Parental Care in the White-rumped Swallow (Tachycineta leucorrhoa)

SIMONETTI, PIA; FERRETTI VALENTINA

Veracruz

Congreso; 4th North American Ornithological Conference; 2006

Parental care in socially monogamous birds is generally shared by males and females of the social couple. Here, we study parental care in a monogamous Neotropical species, the White-rumped Swallow (Tachycineta leucorrhoa), a migratory bird that breeds from central Argentina to southern Brazil (Turner, 1989). We conducted our field work in a population breeding in General Lavalle (Buenos Aires, Argentina). We looked at natural variation in male and female parental care by filming nests for 4 hours when nestlings were 10 days old (N=16). Adults were color banded for correct sex identification back in the laboratory. To look at differences in male and female care we calculated nest visitation rates for each sex as the total number of male/female trips per hour per nestling. We did not find a significant correlation between male and female visitation rates. However we detected a trend towards a positive relationship among sexes. That is, the higher the female’s care, the higher the male’s care. This relationship could be explained if there is a positive feedback among members of a social pair or if members of the pair choose each other based on some cue signaling feeding/insect capture rates. We also measured nestlings’ growth rates to study the relationship between growth and parental care. Nestlings were weighed and their tarsi were measured every other day until age 14. We fitted our data to a sigmoid curve (see Ricklefs 1967, 1968, Remes & Martin 2002) using a non linear regression, and obtained the growth rate (k) as the inflexion point of the curve. We did this for every nest. Growth rates of nestlings did not correlate with our measures of parental care. However, we did find a negative correlation when we analyzed female´s mass versus growth rates. We believe this correlation is attained due to the presence of an outlier; when we removed this datum from our analysis the correlation rendered non significant. Our analyses indicate that nestlings’ growth rates do not seem to depend on visitation rates of the parents. It is possible that some other variables not taken into account in this study, such as food quality or weather, could affect nestlings’ growth.