Factors Affecting the Duration of Nestling Period and Fledging Order in Tengmalm’s Owl (Aegolius funereus): Effect of Wing Length and Hatching Sequence

Abstract

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.

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

“…A male owl provides most of the food to a female and their owlets from prior to egg-laying until the fledglings become independent at the age of five to nine weeks 40,[44][45][46] . The female incubates the eggs, broods the young, and remains almost continually in the nest cavity until the young are about 3 weeks old 40,47 .…”

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

“…The disunity of these results indicates that wing length can differ under extremely different food conditions, but the differences are not pronounced when food availability is relatively stable. This finding is quite unexpected, because the individual duration of nestling periods is related to wing length rather than body mass, sex, prey abundance index or weather conditions [ 5 ].…”

“…In altricial birds, phenotypic characteristics of nestlings such as body mass and wing length can affect sibling competition [ 1 , 2 ], nestlings’ survival [ 3 , 4 ] and at which age each individual fledges [ 5 ]. During the post-fledgling period, the body characteristics affect fledgling survival, behavioural performance and recruitment into the breeding population [ 6 – 8 ].…”

“…Consequently, the nestlings hatch asynchronously and the youngest nestlings usually suffer from a higher mortality risk due to a combination of starvation and sibling aggression [ 32 , 37 ]. The nestlings stay on the nest usually 32 days (range 27 ˗ 38 days) from hatching [ 5 ]. In Tengmalm’s owl, reversed size dimorphism reaches approximately 30–40% in terms of body mass during the breeding season due to female body reserves for egg production and successful incubation, although the difference is only 4% in body mass and 2.5% in wing length outside the breeding season [ 38 , 39 ].…”

“…Hipkiss et al [ 3 ] found that female nestlings in northern populations attained 5% higher asymptotic mass than males, and that experimentally fed nestlings were heavier than control nestlings, suggesting that the females’ larger size gave them a competitive advantage against their male siblings during food scarcity. On the other hand, Kouba et al [ 5 ] demonstrated that wing length is important measurement of individual quality in Tengmalm’s owl young because it determines the duration of the nestling period (i.e., duration of stay of individual nestlings at the nest box from hatching to fledging). However, between-year observational data on this topic are scarce, as well as no long-term study has focused on the effect of extrinsic factors such as prey abundance, brood size, hatching order, and sex on body mass and wing length in nestlings of raptors in general and Tengmalm’s owl in particular.…”