Seasonal decline in health status of Great Tit (Parus major) nestlings

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Abstract:

Seasonal variation in offspring survival and recruitment rates in birds may be mediated by immune function, as it defines the ability of individuals to protect themselves against parasites and infectious diseases. To investigate the relationship between hatching date and health status of Great Tit (Parus major) nestlings, two blood parameters (leukocyte level and haematocrit) were estimated. Leukocyte level decreased as the season progressed within first but not second broods, while haematocrit showed no seasonal variation within either brood type. However, nestlings from first broods had both higher leukocyte levels and higher haematocrit than nestlings from second broods. Nestling body condition (defined as the residual of body mass on tarsus length calculated from linear regression) was not related to hatching date within brood type, while a significant difference between brood types was found. We suggest that the commonly observed decline in juvenile survival rate as the season progresses may be at least partly attributed to seasonal changes in health status.

La variation saisonnière de la survie de la progéniture et du taux de recrutement chez les oiseaux peut dépendre de la fonction immunitaire qui détermine la capacité des individus de se protéger contres les parasites et contre les maladies infectieuses. Nous avons estimé deux paramètres sanguins (la concentration de leucocytes et l'hématocrite) pour établir la relation entre la date de l'éclosion et l'état de santé des oisillons au nid chez la Mésange charbonnière (Parus major). La concentration de leucocytes diminue à mesure que la saison avance chez les oisillons de la première couvée, mais pas chez ceux de la seconde, alors que l'hématocrite ne subit de variation saisonnière chez ni l'une ni l'autre des deux couvées. Cependant, chez les oisillons de première couvée, les concentrations de leucocytes et l'hématocrite sont plus élevés que chez ceux de la seconde couvée. La condition physique des oisillons au nid (définie par les résidus de la masse du corps sur la longueur du tarse dans une régression linéaire) n'est pas reliée à la date de l'éclosion au sein d'une couvée, mais il y a une différence significative entre les deux types de couvées. Nous croyons que la diminution de la survie des juvéniles à mesure qu'avance la saison, un phénomène fréquent, est en partie attribuable à des changements saisonniers de l'état de santé.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: October 1, 2001

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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