Morning At Jim Baker Reservoir: Ospreys and Night Herons. June 28, 2020

Osprey above Jim Baker Reservoir, S. Adams County, Colorado

For the past several years there has been an osprey nest atop a telephone pole on Lowell Blvd across the street from the Jim Baker Reservoir. After every season the telephone company employees  – I assume under orders – rip it down and shortly thereafter it’s there again, rebuilt and ready to welcome new chicks. Last year I got some good photos of a rather large chick in a nest. When I drove down Lowell from 64 Ave several weeks ago, looking up, I was pretty sure I saw a little head sticking up from a rebuilt nest.

This morning, before the heat got too intense, I made my way back to Jim Baker Reservoir. Sure enough, I could clearly make out an osprey head in the refurbished nest. It wasn’t a chick but a female (the coloring of the males and females are slightly different) sitting on the nest. Wasn’t sure if she was sitting on eggs or if there were chicks there. The nests are deep enough so that unless a chick has grown large enough, or out of curiosity sticks its head above the nest line, it is difficult to see. It was only later, driving by the nest on the way home that I spotted two little heads peering out from the safety of the nest.

Ospreys are adaptable raptors.

They make home on every continent minus Antarctica. Here in the United States they make year round homes in the southern states, Florida, the Gulf Coast, Texas. Further north, here in Colorado they tend to migrate south in the winter, returning to the Denver area in the last spring. Jim Baker Reservoir with its abundant fish is an ideal place for ospreys to call home. Master fishermen, they almost always live near water, nest near water, along rivers, lakes, wetlands, and coastal marshes. The osprey nest on the telephone pole near Jim Baker is typical. They frequently nest on telephone poles, pilings, channel markers, and other man-made structures in or near the water.

Last fall, before the weather turned cold, or as cold as it gets these “Climate Change winters”, I saw an adult osprey leave that same nest, soar rather high into the sky, circle the reservoir and make a dramatic and successful catch of a large fish, which I presumed to have been a perch. This morning, a dry run of the same. It left the nest, flew rather high, circled the reservoir hunting. At one moment it dipped down some as if it were on the attack but then pulled back up and flew away, heading south to other nearby ponds (Lowell Ponds, Clear Creek Valley Park I reckoned). Although it failed to find anything this time, it circled for a good five minutes, enough time for me to do the clumsy maneuver of changing the settings on my camera to take a few motion shots. (like the one above).

Fish represent about 99 percent of their diet. Don’t know of what the other 1% consists. Rodents perhaps?

Osprey nesting on telephone pole near Jim Baker Reservoir.

Ospreys are very successful hunters, catching fish on at least one-quarter or more of their dives. What I witnessed this morning is typical: they circle over shallow waters to locate fish below the surface. Once they locate a fish, they hover briefly and then dive into the water feet-first, sometimes becoming completely submerged. Adults are sometimes preyed upon by bald eagles and great horned owls, while eggs and chicks are sometimes taken by snakes and raccoons. I have seen video of the larger bald eagles and ospreys competing for food in Florida marshes. Despite their reputation of strength and prowess, eagles are fundamentally lazy and often let the ospreys do the hard work of fishing, only to attack them in the air and steal the osprey’s prize.

Like so many other bird sprecies, ospreys have had a hard time of it and walked an evolutionary tightrope. Osprey populations in North America declined dramatically from the 1950s to the 1970s due to chemical pollutants such as the pesticide DDT, which caused breeding failures from eggshell thinning. DDT was banned in the United States in 1972, and since that time ospreys have bounced back significantly, although some states still list them as endangered, threatened, or a species of special concern. Today their populations are increasing at a moderate pace and there are few current conservation concerns.

Black Crowned Night Herons

Night Heron over Jim Baker Reservoir

Black Crowned Night Herons, like the one pictured here, are plentiful in Colorado, certainly in the Denver area. One of the largest colonies of them is at Denver City Park. The black-crowned night heron (Nycticorax nycticorax) is the world’s most common heron, inhabiting large regions of North and Central America, as well as Europe, Asia and Africa, where they live in large wetlands.

At a time when bird populations of all kinds are plummeting, those of these herons has remained fairly stable. This wasn’t always the case. Like ospreys, populations  declined in 20th century owing to habitat loss and, in mid-century, effects of DDT and other persistent pesticides. Following the banning of DDT, many local populations have increased in recent years. Water pollution is still a problem in some areas.

This heron is also stocky, with a length of just over 2 feet, a wingspan of 3.8 feet and a weight just over 2 pounds. Their coloring consists of black on their heads and upper backs, with grey wings and tails and lighter grey or white underbodies and black bills. These herons are social, monogamous birds who nest communally and will help raise heron chicks that are not their own. They are foraging birds, feeding on fish, crayfish, amphibians, other birds and even garbage.

As the Audubon Guide To North American Birds notes:

Seen by day, these chunky herons seem dull and lethargic, with groups sitting hunched and motionless in trees near water. They become more active at dusk, flying out to foraging sites, calling “wok” as they pass high overhead in the darkness. Some studies suggest that they feed at night because they are dominated by other herons and egrets by day. A cosmopolitan species, nesting on every continent except Australia and Antarctica.

I have seen them often in and around Lowell Ponds and Clear Creek Valley Park and they do fit the description above.

Night Heron at Lowell Ponds, S. Adams County; early May 2020

They tend to be shy and finicky; as soon as they notice being watch, they fly off to another spot. The ones I that I have run across are adept at hiding among the reeds and marshes where they blend in nicely. Have rarely seen them in trees, but today I did and got a decent photo of him from a distance of about a hundred yards. Typically, aware I was taking his picture, quickly he flew off south, away from me but then circled back across the reservoir close enough for me to get off a couple of shots as he flew by that came out ok.

As Jaymee Squire noted in a blog entry in 2017,

While most birds nest in mated pairs, a few nest communally, sharing the warmth and protection of the roost with other birds, usually of the same species. But a few birds are less particular, sharing the warmth and comfort of the roost with a variety of species. The Black-crowned Night-Heron is one of these birds. They mate for life, but the mated pairs build their nests in communal roosts, sharing the space with all sorts of other water-loving birds.