Markéta Zárybnická

Do Tengmalm’s Owls alter parental feeding effort under varying conditions of main prey availability?

We studied the diet composition and behavioural responses to variable food conditions in Tengmalm’s Owls (Aegolius funereus). The abundance of main prey (voles and mice) of owls was higher in the Ore Mountains, Czech Republic, than in the Kauhava region, Finland. We monitored nests continuously by a camera system to estimate the feeding frequency and to identify prey items provided to nestlings. We recorded 990 prey deliveries at six nests in the Ore Mountains and 1,679 prey deliveries at nine nests in the Kauhava region. Mice (Apodemus) and voles (Microtus and Clethrionomys) were the main foods of owls in the Ore Mountains, whereas voles (Clethrionomys and Microtus) and shrews (Sorex) were the main foods in the Kauhava region. In consequence, on average smaller prey items were brought to nestlings at the Finnish site. However, both absolute and relative (per one nestling) feeding frequency was higher in the Kauhava region, and the biomass available to individual nestlings did not differ between the two areas. Moreover, the Finnish and Czech pairs produced about the same number of fledglings. Our results suggest that male owls are able to maintain the amount of food required for chicks by switching to alternative prey, and to increase their prey delivery rates under conditions of reduced abundance of main food.

Dark or Short Nights: Differential Latitudinal Constraints in Nestling Provisioning Patterns of a Nocturnally Hunting Bird Species

In diurnal bird species, individuals breeding at high latitudes have larger broods than at lower latitudes, which has been linked to differences in the daily time available for foraging. However, it remains unclear how latitude is linked with parental investment in nocturnal species. Here, we investigate nestling provisioning rates of male Tengmalms owls in two populations at different latitudes (Czech Republic 50°N; Finland 63°N) with the help of cameras integrated into nest boxes. Clutch sizes were smaller in the Czech population (CZ: 5.1±0.1; FIN: 6.6±0.1), but given the higher nestling mortality in the Finnish population, the number of fledglings did not differ between the two populations (CZ: 3.5±0.3; FIN: 3.9±0.2). Nestling provisioning patterns varied within days, over the reproductive season and between the two sites. Males delivered most food at dusk and dawn, having peak delivery rates at sun angles of −11° to −15° at both sites, and males increased the prey delivery rates with higher nestling requirements. Given the longer nights during summer in the Czech Republic compared to Finland, Czech males only showed a small shift in their delivery peak during the night from −17° in April to −14° in July. In contrast, Finnish males shifted their peak of prey delivery from −11° in April to −1° in July. Consequently, Czech males had a longer hunting time per night around midsummer when feeding young (360 min) than Finnish males (270 min). This suggests that nocturnal owl species in northern populations are constrained by the short nights during the breeding season, which can limit the number of young they can raise. Moreover, owls in northern populations are additionally constrained through the unpredictable changes in food availability between years, and both these factors are likely to influence the reproductive investment between populations.

Effect of male provisioning on the parental behavior of female Boreal Owls Aegolius funereus

BackgroundSex-specific parental roles of most raptors allow mates to cooperate during breeding; while females incubate and brood, males provide food. If one partner fails in its parental duties, however, sex-specific parental roles can limit the ability of each sex to carry out the role normally performed by its partner. We observed the effect of male food provisioning on female parental care in Boreal Owls Aegolius funereus using cameras at 12 nests in western Finland in 2005. We compared the parental care of eight females in nests with a high male feeding rate (successful nests) with that of the females in four nests with a low or zero male feeding rate (failed nests).ResultsFemales brooded more intensively in nests where males provided sufficient food for the family. These females continually stayed with the young until the late brooding stage (18 days after hatching). After completing the brooding period (21 days after hatching), they either no longer visited their nests or began to provide food to their young together with males. Females exposed to a low or zero male feeding rate left their young for long periods without brooding during the early brooding stage (8 days after hatching) and provisioned nestlings at a mean rate of 0.6 ± 0.8 prey items/night. As a consequence, all of these nesting attempts failed. One female that was widowed 21 days after hatching stopped brooding and began food provisioning alone, but only one of six young successfully left the nest. Body masses of females in successful and unsuccessful nests were similar, indicating that females in nests with insufficient provisioning did not markedly suffer from a lack of food.ConclusionsFemale Boreal Owls adjusted their parental care based on the level of parental effort of their mates and the nesting phase. The nesting attempts, in which males did not provide enough food for the family during the early brooding stage, failed. We concluded that bi-parental care in northern populations of Boreal Owls is essential until brooding is completed.

A Webcast of Bird Nesting as a State-of-the-Art Citizen Science

The quality of people’s knowledge of nature has always had a significant influence on their approach to wildlife and nature conservation. However, direct interactions of people with nature are greatly limited nowadays, especially because of urbanization and modern lifestyles. As a result, our isolation from the natural world has been growing. Here, we present an example of a state-of-the-art Citizen Science project with its educational, scientific, and popularizing benefits. We conclude that modern media and new forms of education offer an effective opportunity for inspiring children and others to have fun learning to act like scientists. This approach provides broad opportunities for developing the hitherto neglected educational potential of Citizen Science.

Different temperature and cooling patterns at the blunt and sharp egg poles reflect the arrangement of eggs in an avian clutch.

Incubation is an energetically demanding process during which birds apply heat to their eggs to ensure embryonic development. Parent behaviours such as egg turning and exchanging the outer and central eggs in the nest cup affect the amount of heat lost to the environment from individual eggs. Little is known, however, about whether and how egg surface temperature and cooling rates vary among the different areas of an egg and how the arrangement of eggs within the clutch influences heat loss. We performed laboratory (using Japanese quail eggs) and field (with northern lapwing eggs) experiments using infrared imaging to assess the temperature and cooling patterns of heated eggs and clutches. We found that (i) the sharp poles of individual quail eggs warmed to a higher egg surface temperature than did the blunt poles, resulting in faster cooling at the sharp poles compared to the blunt poles; (ii) both quail and lapwing clutches with the sharp poles oriented towards the clutch centre (arranged clutches) maintained higher temperatures over the central part of the clutch than occurred in those clutches where most of the sharp egg poles were oriented towards the exterior (scattered clutches); and (iii) the arranged clutches of both quail and lapwing showed slower cooling rates at both the inner and outer clutch positions than did the respective parts of scattered clutches. Our results demonstrate that egg surface temperature and cooling rates differ between the sharp and blunt poles of the egg and that the orientation of individual eggs within the nest cup can significantly affect cooling of the clutch as a whole. We suggest that birds can arrange their eggs within the nest cup to optimise thermoregulation of the clutch.

Factors affecting the duration of nestling period and fledging order in Tengmalm's owl (Aegolius funereus): effect of wing length and hatching sequence.

In altricial birds, the nestling period is an important part of the breeding phase because the juveniles may spend quite a long time in the nest, with associated high energy costs for the parents. The length of the nestling period can be variable and its duration may be influenced by both biotic and abiotic factors; however, studies of this have mostly been undertaken on passerine birds. We studied individual duration of nestling period of 98 Tengmalm’s owl chicks (Aegolius funereus) at 27 nests during five breeding seasons using a camera and chip system and radio-telemetry. We found the nestlings stayed in the nest box for 27 – 38 days from hatching (mean ± SD, 32.4 ± 2.2 days). The individual duration of nestling period was negatively related to wing length, but no formally significant effect was found for body weight, sex, prey availability and/or weather conditions. The fledging sequence of individual nestlings was primarily related to hatching order; no relationship with wing length and/or other factors was found in this case. We suggest the length of wing is the most important measure of body condition and individual quality in Tengmalm’s owl young determining the duration of the nestling period. Other differences from passerines (e.g., the lack of effect of weather or prey availability on nestling period) are considered likely to be due to different life-history traits, in particular different food habits and nesting sites and greater risk of nest predation among passerines.

Sequential polyandry in female Tengmalm's owl (Aegolius funereus) during a poor rodent year

Abstract. In birds of prey, food availability affects the entire breeding process, including reproductive success. Sequential polyandry, sometimes documented in raptors and owls, has been observed occasionally in Tengmalms owl in years of high food availability. In this study, the effect of food supply on the reproductive strategy of the central European Tengmalms owl population has been investigated. The availability of the main prey of owls was significantly below average in the study year 2014. This resulted in low breeding density of owls, delayed egg laying, small clutch sizes, and low reproductive success. Nevertheless, successful sequential polyandry of one Tengmalms owl female was recorded during the breeding season. The polyandrous female laid four eggs in each nests, and 50 % and 75 % of four hatched nestlings left the nest during the first and second breeding, respectively. In both nesting attempts, the two-year old female was of a substandard body mass and she abandoned the fledglings before they left the nests. Prey delivered by males to both nests was comprised mainly of alternative prey (birds and shrews). The results of this study suggest that there are probably some other factors, in addition to food availability, that may play a role in Tengmalms owls decisions in matters of parental care.

Home range size of Tengmalm’s owl during breeding in Central Europe is determined by prey abundance

Animal home ranges typically characterized by their size, shape and a given time interval can be affected by many different biotic and abiotic factors. However, despite the fact that many studies have addressed home ranges, our knowledge of the factors influencing the size of area occupied by different animals is, in many cases, still quite poor, especially among raptors. Using radio-telemetry (VHF; 2.1 g tail-mounted tags) we studied movements of 20 Tengmalm’s owl (Aegolius funereus) males during the breeding season in a mountain area of Central Europe (the Czech Republic, the Ore Mountains: 50° 40’ N, 13° 35’ E) between years 2006–2010, determined their average hunting home range size and explored what factors affected the size of home range utilised. The mean breeding home range size calculated according to 95% fixed kernel density estimator was 190.7 ± 65.7 ha (± SD) with a median value of 187.1 ha. Home range size was affected by prey abundance, presence or absence of polygyny, the number of fledglings, and weather conditions. Home range size increased with decreasing prey abundance. Polygynously mated males had overall larger home range than those mated monogamously, and individuals with more fledged young possessed larger home range compared to those with fewer raised fledglings. Finally, we found that home ranges recorded during harsh weather (nights with strong wind speed and/or heavy rain) were smaller in size than those registered during better weather. Overall, the results provide novel insights into what factors may influence home range size and emphasize the prey abundance as a key factor for breeding dynamics in Tengmalm’s owl.

Factors Affecting Growth of Tengmalm's Owl (Aegolius funereus) Nestlings: Prey Abundance, Sex and Hatching Order.

In altricial birds, energy supply during growth is a major predictor of the physical condition and survival prospects of fledglings. A number of experimental studies have shown that nestling body mass and wing length can vary with particular extrinsic factors, but between-year observational data on this topic are scarce. Based on a seven-year observational study in a central European Tengmalm’s owl population we examine the effect of year, brood size, hatching order, and sex on nestling body mass and wing length, as well as the effect of prey abundance on parameters of growth curve. We found that nestling body mass varied among years, and parameters of growth curve, i.e. growth rate and inflection point in particular, increased with increasing abundance of the owl’s main prey (Apodemus mice, Microtus voles), and pooled prey abundance (Apodemus mice, Microtus voles, and Sorex shrews). Furthermore, nestling body mass varied with hatching order and between sexes being larger for females and for the first-hatched brood mates. Brood size had no effect on nestling body mass. Simultaneously, we found no effect of year, brood size, hatching order, or sex on the wing length of nestlings. Our findings suggest that in this temperate owl population, nestling body mass is more sensitive to prey abundance than is wing length. The latter is probably more limited by the physiology of the species.

Microsatellite analysis detects low rate of extra-pair paternity in Tengmalm's owl, Aegolius funereus

Abstract. Genetic methods enable to reveal cryptic parental contributions in reproduction, especially in socially monogamous species. The rate of extra-pair paternity is generally low in raptors and owls and its presence in some species is tightly associated with sequential polyandry which can rarely occur in years with high food availability. In this study we investigated the mating system of the Tengmalms owl (Aegolius funereus) in the Ore Mountains (Czech Republic). In this area, the species usually nests in high breeding densities which could increase an opportunity for extra-pair copulations. In total, 297 individuals (54 females, 47 males and 196 juveniles) from 46 nest boxes were genotyped at seven microsatellite loci. We present results of a five-year study and four extra-pair nestlings (2.3 %) were detected which did not result from sequential polyandry.