In this thesis I investigated how genetic relatedness influences different aspects of social behaviour in a relatively simple social system as the wintering flocks of house sparrows. One important finding of these studies was to provide the first evidence for the ability of sparrows to recognize their kin in the flocks. The most frequent mechanism of kin recognition in birds is associative learning: individuals reckon those conspecific as kin with whom they encounter frequently during their early lifetime, most often their same-brood siblings and parents (Komdeur & Hatchwell 1999, Komdeur et al. 2004, Sharp et al. 2005).
So far, no experiment has been carried out to investigate kin recognition per se in house sparrows; however, our studies show that sparrows behave differently toward their kin in some contexts. In Study 2, we found differences in several aspects of scrounging behaviour towards close kin and non-kin birds, where the close kin group also contained sibling and parent flock-mates in about half of the individuals. Additionally, in Study 4 we found evidence for same-brood sib preference during social activities. These results suggest that sparrows are able to discriminate between kin and unrelated individuals, at least when kin is familiar from the nestling period - similarly to most other bird species. We propose that further research is needed, e.g. using cross-fostering experiments to clarify whether sparrows are also able to recognize their non-familiar relatives.
According to our findings, sparrows have the opportunity to interact with a few closely related group-mates in their flocks. Although in the feeding groups of wintering house sparrows closely related individuals were not present in a great number and were not more associated with each other than non-related birds, every bird had at least 1-2 close kin companions out of 10, which may provide suitable circumstances for kin discrimination to evolve during social interactions in the flocks. In accordance with that, relatedness between individuals influenced some kinds of their social interactions. The captive birds, especially males, avoided exploiting their kin’s food findings during social foraging, and also siblings preferred to follow each other during various social activities. Kin-biased behaviour has never been described in the house sparrow, and only a handful of other studies documented similar effects of relatedness in other non-breeding bird flocks (e.g. Burley et al. 1990, Stamps et al.
1990, Hatch & Lefebvre 1997, Ha et al. 2003). On the other hand, kinship did not affect either the frequency or the intensity of aggression between group-mates. Although reduced aggression between parents and fledged offspring was found in bird species with extended
parental care (Sklepkovych 1997, Pravosudova et al. 2001), our findings suggests low benefits to costs ratio of kin discrimination during agonistic interactions in the studied flocks. The lack of kin discrimination during aggressive encounters also suggests that pay-offs of kin-helping might vary considerably in different social activities in house sparrows.
Our results showing that siblings preferentially follow each other (Study 4) seemingly contradict what we found in free-living flocks (no correlation between relatedness and association; Study 1). However, the two types of associations we used in these studies are different: one is based on the joint presence in feeding groups and the other is on the preference for following certain flock-mates within the flocks, not describing exactly the same relationships between two group-members. Besides, in the captive flocks familiarity from nestling period and not pair-wise genetic relatedness were the main determinant factors that affected the frequency of followings. As fledged young sparrows may disperse widely (Fleischer et al. 1984) and suffer a high mortality (Anderson 2006) before settling at a breeding or wintering site, same-brood siblings may rarely stay together in wild flocks.
Another interesting aspect of the studies was that, despite the clear effects of kinship on some types of dyadic interactions, none of our analyses suggests that different forms of
“social status” of the individuals was affected by the kinship structure: the number of relatives present was unrelated both to the dominance rank and centrality (in terms of connectivity to others) in the studied flocks. Why was kin-biased behaviour not translated to these aspects of social role in sparrow flocks? We have no clear explanation for that, but it is possible that the variance in the number of close relatives was too low in our captive flocks (approximately fourth of that in the wild flocks), which could prevent kinship to be an influential determinant in status-forming processes.
Finally, an important question is whether the revealed kin-biased behaviours can be explained by kin selection, i.e. indirect fitness benefits originating from the help directed toward kin flock-mates. The presence of closely related individuals in wintering flocks found in Study 1 and the ability of kin discrimination indicated by Study 2 and 4 are important prerequisites for any kin-selective behaviour to evolve. Besides, the fact that individuals differentiated between close kin and non-kin during social foraging and within-group followings implies that these interactions may have particular fitness consequences when directed toward related flock-mates. Even so, whether the benefits associated with these behaviours are direct or indirect, or in another way around, whether these acts can be considered altruistic or mutually beneficial need to be judged cautiously. Recent papers often
interacting individuals was found, taking high relatedness itself to be an evidence for kin-favouring behaviour with indirect fitness consequences (e.g. Reeve et al. 1990, Ha et al.
2003). However, as West et al. (2002) pointed out, interactions between related group-mates can also have important direct fitness benefits that may outweigh any indirect effects. For example, cooperative breeding (i.e. helping the reproduction of relatives) in many vertebrate species is related to direct benefits such as possibility of obtaining future reproductive dominance in the group (Reyer 1980, Creel & Waser 1994), benefits from delayed reciprocity (Kokko 2001) or increasing social status (Nowak & Sigmund 1998, Roberts 1998). Because of that, the behaviours’ fitness consequences should be measured ideally over the individuals’
lifetime (Hamilton 1964). As fitness was not measured straightforwardly in this thesis, only conservative statement should be made about the fitness consequences of the revealed kin-biased behaviours among which direct benefits should not be ignored. According to that, preference for kin during followings is more likely to be entailed by direct benefits to the actors (e.g. through social facilitation and learning), whereas the avoidance of relatives’
exploitation during social foraging can be related to both direct and indirect fitness benefits.
For instance, reduced exploitation of kin is beneficial for an actor individual not only indirectly through the benefit of the kin flock-mates but also directly if such avoidance is reciprocal. Nevertheless, even if the effects of indirect fitness benefits cannot be proven undoubtedly, this thesis provided an interesting evidence for the presence of kin-biased social behaviour in a species that neither breed cooperatively nor live in permanent kin groups, as do most model species of kin selection that had been investigated before.