Erik Kleyheeg, Loes van den Bremer, Chris van Turnhout, Ties Maris, Eelke Jongejans & Niek van Rabenswaaij (2024) Survival and phenology of dablings of Mallard Anas platyrhynchos, Domestic Duck A. platyrhynchos forma domestica and Gadwall Mareca strepera in the Netherlands. LIMOSA 97 (2): 49-61.

After peaking in the 1980s, the Dutch breeding population of the Mallard has declined with approximately 25% in the past decades, similar to the trend of the substantial domesticated population of the species. This is in sharp contrast with the ecologically similar Gadwall, which has shown a fivefold increase since 1990. Previous analysis of demographic parameters of the Mallard population hinted at low duckling survival driving the decline, but no empirical data on duckling survival in the Netherlands were available. To address this knowledge gap, we initiated a citizen science project in 2016 to collect basic information about Mallard breeding biology and duckling survival. In the slipstream of this project, we also collected data for Domestic Duck and Gadwall for comparison. In the analyses we also made a first inventory of factors possibly affecting duckling survival.
Between 2016 and 2020 we collected a total of 25 634 observations of duck broods, including 1730 broods of Domestic Duck and 505 broods of Gadwall (Fig. 1), with a good distribution across the Mallard range (Fig. 2). Based on the estimated duckling age, we first back-calculated the hatch date, which peaked in the second half of April for Mallard, whereas for Gadwall hatching peaked in early June (Fig. 3 & 4). Domestic Duck showed the same phenology as Mallard.
On average, Mallard broods of 0-2 days old consisted of nine ducklings, dropping to less than five after one week (Fig. 5). For all three ‘species’ brood size stabilized around four after three weeks. We used repeated observations of the same broods to calculate daily duckling survival rates in a Mayfield-type analysis (Fig. 6). In 2020, Mallard ducklings had a 22.7% probability of reaching fledging age (56 days), compared to 17.8% for Domestic Ducks and 34.4% for Gadwall. Mortality was highest in the first three weeks, with only half of the Mallard ducklings surviving their first week. In contrast, 73.8% of Gadwall ducklings survived their first week.
A first analysis of potential driving factors revealed that survival was correlated with water quality (turbidity), presence of emergent shoreline vegetation, land use, and abundance of predators and competitors. However, these relationships were not very consistent and require further investigation.
Compared with values in literature, we conclude that Mallard duckling survival is currently low in the Netherlands. The difference in duckling survival between Mallard and Gadwall suggests that this may be a factor the contrasting population trends. We also found first indications that management of shorelines and other measures to reduce exposure of ducklings to predators may help to increase duckling survival. Many questions still remain, and we will continue the citizen science project in the coming years to collect more data and find answers.

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