of chicks in poor condition. This, in combination with earlier, studies suggests that Sandwich tern parents on Griend are exposed to severe food stress.     

Predator–prey interactions between the South Polar skua Catharacta maccormicki and Antarctic tern Sterna vittata

Antarctic terns have to co‐exist in a limited space with their major nest predator, the skuas. We conducted artificial nest experiments to evaluate the roles of parental activity, nest location and nest and egg crypsis in this simple predator–prey system. Predation on artificial (inactive) nests was higher in traditional nesting sites than in sites previously not occupied by terns, which suggests that skuas memorized past tern breeding sites. Predation on artificial nests in inactive colonies was higher than in active (defended) colonies. Parental defense reduced predation in colonies to the level observed in artificial nests placed away from colonies. This suggests that communal defense can balance the costs of attracting predators to active colonies. Within colonies, predation was marginally higher on experimental eggs put in real nests than on bare ground. Although it seems that the presence of a nest is costly in terms of increased predation, reductions in nest size might be constrained by the need for protective nest structures and/or balanced by opposing selection on nest size. Predation did not differ markedly between artificial (quail) and real tern eggs. A simultaneous prey choice experiment showed that the observed predation rates reflected egg/nest detectability, rather than discrimination of egg types. In summary, nesting terns probably cannot avoid being detected, and they cannot defend their nest by attending them. Yet, by temporarily leaving the nest, they can defend it through communal predator mobbing, and at the same time, they can benefit from crypsis of unattended nest and eggs.     

Management-Induced Reproductive Failure and Breeding Dispersal in Double-Crested Cormorants on Lake Champlain

ABSTRACT We studied breeding dispersal of double-crested cormorants (Phalacrocorax auritus) associated with management practices that suppressed their reproduction on Lake Champlain in the northeastern United States. We implemented an experiment on one colony by spraying corn oil on cormorant eggs in portions of the colony and leaving other portions untreated. Gulls (Larus spp.) consumed cormorant eggs during the oiling process, but we reduced and then eliminated predation levels after the first year of the study. We used mark-recapture techniques within the experimental framework to measure rates of breeding dispersal for cormorants from the experimental colony and an unmanaged colony in Lake Champlain. Egg oiling increased the movement rate to the unmanaged colony by 3% during the year with no egg predation by gulls. When gulls depredated cormorant eggs at high rates during egg oiling, movement to the unmanaged colony increased by 20%. When cormorants are managed to reduce population sizes, methods that limit dispersal away from the managed colony may be most effective. Such methods would mitigate effects to nontarget populations and allow for a greater portion of the metapopulation to be managed.     

Test of the efficacy of two chemical repellents in the control of Hermann’s tortoise nest predation

The survival of the tiny native population of the western Hermann’s tortoise Testudo hermanni hermanni at the Albera Nature Reserve is threatened by nest predation. The initial purpose of this work was to test the efficacy of a commercial chemical repellent aimed at carnivores in the control of this predation. A total of 128 artificial nests containing quail eggs were distributed among eight 625-m² plots. There were four control plots and four plots protected by repellent devices in a natural nesting area of the Albera; each plot contained 16 nests. All the nests, including the protected ones, were depredated after only 4 days. Due to the major role of the wild boar Sus scrofa as predator in this experiment, we decided to assess, by means of a second experiment (n = 160 artificial nests, 20 nests/plot), the efficacy of a specific repellent for this mammal combined with the initial repellent. The only noticeable effect of the combination of repellents was to delay predation, although after 4 days almost all protected nests had been depredated. We found both repellents unsatisfactory for reducing nest predation, necessitating the search for other methods of predator control.     

Aggressive neighbors and dense nesting: nest site choice and success in high-Arctic common eiders

Minimizing the risk of nest predation has led some bird species to exploit the nest defense behavior of other species. At Nasaruvaalik Island, Nunavut, Canada, some common eiders (Somateria mollissima borealis) nest within the boundaries of Arctic tern (Sterna paradisaea) colonies, while others nest elsewhere on the island, away from the terns. We tested the effects of location (within vs. outside the tern colonies), density of common eider nests, and annual variation on the nesting parameters of common eiders. Our results suggest that nesting in association with Arctic terns does not confer an obvious benefit to eiders. Such associative nesting of eiders and terns may be the result of overlapping habitat preferences between the two species, or a general scarcity of suitable nesting habitat for ground-nesting species in the high Arctic. However, eiders nesting in higher densities with other eiders had greater nest success and lower total clutch predation, indicating a positive correlation between nest density and success.     

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.     

Impacts of Argentine ants on avian nesting success

Biological invasions can have severe and widespread impacts on ecological communities. A few species of ants have become particularly damaging invaders but quantitative data of their impacts on many taxa is still lacking. We provide experimental evidence using artificial nests baited with quail eggs that the invasive Argentine ant (Linepithema humile) can be a significant avian nest predator – Argentine ants recruited to more nests and in higher abundance than the native ant species they displace. However, at a site invaded by Argentine ants, we monitored over 400 nests of a ground-nesting species, the Dark-eyed Junco (Junco hyemalis), and found that less than 2% of nests failed as a result of Argentine ant predation/infestation. A review of the literature also suggests that Argentine ants may not be a serious threat to bird nests relative to other predators or parasites. However, invasive ants with the capability of overwhelming prey though stinging (specifically the red-imported fire ant, Solenopsis invicta), may have a higher impact on avian nesting success. Received 14 January 2005; revised 28 April 2005; accepted 12 May 2005.     

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.     

The Protector Species Hypothesis: Do Black Skimmers Find Refuge from Predators in Gull-billed Tern Colonies?

The protector-species hypothesis explains mixed-species coloniality on the basis of benefits individuals of a species may receive by nesting with another species, the ‘protector’ species, that responds aggressively to potential threats. The reactions of nesting individuals to both natural and model predators were observed to determine whether black skimmers (Rhynchops niger) gain an antipredator advantage by nesting with gull-billed terns (Sterna nilotica). Observations of natural predators were gathered from three mixed-species and three single-species (black skimmers) subcolonies. Natural predators most commonly encountered by the colonies were herring gulls (Larus argentatus), laughing gulls (Larus atricilla), and ruddy turnstones (Arenaria interpres). Gull-billed terns responded to the gulls, but not to the turnstones, in higher proportions than did black skimmers. Two decoys, a mink and a gull, were used to simulate predatory encounters, and a duck decoy was used as a control at two mixed-species and one single-species subcolonies. Gull-billed terns responded in significantly higher proportions than did skimmers to all decoy treatments in the mixed-species subcolonies. Mobbing of both natural and model predators by the terns suggests that skimmers may gain a reproductive advantage by nesting with these terns. However, the response of black skimmers to both natural and simulated predators was independent of the presence of gull-billed terns in the colony, indicating that black skimmers may not perceive these objects as threats, or may react differently to predators than do gull-billed terns.     

Colonial breeding reduces nest predation in the common gull (Larus canus)

It is often suggested that colonial breeding reduces nest predation for birds with a high defence capacity, but experimental comparison of predation at solitary and colonial nests is seldom feasible within a single species. We here report on such a test in the common gull (Larus canus). The rate of predation on experimental eggs was significantly lower near colonies than near solitary gull nests, and the eggs survived longer at the edge of a colony than farther away. Communal mobbing of nest predators is the likely reason. In both of two years, almost all nests of solitary gulls were destroyed by predators, while most clutches survived in colonies. Nest predation hence selects strongly for colonial breeding in the present population of common gulls.     

SELECTION OF COLONY SITES AND NEST SITES BY COMMON TERNS STERNA HIRUNDO IN OCEAN COUNTY, NEW JERSEY

Common Terns nested on 34 of 259 saltmarsh islands along 46 miles of Ocean County coastline, New Jersey. They nested on low islands of Spartina with less than 12%, windrow ranging in size from 0.6 to 108 acres. All islands selected by terns faced at least two miles of open water from at least one direction. Selection of islands seemed a response to vegetation, size, distance to the nearest island, distance to the nearest shore and exposure to open water. Of the 225 islands without nesting terns, only three fulfilled appropriate criteria. Eighty per cent of nests were situated on windrow. Terns laid larger clutches on windrow compated to those nesting in Spartina. Nearest neighbour distance on islands with low predation varied from 85 to 485 cm and was a function of space, vegetation, and the size of the island. Terns nested closer together on windrow compared with Spartina. Considering all colonies, the mean nearest neighbour distance negatively correlated with the number of nests. Skimmers, Oystercatchers, Laughing Gulls, and Herring Gulls nested in some of the tern colonies. All tern colonies on islands also occupied by nesting Herring Gulls suffered over 10% egg-loss by predation. Proportionally more nests were preyed upon in windrow than in Spartina. Clutch sizes in nests in windrow on islands with predation were significantly lower than those in windrow on islands without predation, even though clutch sizes in Spartina were similar on islands with and without predation. Flooding by exceptional high tides destroyed significantly more nests in Spartina than in windrow. The nests that survived in Spartina were built deeper, and their rim heights were higher than nests destroyed by tides. Choice of colony and nest sites is discussed in terms of the balance of two selection pressures: predation and tidal flooding. Tern nests on windrow are more exposed to predators, but safer from flooding, whereas those nests in Spartina are more susceptible to flooding and less vulnerable to predators. The recent invasion of Herring Gulls into Ocean County has significantly increased the rate of nest predation among affected colonies of Common Terns. It is possible that in future years the terns' behaviour may be modified in response to this new selective pressure.     

Factors affecting tissue distribution of heavy metals

Metal distribution in an organism at any one time is a resultant of many extrinsic and intrinsic factors. Improved analytic methodology has made it feasible to obtain highly sensitive determinations for many metals in a single sample. Thus, it is now feasible to examine patterns of metal distribution. We report on a study of the effect of age on metal patterns in the common tern,Sterna hirundo, a fisheating seabird. We contrast the levels of nine metals in the liver of adult and young terns and compared these with levels in tern eggs. Unlike many previous studies, adults did not have significantly higher levels of metals, although for most metals, levels in eggs were significantly lower than liver levels of young and adults. The intermetal correlations showed more significant positive correlations for adults and eggs than for chicks, the latter showing instead a correlational chaos, probably reflecting the immaturity of their physiologic defense mechanisms and the absence of dynamic equilibrium.     

Use of temperature sensors to monitor patterns of nocturnal desertion by incubating Common Terns

ABSTRACT.   Adult Common Terns ( Sterna hirundo ) reportedly respond to nocturnal predation by deserting colonies from the time of disturbance until dawn the following morning. However, direct evidence for this behavioral response is limited because the nocturnal behavior of individual terns is difficult to monitor due to low visibility and the vulnerability of terns to disturbance at night. We monitored the nocturnal incubation behavior of 10 pairs of nesting Common Terns using continuously recording temperature sensors disguised in dummy eggs and placed in the nests. Changes in egg temperature during the night suggested that a range of desertion behaviors occurred in response to visits by a Great Horned Owl ( Bubo virginianus ) that preyed on chicks and adult terns. As many as three desertion events (desertion at one or more nests in a single 12-min period) were detected on a single night and nests were unattended for an average of 54 min (range 8–352 min) per desertion event. Nest temperature sensors allowed us to detect individual responses to nocturnal predators and to determine that desertion behavior was more varied than previously assumed. Desertion events were most frequent when physical evidence indicated the presence of an owl in the colony and during nights after owl predation, suggesting that desertion is a response to the actual risk of predation as well as to the possibility of predation.     

Factors affecting egg predation in Black-tailed Gulls

In colonial seabirds, nesting density, egg-laying date and nest microhabitat affect the probability of eggs being taken by avian predators. Jungle Crows (Corvus macrorhynchos) are dominant predators of eggs of Black-tailed Gulls (Larus crassirostris). Factors affecting the probability of gulls allowing the crows to attack their nests or depredate their eggs and the probability of eggs being taken were studied by direct observation and egg census, respectively. The effect of vegetation heights, position in the colony, egg-laying date and neighbour nests on the probability of eggs being taken were examined at multiple spatial scales. Gull nests were depredated more easily by larger groups of crows. Nests in peripheral areas (<4 m from the edge of the colony) were also depredated more easily by the crows walking on the ground. Although the nests where eggs were laid early in the season were depredated more frequently, such nests highly synchronised in egg laying within a <2-m radius were less likely to be depredated than less-synchronised nests. The nests in tall vegetation were less likely to be depredated though those having neighbour nests in tall vegetation were not. The number of neighbour nests did not affect the probability of eggs being taken. Antipredation effects of nesting microhabitats vary with spatial scales at which the crows search and attack the nests of gulls.     

PIRACY BY LAUGHING GULLS LARUS ATRICILLA: AN EXAMPLE OF THE SELFISH GROUP

In 1969, 1500 pairs of terns Sterna spp. and 50 pairs of Laughing Gulls Larus atricilla nested on Petit Manan Island, Maine, U.S.A. The gulls formed groups of up to eleven individuals to steal fish from the terns. The start of piracy coincided with hatching of the gull's eggs. Larger groups more often succeeded in stealing fish than smaller groups. Group formation cannot be ascribed to rarity of terns to chase, and is not due to shared advantage in fish seized or time spent chasing (hence energy expended). A sufficient explanation is the individual advantage to some gulls that join a small group at the expense of the initiator. Individual gulls are likely to follow different strategies. Chasing appeared to be more readily elicited by a chase in progress than by a tern carrying a fish.     

Nest taphonomy of common terns (Sterna hirundo) on Poplar Island,Chesapeake Bay,Maryland

Mesozoic non-avian theropod dinosaurs displayed a diverse range of egg types and clutch forms, suggesting a variety of nesting behaviours, some of which may be shared with birds. More accurate inferences of these behaviours require taphonomic studies of modern nesting sites. Here, we document common tern (Sterna hirundo) nesting sites on Poplar Island in Chesapeake Bay, Maryland. Nests were surveyed on multiple occasions, documenting nest composition, density and distribution, as well as eggshell concentration and orientation. Three colonies yielded 79 tern nests with 193 eggs. Twelve nests hatched, 7 were predated, 30 failed and the fates of 30 remain unknown. Abundant eggshells occurred at the centre of the nests. Concave-up eggshell in or on the nest surface characterised hatched and predated nests, whereas eggshell forced into the subsurface seemed to favour concave-down orientation and may reflect post-hatching extended use of the nest. Eggs buried deep within the nest materials and/or substrate suggest adult abandonment. Quantitative data on eggshell orientation and observations regarding controls on nest distribution, egg predation and incorporation of intact eggs into the substrate at modern nesting sites provide physical guidelines for the improved interpretation of fossil nesting localities.