Effects of cyclic food supply on breeding performance in Tengmalm's owl (Aegolius funereus)

1990 ◽  
Vol 68 (3) ◽  
pp. 522-530 ◽  
Author(s):  
Birger Hörnfeldt ◽  
Bengt-Göran Carlsson ◽  
Ola Löfgren ◽  
Ulf Eklund
Keyword(s):  
Clutch Size ◽  
Relative Abundance ◽  
Food Supply ◽  
Snow Depth ◽  
Nest Survival ◽  
Clethrionomys Glareolus ◽  
Laying Date ◽  
Aegolius Funereus ◽  
Bank Voles ◽  
Tengmalm's Owl

Cyclic populations of bank voles (Clethrionomys glareolus), grey-sided voles (Clethrionomys rufocanus), and field voles (Microtus agrestis) made up > 90% of the diet of Tengmalm's owl (Aegolius funereus) in northern Sweden during the breeding seasons of 1980–1986. These voles also made up > 90% of snap-trapped small mammals in the study area. Comparisons of the species composition in the diet during laying with that of animals trapped indicated that bank voles were usually taken approximately in proportion to their relative abundance, whereas field voles were frequently taken more and grey-sided voles less than expected from their relative abundance. However, bank voles predominated in the diet during laying early in the season (snow depth > 40 cm). Later in the season (snow depth ≤ 40 cm) the porportion of field voles and grey-sided voles increased during laying, suggesting increased availability of these species as the snow melted. Breeding density (percentage of nest boxes with ≥ 1 egg) showed a positive correlation whereas laying date showed a negative correlation with food supply in autumn. In contrast, clutch size, number of fledglings per successful nest, and an index of the annual production of fledglings showed positive correlations with food supply in spring. Clutch size declined with season but at different levels in different years, and laying date per se only explained 11% of clutch size variation among years. In contrast, the "year effect" (related to food supply) explained 29% of the variation in clutch size. Clutches were even larger at later laying dates (when, however, the food supply was better) in 1984 than in 1985. Nest survival and survival per egg (until fledging) in successful nests varied over the years, but did not covary with the cyclic food supply. However, the lowest nest survival was found in a year when voles declined dramatically over winter. Egg size did not show any variation among years.

Fluctuating food supply affects the clutch size of Tengmalm's owl independent of laying date

Oecologia ◽  
1991 ◽  
Vol 85 (4) ◽  
pp. 543-552 ◽  
Author(s):  
Erkki Korpimäki ◽  
Harri Hakkarainen
Keyword(s):  
Clutch Size ◽  
Food Supply ◽  
Laying Date ◽  
Tengmalm's Owl

Prey choice of Tengmalm's owls (Aegolius funereus funereus): preference for substandard individuals?

1996 ◽  
Vol 74 (5) ◽  
pp. 816-823 ◽  
Author(s):  
Vesa Koivunen ◽  
Erkki Korpimäki ◽  
Harri Hakkarainen ◽  
Kai Norrdahl
Keyword(s):  
Common Shrew ◽  
Common Vole ◽  
Clethrionomys Glareolus ◽  
Prey Choice ◽  
Aegolius Funereus ◽  
Nest Boxes ◽  
Bank Voles ◽  
The Common ◽  
Common Voles ◽  
Prey Items

Errington proposed that predators mainly kill substandard prey, because dominant individuals force subordinate ones into poor habitats, where the predation risk is higher. We studied the prey choice of breeding male Tengmalm's owls (Aegolius funereus funereus) in 1992, when vole densities crashed. We trapped small mammals in the main habitat types in 21 owl territories, and simultaneously identified prey items cached by the same owls in their nest boxes. The main prey of owls in western Finland are the common vole (Microtus epiroticus), field vole (M. agrestis), bank vole (Clethrionomys glareolus), and common shrew (Sorex araneus). Common voles were the preferred prey of owls, followed by field voles, bank voles, and common shrews. Prey captured by owls tended to be lighter and smaller than those available in the field. This tendency was significant for field voles and common shrews. Field voles, common voles, and female common shrews captured by owls tended to have more internal fat than those available in the field. This tendency was significant for male field voles and female common shrews. Owls appeared to choose small individuals of some, but not all, prey species, and that these prey items were not in poor physiological condition.

Consistency and change in bank vole (Clethrionomys glareolus) home ranges across a decade

1998 ◽  
Vol 76 (7) ◽  
pp. 1329-1334 ◽  
Author(s):  
A Fredric Karlsson ◽  
Eugene R Potapov
Keyword(s):  
Home Range ◽  
Snow Cover ◽  
Bank Vole ◽  
Snow Depth ◽  
Clethrionomys Glareolus ◽  
Home Ranges ◽  
Partial Explanation ◽  
Mating Period ◽  
Bank Voles ◽  
Significant Difference

Minimum distance moved (MDM) and home-range sizes were studied in overwintering bank voles (Clethrionomys glareolus) during March and April in 1985, 1986, and 1996 near Uppsala, Sweden. In 1985 and 1986, the average snow depth was 50 and 35 cm in March and 7 and 18 cm in April, respectively. In 1996 the snow depth was only 16 cm in March and 2 cm in April. Bank voles were found to have winter nests at exactly the same grid coordinates in 1985, 1986, and 1996. Among females there was a high degree of consistency in home-range sizes, both between months and between years. Daily MDM of females was shorter in March 1996 than in 1985 and 1986, while no significant difference occurred during April. Males' home-range sizes, on the other hand, increased significantly from March to April in all 3 years, i.e., at the onset of the mating period. There was no significant difference in males' home-range sizes in March across years, but in April, home ranges were significantly larger 1985 and 1986 than in 1996. Males' average home-range sizes in April showed a positive correlation with snow depth. MDM of males in both March and April was also significantly higher during the snowy years of 1985 and 1986 than in 1996, when there was much less snow. These observations suggest that adequate snow cover is a favourable factor, allowing the males to expand their home ranges, while lack of snow or a thin, patchy snow cover prevents them from travelling longer distances during the mating period and consequently from visiting a large number of potential mates. These differences in the behaviour of male bank voles between snow-rich and snow-poor years may offer a partial explanation of the hypothetical connection between the less severe winter conditions during the past decade and the decline in population density and cyclicity in boreal bank vole populations.

scholarly journals Interactive influences of fluctuations of main food resources and climate change on long-term population decline of Tengmalm’s owls in the boreal forest

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Marek Kouba ◽  
Luděk Bartoš ◽  
Jitka Bartošová ◽  
Kari Hongisto ◽  
Erkki Korpimäki
Keyword(s):  
Climate Change ◽  
Reproductive Success ◽  
Population Decline ◽  
Egg Laying ◽  
Laying Date ◽  
Late Winter ◽  
Aegolius Funereus ◽  
Increasing Temperature ◽  
Tengmalm's Owl

AbstractRecent wildlife population declines are usually attributed to multiple sources such as global climate change and habitat loss and degradation inducing decreased food supply. However, interactive effects of fluctuations in abundance of main foods and weather conditions on population densities and reproductive success have been studied rarely. We analysed long-term (1973–2018) data on Tengmalm’s owl (Aegolius funereus) and the influence of prey abundance and weather on breeding densities and reproductive success in western Finland. We found that fledgling production per breeding attempt declined and laying date of the owl population delayed during the period between 1973 and 2018. The breeding density of the owl population decreased with increasing temperature in winter (October–March), fledgling production increased with increasing temperature and precipitation in spring (April–June), whereas the initiation of egg-laying was delayed with increasing depth of snow cover in late winter (January–March). The decreasing trend of fledgling production, which was mainly due to starvation of offspring, was an important factor contributing to the long-term decline of the Tengmalm’s owl study population. Milder and more humid spring and early summer temperatures due to global warming were not able to compensate for lowered offspring production of owls. The main reason for low productivity is probably loss and degradation of mature and old-growth forests due to clear-felling which results in loss of coverage of prime habitat for main (bank voles) and alternative foods (small birds) of owls inducing lack of food, and refuges against predators of Tengmalm’s owls. This interpretation was also supported by the delayed start of egg-laying during the study period although ambient temperatures increased prior to and during the egg-laying period.

scholarly journals Temporal changes in reproductive success and optimal breeding decisions in a long-distance migratory bird

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Cynthia Reséndiz-Infante ◽  
Gilles Gauthier
Keyword(s):  
Reproductive Success ◽  
Clutch Size ◽  
Environmental Changes ◽  
Migratory Bird ◽  
Laying Date ◽  
Negative Consequences ◽  
Breeding Phenology ◽  
Additional Time ◽  
Long Distance ◽  
Seasonal Decline

AbstractMany avian migrants have not adjusted breeding phenology to climate warming resulting in negative consequences for their offspring. We studied seasonal changes in reproductive success of the greater snow goose (Anser caerulescens atlantica), a long-distance migrant. As the climate warms and plant phenology advances, the mismatch between the timing of gosling hatch and peak nutritive quality of plants will increase. We predicted that optimal laying date yielding highest reproductive success occurred earlier over time and that the seasonal decline in reproductive success increased. Over 25 years, reproductive success of early breeders increased by 42%, producing a steeper seasonal decline in reproductive success. The difference between the laying date producing highest reproductive success and the median laying date of the population increased, which suggests an increase in the selection pressure for that trait. Observed clutch size was lower than clutch size yielding the highest reproductive success for most laying dates. However, at the individual level, clutch size could still be optimal if the additional time required to acquire nutrients to lay extra eggs is compensated by a reduction in reproductive success due to a delayed laying date. Nonetheless, breeding phenology may not respond sufficiently to meet future environmental changes induced by warming temperatures.

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