Natal conditions, lifespan and lifetime reproductive success of European blackbirds

Abstract

Even though much has been published in recent years on the factors affecting the lifespan and lifetime reproductive success of birds, there are still gaps in our knowledge. Here, we present the results of a long-term study of European blackbirds which examined the effect of natal conditions on lifespan and lifetime reproductive success (expressed by the number of fledglings) of 152 nestlings (72 males and 80 females) ringed in the Stefan Żeromski Park in Szczecin (NW Poland). We have complete information regarding parental age, family brood (first-egg laying date, clutch size, and hatching sequence), bird size, lifetime reproductive success, pair density and weather conditions during the natal year. For males, total fledgling production was the smaller, the later the laying date of the family brood, but increased with mean daily precipitation and pair density in the natal year. In the case of females, we did not find any significant relationships between their lifetime reproductive success and the above parameters. Male lifespan increased with mean daily precipitation and bird density, but only pair density had a positive effect on female lifespan. We suggest that for females, genetic factors could be more important for their reproductive success than for males. In addition, a blackbird’s lifespan depends strongly on environmental factors.

Factors affecting fledglings survival in urban population of European blackbirds in Szczecin (NW Poland)

“…The most unexpected result obtained in this study was that precipitation during the first 30 days of life is negatively related to fledgling survival. Food availability is the most important factor impacting fledgling survival 6 , 11 , but because precipitation affects food availability for Blackbirds 21 , 22 , 43 , 44 , this result did not support our hypothesis. Similar results were obtained for northern wheatears ( Oenanthe oenanthe ), where rainfall during parental care reduces not only fledgling survival but also their recruitment probability.…”

“…The time of hatching strongly impacts the condition and survival of many bird species 40 , including this population of Blackbirds 22 . Offspring that fledge earlier in the season may benefit from milder environmental conditions, more plentiful food, reduced intraspecific competition for resources, as well as lower predation rates and parasitism (see 41 for a review).…”

“…The European Blackbird (henceforth: Blackbird) is a model species with a well-known biology 19 , 20 , but fledgling survival has only been studied once, by Magrath 21 , who used fewer potential survival predictors compared to our study. Compared to other urban populations studied in Europe, productivity in the target population is low 22 , with breeding success, as well as some other life-history traits, impacted by the Blackbirds’ age 23 – 28 . Our earlier studies 29 , 30 indicated that a Blackbird’s reproductive performance peaks at 5–6 years old and then declines as senescence sets in, which potentially could impact the fledglings’ survival.…”

The effects of parental age difference on the offspring sex and fitness of European blackbirds

“…We found, however, that paternal age was almost non-linearly positively related to filial breeding success, which does not falsify the “good genes” hypothesis. We think that a male’s advanced age could be a signal of his high quality (the most successful males survive better and live longer ( Jankowiak, Zyskowski & Wysocki, 2018 ); in this population, lifespan is generally closely related to higher lifetime reproductive success ( Wysocki et al 2019 ; Zyskowski, 2015 ). The observed slight decline in the breeding success of sons of >6 years old fathers appears to be acting as a trade-off between the costs of senescence and the benefits of “good genes”: after the sixth year of life, the costs of paternal senescence outweigh the benefits.…”

“…In this study, we examined possible offspring sex bias in an open-cup nesting passerine—the European Blackbird Turdus merula (henceforth Blackbird). There were several reasons for this: (1) Blackbirds are socially monogamous, dimorphic birds (the only Turdus species with clear differences in plumage colouration), where adult males are bigger than adult females ( Piliczewski, Ł& Wysocki, 2018 ); female mating preference could therefore depend on a male phenotypic trait, or else a single male trait, such as age, could affect male mating opportunities; (2) high-quality males of this species engage in extra-pair copulations ( Wysocki & Halupka, 2004 ); (3) the population studied exhibits many different breeding strategies in order to maximise breeding success ( Wysocki, 2004 ; Wysocki, 2005 ; Wysocki, 2006 ; Wysocki & Walasz, 2004 ; Wysocki & Jankowiak, 2018 ); (4) egg size in this species has been found to be sexually dimorphic—larger eggs contain male embryos ( Martyka et al, 2010 )—and hatching in this species is highly asynchronous ( Magrath, 1989 ), so we can expect a relationship between offspring sex and hatching sequence, and older females should produce smaller eggs because of their poor condition due to senescence; (5) chick productivity in the target urban population is low and lifetime breeding success is subject to considerable variance: during a 21-year study, just 7% of males and 16% of females raised 50% of all fledglings; the less numerous, oldest individuals are the birds with the highest lifetime breeding success ( Wysocki et al, 2019 ; Zyskowski, 2015 ). A few studies have shown that age is a significant factor influencing reproductive life-history traits of blackbirds ( Desrochers, 1992a ; Desrochers, 1992b ; Desrochers & Magrath, 1993 ; Streif & Rasa, 2001 ).…”