A PhD student from Lancaster University has provided the most detailed understanding to date of why some White-throated Dippers attempt a second brood during the breeding season while others do not. Ms Noelia Alvarez’s research has shown a strong influence of seasonal timing, environmental conditions and individual characteristics on this key reproductive strategy.

The study analysed data from a long-term study population in the Yorkshire Dales National Park run by Dr Stuart Sharp (Lancaster Environment Centre). Over nine breeding seasons, between 30 and 50 Dipper pairs were monitored each year, recording more than 300 first breeding attempts.

They found double brooding was common, with an average of 29 percent of pairs producing a second brood each year. By providing a greater number of young overall, double-brooding may be a potentially important factor in sustaining populations.

The strongest effect on whether a pair would attempt a second brood was the timing of their first clutch, with birds breeding earlier in the season more likely to go on to raise another. No second broods occurred when first clutches were laid after mid-April, showing how rapidly opportunities decrease as the breeding season progresses.

Certain individual characteristics were also found to shape breeding decisions. Older males were more frequently involved in second broods, while female age did not appear to influence outcomes. This suggests that experience or differences in territory quality may contribute to the greater reproductive success observed among older males.

Pairs nesting at lower elevations were also more likely to attempt a second brood, possibly indicating the more challenging conditions of upland areas may limit the resources available for additional breeding attempts. The analysis also identified a modest positive association between rainfall during the period between broods and the likelihood of producing a second clutch, possibly reflecting the increased availability of food sources for the Dippers.

While double-brooding increased total reproductive output, second broods generally contained fewer eggs and fledged fewer chicks than first broods. Only around eight percent of young from second broods were recruited into the breeding population the following year, compared with 12 percent from first broods.

One particularly encouraging result for conservation was the role of nestboxes. Second broods raised in nestboxes were almost twice as likely to fledge at least one chick compared with those in natural nest sites. The provision of nestboxes may therefore support improved breeding success, especially during the later part of the season.

Ms Alvarez said of the study: “Long-term studies such as this that help answering fundamental questions on breeding ecology are important to understand how birds may adapt to increasing anthropogenic threats, particularly for those species in decline such as the White-throated Dipper.”

The research offers valuable insight into how Dippers may respond to future environmental change. As rising temperatures continue to advance the timing of breeding in many bird species, opportunities for second broods may increase, helping to buffer populations against ongoing declines. However, these benefits must be balanced against possible long-term costs, such as reduced adult survival or future breeding output.

The full paper, published in Ibis, can be found here