2023 Harbor Herons Report: A Q&A

Egret Colony. Photo by Don Riepe.

Olivia Liang | January 8, 2024

NYC Bird Alliance’s annual Harbor Herons Nesting Survey has monitored and protected these birds since 1982. This year, NYC Bird Alliance (in partnership with American Littoral Society, Huckleberry Indians, Inc., NPS, NYC Parks, USDA/APHIS, and Wild Bird Fund) surveyed 19 New York harbor islands and found 1,398 pairs of seven different wading bird species. 

To get a behind-the-scenes look at this year’s data collection, NYC Bird Alliance sat down with Tod Winston, our Urban Biodiversity Specialist, creator of the 2023 State of the Harbor Herons, and former Harbor Herons Nesting Survey Coordinator, and Dr. Shannon Curley, PhD, our current Harbor Herons Nesting Survey Coordinator who has collaborated on the last 38 years of Harbor Heron data.

This interview has been condensed and edited for clarity.

View the 2023 State of the Harbor Herons Report here

Let’s start with some background of the State of the Harbor Herons Report. Tod, this report looks very different from previous years. 

Tod Winston: Yes! The idea of this report is to make the Harbor Herons a lot more accessible to people who aren't scientists already working with these birds. We already know and love them; we need to spread the love. 
Our past reports were very dense, technical texts, many pages long. When creating this report, we’ve tried to keep things very simple. We have good news: first, when birds are disturbed and abandon their colony, they are successfully moving to new islands in New York Harbor. Second, Great Blue Herons nested on Millrock Island, a record for Manhattan! But there are also causes for alarm: the main threats to these species are human disturbance, predators, pollution, and climate change. 

And of course, we want people to know how they can help these beautiful birds. So this year’s report really has an entirely different goal. I hope it's effective and that it connects people to our work—and to the Harbor Herons.

Shannon, could talk about what it's like performing these surveys and the experience of collecting this data? 

Shannon Curley: Every year, our surveys are conducted from the 15th to the 31st of May. It's the peak of the breeding season so we expect that most birds have already started incubating their eggs or have nestlings, which is why we time the surveys that way. We typically bring out a group of six to 12 volunteers, depending on how large the island is for the survey, and we split into groups and record nests by species.  We look at the nests, the contents, whether it has nestlings or unhatched eggs, and we record the tree or shrub species of the type of vegetation the nest is in to get as much data as we can. And essentially, we want to make sure we document as many nests as possible to get the most accurate counts for each island. 

Every island is its own new adventure. The composition of species is different on each island, and every island has a unique history about it. So it's a very interesting dynamic. At first, it seemed like a lot of islands to get to know, but then once you realize how different they are, and as you go back each time, it becomes a little more second nature. 

Looking at the species numbers on page 2, what are your thoughts? As the ornithologist leading these surveys and conducting this research, how do you read these numbers? 

SC: The Glossy Ibis decline is what I'm finding troubling. The Black-Crowned Night Heron decline is also troubling, but the Glossy Ibis numbers are becoming quite low… I think the 2022 season was the first year Glossy Ibis were not recorded on our largest Harbor Heron colony, so that's a bit alarming. But the Black-crowned Night Heron populations have also been steeply declining since 2000. So they're both cause for alarm.

TW: My main thoughts are similar to Shannon's. The Black-crowned Night-Heron numbers represent a more clear and stable decline over time. Glossy Ibis numbers, on the other hand, have gone up and down a lot from year to year. They vary a lot. But a statistical analysis takes out those highs and lows and shows they are also declining.

For me, these findings raise a lot of questions as to why. Are there some causes that they have in common? And maybe some that affect one species and not the other? Glossy Ibis nests are very close to the ground, so they seem very vulnerable to sea level rise and predators, while Black-crowned Night-Herons actually nest quite a bit higher. So I wouldn't think they would be more vulnerable than other species that nest in similar places, like Snowy Egrets—but perhaps other issues like contaminants or things that we don't yet know are in play.

With these larger questions, what’s the next step in answering those? What’s the next step for a report like this? 

TW: Next year, we will fully analyze the last 37 years of data which will help us get a clearer idea of what the declines really are. But also sharing that with the wider community will help us communicate with other scientists who are studying the same species. Understanding these declines may be beyond our ken just in New York City. The bigger trends that require research should combine the minds of researchers who are studying the species over much larger areas. Would you agree, Shannon? 

SC: Absolutely. Because it's likely not just one thing that is contributing to these declines. It's likely a multitude of things combined. And I think publishing these declines, first and foremost, is the most important step in getting that information out there. And, hopefully, this will garner more interest in the regional community so that we can start collaborating on other research projects and research goals from an applied conservation perspective.

TW: Right, because the thing is that it's not just New York City. These are wide-ranging species, so the causes of the decline could be in NYC, they could be in NYC and on their wintering grounds. They could be on the wintering grounds and not in NYC. They could also be along the birds’ migration routes! And there may be multiple causes, so it's very complex. And as Shannon said, publishing our findings allows other people to see and respond to the data, kicking off new questions that could actually lead to more research. 
We have a really long data set that includes not just the numbers of each species year to year, but also which islands they’re nesting on and what kind of habitats they're using. So it's possible that our data might hold more answers if we ask the right questions.
Dr. Shannon Curley, PhD, and Tod Winston survey Elder’s East Island in Jamaica Bay. Photo: NYC Bird Alliance

Do you have any particular highlights from this season’s surveys?

SC: I remember getting to one Jamaica Bay island and thinking it was going to be one of the easier surveys. Some surveys are harder than others and with this island, you would expect it to be [consistent with the previous year’s decline]. I remember the weather was beautiful. It just seemed like a perfect day and it really was because we got to the island and realized, oh, there's a lot of birds. Usually some surveys can be more of a leisurely stroll, but this time, it was no, we gotta go. We gotta count quickly! So I was really happy to see this colony doing so well this year. That was a lot of fun—a little intimidating because that was the first time as survey coordinator that I realized it was a much bigger survey than I initially expected, but I had a great group of volunteers with me, so I got very lucky.

TW: It is very exciting going to the islands every year because they change every year! We find different birds, we find birds we don't expect, we find that the birds are gone from where they were before—which always worries us. The islands that Shannon was talking about are ones that have shifted around a lot in Jamaica Bay. We found one island that had been a really productive colony, but now it was abandoned. But at the same time, we discovered that birds were greatly increasing on several other islands, so that makes an exciting season. The birds are still there. They've just moved on to new places.

As scientists, how do you juggle the good with the bad? This year, we have new data on declining populations, but at the same time, Great Blue Herons nested in Manhattan, a first for modern times! How do you process that progress with the decline? 

SC: Being a Harbor Herons survey leader has a lot of ups and downs because-–and Tod you can attest to this—you are so emotionally invested. When you start running these surveys, you take on everything. It's hard to not get upset when a colony becomes abandoned, it's hard to not get upset about certain things. But at the same time, you realize what a neat responsibility this is that we are out there collecting this data because it's so important. And though it can be heartbreaking at times, it is also very rewarding. And I think having this data, and being able to use this data in a bunch of different ways—whether it's conservation or advocacy—I think it's all for the greater good. 

TW: Like Shannon says, it can be really upsetting to find that a beautiful colony has been devastated. I remember when I was on a survey, this is maybe 10 years ago now, we discovered Goose Island in the Bronx had been not only abandoned, but raccoons had gotten on the island and killed a bunch of birds. We found cracked eggs and dead adults, and we all responded really emotionally. We love these birds. That's why we do this work. 
At the same time, since we have access to 30 years of these surveys, you can see that the birds have moved all over the harbor. They used to be on completely different islands than they are now, and they've moved several times among all of these several dozen islands. So that gives us hope. It is important to note that the birds have not returned to previously abandoned islands, so one of our main pushes in this project is to make sure as many islands as possible remain open and available to these birds. Because if they do have habitat available, they seem quite capable of adapting to changes and continuing to live and thrive here.

So with that said, if someone were to ask you: The Black-crowned Night-Heron currently has the largest number of nesting pairs. Does it really matter that they’re in decline? What do you say to those who might not understand the importance of each of these nesting pairs and populations? 

SC: I love that question, and it's a really important question. I think when people say, oh, there's a lot of pairs nesting here, why does it matter if they’re declining so quickly? The answer is: birds are bioindicators. They give us an idea of the health of an ecosystem, so they're important, especially Black-crowned Night Herons who are more sensitive to things like pollutants.

TW: My first thought too was that if bird populations are changing that quickly, it means that something is wrong, and we need to figure out what that is. Both because it affects the beautiful birds that have value in their own right, and because it could be affecting all sorts of other parts of the ecosystem, including people. 

These birds are bioindicators because they're at the top of the food chain. They eat a lot of smaller critters, so pollutants show up in them in high concentrations. People are also at the top of the food chain! The same pollutants that show up in these birds could show up in us. We all drink the same water and live in the same area. We're not living in a bubble… or I guess, we're living in the same bubble!
Black-crowned Night-Heron surveyed on Elder’s East Island in Jamaica Bay. Photo: Jeffrey_Kolodzinski

As you know, our NYC Bird Alliance community is an incredibly passionate and curious bunch. What would you say to those who want to learn more about our Harbor Herons and possibly visit these islands? 

SC: We want the public to know what's happening with these birds in our region, but without them feeling the need to be like: I have to go to this island and check for myself.

TW: That's always a concern of ours. When we talk about these birds, we want people to know about them but we also don't want people to visit the islands and potentially hurt them. So we're asking people to admire them from afar, to get to know them and see how beautiful they are, but also realize that it's all of our responsibility to protect them. It’s critical that we allow them to do their thing without being disturbed.

SC: And “disturbance” is the key word here. These are colonial nesting birds; they are attracted to the presence of other birds. If some of them get spooked, the whole colony could get scared away. So I think being mindful of how sensitive they are to human disturbance and the presence of predators means we keep our distance and admire from afar.

TW: But also, when people go out into their neighborhoods, they can see these birds! They breed on these remote islands, but they come to find food in little lakes and ponds and along the shoreline all over the City. So in the spring and summer, when people are out in their neighborhoods, they can see a Great Egret or a night-heron. Lots of people live in areas where these birds forage regularly if they want to go looking for them. They're probably seeing the same birds we count on the islands, catching a frog or crawfish to bring back to their babies.

Read the complete 2023 State of the Harbor Herons Report here