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.
Highlights
Growth and development rates of juveniles are closely related to levels of parental care and are crucial components of the life-history of every animal species, with fitness benefits to parents provided through increased growth and survival of offspring [1]
With the exception of individual duration of nestling period (I) and fledging order (II) in particular analyses where these were dependent variables, fixed effects employed within both models were: date and order of hatching, body weight at fledging (g), wing length extrapolated to the age of 30 days from hatching, number of eggs, hatchlings and fledglings from a particular nest box, date and order of fledging, individual duration of nestling period, sex of nestlings, mean daily temperature (°C), mean wind speed (m/s), daily precipitation and type of year
We did not find any obvious relationship between fledging order and wing length this has been observed in several passerines [4,7,27,58]
Summary
Growth and development rates of juveniles are closely related to levels of parental care and are crucial components of the life-history of every animal species, with fitness benefits to parents provided through increased growth and survival of offspring [1]. The results of various studies of the factors affecting length of nestling period in natural conditions conclude that the most important variables explaining intraspecific variability in time to fledging are: weather conditions, food availability, nestling size and nest parasitism [7,11,15,24,25,26,27,28,29]. Because neither food availability nor weather conditions affected growth rate of both nestlings’ body weight and wing length [48] we further predicted that the duration of individual nestling period will not be related to (iv) food availability and/or (v) weather conditions. One can predict (vi) that smaller male chicks fledge at a younger age than larger female chicks to escape the dominance of female chicks in competition for food in the nest
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