Lucyna Halupka

The response of the Great Reed Warbler Acrocephalus arundinaceus to climate change

We examined long-term responses in the breeding performance of the Great Reed Warblers Acrocephalus arundinaceus to climate change. The study took place in various years from 1970 to 2007. During the study period, mean temperatures in the breeding season of the species increased and precipitation decreased significantly. We found evidence for the significant advancement in both earliest and annual median first-egg-laying dates. This advancement correlated with temperature increases early in the season. The latest first-egg laying dates, however, remained unchanged. Other breeding statistics: clutch size, nest losses, and production of young per nest, did not change significantly over the study period. Precipitation did not affect any of the analysed measures. It is important to note, though, that during dry seasons, the production of young per successful nest was higher. In contrast to some woodland species, the Great Reed Warbler seems to adapt well to climate change by shifting laying dates. The reason for this is probably to optimise food resources.

Great reed warbler Acrocephalus arundinaceus and reed warbler Acrocephalus scirpaceus respond differently to cuckoo dummy at the nest

A cuckoo Cuculus canorus dummy was exposed at 24 nests of great reed warbler Acrocephalus arundinaceus (GRW) and 34 nests of reed warbler Acrocephalus scirpaceus (RW) during the egg-laying stage. The eight GRW pairs attacked the cuckoo directly, striking the dummy, but such a behaviour was not recorded in RWs. Also, other behavioural measures (closest distance from the model, duration of distress calls and number of excitement calls) indicated a lower level of defence by RWs compared to GRWs. In the study area, the parasitism rate was much lower in GRWs (1.7% of nests) than in RWs (11.3%). We suggest that one of the reasons for the lower level of cuckoo parasitism on GRWs is its stronger nest defence and hence higher risk of injury or even death for the cuckoo during egg dumping.

Embryonic eggshell thickness erosion: A literature survey re-assessing embryo-induced eggshell thinning in birds

Although eggshell thinning has been described mainly in the context of environmental pollution, it can also be the effect of reproductive changes induced by a developing embryo. On the basis of a literature survey of 25 bird species (26 published papers) we reviewed data on embryo-induced eggshell thinning (EET) in three groups of birds: precocials, semi-precocials and altricials. The average EET at the equator of the eggs was 6.4% (median = 4.7%). Our review did not confirm a general prediction of elevated EET at the egg equator in precocial species: altricial birds exhibited the highest EET (average = 12.0%), followed by precocials (7.6%) and semi-precocials (4.2%). We make certain critical recommendations based on the results of this study. Studies aiming to assess variation in eggshell thickness should examine intrinsic factors affecting shell properties of avian eggs, like thickness, which are the result of anatomical or reproductive changes.

Coping with Shifting Nest Predation Refuges by European Reed Warblers Acrocephalus scirpaceus

Predation, the most important source of nest mortality in altricial birds, has been a subject of numerous studies during past decades. However, the temporal dynamics between changing predation pressures and parental responses remain poorly understood. We analysed characteristics of 524 nests of European reed warblers monitored during six consecutive breeding seasons in the same area, and found some support for the shifting nest predation refuge hypothesis. Nest site characteristics were correlated with nest fate, but a nest with the same nest-site attributes could be relatively safe in one season and vulnerable to predation in another. Thus nest predation refuges were ephemeral and there was no between-season consistency in nest predation patterns. Reed warblers that lost their first nests in a given season did not disperse farther for the subsequent reproductive attempt, compared to successful individuals, but they introduced more changes to their second nest sites. In subsequent nests, predation risk remained constant for birds that changed nest-site characteristics, but increased for those that did not. At the between-season temporal scale, individual birds did not perform better with age in terms of reducing nest predation risk. We conclude that the experience acquired in previous years may not be useful, given that nest predation refuges are not stable.

Factors Driving Variation in Biparental Incubation Behaviour in the Reed Warbler Acrocephalus scirpaceus

Biparental incubation is a common pattern of parental care in birds. Within species with biparental incubation, the contribution of each sex can vary widely. Many studies have addressed the factors that influence variation in female incubation behaviour, but the underlying causes of within-species variation in male incubation behaviour remain poorly understood. In this paper we analyse incubation behaviour in the Reed Warbler, a small, predominantly socially monogamous passerine nesting in reed beds. We examined the impact of time of day, weather conditions (ambient temperature, wind speed, rainfall) and progress of the breeding season on male and female incubation behaviour in 81 pairs of Reed Warbler breeding in the Barycz Valley (SW Poland). We found that females had on average higher nest attentiveness (total time spent incubating per hour) than their partners (47% vs. 29%) but mean incubation bout length (a single, uninterrupted stay at the nest) did not differ significantly between the sexes (9 min vs. 7 min). The two parents responded differently to changing environmental parameters. Female nest attentiveness was unaffected by date, time of the day, advancement of incubation and weather conditions, while males spent more time on the nest at higher wind speeds and lower temperatures. In contrast, male incubation bout length was not affected by these factors, whereas female bout length increased throughout the breeding season and was longer at lower temperatures. Incubation recesses (periods where both parents were off the nest) were longer during favourable weather conditions (at high temperatures and low wind), probably because cooling of the eggs takes much longer under such conditions and parents can spend more time foraging. A comparison of our results with those from other populations revealed important betweenpopulation and sex-specific differences in nest attentiveness expressed as the percentage of male/female time spent on the nest. We suggest that betweenpopulation variation may result from differences in habitat quality and/or food resources affecting the necessity of male contribution to parental care, variation in breeding synchrony and densities influencing male engagement in extra-pair copulations, differences in predation levels, or methodological differences.

Survival during the breeding season: Nest stage, parental sex, and season advancement affect reed warbler survival

Avian annual survival has received much attention, yet little is known about seasonal patterns in survival, especially of migratory passerines. In order to evaluate survival rates and timing of mortality within the breeding season of adult reed warblers (Acrocephalus scirpaceus), mark-recapture data were collected in southwest Poland, between 2006 and 2012. A total of 612 individuals (304 females and 308 males) were monitored throughout the entire breeding season, and their capture-recapture histories were used to model survival rates. Males showed higher survival during the breeding season (0.985, 95% CI: 0.941–0.996) than females (0.869, 95% CI: 0.727–0.937). Survival rates of females declined with the progression of the breeding season (from May to August), while males showed constant survival during this period. We also found a clear pattern within the female (but not male) nesting cycle: survival was significantly lower during the laying, incubation, and nestling periods (0.934, 95% CI: 0.898–0.958), when birds spent much time on the nest, compared to the nest building and fledgling periods (1.000, 95% CI: 1.00–1.000), when we did not record any female mortality. These data (coupled with some direct evidence, like bird corpses or blood remains found next to/on the nest) may suggest that the main cause of adult mortality was on-nest predation. The calculated survival rates for both sexes during the breeding season were high compared to annual rates reported for this species, suggesting that a majority of mortality occurs at other times of the year, during migration or wintering. These results have implications for understanding survival variation within the reproductive period as well as general trends of avian mortality.

Alarm calls and chick reaction: comments on Kleindorfer et al. (1996)

Correspondence: K. Halupka, Department of Avian Ecology, University of Wroclaw, Sienkiewicza 21, 50335 Wroclaw, Poland (email: halupka@biol.uni.wroc.pl). In a study of relationships between alarm calling by parents and the reactions of nestlings in the moustached warbler, Acrocephalus melanopogon, Kleindorfer et al. (1996) concluded that the antipredator response of chicks is the proximate cue for adult alarm calls. In this note we review sampling errors in the study and the reasoning behind the chick reaction hypothesis. The most serious problems in Kleindorfer et al.’s paper are pseudoreplication and lack of control for potential confounding factors. In 1991–1994, during 5 months of the breeding season, they made 191 1-h observations of 33 nests. The data (frequency of alarm calling) were treated as independent and pooled without any control for the influence of the nest (parent birds, nest site) advancement of the breeding season and year (all these factors could affect alarm-calling frequency: Montgomerie & Weatherhead 1988). Kleindorfer et al. used 23 nests to perform 250 experiments (observations of the parental and offspring reactions to three species of predators). Thus, on average, there were 10.9 tests per nest and each predator was exposed more than three times at the same nest. However, the data were treated as if they were independent. The following passage (Kleindorfer et al. 1996, page 1201) indicates another problem with sampling. ‘The cases ‘‘without alarm calls’’ include approaches (. . .) to three nests where alarm calls began after 1 min at the nest (these three nests are repeated entries in the ‘‘with call’’ category, because later calls elicited chick jumping).’ Thus, the data set was ‘enlarged’ by using invalid definitions of displays: the same parent birds in the same test could be both active and silent and the same offspring could both jump out and remain in the nest (data prepared in this way were

Conditions at autumn stopover sites affect survival of a migratory passerine

Weather is an important factor affecting many aspects of avian ecology, yet its importance for survival during various periods of the avian annual cycle has received relatively little attention and remains poorly understood. We have investigated the effect of weather conditions at the breeding and wintering grounds and during migration on the survival probability of Eurasian Reed Warblers Acrocephalus scirpaceus, a long-distance Palaearctic-African migrant species. We found that annual survival was significantly affected by precipitation at the autumn stopover sites in Spain and Morocco, where Reed Warblers accumulate energy reserves prior to crossing the Sahara desert: low rainfall was associated with decreased survival. We suggest that arid conditions at these crucial stopover sites may cause limitations in food availability, prevent proper refueling and hence result in lower survival. Survival estimates were not related to weather conditions in Africa during the bird wintering period or the preceding wet season. Likewise, meteorological conditions at the breeding area did not influence survival. Survival estimates for males and females did not differ, although recapture probability was significantly lower for females than for males. Our results indicate that weather significantly influences Reed Warbler survival, although its effect may vary for different stages of the annual cycle. Our findings suggest that marked climatic changes occurring along migratory routes, in particular at important stopover sites, may have far-reaching consequences on bird survival and population size.ZusammenfassungDie Bedingungen an den Herbstrastplätzen beeinflussen das Überleben eines ziehenden Singvogels Das Wetter ist ein wichtiger Faktor, der bei Vögeln viele Aspekte der Ökologie beeinflusst; dennoch wurde seiner Bedeutung für das Überleben während verschiedener Phasen des jährlichen Zyklus der Vögel relativ wenig Aufmerksamkeit zuteil und man weiß nach wie vor nur wenig darüber. Wir untersuchten die Auswirkungen der Wetterbedingungen in den Brut- und Überwinterungsgebieten sowie auf dem Zugweg auf die Überlebenswahrscheinlichkeit von Teichrohrsängern Acrocephalus scirpaceus, Langstreckenziehern zwischen Paläarktis und Afrika. Die jährlichen Überlebensraten wurden signifikant von den Niederschlagsmengen in den Herbstrastgebieten in Spanien und Marokko beeinflusst, wo die Teichrohrsänger Energiereserven anlegen, bevor sie die Sahara überqueren: Geringe Regenmengen standen mit vermindertem Überleben im Zusammenhang. Wir legen nahe, dass aride Bedingungen an diesen entscheidenden Rastplätzen eine begrenzte Nahrungsverfügbarkeit zur Folge haben können, welche ein richtiges “Auftanken” verhindern und somit zu schlechterem Überleben führen kann. Die Überlebensschätzwerte hingen nicht von den Wetterbedingungen in Afrika während des Überwinterungsaufenthaltes der Vögel oder zur vorhergegangenen Regenzeit ab. Ebenso wenig beeinflussten die meteorologischen Bedingungen im Brutgebiet das Überleben. Überlebensschätzwerte für Männchen und Weibchen unterschieden sich nicht, obwohl die Wiederfangwahrscheinlichkeit bei den Weibchen signifikant geringer war als bei den Männchen. Unsere Ergebnisse deuten darauf hin, dass das Wetter einen signifikanten Einfluss auf das Überleben der Teichrohrsänger ausübt, obgleich sich seine Auswirkungen zu den verschiedenen Stadien des Jahreszyklus unterscheiden können. Unsere Befunde legen nahe, dass ausgeprägte klimatische Veränderungen entlang der Zugrouten, speziell an wichtigen Rastplätzen, weitreichende Folgen für das Überleben der Vögel und die Populationsgröße haben können.

The pattern of distribution and interaction of metals and calcium in eggshells and egg contents in relation to the embryonic development of eggs in a small passerine bird

Differences in element concentrations have been observed between embryonated and non-embryonated eggs of the Eurasian Reed Warbler Acrocephalus scirpaceus, presumably due to the resorption of calcium and other elements from the shell. To investigate this difference, we tested the hypotheses that (1) the distribution of elements in eggshells and egg contents, (2) the individual element–element relationships between shells and contents, and (3) the relationships among the elements in eggshells and egg contents vary between the two egg samples. Based on the levels of 11 elements (Cr, Cu, Ni, Cd, Pb, Mn, Fe, Co, Zn, Mg and Ca) in Reed Warbler eggs, our results confirmed the second and third hypotheses. Importantly, we found that embryonic development tended to blur the lines between two types of relationships: (1) between elements in eggshells and egg contents through an increase in the number of significant correlations, some of which may be enhanced by high levels of certain elements (Cd, Co, Pb, Zn are indicative of trace metal pollution in fish ponds); (2) among the various elements in eggshells and egg contents, as demonstrated by the differential grouping of elements in principal components analysis (PCA). The consistent positive direction of relationships for almost all elements in both the shells and contents of eggs is presumed to result from the initial parallel co-sequestration of all the elements which accompanies intensive calcium transfer from the female body into the incipient egg. Our study highlights the fact that only limited inferences can be drawn from the interactions of metals and calcium in eggshells and egg contents if the fertility status of the eggs is unknown.ZusammenfassungVerteilungsmuster und Wechselwirkungen von Metallen und Calcium in Eischale und Eiinhalt in Bezug zum embryonalen Entwicklungszustand der Eier eines kleinen Singvogels Bebrütete und nicht bebrütete Eier des Teichrohrsängers Acrocephalus scirpaceus scheinen sich in den Konzentrationen der Elemente zu unterscheiden—vermutlich aufgrund der Resorption von Calcium und anderen Elementen aus der Schale. Vor diesem Hintergrund überprüften wir die Hypothesen, dass sich (1) die Verteilung der Elemente in den Eischalen und Eiinhalten, (2) die individuellen Element–Element-Verhältnisse zwischen Eischalen und Eiinhalten und (3) die Beziehungen zwischen den Elementen in Eischalen und Eiinhalten bei Proben der zwei Eitypen unterscheiden. Basierend auf dem Gehalt an elf Elementen (Cr, Cu, Ni, Cd, Pb, Mn, Fe, Co, Zn, Mg und Ca) in Teichrohrsängereiern bestätigten unsere Ergebnisse die zweite und die dritte Hypothese. Eine wichtige Erkenntnis war, dass die Embryonalentwicklung zwei Typen von Beziehungen tendenziell verschleiert: (1) zwischen den Elementen in den Eischalen und den Eiinhalten durch die Zunahme signifikanter Korrelationen, von denen manche durch den hohen Gehalt an einigen Elementen noch verstärkt werden können (Cd, Co, Pb und Zn weisen auf Spuren von Metallbelastung in Fischteichen hin); (2) zwischen den verschiedenen Elementen in den Eierschalen und Eiinhalten, wie durch die differenzielle Gruppierung der Elemente bei der Hauptkomponentenanalyse (PCA; principal components analysis) veranschaulicht wird. Die durchgehend positive Ausrichtung der Beziehungen für fast alle Elemente, sowohl in den Eischalen als auch in den Eiinhalten, ist vermutlich auf die ursprünglich parallele Zuteilung aller Elemente zurückzuführen, welche den intensiven Calciumtransfer aus dem Körper des Weibchens in das entstehende Ei begleitet. Unsere Studie unterstreicht die Tatsache, dass sich aus den Wechselwirkungen zwischen Metallen und Calcium in Eischale und Eiinhalt nur begrenzte Schlüsse ziehen lassen, wenn der embryonale Entwicklungszustand der Eier unbekannt ist.

The effect of climate change on the duration of avian breeding seasons: a meta-analysis

Many bird species are advancing the timing of their egg-laying in response to a warming climate. Little is known, however, of whether this advancement affects the respective length of the breeding seasons. A meta-analysis of 65 long-term studies of 54 species from the Northern Hemisphere has revealed that within the last 45 years an average population has lengthened the season by 1.4 days per decade, which was independent from changes in mean laying dates. Multi-brooded birds have prolonged their seasons by 4 days per decade, while single-brooded have shortened by 2 days. Changes in season lengths covaried with local climate changes: warming was correlated with prolonged seasons in multi-brooded species, but not in single-brooders. This might be a result of higher ecological flexibility of multi-brooded birds, whereas single brooders may have problems with synchronizing their reproduction with the peak of food resources. Sedentary species and short-distance migrants prolonged their breeding seasons more than long-distance migrants, which probably cannot track conditions at their breeding grounds. We conclude that as long as climate warming continues without major changes in ecological conditions, multi-brooded or sedentary species will probably increase their reproductive output, while the opposite effect may occur in single-brooded or migratory birds.