# The Same River, Different Generations: How Spot-billed Ducklings Change in Just 40 Days
Watching multiple duck families on the same river during the same day offers a rare opportunity to compare how ducklings develop at different ages. On this particular observation day, I encountered Spot-billed Duck (Anas zonorhyncha) families ranging from only 12 days old to 55 days old. Seeing these families negotiate the same river obstacles revealed just how rapidly ducklings change in little more than a month.
This article is based on my daily field observations rather than scientific research. Any behavioral interpretations are personal observations from a long-term wildlife watcher, not conclusions from professional ornithological study. Nevertheless, I believe that preserving these observations day after day may provide useful documentation of urban wildlife behavior over time.
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## A River Shared by Many Duck Families
The river has become home to an unusually large number of Spot-billed Duck families during this breeding season.
Throughout this day's walk, I encountered family after family occupying different sections of the river. Some preferred quiet ponds, others rested beneath vegetation, while others remained close to weirs or shallow flowing water. Many of these locations have been used repeatedly for weeks, suggesting that each family develops its own preferred range within the river system.
One purpose of today's survey was to relocate several families that had not been seen recently. Although some remained missing, two families that had disappeared from my recent observations were found again farther downstream. Finding them reminded me that temporary absence does not necessarily indicate mortality; vegetation, river structure, and daily movement patterns often make families surprisingly difficult to locate.
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## Comparing Ducklings Across Forty Days of Growth
Perhaps the most striking aspect of this observation was the opportunity to compare ducklings at very different developmental stages.
The youngest family observed consisted of ducklings only 12 days old. At this age they still relied heavily on gentle routes, avoiding steep obstacles whenever possible. When approaching a weir, the mother climbed first while the ducklings selected a sloped path instead of attempting the vertical section.
In contrast, ducklings around 30 days old already moved with much greater confidence. They rested frequently but showed increasing independence, exploring around their mother while still responding when she called.
Families around 50 to 55 days old appeared dramatically different. Their bodies had grown substantially, swimming was stronger, and climbing obstacles required far less effort than it had only weeks earlier. Although they were not fully mature, the difference between these birds and the youngest ducklings was remarkable considering that only about forty days separated them.
Watching multiple age classes on the same obstacle highlighted how quickly survival skills develop during the early stages of life.
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## Mothers Continue Coordinating Their Families
Even older ducklings still depended on their mother's leadership.
One mother repeatedly gathered ducklings that had wandered too far apart before continuing downstream. Another attempted to lead her young away, only to discover that some had failed to follow. She returned and tried again rather than abandoning them.
These events illustrate that parental care remains active well beyond the first days after hatching. While older ducklings become increasingly independent, family coordination is still necessary when navigating a complex urban river.
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## Resting Is Also Part of Survival
Many of the families spent surprisingly long periods resting.
Some groups slept beneath vegetation, while others selected shaded concrete structures or quiet pools. Certain resting sites have been used repeatedly over many days, suggesting that these locations may provide safety from predators, reduced disturbance, or comfortable thermal conditions.
Because I visit almost every day, I have begun noticing individual preferences. Some families appear consistently active, whereas others spend much of the day sleeping before suddenly becoming active again. Whether this reflects weather, food availability, predator avoidance, or simply individual differences remains uncertain.
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## Other Birds Sharing the River
The duck families were not alone.
A female Common Kingfisher allowed unusually close observation from several different angles before departing.
A Little Egret searched for prey but eventually appeared unsuccessful and flew away.
Groups of Great Cormorants rested beneath the bridge, while Rock Pigeons continued bathing in shallow water—a seasonal behavior that becomes increasingly common during warm weather.
House Sparrows also shared the riverbank with one of the duck families, illustrating how many species use the same urban habitat simultaneously.
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## Following Individual Families Through Time
By this point in the breeding season, I am simultaneously tracking more than twenty duck families along this river.
Each family is identified by the distinctive wing pattern of the mother together with my own observation code. This system allows me to recognize individuals over weeks and compare how each family changes through time.
Several families have disappeared from the areas where they were previously observed. Some may simply have moved farther downstream, while others may have suffered natural losses. At the same time, many families that once seemed vulnerable continue to survive and grow, reminding me that field observations often reveal outcomes very different from initial expectations.
Long-term documentation makes these gradual changes visible in ways that isolated observations cannot.
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## About This Observation Record
This article accompanies video footage that is released as close as possible to the filming date.
The recordings are published with minimal editing so that they serve both as personal field notes and as chronological evidence of what was observed on each day. While this approach results in lengthy videos with relatively little narration, it preserves behavioral sequences that might otherwise be overlooked.
The interpretations presented here should therefore be regarded as observational notes from a long-term wildlife enthusiast rather than scientific conclusions. My hope is that these continuous daily records may become valuable references for anyone interested in the lives of urban wild ducks and other wildlife.
Detailed explanations of the duck family identification codes and filming date codes used throughout these records are available here:
https://okasinaikimono.blogspot.com/p/welcome-to-wild-duck-diaries.html
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# Species Recorded
- カルガモ
- English: Spot-billed Duck
- Scientific name: *Anas zonorhyncha*
- A resident East Asian duck that adapts well to urban rivers. Ducklings grow rapidly during their first two months while remaining dependent on maternal guidance.
- カワセミ
- English: Common Kingfisher
- Scientific name: *Alcedo atthis*
- A small fish-eating bird famous for its brilliant blue plumage and remarkable diving ability.
- コサギ
- English: Little Egret
- Scientific name: *Egretta garzetta*
- A white heron that hunts fish and aquatic animals in shallow water with patient stalking behavior.
- カワウ
- English: Great Cormorant
- Scientific name: *Phalacrocorax carbo*
- A diving waterbird that often rests beneath bridges after underwater fishing.
- カワラバト
- English: Rock Pigeon
- Scientific name: *Columba livia*
- Common in urban environments and frequently observed bathing during warm weather.
- スズメ
- English: Eurasian Tree Sparrow
- Scientific name: *Passer montanus*
- One of Japan's most familiar small birds, commonly sharing riverbanks and parks with larger bird species.
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