Botaurus Stellaris Research Articles

Understanding local knowledge and attitudes toward potential reintroduction of a former British wetland bird

AbstractStakeholder acceptance and support is essential for long‐term success in species reintroductions, and assessing social feasibility of reintroductions within human‐occupied landscapes is an integral component of effective decision‐making.The Dalmatian pelicanPelecanus crispusis an extirpated British bird, and possible pelican reintroduction to British wetlands is under discussion. Any reintroduction planning must first assess local community awareness, attitudes, and acceptance of potential pelican arrival and associated habitat management, as part of wider socio‐ecological feasibility assessment. Pelicans are distinctive species with potential to increase support for wetland conservation, but might provoke conflict through real or perceived competition with landscape users such as fishers; such conflict is already seen within Britain between fishers and cormorants.We conducted an online survey of 590 respondents in the Somerset Levels and East Anglian Fens, Britain's largest wetland landscapes, to understand local views on pelican reintroduction, other reintroductions and wetland restoration, and to investigate correlates of varying attitudes toward coexistence with pelicans and five other waterbirds (grey heron, Eurasian bittern, little egret, common crane, great cormorant).Respondents had generally positive views about previous reintroductions of other species, and had overall positive attitudes toward all six waterbirds. Two‐thirds of respondents supported or strongly supported pelican reintroduction, but both benefits and concerns were identified in relation to its possible reintroduction. Anglers and hunters were more likely to hold negative attitudes toward pelicans, other waterbirds and wetland restoration. However, although anglers raised more concerns, they were not more likely to be unsupportive toward reintroduction. More socio‐demographic predictors were associated with negative attitudes toward restoration required to establish pelican habitat, suggesting that positive feelings toward biodiversity are outweighed by concerns around potential exclusion from local landscapes.Our findings suggest pelican reintroduction might be supported by local stakeholders. Attitudes toward cormorants do not represent a blueprint for attitudes toward pelicans, and anglers may support reintroduction if concerns around impacts to fish stocks are addressed. Community engagement for species‐specific and landscape‐scale actions require separate approaches, with landscape management planning needing to target a wider range of stakeholder groups with separate concerns to those about coexistence with pelicans.Read the freePlain Language Summaryfor this article on the Journal blog.

Low-cost open-source recorders and ready-to-use machine learning approaches provide effective monitoring of threatened species

Passive acoustic monitoring is a powerful tool for monitoring vocally active taxa. Automated signal recognition software reduces the expert time needed for recording analyses and allows researchers and managers to manage large acoustic datasets. The application of state-of-the-art techniques for automated identification, such as Convolutional Neural Networks, may be challenging for ecologists and managers without informatics or engineering expertise. Here, we evaluated the use of AudioMoth — a low-cost and open-source sound recorder — to monitor a threatened and patchily distributed species, the Eurasian bittern (Botaurus stellaris). Passive acoustic monitoring was carried out across 17 potential wetlands in north Spain. We also assessed the performance of BirdNET — an automated and freely available classifier able to identify over 3000 bird species — and Kaleidoscope Pro — a user-friendly recognition software — to detect the vocalizations and the presence of the target species. The percentage of presences and vocalizations of the Eurasian bittern automatically detected by BirdNET and Kaleidoscope Pro software was compared to manual annotations of 205 recordings. The species was effectively recorded up to distances of 801–900 m, with at least 50% of the vocalizations uttered within that distance being manually detected; this distance was reduced to 601–700 m when considering the analyses carried out using Kaleidoscope Pro. BirdNET detected the species in 59 of the 63 (93.7%) recordings with known presence of the species, while Kaleidoscope detected the bittern in 62 recordings (98.4%). At the vocalization level, BirdNet and Kaleidoscope Pro were able to detect between 76 and 78%, respectively, of the vocalizations detected by a human observer. Our study highlights the ability of AudioMoth for detecting the bittern at large distances, which increases the potential of that technique for monitoring the species at large spatial scales. According to our results, a single AudioMoth could be useful for monitoring the species' presence in wetlands of up to 150 ha. Our study proves the utility of passive acoustic monitoring, coupled with BirdNET or Kaleidoscope Pro, as an accurate, repeatable, and cost-efficient method for monitoring the Eurasian bittern at large spatial and temporal scales. Nonetheless, further research should evaluate the performance of BirdNET on a larger number of species, and under different recording conditions (e.g., more closed habitats), to improve our knowledge about BirdNET's ability to perform bird monitoring. Future studies should also aim to develop an adequate protocol to perform effective passive acoustic monitoring of the Eurasian bittern.

First definite record of Collared Pratincole Glareola pratincola Linnaeus, 1766 (Aves: Charadriiformes: Glareolidae) from Goa, India

Collared Pratincole Glareola pratincola has been recorded from various regions in southern India and is known to be a two way passage migrant to Western Ghats. However, this species had not been included in Goa’s avifaunal checklist since the old records for the bird could not be confirmed. Hence, the present sighting of this bird at Maina-Curtorim fields, Goa qualifies as the first definite record for Goa. During the period 2013–2021, three birds namely the Spot-billed Pelican Pelecanus philippensis, Lesser Flamingo Phoeniconaias minor and Eurasian Bittern Botaurus stellaris were spotted within one-kilometer radius of the Maina-Curtorim wetlands and added to the avifaunal checklist of Goa. This offers an opportunity for additional surveys to establish the migratory route and also highlights the conservational value of the region.

Auditory Survey of Endangered Eurasian Bittern Using Microphone Arrays and Robot Audition.

Bioacoustics monitoring has become increasingly popular for studying the behavior and ecology of vocalizing birds. This study aims to verify the practical effectiveness of localization technology for auditory monitoring of endangered Eurasian bittern (Botaurus stellaris) which inhabits wetlands in remote areas with thick vegetation. Their crepuscular and highly secretive nature, except during the breeding season when they vocalize advertisement calls, make them difficult to monitor. Because of the increasing rates of habitat loss, surveying accurate numbers and their habitat needs are both important conservation tasks. We investigated the feasibility of localizing their booming calls, at a low frequency range between 100–200 Hz, using microphone arrays and robot audition HARK (Honda Research Institute, Audition for Robots with Kyoto University). We first simulated sound source localization of actual bittern calls for microphone arrays of radii 10 cm, 50 cm, 1 m, and 10 m, under different noise levels. Second, we monitored bitterns in an actual field environment using small microphone arrays (height = 12 cm; width = 8 cm), in the Sarobetsu Mire, Hokkaido Island, Japan. The simulation results showed that the spectral detectability was higher for larger microphone arrays, whereas the temporal detectability was higher for smaller microphone arrays. We identified that false detection in smaller microphone arrays, which was coincidentally generated in the calculation proximate to the transfer function for the opposite side. Despite technical limitations, we successfully localized booming calls of at least two males in a reverberant wetland, surrounded by thick vegetation and riparian trees. This study is the first case of localizing such rare birds using small-sized microphone arrays in the field, thereby presenting how this technology could contribute to auditory surveys of population numbers, behaviors, and microhabitat selection, all of which are difficult to investigate using other observation methods. This methodology is not only useful for the better understanding of bitterns, but it can also be extended to investigate other rare nocturnal birds with low-frequency vocalizations, without direct ringing or tagging. Our results also suggest a future necessity for a robust localization system to avoid reverberation and echoing in the field, resulting in the false detection of the target birds.

Checklist of Fish Hosts of Species of Contracaecum Railliet & Henry, 1912 (Nematoda: Ascaridida: Anisakidae) in Iraq

Surveying literature concerning the occurrence of the nematode larval forms of the genus Contracaecum in fishes of Iraq, showed the infection of 44 freshwater and marine fish species in Iraq with such larvae. The infection included larvae of unidentified Contracaecum species, Contracaecum rudolphii type-B and Contracaecum septentrionale Kreis, 1955. The infections were distributed in Tigris, Euphrates and Shatt Al-Arab rivers as well as some of their tributaries, lakes, marshes, drainage networks in addition to many fish ponds and floating cages in different parts of Iraq. This checklist also provided references on some histopathological and biochemical changes, some ecological aspects of the infection, life cycle and scanning electron microscopy. In addition, this checklist includes literature on six species of adult Contracaecum species as well some unidentified species of this genus from 17 bird species from different parts of Iraq, of which both Eurasian bittern Botaurus stellaris and pygmy cormorant Microcarbo pygmaeus were infected with a maximum number of three Contracaecum species as well as unidentified species of this genus.

The influence of weather on the migration behaviour of Eurasian Bitterns Botaurus stellaris

ABSTRACT Capsule Migration studies of tagged Eurasian Bitterns Botaurus stellaris provide information on the behaviour of this secretive species in relation to weather conditions. Aims To study if cold spells trigger southward migration in resident Eurasian Bitterns. To describe migratory behaviour including flight routes, altitudes, flight direction in relation to wind speed and direction, and general characteristics of stopping sites. Methods Six adult Eurasian Bitterns from Dutch breeding areas were followed for two to five years using ARGOS-PTT/GPS transmitters or GPS trackers. Results Four individuals remained at the breeding sites in winter and did not migrate in response to cold spells. Two individuals covered distances of 300 and 1600 km between stopping sites. They migrated predominantly at night, but over the Sahara they extended flights into daylight hours. Depending on wind assistance, flight speeds (groundspeed) varied between 3.6 and 26 ms−1. Flight altitude varied from just above sea level when facing headwinds, to almost 2000 m above sea level under tail wind conditions. Repeatedly tracked individuals showed substantial variation in routes and stopping sites between successive migrations. These flight patterns appeared influenced by the speed and direction of the winds encountered en route. Conclusions Eurasian Bitterns were either migratory or resident and the latter individuals did not perform facultative movements at the onset of cold spells. The flight speed, flight altitudes, and routes of migrating birds were influenced by wind conditions. This likely explains the variable use of stopping sites between years.

Distribution and numbers of waterbird species breeding in the city of Wrocław

Abstract During the years 2003-2010, the numbers of pairs of waterbird species breeding in the city of Wrocław (293 km2) were assessed. The city is situated in Odra valley, where four smaller rivers join it. The city abandons in oxbows, gravel and sand, and clay pits and other water bodies. In total, 20 waterbird species were recorded as breeding in Wrocław. The most common were Anas platyrhynchos (145-212 pairs), and Fulica atra (70-104 pairs). Relatively common were also the Gallinula chloropus (28-37 pairs), Rallus aquaticus (9-25 pairs) and Cygnus olor (9-11 pairs). For each remaining species less than 10 pairs were recorded. Among rare species, the following were recorded as breeding in Wrocław: Grus grus, Mergus merganser, and Porzana porzana. In the few recent decades, the increase in the number of breeding pairs was recorded for Anas platyrhynchos and Cygnus olor; while a parallel decrease was recorded for Fulica atra, Gallunula chloropus, Chroicocephalus ridibudnus, and Tachybaptus ruficollis. Species such as the Aythya fuligula, Aythya ferrina, grebes, gulls and terns avoid the city. Some of them even ceased to breed (Anas quarquedula, Anas clypeata and Botaurus stellaris). The city plays an important role in protecting water bird species such as Grus grus, Cygnus olor, Porzana porzana and Alcedo atthis.

Sex-Related Migration Distances in the Dimorphic Eurasian Bittern Botaurus stellaris Breeding in the Netherlands

In many bird species intraspecific variation in migration strategies is related to sex or size. The Eurasian Bittern Botaurus stellaris is a sexually size-dimorphic heron species with a vast breeding and wintering range spanning a range of climates. Ringing data show that Bitterns from northern populations migrate westwards or southwards over thousands of kilometres, while Bitterns from southern or temperate breeding areas migrate much shorter distances or remain resident. So far, any differences in the migrations of males and females have remained unstudied. In temperate climates, relatively benign winters alternate with the occasional harsh winter, and under these conditions, males as the larger sex might take the risk to stay rather than show seasonal migration. In the years 2010–2012 we equipped three females and three males from breeding areas in The Netherlands with a tracking device, recording their movements over periods of 2–5 years. All three males and one female stayed within or near the breeding area during the non-breeding season, but two females moved to distant wintering sites. One female migrated 4900 km to The Gambia providing the first direct evidence for trans-Saharan migration in this species. Another female migrated 700 km to winter in Devon, UK, for five consecutive years. The Bitterns were site-faithful to their breeding area and, mostly, to their wintering areas as well, although one male and one female progressively wintered closer to the breeding area in three successive years. Our results suggest that larger males from The Netherlands, a breeding area with fluctuating winter conditions, are predominantly resident, while the females are partial migrants with individually different and flexible strategies.

Annual migration routes, stopover patterns and diurnal activity of Eurasian Bitterns Botaurus stellaris wintering in China

ABSTRACTCapsuleEurasian Bitterns Botaurus stellaris caught in winter in eastern China summered in the Russian Far East.AimsTo identify migration timing, duration and routes, as well as stopover sites, used by Eurasian Bitterns in the Russian Far East flyway and obtain basic information on behaviour and ecology from tracking data.MethodsWe tracked two Eurasian Bitterns caught in China with global positioning system/mobile communications loggers for one and three years respectively, to identify their migration routes and schedules. We used the distance moved between successive fixes to determine their diurnal activity patterns.ResultsThe two individuals wintered in eastern China and travelled a mean of 4221 ± 603 km (in 2015–17) and 3844 km (2017) to summer in the Russian Far East. Results from one bird have shown that in all three years, the bird was significantly more active during the day than at night, although the absolute differences varied with season, being most nocturnally active in summer. The most surprising result from this bird was the flexibility in spring migration and the lack of summer site fidelity.ConclusionThe study identified previously unknown migration routes of the Eurasian Bittern in East Asia, and suggested that the species is generally more active during the day throughout the year.

The declining abundance of Great Bittern during the breeding season at Watarase Marsh

The declining abundance of Great Bittern during the breeding season at Watarase Marsh

An FPGA-Based WASN for Remote Real-Time Monitoring of Endangered Species: A Case Study on the Birdsong Recognition of Botaurus stellaris.

Fast environmental variations due to climate change can cause mass decline or even extinctions of species, having a dramatic impact on the future of biodiversity. During the last decade, different approaches have been proposed to track and monitor endangered species, generally based on costly semi-automatic systems that require human supervision adding limitations in coverage and time. However, the recent emergence of Wireless Acoustic Sensor Networks (WASN) has allowed non-intrusive remote monitoring of endangered species in real time through the automatic identification of the sound they emit. In this work, an FPGA-based WASN centralized architecture is proposed and validated on a simulated operation environment. The feasibility of the architecture is evaluated in a case study designed to detect the threatened Botaurus stellaris among other 19 cohabiting birds species in The Parc Natural dels Aiguamolls de l’Empordà, showing an averaged recognition accuracy of 91% over 2h 55’ of representative data. The FPGA-based feature extraction implementation allows the system to process data from 30 acoustic sensors in real time with an affordable cost. Finally, several open questions derived from this research are discussed to be considered for future works.

Information obtained from long-term acoustic recordings: applying bioacoustic techniques for monitoring wetland birds during breeding season

Digital acoustic recording devices allow for recording of vocal activity of animals over long time periods and therefore open new perspectives for monitoring. In this paper results of a bioacoustic monitoring of birds in a wetland restoration area in Mecklenburg-Western Pomerania in Northeastern Germany are presented. Ninety minutes of sound recordings were made daily from March 29 until May 30 2012 using a four-channel recording setup. The recording schedule was mainly designed for nocturnal birds but also included dawn and dusk choruses. By listening to the recordings, supported by spectrographic visualization, 61 bird species could be detected. Despite the fact that most of the recordings were made during the night, no period of absolute silence was detected. The occurrence data allow some conclusions on the state of the bird species, e.g., breeding bird, resting during migration, or guest only. The bioacoustic monitoring revealed the occurrence of rare nocturnal birds such as Little Crake (Porzana parva), Spotted Crake (Porzana porzana) and Short-eared Owl (Asio flammeus). For the Eurasian Bittern (Botaurus stellaris) data on vocal activity and population size could be obtained. The study has shown that automated acoustic recordings can be applied for long-term monitoring of bird populations in remote areas.

Mercury concentration in the feathers of birds from various trophic levels in Fereydunkenar International wetland (Iran).

Mercury (Hg) is one of the main global pollutants that may biomagnify in food nets, especially in wetlands. Birds may be useful in the biomonitoring of Hg in such habitats and may even serve in vivo samples. This paper examined Hg concentration in the feathers of seven bird species foraging on Fereydunkenar International wetland (in 2013). Mean Hg concentrations found ranged from 0.005 ± 0.002 μg g−1 d.w. (dry weight) (Common hoopoe) to 0.38 ± 0.047 μg g−1 d.w. (Greylag goose). Significant differences in Hg concentrations were noted between bird species as well as between trophic levels (one-way ANOVAs, p < 0.001). The decrease in mean Hg concentration in feathers was as follows: Greylag goose > Northern pintail ≥ Gadwall ≥ Mallard > Eurasian bittern ≥ Little bittern > Common hoopoe. The position in the trophic chain significantly influenced Hg concentrations, which were the highest in omnivorous species. Hg concentrations may also depend on migration routes and breeding habitats, but the evaluation of the exposure exceeds the ambit of this paper. The Hg concentrations found generally were low, lower than the safe thresholds reported in the literature.

Nest survival patterns in Eurasian Bittern: effect of nest age, time and habitat variables.

Determining the key factors affecting the reproductive success of nesting birds is crucial in order to better understand the population dynamics of endangered species and to introduce effective conservation programmes for them. Inhabiting a variety of wetland habitats, aquatic birds actively select safe nesting sites so as to protect their nests against predators. The main aim of the present work was to assess the effect of temporal and habitat variables on the daily nest survival rate of Eurasian Bitterns colonizing semi–natural fishpond habitat in eastern Poland. MARK software was used for the modelling. Eurasian Bittern nests were most vulnerable to depredation at the beginning of the breeding season. This was probably because the reedbed vegetation at this time was not yet dense enough to effectively conceal the nests. There was a positive relationship between nest age and the daily survival rate. Two of the habitat variables analysed were of the greatest significance: water depth and vegetation density. In the Eurasian Bittern population studied here, nests built over deep water and in dense vegetation had the best chances of survival. The results of this work may be useful in the preparation of plans for the conservation and management of populations of this rare and endangered species. Conservation and restoration efforts that attempt to maintain high water levels will be especially beneficial to this avian species that is dependent on wetland ecosystems for breeding.

Effects of Weather Conditions, Time of Breeding, Brood Size and Hatching Order on Eurasian Bittern Nestling Growth in a Food-Rich Fishpond Habitat

The development of nestlings depends on both biological and weather factors. However, their combined effect differs among bird species. In this study, the impacts of three temperature variables, precipitation, wind speed, timing of breeding, brood size and hatching order on the growth of Eurasian bittern Botaurus stellaris chicks were analysed. Measurements of 183 nestlings from 57 nests were made at fishpond complexes in eastern Poland. Relative growth rates (RGR) were calculated on the basis of tarsus length and body mass. Generalised linear mixed models showed that brood size, hatching order and precipitation were the most important factors. Nestlings in broods of two and three grew faster than those from broods of four and five. In the largest broods, the fifth-hatched chicks had lower growth rates; this also applied to the oldest chicks in all brood-size categories. Nestlings from late-season nests showed enhanced mass and tarsus growth, while heavier precipitation and strong winds depressed growth rates. The study emphasises that even among bitterns breeding in food-rich habitats like fishponds, the chicks in largest broods run the risk of lower growth rates.

Environmental variables predict timing of breeding in the polygynous Eurasian bitternBotaurus stellaris

The timing of clutch initiation in migratory birds is determined by many factors and affects fitness. In polygynous species the date of egg laying may also be determined by mating status. In order to identify the habitat factors enabling Eurasian bittern females to breed early, a study was carried out on nine fishpond complexes in eastern Poland during 2003–2009. The habitat characteristics of the nesting sites, including fish stock type and the breeding success were recorded for 48 monogamous, 31 primary, 30 second and 12 third or fourth females. The analysis showed that early nesting females preferred a higher density of old reed stems and chose less attractive ponds with poorer food resources. Monogamous and primary females laid first eggs eight days earlier on average and had higher breeding success than the second, third and fourth females. The relationship between the fate of broods and the breeding success of neighbouring nests was found for second females. Our results suggest that Eurasian bittern females benefit from early nesting, provided they can find appropriate vegetation at the nesting site.

Composition, structure and pattern of helminth assemblages associated with central European herons (Ardeidae)

Helminths parasitizing the ardeid birds are poorly understood, and the majority of studies are limited to checklists and records of novel host–parasite interactions. Here we analyzed the prevalence, intensity and diversity of the helminth component communities associated with an extensive cohort of the five most common Czech herons (Ardea cinerea, Ardea alba, Nycticorax nycticorax, Botaurus stellaris and Ixobrychus minutus) collected in the years 1962–2013. Comparison with Ukrainian datasets supports the existence of local helminth component communities, subject to strong geographic variation. The diversity of the component communities ranged between 37.3±9.6 (A. cinerea) and 2.5±1.1 (I. minutus) species. Similarly, the frequency of particular helminths differed by over one order of magnitude, whereas the helminth load differed by over two orders of magnitude. Typically, the dominant species (Echinochasmus beleocephalus, Uroproctepisthmium bursicola, Posthodiplostomum cuticola, Apharyngostrigea cornu, Desmidocercella numidica and Neogryporhynchus cheilancristrotus) were considered local, with intermediate host species available onsite, as represented by freshwater mollusks. Of the digeneans, 52% of the species likely infected their definitive hosts outside the study area, frequently utilizing invertebrates of salt or brackish waters. For A. cinerea, the largest number of species was in adult males; however the helminth load of the adults was lower than in their juvenile counterparts. This study provides the first systematically collected evidence for the intra-annual changes of the helminth assemblages in herons.

Applying bioacoustic methods for long-term monitoring of a nocturnal wetland bird

Bioacoustic monitoring is becoming more and more popular as a non-invasive method to study populations and communities of vocalizing animals. Acoustic pattern recognition techniques allow for automated identification of species and an estimation of species composition within ecosystems. Here we describe an approach where on the basis of long term acoustic recordings not only the occurrence of a species was documented, but where the number of vocalizing animals was also estimated. This approach allows us to follow up changes in population density and to define breeding sites in a changing environment. We present the results of five years of continuous acoustic monitoring of Eurasian bittern (Botaurus stellaris) in a recent wetland restoration area. Using a setup consisting of four four-channel recorders equipped with cardioid microphones we recorded vocal activity during entire nights. Vocalizations of bitterns were detected on the recordings by spectrogram template matching. On basis of time differences of arrival (TDOA) of the acoustic signals at different recording devices booming bitterns could be mapped using hyperbolic localization. During the study period not only changes in the number of calling birds but also changes in their spatial distribution connected with changes in habitat structure could be documented. This semi-automated approach towards monitoring birds described here could be applied to a wide range of monitoring tasks for animals with long distance vocalizations.

Population dynamics of Great Bittern (Botaurus stellaris) in the Netherlands: interaction effects of winter weather and habitat fragmentation

The increased variability in weather as a manifestation of climate change is expected to have negative impacts on population survival in wildlife species, because it will likely lead to increased variation in vital demographic rates (mortality and reproduction) in these populations. For the effective protection of biodiversity, adaptation measures are needed to compensate for the expected increase in weather variability and the negative interaction with habitat fragmentation. As a case study, we studied the fluctuations in Great Bittern numbers (Botaurus stellaris) from 28 monitoring plots scattered over the Netherlands to explore the interaction between the effect of weather and possible remediating effects of the landscape structure. Great Bittern habitat surrounding these plots differs with respect to area, quality, and degree of isolation of this habitat. In western Europe, Great Bitterns are found to be susceptible to continuous loss of suitable habitat due to vegetation succession and fragmentation. Moreover, year-to-year fluctuations in local Great Bittern populations can be caused by severe winter weather or other weather extremes. Our results show that severe winter weather has indeed a significant negative impact on Great Bittern population growth rates. Furthermore, we found that an increased carrying capacity and spatial cohesion (i.e. inverse of habitat fragmentation) contribute to an increase in mean growth rates over the years. As growth rates are higher in large, well-connected habitats, we argue that recovery from negative effects of, e.g. severe winters on Great Bittern population numbers is enhanced in these less-fragmented habitats. We derived generic adaptation measures for enhancing the recovery rate of populations of species in general: one should invest in more large, well-connected nature areas, not only to diminish the negative effects of habitat fragmentation on wildlife populations, but additionally to reduce the impacts of climatic variability.

The effect of weather conditions on the breeding biology of the Eurasian Bittern Botaurus stellaris in eastern Poland

Numerous studies carried out on different bird species have shown that weather conditions can modify their breeding biology at various stages in their reproduction. Directly or indirectly, meteorological factors can affect breeding success by modifying brood survival and the availability of food resources. The present study examined the relationships between weather conditions and selected breeding parameters in the Eurasian Bittern. It was carried out in 2003–2009 on extensively farmed carp ponds located in eastern Poland. With the aid of multiple regression models, we analysed the effect of the mean ambient temperature, mean daily temperature range, mean daily minimum temperature, total precipitation and mean wind speed on the number of eggs in a clutch, egg size, and partial losses of eggs and chicks. A significant adverse relationship between the sum of rainfall in the laying period and the mean egg volume in a clutch was found. Greater mortality among young Eurasian Bitterns was also correlated with strong rains and winds during the chick-rearing period. There were two critical periods in the population we studied – before the first egg was laid, and the chick-rearing period – which were particularly sensitive to changes in the weather.