The key to finding chiffchaff nests is to follow the female back to the nest, using her ‘off-nest’ call to both locate and identify her. This call, a soft and repeated ‘hueet’, alerts the male that his mate is away from the nest; it is not dissimilar to the more general contact call used by the species. The ‘hueet’ is most characteristically delivered when the female has eggs in the nest, providing an ideal opportunity for those involved in nest monitoring to collect vital information on clutch size and laying date.
The technique of following female chiffchaffs (and other ‘leaf warblers’) back to the nest works best in more open habitats, with good lines of sight. Here, however, the feeding female would move through the wood to feed in different places, making watching back particularly problematic. The two previous visits had narrowed down the nest location to the damp ground where I was now waiting patiently. After an incubation bout of 30 to 45 minutes the female should leave the nest to feed and I could then watch her back to the nest.
True to form the female leaves to feed and disappears into the wood. Some 10 minutes later she is back and I follow her calls to a single scrubby hawthorn on a bank. From here she drops down into the grass beneath, leaving me with a mental note of where to look once I have given her another 20 minutes to incubate before making an approach to the nest. The complex structure of the vegetation requires a very cautious approach – chiffchaffs nest as low as two inches above the ground – and it is as I am inching my way forward that I spot the nest, a ball of woven reed and grass stems placed in a tangle of sward. I ‘pish’ through my teeth to alert the female of my approach and then gently tap the nearby vegetation to lift her from the nest. A quick check of the nest contents – six warm eggs – then I leave. Three hours work for an important reward.