3 days ago6 min read

Concerning Decline Of Red-Billed Gull Population

The following blog highlights the concerning decline of at-risk red-billed gulls/tarapungā, a protected species that is part of our national coastal landscape and disappearing fast.

What do we know about the size of the colony in Kaikōura - and what is being seen when it comes to its decline?

If you pull up at a beach with fish and chips, it can seem like red-billed gulls are common and thriving. However, we know that nationally, the population is plummeting at an alarming rate, with total population crashes at offshore island colonies and huge declines at remaining mainland strongholds.

Red-billed gull numbers have fallen so rapidly that the species now appear on threatened species lists classified as At-Risk. Numbers have dropped sharply at breeding colonies and are expected to plummet up to 70% over the next three decades. Experts state the red-billed gull is severely at risk.

Kaikoura is home to the largest remaining mainland colony, with two large mainland colonies already having collapsed. 60 years of monitoring data showcasing huge population losses. At Kaikoura, major declines began in 1994, with the population declining by 51% between 1983 and 2005.

The population has continued to decline at an alarming rate since then, with the colony shrinking and fragmenting. At the current rate of decline, the Kaikōura colony will vanish.

What are wildlife rehabilitation facilities seeing?

In Kaikōura, we are receiving increased reports of deceased gulls and seabirds every year, with high mortality rates due to starvation - attributed to human-related impacts. Many of these birds have suffered from prolonged starvation and succumb to death without intervention. In some years, mass mortality occurs.

Seabirds make up the majority of wildlife patient cases in Kaikoura, given that the region is a global seabird capital and biodiversity hotspot.

Red-billed gulls are a primary patient in care, but are often not reported in a timely manner to enable successful treatment for recovery and release. Gulls in poor body conditions are emaciated and generally in organ failure, with secondary issues such as Aspergillosis infections presenting in these subsequently immune-compromised birds.

As there is little public compassion around the welfare of this at-risk species due to a lack of education, people are less likely to report an unwell gull vs an unwell penguin. Early reporting and intervention are critical in giving threatened species the best chance of survival and a second chance at life in challenging conditions.

Photo Credit Sabrina Luecht

How much of this comes down to predators like cats, and how much of this can be attributed to a decline in food sources?

Introduced predators are part of the story and so are tiny high-protein crustaceans called krill, which are the primary food source of red-billed gulls.

Being a ground-nesting bird, red-billed gulls are highly susceptible to predation at night by mustelids and cats. We know that feral and stray cats, as well as pet cats, are a primary threat to gull survival - and shorebirds in coastal areas in general. Without predator control, the Kaikoura gull colony would be wiped out within two years.

Red-billed gulls are highly specialised, and without naturally occurring krill upwellings have been subject to prolonged starvation. Climate change is impacting the marine ecosystem, with increasing sea surface temperatures suppressing prey availability. This means fewer upwellings of krill and shoaling fish, which remain at deeper, cooler depths - out of reach of foraging seabirds. Surface-feeding seabirds such as gulls and albatrosses, which cannot dive, have no means of accessing this food source.

This is compounded by overfishing, with large apex predatory fish removed from the food chain, resulting in decreased workups of krill and shoaling fish brought to the sea surface.

The red-billed gull has an increasing presence in urban areas - why is that, and what does that indicate about their food sources?

Due to a lack of krill upwellings at sea, red-billed gulls are increasingly noted in urban areas. The perception of increased visibility, unfortunately, leads to misunderstanding and assumptions the species are increasing and common - when the opposite is true, and there are fewer than ever.

The shift in behaviour in residential areas is because of an increased reliance on human-related scavenging in the face of starvation. Red-billed gulls are highly specialised, with their primary food source being krill. Apart from this, they will feed on kelp flies when available in washed-up seaweed and on earthworms in coastal pasture land after heavy rain. Without regular krill upwellings, breeding success and survival is massively impaired - and the species will perish. Their food sources are disappearing because of human impacts.

This is not only a cause of concern for red-billed gulls but all seabirds, 90% of which are threatened with extinction. We know that seabird species are impacted by starvation. This has also been extensively documented in fish with milky white flesh syndrome, mass fur seal mortality, and is leading to the displacement of cetaceans such as whales.

Krill are the largest and most ecologically important zooplankton, which feed on phytoplankton. With phytoplankton and zooplankton impacted by warming oceans, marine ecosystems are failing.

From a conservation viewpoint, this is the sounding of alarm bells for marine wildlife. From a human reliance standpoint on functioning marine ecosystems, we are looking at the collapse of food webs. These species are indicators of ocean health; they are the canary in the coal mine. It’s a warning of what lies ahead unless we implement urgent changes.

How much does the perception of the birds being a nuisance stealing chips harm the advocacy for the species?

The misconception of the species is absolutely harmful to advocacy. Beyond a lack of understanding and compassion, there is often a downright hatred towards these birds. This is evident in public opinion, as well as gulls being an ongoing target for wildlife crimes.

Humans have a tendency to protect cute and cuddly species. If these were Kiwi or Kakapo, there would be increased media coverage and a push to scale up conservation efforts and facilitate policy changes.

Just how small in size are some of the deceased gulls being found compared to what they should be?

Beyond documenting poor body condition, with emaciation and organ failure leading to death in red-billed gulls, research and wildlife rehabilitation has shown that gulls are shrinking in anatomy due to lack of food sources. This is due to impaired development, leading to birds being physically smaller overall. On the other hand, the stark difference is alarming, with one bird being half the size of a normal size bird. This is also being documented in endangered Hutton’s shearwaters.

How long has the Kaikōura colony been studied, and why is this significant when it comes to monitoring gulls in particular - a long-lived species?

Biologist James Mills has researched red-billed gulls for 60 years, making it one of the longest-running avian studies in the world. The research has proven the levels of decline and related impacts. In long-lived species such as gulls, with lifespans over 30 years, it can take decades until declines are apparent to the public - with high mortality rates, an ageing population, and decreased juvenile recruitment due to low fledgling survival.

What does this indicate about the health of our oceans, and how to address this?

If a species that was once common can decline so rapidly, that’s alarming. What we’re seeing is reduced ocean productivity as a result of climate change and overfishing. Starvation across species indicates impaired health of our oceans and marine ecosystem failure. We are moving towards a precarious scenario.

We must focus on a holistic approach to ecosystem protection, focused on appropriate management to address challenges in the marine environment. We need to not only concentrate efforts on individual species but also address the causes of species declines as a whole. There are known solutions to the issues marine ecosystems face. Without urgent attention to alleviate human-related pressures such as overfishing, in the face of global threats such as climate change, we face the collapse of wildlife populations and fish stocks. In the interim, we can increase marine reserve coverage, review fishing quotas, and implement policy changes to address emissions.