Social networks

I’m attending the BOU conference on Avian Reproduction this week. They accepted my abstract to present a talk and it should have been my first big in-person conference presenting fody analyses, but they made it online on Zoom because of Covid. So my talk about the impacts of social networks on fody breeding success is online only, and linked below.

As it turns out this particular little set of analyses probably isn’t going to be in my thesis, but that doesn’t mean it’s not interesting. I spent a lot of time in the first couple of years of my thesis looking at the many and varied mating systems the Ile aux Aigrettes fodies use; and as a part of this I built a social network metric for every single bird that ever parented eggs within the time series of my data.

This was a massive pain in my a****, to be honest. I based these analyses on a dataset of nesting attempts, which is 1133 nests over 12 years; for every bird that appeared here as a parent, I had to work out how many birds they had partnered with before, which were still alive. This involved checking the nesting history and then cross-referencing with the studbook and the resightings sheet to determine when each partner was born and when we think they died. It took ages and I couldn’t work out a way of automating it. It took forever, but I got there in the end!

I had been assuming that there was a link between social networks and mating systems; simply, I’d been expecting that males with a larger social network would have more overlapping nests, because of increased availability of mates. But fodies are nothing if not surprising, and it turns out there’s no link there at all.

To unpack all of this we built models in two stages. The first model looked at productivity correlates for all individuals in the population, separated by sex. Predictors we included were age, territory quality, mating systems used, social network size, and the number of unpaired birds of the opposite sex. Each of these might be expected to impact on productivity in different ways. Secondly, because while we do see a lot of varied mating behaviours, 85% of nests are monogamous- so we then repeated these analyses looking only at monogamous birds, and of course not including mating systems as predictors.

We found that social network is only important for monogamous females. This was a real surprise, for the reasons outlined above, so we did some more digging into this to find out why and what the mechanism might be. So the next step was to do some modelling of predictors of the intervals between nests. Why? We know that some birds, particularly males, can overlap nests with multiple females and increase their productivity as a result; if the benefits of larger social networks aren’t associated with overlapping nests in this way, then they must be associated with the interval between nests, because there’s no other way to have more nests per season. You can either overlap nests, or have them more closely together.

And it turns out that we were right about this. Modelling of these intervals in between nests for monogamous females showed that if a female chooses to mate with a male that she knows, and who is already in her social network, the intervals between her nests are much shorter.

Intervals between nests for monogamous females when she chooses a new (left) or previous / familiar mate (right).

This is important because it means that she can get more nesting attempts into each breeding season. Larger social network -> smaller intervals between nests -> more nests -> more fledglings. Simple! We also found that, as with many other birds, a female takes longer to re-nest after a successful breeding attempt, as the production of fledglings takes a lot of effort and she takes more time after this to recover body condition before breeding again.

In all of my analyses across my PhD, we have only been including nests which have eggs laid in them. This is because fodies use nest building as a social and pair bonding activity, and only egg laying confirms that a nest is a serious breeding attempt. This leads me to wonder whether females with smaller social networks, and consequently longer intervals between egg-laying, are spending time with new males building practice nests? I don’t know this for sure and it would be really interesting to find out.

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