Tern Species Research Articles

Assessment of genetic diversity in a locally endangered tern species suggests population connection instead of isolation

AbstractMany bird populations are declining globally, with migratory sea- and waterbirds among the most threatened groups. Increased isolation between populations, due to habitat loss leading to limited connectivity and reduced gene flow, may accelerate population declines or even cause local extinctions. To address this threat and inform conservation efforts, assessment of the genetic diversity of endangered populations is required. In Central Europe, gull-billed terns (Gelochelidon nilotica) have experienced a severe population decline in the past century, with only one last population of c. 40 breeding pairs remaining. Here, we aimed to characterise the genetic diversity of this population, and to compare it to that of two separate Mediterranean colonies to assess potential population connectivity. To achieve this, we developed a PCR protocol to amplify and sequence the complete mitochondrial genome (mtDNA). We found high genetic diversity in all three populations, and no population structure based on breeding location, as well as moderate population differentiation between Germany and Italy, and low differentiation between Germany and Spain, and between Italy and Spain. The German population, however, showed signs of population restriction, while both Mediterranean colonies showed evidence for population expansion. These results indicate that the last population of gull-billed terns in Central Europe is not acutely threatened by loss of genetic diversity, but instead shows signs of connectivity with other European colonies, which in turn suggests that conservation efforts should best focus on habitat and predation management.

Radiotelemetry reveals the dependence of inland tern breeding and foraging habitats on ADCP-identified sediment aggradation reaches in lowland rivers

The largest rivers in developed countries have usually been turned into waterways by straightening them and removing large bedforms hampering navigation. For river restoration and their sustainable management it is important to know how large bedforms support biodiversity, whether they could be protected and what potential conflicts in river management they can pose. We have addressed these questions by studying the role of large bedforms in supporting populations of two inland tern species Sternula albifrons and Sterna hirundo. We spatially analysed the behaviour of these two species with reference to the bedform structure mapped over a long semi-natural reach of the River Wisła (Vistula) (S. Poland). The results show that radiotagged terns breed on islands within the aggradation reaches, foraging in the adjacent shallows inhabited by populations of small fish. For Little Terns, the more complex the water line of emergent forms, the greater their foraging intensity. The islands do not pose any flood risk to human settlements. The whole geofeature forms an integral habitat for fish and birds; it is maintained by its geographic settings and so is stable over long periods of time (over 200 years). Protection of such habitats is thus feasible.

Trace element levels in the muscles of three tern species (Aves: Laridae) from the western Arabian Gulf: environmental assessment and implications for conservation

In the Arabian Gulf (called also Persian Gulf; hereafter 'the Gulf'), Jana and Karan Islands are recognized as one of the most Important Bird Areas in the region. Many migratory breeding seabirds, like the Greater Crested Tern Thalasseus bergii, White-cheeked Tern Sterna repressa and Bridled Tern Onychoprion anaethetus, depend on these islands during the breeding season. However, these aquatic wildlife species are suffering from intensified urban and industrial coastal development and various contamination events including wars and related oil spills. In this study, we used these three piscivorous top predator birds to analyse the levels of 19 trace elements (TEs; i.e. Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, Pb, Sr, V and Zn) in 15 muscular tissue samples from Jana and Karan Islands. PERMANOVA analysis showed no difference in contamination profile between sites nor between species probably due to their spatial and ecological proximity and therefore similar levels of exposure to TEs. Comparing these levels with existing literature, our results showed no particular concern for all elements, except for Al (maximum values recorded = 116.5 µg g−1 d.w.) and, in two samples, Ba (33.67 µg g−1 d.w.) and Pb (5.6 µg g−1 d.w.). The results can be considered as an initial step for supplementary evaluations with a larger number of samples and specified time intervals for the collection of specimens. This study provided baseline information on the pollution status of these two ecologically important sites which require a continuous biomonitoring programme.

Very low prevalence of haemosporidian parasites in two species of marsh terns

Vector-transmitted haemosporidians are among the most common parasites in birds, but our knowledge of the inter-specific patterns of infection rates and the parasite community composition is far from complete because of the unequal distribution of the screening effort across bird families and genera. To assess infection rates and the diversity of haemosporidians from the genera Plasmodium, Haemoproteus, and Leucocytozoon in marsh terns, which represent poorly explored in this regard genus of the family gulls, terns, and skimmers (Laridae), we screened two species: the Whiskered Tern (Chlidonias hybrida) and the Black Tern (Chlidonias niger). We sampled these long-distance migratory birds on breeding grounds: the Whiskered Tern in south-central Poland and north-central Ukraine, and the Black Tern—in north-central Ukraine. We found that birds from both species were infected only sporadically, with prevalence at the population level not exceeding 3.4%. Only parasites from the genera Plasmodium and Leucocytozoon were detected. There was neither an inter-specific difference nor a difference between populations of the Whiskered Tern in infection rates. In total, we registered three lineages—one Plasmodium and two Leucocytozoon—that were previously recorded in other bird species, and two unidentified Plasmodium infections. One of the lineages (Leucocytozoon LARCAC02) represents a specialist parasite with the host range restricted to larids and geographic range restricted to Poland, and two others (Plasmodium SGS1 and Leucocytozoon CIAE02) represent generalist parasites with very broad host and geographic ranges. This study reinforces the existing evidence that terns host parasites from genera Haemoproteus, Plasmodium, and Leucocytozoon only sporadically.

Common Terns Sterna hirundo and Roseate Terns Sterna dougallii frequently rest on the sea surface in winter quarters and during migration

ABSTRACT Capsule Common Terns Sterna hirundo and Roseate Terns S. dougallii rarely rest on the sea surface during the breeding season but frequently do so in winter and on migration. Aims To investigate the behaviour of Common and Roseate Terns throughout the annual cycle using immersion sensors. Methods We analyzed data from immersion sensors attached to 11 Common Terns and 6 Roseate Terns that bred in the northeastern USA and wintered either on the north or east coasts of South America, to investigate temporal patterns of resting on saltwater throughout the annual cycle. Results Both species of tern rarely contacted salt water during the breeding season, except when bathing or plunge-diving, but in winter they spent several hours each day resting on the sea surface. This resting was most frequent around midday and least frequent in early mornings and late afternoons. Night-time immersion varied widely among individuals but terns wintering in eastern Brazil were less likely to spend the night on the sea surface than those wintering on the north coast of South America. We suggest that this reflected the availability of dry-land roosting sites. Conclusion Our results are consistent with and extend studies from Europe, confirming that although Common and Roseate Terns spend very little time resting on the sea surface in the breeding season, this behaviour is frequent during migration and wintering periods.

New insights into the influence of turbines on the behaviour of migrant birds: implications for predicting impacts of offshore wind developments on wildlife

Knowledge of the movement and behaviour of birds and bats around turbines in the offshore marine environment is critical for assessing the environmental impacts of offshore wind developments in the eastern USA. To address the problem of gathering high-quality, long-term data on these species in this remote environment, we designed a multi-sensor system that was recently deployed for 6 months in 2021 and 2022. Two Acoustic and Thermographic Offshore Monitoring (ATOM™) systems were deployed on wind turbines 23 nautical miles off the coast of Virginia, USA. The systems were operational during the day and night and recorded 1,581 detections of birds and bats, with 99% of detections occurring in the fall. Most detections were of birds, including 5 shorebird species, 3 gull species, 1 tern species, 3 raptor species, 1 woodpecker species, and 18 passerine species. Skuas, corvids, and swallows were also observed. There were 521 detections of bats. Differences between species detected and identified in each sensor confirms that a multi-sensor approach for monitoring is beneficial. There were no observed collisions; two individuals (1 bird and 1 bat) suffered air displacement, causing them to fall, but they recovered and continued flying. ATOM also collected novel data on insects, tracking over 7,000 insects around the turbine rotor swept zone and revealed foraging behaviour in 596 of the 1,581 bird and bat detections. Offshore wind turbines thus provide potential sites for perching and foraging. Although these turbine sites provide a new opportunity to feed, which may be beneficial for insectivores and omnivores in enabling them to reach migration destinations in better condition, the consequences of a potentially delayed arrival are unknown (positive, negative, or neutral). Overall, our approach produced the first detailed insights into terrestrial land bird and bat activity around offshore turbines, providing novel information on changes in behaviour when turbine blades are moving and during higher wind speeds. Moreover, our data show that foraging activity appears to be conducted with an awareness of the moving blades and in safe zones close but parallel to blade movements. We recorded 113 observations of activity within 10 m of the moving blades and 70 observations where interactions with moving turbine blades were within 1 m; we call these latter avoidance measures nanoavoidance. No collisions were observed.

Factors Affecting Colony Size and Breeding Parameters of Eared Grebe (Podiceps nigricollis) in Carp Ponds

Understanding important factors for breeding Eared Grebes (Podiceps nigricollis) is essential for its conservation. We aimed to study the impact of some factors on nests and breeding success in this species in fishponds (S Poland). Number of Eared Grebe nests were counted on particular carp ponds. Pond size, vegetation cover, number of nests in colonies of associated gull or tern species, and age of stocked common carp (Cyprinus carpio) were determined for all ponds with nests. We also investigated the relationship between nest size, material used to construct them and clutch size. Number of Eared Grebe nests positively correlated with number of breeding pairs of associated colonial species (terns or gulls). Selection of the breeding site by the Eared Grebe can be explained by appropriate nest protection by large colonies of associated species (Whiskered Tern Chlidonias hybrida and Black-headed Gull Chroicocephalus ridibundus). Nest size was not related to clutch size. A negative relationship between breeding success and number of nests of Eared Grebe was found. Food is a not limiting factor for the Eared Grebe on fishponds with extensive production, and presumably other factors such as weather conditions may explain the low breeding success of this species.

Prey Identification of the Little Tern, Sternula albifrons (Pallas, 1764), by Applying DNA Barcoding to Fecal Materials

This study describes the prey DNA fragments found in the feces of a migratory bird species, the little tern, Sternula albifrons (Pallas, 1764), based on a DNA barcoding approach. This species is found in Nakdong Estuary, South Korea, and is a species designated as ‘Least Concern’ (IUCN Red List). Prey identification is a central issue of population conservation, and we applied DNA barcoding (using cytochrome oxidase I; COI) to fecal materials from little tern individuals. We successfully identified prey consumed by little tern individuals. All prey items comprised one phylum including three classes, six orders, and eight families based on a robust dual certification scheme (combined analysis of BLASTn searches and phylogenetic tree construction). Even though the success of identification was largely dependent on the degree of completion of the database in the genebank or BOLD systems, an increased resolution of prey identification to species level is important in predator–prey research. The current study used a small number of fecal samples to evaluate the applicability of the COI barcoding region to avifaunal feces, and more fecal samples are expected to convey increased information that can be used to infer the range of the prey species of little terns.

To fly or not to fly? Comparing vantage point and uncrewed aerial vehicle surveys for assessments of seabird abundance and fine-scale distribution

Marine renewable energy developments (e.g. offshore wind, wave, and tidal) are an increasing feature within the marine environment. It is therefore important to understand the potential impacts of such developments on seabirds that use these environments. Land-based vantage point (VP) surveys are widely used to collect data for environmental impact assessments (EIAs) within tidal stream energy sites. However, tidal stream environments are highly dynamic and present challenges when conducting VP surveys, for example there can be varying detectability of seabirds due to near-surface turbulence. In recent years, there has been increasing interest in the use of uncrewed aerial vehicles (UAVs) to quantify animal abundance and distribution. Yet, to be effective for its use in EIAs, this approach needs to be assessed alongside standardised methods. This study provides the first comparison of at-sea abundance and distribution of surface-foraging seabirds in flight within a tidal stream environment using concurrent VP surveys and UAV transects. Applying a combination of GLMMs and GAMs, our results show that the two survey types produced similar counts of surface-foraging seabirds (tern species) in flight and reveal the influence of covariates affecting counts, including tidal state, sea state, and observer ID. Further, we estimated the overlap (Bhattacharyya's affinity) between tern utilization distributions as a function of tidal state to compare the fine-scale distributions derived from each survey type. The distribution of terns detected, particularly by UAV transects indicated that the highest tern density occurred within the near-shore shallows during the ebb tide and extended into the main channel during the flood tide. Specifically, the UAV transects captured the association of terns with a visible shear line extending into the main channel. Therefore, EIAs may benefit from the use of UAV transect surveys alongside VP surveys to identify fine-scale distributions of seabirds more accurately. Despite these potential benefits, the application of UAVs for use in EIAs may be limited by the species resolution achievable using UAV imagery as well as the impacts of adverse weather conditions and low sun angles (glare). Ultimately, the selection of survey techniques will depend on the specific aims of the EIA, the target species, and species behaviour.

The status and distribution of three species of Sternula terns on the eastern coast of Africa and in the western Indian Ocean, with two species new for Mozambique

The status of three Sternula terns in southern and eastern Africa and the Indian Ocean is updated based on observations in Mozambique during October 2009–August 2021. Damara Tern S. balaenarum and Saunders's Tern S. saundersi, both new to Mozambique, were found at the San Sebastian Peninsula in August 2018 and have been recorded regularly since. Damara Tern arrived in May, numbers were lower June–July, with a peak of 100+ in August–October. Breeding plumage was assumed by late October and all departed in early November; those aged were all adults. Observations of ringed birds suggested they originated from colonies in South Africa. Numbers of Damara Tern reached the Key Biodiversity Area designation threshold population for the site in 2020. These are the first records of large numbers of Damara Tern in the Indian Ocean, whilst timings suggest the species is partly transient at the site and may also occur further north. Saunders's Tern was recorded at San Sebastian in all months except March and April, with 5–80 regularly present, and peak numbers perhaps in October–December. Birds were observed in a range of plumages in all months, from non-breeding, transitional to full breeding. Courtship feeding was observed in September–November suggesting at least some attempt to breed locally, although disturbance is high. Birds in non-breeding plumage may stem from Northern Hemisphere breeding localities. Little Tern S. albifrons was a numerous migrant in southern Mozambique in October–May, peaking in April when large numbers were observed during pelagic trips to the continental shelf edge, and at onshore roost sites including San Sebastian. Smaller numbers fed in coastal lagoons and freshwater lakes. Three Little Terns had been colour-ringed in Israel.

Presence and antimicrobial resistance profiles of Escherichia coli, Enterococcusspp. and Salmonellasp. in 12 species of Australian shorebirds and terns.

Antibiotic resistance is an ongoing threat to both human and animal health. Migratory birds are a potential vector for the spread of novel pathogens and antibiotic resistance genes. To date, there has been no comprehensive study investigating the presence of antibiotic resistance (AMR) in the bacteria of Australian shorebirds or terns. In the current study, 1022 individual birds representing 12 species were sampled across three states of Australia (Victoria, South Australia, and Western Australia) and tested for the presence of phenotypically resistant strains of three bacteria with potential to be zoonotic pathogens; Escherichia coli, Enterococcusspp., and Salmonellasp. In total, 206 E. coli, 266 Enterococcusspp., and 20 Salmonellasp. isolates were recovered, with AMR detected in 42% of E. coli, 85% of Enterococcusspp., and 10% of Salmonellasp. Phenotypic resistance was commonly detected to erythromycin (79% of Enterococcusspp.), ciprofloxacin (31% of Enterococcusspp.) and streptomycin (21% of E. coli). Resident birds were more likely to carry AMR bacteria than migratory birds (p ≤ .001). Bacteria isolated from shorebirds and terns are commonly resistant to at least one antibiotic, suggesting that wild bird populations serve as a potential reservoir and vector for AMR bacteria. However, globally emerging phenotypes of multidrug‐resistant bacteria were not detected in Australian shorebirds. This study provides baseline data of the carriage of AMR bacteria in Australian shorebirds and terns.

An evaluation of transmitter effects on adult and juvenile Common Terns using leg-loop harness attachments

Marking birds with transmitters allows for the collection of data that are critical for fully understanding avian life history, but researchers must also be confident that performing such studies is as safe as possible for transmittered individuals. While much could be learned from tracking juveniles across dependency periods and first migration, doing so would require a harness-based attachment method which has not been evaluated on any species of juvenile tern. Therefore, we monitored the reproductive success and behavior of adult Common Terns (<em>Sterna hirundo</em>) and the growth and behavior of juvenile Common Terns after attaching transmitters to adults and juveniles with leg-loop harnesses made of elastic cord. We found that transmittered adults had similar reproductive success to untransmittered controls (hatching success for nests of transmittered adults = 0.553; nests of control adults = 0.665). Transmittered adults also expressed minimal behavioral differences from untransmittered controls when the groups were compared via paired treatment-control nest observations along with observations away from the nest. Transmittered juveniles had similar fledging success and growth rates to untransmittered control juveniles (fledging success for transmittered juveniles = 0.766; control juveniles = 0.817). Transmittered juveniles exhibited slight differences in behavior from controls, with increased rates of preening, although these differences did not appear to be detrimental. Finally, monitoring efforts during the breeding season following transmitter deployment found no difference in the return rate, nesting attempt rate, or hatching success rate based on treatment (P > 0.05). However, despite evidence of an individual retaining its transmitter into fall migration, no individuals retained their transmitters when resighted the following breeding season. While our results show that leg-loop harnesses made of elastic cord present a potential option for transmitter attachment to both adult and juvenile Common Terns, additional testing could provide further insight into potential long-term impacts.

Pre-breeding foraging ecology of three tern species nesting in the Gulf of Maine

Bratton, R. M., H. D. Legett, P. Shannon, K. C. Yakola, A. R. Gerson, and M. D. Staudinger. 2022. Pre-breeding foraging ecology of three tern species nesting in the Gulf of Maine. Avian Conservation and Ecology 17(1):19. https://doi.org/10.5751/ACE-02112-170119

An investigation into factors contributing to mortality of young terns at a managed colony

Terns are a highly migratory group of seabirds that are found worldwide. In Ireland, there are five species of commonly breeding tern: Little Tern Sternula albifrons, Roseate Tern Sterna dougallii, Arctic Tern S. paradisaea, Common Tern S. hirundo and Sandwich Tern S. sandvicensis. Prior work has demonstrated that whilst many Irish tern species, including Common and Roseate Terns, are increasing in abundance, the productivity of these species can be low. Multiple factors may influence the ability of adult terns to successfully raise chicks, including food availability, provisioning rates, colony density, dependence effects, and/or disease. Here, we investigated factors contributing to the mortality of young terns from Rockabill Island in the Republic of Ireland, which supports the largest breeding population of Roseate Terns in Europe. To better understand the factors contributing to the deaths of young birds, we analysed the macroscopic and microscopic characteristics of necropsies of 60 young Common, Arctic and Roseate Terns. Of the carcasses that we examined, 41 showed congested blood circulation in the lungs and head simultaneously, and of the remaining 19 birds, only five presented a clear cause of death. Here, we outline descriptions of these carcasses in addition to recommendations of further investigations that might help to confirm the causal factors leading to young tern mortality.

Interspecific and Local Variation in Tern Chick Diets Across Nesting Colonies in the Gulf of Maine

The Gulf of Maine, USA is home to four colonial co-nesting tern species: Least Tern (Sternula antillarum), Common Tern (Sterna hirundo), Arctic Tern (Sterna paradisaea), and the federally endangered Roseate Tern (Sterna dougallii). Over three decades of visual observations of chick provisioning were compiled for a comparative dietary study in the region, including the first detailed descriptions of Least and Roseate Tern chick diets. Three prey groups comprised the majority of chick diets among tern species between 1986–2017: hake (Urophycis spp. or Enchelyopus cimbrius) 28–37% frequency of occurrence (FO), sand lance (Ammodytes americanus or A. dubius) 8–22% FO, and herring (Clupea spp. or Alosa spp.) 3–30% FO. Dietary contributions varied across species and islands. At two inshore colonies, Common Tern diets contained higher amounts of sand lance (30–42% FO), while offshore islands contained lesser amounts (5–9% FO). Overall dietary diversity (H′) was similar between Common (H′ = 1.57) and Arctic Terns (H′ = 1.74) and notably lower in Roseate (H′ = 1.24) and Least Terns (H′ = 1.37), whose diets were primarily piscivorous. The degree of dietary plasticity and general feeding ecology provided by baseline dietary information can inform holistic assessments of risk to ongoing and future disturbances from fishing and climate change.

Not going with the flow: Ecological niche of a migratory seabird, the South American Tern Sterna hirundinacea

Defining a species’ ecological niche is not a trivial task particularly for marine taxa, since physical and biological constraints are not easily perceived in these environments. Yet, coastal habitats are divided into provinces, influenced by different environmental conditions, such as superficial marine currents, causing seasonality in marine productivity and biomass. The South American Tern Sterna hirundinacea is a poorly known, migratory seabird distributed along the Pacific and Atlantic coasts of South America, including the Malvinas/Falkland Islands, and occurring in most of the South American coastal provinces. Limited knowledge on the migratory behaviour of the species points to differential habits between southern and northern populations. The species’ breeding season also varies with latitude and season, occurring during spring in the south and in the fall in northern areas of the species occurrence. These observations point to putatively ecologically distinct populations along the species range that seem to be coincident with coastal provinces. To test our hypotheses, we estimated full-range ecological niche models per season, and we used coastal provinces to model ecological niches for each of the known breeding areas/seasons. We also tested for environmental space differentiation between seasons and breeding and non-breeding areas. Overall, the species does not seem to occupy significantly different ecological niches throughout the year, except during the breeding season, particularly between the Warm Temperate Southeastern Pacific and Warm Temperate Southwestern Atlantic provinces in fall. This suggests that the South American Tern migratory behaviour, the selection of different microhabitats and reproductive areas or distinct biological interactors might be influencing the species environmental space. Nonetheless, our models reinforce the gradual migration of this tern species towards the south, spending the summer mostly in the Malvinas/Falkland Islands. Interestingly, the species seems to be resident in Peru coastal area. Thus, despite the absence of ecological divergence, population structure should be tested and demographic trends assessed along the species range.

Variation in male-built nest volume with nesting-support quality, colony, and egg production in whiskered terns.

Nest building can represent an energetically costly activity for a variety of animal taxa. Besides, the determinants of within‐species variation in the design of nests, notably with respect to natural and sexual selection, are still insufficiently documented. Based on an observational study, we examined the influence of nesting conditions (nesting‐support quality, colony, laying date, and year) on male‐built nest volume and also its potential role as a postmating sexually selected display in the whiskered tern Chlidonias hybrida. This tern species is a monogamous colonial bird with obligate biparental care breeding on aquatic vegetation. Hence, large nesting platforms are expected to be a selective advantage because they would better withstand adverse environmental conditions and provide a secure structure for eggs. Nest size may also serve as a postmating sexual trait, and variation in egg production would be positively associated with nest size. We found that nest volume was adjusted to different environmental cues. A positive relationship was found between nest volume and nesting‐support quality, indicating that the leaf density of white waterlily is essential for nest stability. Variation in nest volume was not correlated to colony size but varied among colonies and years. Male‐built nest volume was also positively associated with mean egg volume per clutch but not with clutch size. The fitness consequences of building a large nest are yet to be studied, and additional investigations are recommended to better understand whether the activity of males early during breeding season (e.g., nest building and courtship feeding performance) really serves as postmating sexually selected signals.

A bird's-eye view on turbulence: seabird foraging associations with evolving surface flow features.

Understanding physical mechanisms underlying seabird foraging is fundamental to predict responses to coastal change. For instance, turbulence in the water arising from natural or anthropogenic structures can affect foraging opportunities in tidal seas. Yet, identifying ecologically important localized turbulence features (e.g. upwellings approximately 10–100 m) is limited by observational scale, and this knowledge gap is magnified in volatile predators. Here, using a drone-based approach, we present the tracking of surface-foraging terns (143 trajectories belonging to three tern species) and dynamic turbulent surface flow features in synchrony. We thereby provide the earliest evidence that localized turbulence features can present physical foraging cues. Incorporating evolving vorticity and upwelling features within a hidden Markov model, we show that terns were more likely to actively forage as the strength of the underlying vorticity feature increased, while conspicuous upwellings ahead of the flight path presented a strong physical cue to stay in transit behaviour. This clearly encapsulates the importance of prevalent turbulence features as localized foraging cues. Our quantitative approach therefore offers the opportunity to unlock knowledge gaps in seabird sensory and foraging ecology on hitherto unobtainable scales. Finally, it lays the foundation to predict responses to coastal change to inform sustainable ocean development.

21 000 birds in 4.5 h: efficient large‐scale seabird detection with machine learning

AbstractWe address the task of automatically detecting and counting seabirds in unmanned aerial vehicle (UAV) imagery using deep convolutional neural networks (CNNs). Our study area, the coast of West Africa, harbours significant breeding colonies of terns and gulls, which as top predators in the food web function as important bioindicators for the health of the marine ecosystem. Surveys to estimate breeding numbers have hitherto been carried out on foot, which is tedious, imprecise and causes disturbance. By using UAVs and CNNs that allow localizing tens of thousands of birds automatically, we show that all three limitations can be addressed elegantly. As we employ a lightweight CNN architecture and incorporate prior knowledge about the spatial distribution of birds within the colonies, we were able to reduce the number of bird annotations required for CNN training to just 200 examples per class. Our model obtains good accuracy for the most abundant species of royal terns (90% precision at 90% recall), but is less accurate for the rarer Caspian terns and gull species (60% precision at 68% recall, respectively 20% precision at 88% recall), which amounts to around 7% of all individuals present. In sum, our results show that we can detect and classify the majority of 21 000 birds in just 4.5 h, start to finish, as opposed to about 3 weeks of tediously identifying and labelling all birds by hand.

Monitoring the Hatching Success of Gulls Laridae and Terns Sternidae: A Comparison of Ground and Drone Methods

Measuring the productivity of gulls Laridae and terns Sternidae is often difficult, due to natural obstacles of site access and the need to avoid disturbing nesting birds. Drones are increasingly being used for conservational and ecological applications and their use seems to overcome these problems, but data are still scarce on their use to assess breeding success. Our objective was to compare the effectiveness, time consumption, and safety for birds of drone-conducted monitoring of nest-specific hatching success with usual ground surveys of two species of gulls, including Slender-billed Gulls Chroicocephalus genei and Mediterranean Gulls Larus melanocephalus, and two species of terns, including Gull-billed Terns Gelochelidon nilotica and Sandwich Terns Thalasseus sandvicensis, breeding in the Adriatic wetlands of northeast Italy. We studied 400 nests (100 per species distributed in eight plots, each with 50 nests) and found no significant difference between the two methods in determining the number of eggs either laid or hatched per nest for all four focal species. The average coefficient of agreement between methods was high (kappa > 0.80 for all comparisons). The mean time spent determining the hatching success of 50 clutches with a drone (263 sec per plot) was significantly less than with ground surveys (760 sec per plot). There were no apparent negative effects of drone flights on nesting pairs, clutches, or young. Our results suggest that drones allow effective, rapid, and safe measurement of seabird breeding success in coastal areas.