Walk the breakwater on a mild September evening and you’ll see plenty of penguins ferrying stones and dry grass into their cavities, clearly gearing up for eggs. But if you could tag every adult on the wall and follow them individually — which is more or less what decades of volunteer monitoring has done — you’d notice something else. Not all of them are doing it. Some birds, in some years, simply don’t breed at all.
This isn’t a St Kilda oddity. It’s a pattern seen across little penguin colonies on the southern Australian coast, and it’s one of the more quietly interesting things about how this species manages a hard life on a rock wall next to a working harbour. I’ve spent a few evenings at the breakwater this year watching the same burrow entrances week to week, and the variation between neighbouring pairs is honestly one of the more underrated parts of visiting — most people come to see the penguins land, not to notice the ones who aren’t building anything at all.
What “skipping” a season actually looks like
A little penguin that skips breeding isn’t absent from the colony. It still comes ashore most nights, still moults over its usual two-week stretch in summer, still occupies (or defends) a burrow. What it doesn’t do is lay, incubate, or feed chicks that year. From the outside, at dusk, this looks almost identical to a breeding bird on a night off — the tell is really only visible to volunteers doing the close-up work of population counts, weighing and banding across a season, which is exactly the kind of monitoring this colony has had, in one form or another, since Professor Mike Cullen of Monash University began his fortnightly night trips back in 1986.
Cullen’s original interest was actually a harbour redevelopment proposal, not breeding gaps specifically, but the long run of nest checks and burrow records that followed — with Neil Blake from St Kilda Council assisting in the early years — is what makes it possible to say with any confidence that this happens, rather than just guessing. You can read more about that history on our History of St Kilda Penguins page and in the original J.M. Cullen Report.
Body condition is the main driver
The clearest link researchers point to is body condition going into the breeding season. Little penguins need to build up fat reserves before courtship starts in late July, because incubation is a long, largely fasting business for whichever parent is sitting on the clutch of two eggs while the other forages. A bird that comes out of its summer moult, or out of a run of poor foraging months, underweight simply doesn’t have the physiological buffer to commit. Skipping isn’t a failure of instinct. It’s closer to a bird making a call, in the only way it can, that this isn’t its year.
That matters because incubation shifts on this species run for around five weeks and are shared unevenly between partners — if one bird can’t hold its own weight through a long shift, the whole attempt is at risk of failing anyway, and abandoning it costs less than starting it. Our foraging behaviour page covers how variable a day at sea can be for these birds, which flows directly into whether they’re carrying enough condition to breed at all in a given season.
Age, first pairings and the mate question
Younger, first-time breeders are more likely to sit a season out than experienced pairs who’ve bred together before. Little penguins are broadly monogamous season to season and tend to reuse the same nest cavity for years, which is efficient — no time wasted relocating or re-establishing a burrow — but somewhere between 18 and 50% of young birds find that their first pairing doesn’t work out and end up seeking a new mate. That process of finding, or re-finding, a compatible partner can itself eat into a season, especially if it drags into the months when laying should already be underway.
A bird without a settled partner by the time eggs are going down elsewhere in the colony has, in effect, missed its own window. It’s not dramatic. It’s closer to a logistics problem than a crisis, and most of these birds are back breeding again the following year.
A poor foraging year leaves its mark
Because little penguins forage at sea all day and only return to the breakwater after dark, their condition is tied tightly to how good the fishing has been in Port Phillip Bay and beyond in the months before breeding starts. A run of poor foraging conditions — patchy prey, rough weather keeping trips short, whatever the cause — shows up later as a dip in how many adults attempt to breed at all, not just as smaller clutches or fewer fledged chicks. This is one reason volunteer counts matter beyond simple curiosity: a colony-wide shift in the proportion of birds not breeding is a genuine early signal of how the season at sea has gone, well before anyone would otherwise notice.
Bureau of Meteorology seasonal outlooks and coastal water temperature data are part of the broader picture researchers use to understand these swings, alongside the fortnightly ground-truth of actually counting birds on the wall.
The human-made pressures layered on top
None of this happens in a vacuum. This colony lives inside a rubble-stone breakwater built in 1955 as a pier upgrade, not a purpose-built sanctuary, and it sits about 7km from the Melbourne CBD next to a genuinely busy stretch of harbour. Off-leash dogs, boat traffic, artificial light disrupting the after-dark return to shore, and marine plastic or fishing-line entanglement are all real, documented pressures on this specific population, and any one of them landing on a bird at the wrong moment — an injury, a stressful encounter, a disturbed burrow — can be enough to tip a marginal bird out of breeding for the year.
I’d argue this is where the “it’s just a rock wall” framing some visitors bring undersells things. This is a wild colony absorbing city-adjacent pressures that a more isolated Victorian colony simply doesn’t have to deal with, and the skip-a-season pattern is arguably part of how it copes rather than a sign something’s badly wrong. Zoos Victoria’s work on little penguin conservation makes a similar point about urban and peri-urban colonies more broadly — proximity to a city changes the risk profile without necessarily collapsing the population, provided the pressures are managed.
Why volunteers keep count of the non-breeders too
It would be easy to design a monitoring programme that only tracks active nests — eggs, chicks, fledging rates. But part of what makes the long record at St Kilda useful is that trained volunteers also track occupancy and condition in birds that aren’t breeding that season. That’s the only way to distinguish “the colony had a bad breeding year” from “the colony had a bad foraging year that’s showing up as more skipped attempts,” which are related but genuinely different problems with different implications.
If you want to see this kind of work up close, guided public viewing at the breakwater happens at dusk, timed to when the penguins actually come ashore, and volunteers on-site can talk through what they’re seeing on a given night far better than any general guide can. Details on how that’s run are on our guided viewing page, and if you’re planning a first visit the Penguin Viewing at St Kilda Breakwater page and our seasonal calendar are worth reading beforehand so you know roughly what stage of the breeding cycle you’re looking at.
What this means for a casual visitor
None of this should put anyone off a visit. If anything it’s a good reason to come more than once across a season, because the colony genuinely looks different in October compared to January. A visitor who only ever sees breakwater penguins in high summer, mid-moult and fasting on stored fat, gets a very different impression to one who sees the same wall in early spring with birds ferrying nesting material into the cavities.
The short version: a penguin skipping a season isn’t sick, isn’t failing, and almost certainly isn’t gone for good. It’s a small, sensible calculation by an animal that’s spent its whole life balancing a limited energy budget against a demanding, occasionally hostile stretch of coastline. Watching for it is one of the quieter pleasures of paying proper attention to this colony, rather than just ticking off a sighting and heading back up the pier.
