6 / OutdoorIllinois May 2008

At sites like the Lake Renwick Heron Rookery Nature Preserve inare helping to shore up the fragile status of heron breeding colo

Story By Michelle SimonePhotos By Adele Hodde

As the summer sun rises over aheron rookery, the silvermaple and cottonwood treesare alive with noisy activity.Adult herons and egrets

fly in and out of the rookeryas they go to foraging areas

and return with food for their young.Immature birds sit in the nests, or outon tree limbs, squawking and clucking

as they wait for their meal. Both youngand adult birds would appear to bewildly messy housekeepers, with splat-tered evidence of the feeding above lit-tered understory plants. In a rookerywhich may have thousands of youngherons, it is quite a display of sounds,sights and smells.A rookery might range from a hand-

ful of nesting great blue herons along asmall creek to more than a thousandnests, including several different speciesof birds, along a large river or lake. Inthe last 10 years, more than 100 activeheron rookeries have been found in Illi-

nois. Wading birds nesting in thesecolonies include great blue herons,great egrets, snowy egrets, black- andyellow-crowned night herons, little blueherons and cattle egrets. Double-crestedcormorants are not wading birds butthey also nest colonially, frequentlywith herons and egrets.Herons build platform nests made of

sticks which are usually in trees andshrubs, although some species also willnest in marsh vegetation. Nests oftenare used year after year, with mainte-nance done each year when the pairarrives on the rookery.

Will County, volunteersnies in Illinois.

Both parents participate in nestbuilding, egg incubation and care ofyoung. Although the dates vary byspecies, eggs are typically laid in Apriland May and incubation takes an aver-age of three to four weeks. Many birdsremain in the rookery until July or later.In the late fall, most herons migratesouth, although some great blue heronsand black-crowned night herons remainthrough the winter.An average Illinois heron rookery is in

bottomland forest close to shallow-waterareas for foraging. Most herons andegrets primarily eat fish, although snowy

egrets and yellow-crowned night heronsprefer crayfish and cattle egrets con-sume mainly insects. All of these specieswill eat other small prey if available.Through the generations, herons

and egrets tend to have a strong fidelityto some of the larger rookery sites.While the size of a rookery and speciesusing it may vary over time, someheron colonies in the state have beendocumented in the same location forseveral decades, and one for more than70 years. Sometimes the appeal of thesite is not apparent to humans. Themost diverse heron rookery in the state,which includes six species with morethan a thousand nests, is found in anexotic species thicket in an urban area.In some cases, the attachment to a

rookery site has overcome severe dis-turbance factors.Several years ago a rookery in east-

ern Illinois was hit by a tornado andmany of the trees were destroyed.Recovery began slowly, with onlyabout half the breeding pairs returningto the area, but numbers have returnedto nearly pre-tornado levels. Anotherrookery on the Illinois River was dis-

turbed by logging, but after a 12-yearabsence from the site, the heronsreturned and it is now one of the largerheron colonies on the Illinois River.Typically, herons nest in secluded

locations away from people. Despite thefidelity of herons to a particular site, toomuch disturbance can cause abandon-ment of a rookery. Some colonies havebeen permanently abandoned from dis-

May 2008 OutdoorIllinois / 7

In the past decade, more than

100 active heron rookeries have

been documented in Illinois,

supporting eight species of

colonial nesting birds. Many

rookeries have been active for

decades; the oldest in Illinois

has been in use for more than

70 years. Most rookeries are

located in bottomland forests,

with shallow-water areas nearby.Active from dusk to dawn, the

state-endangered black-crowned

night heron constructs a fragile

platform nest of interwoven twigs.

The state-endangered little blue

heron primarily nests in the

southernmost part of the state.

Illinois is at the northernmost

edge of its range.

8 / OutdoorIllinois May 2008

once highly desired for their use in dec-orating hats. Although the plume tradeceased in the early 1900s, factors suchas illegal shooting, pollution, breedingseason disturbance, and destruction ofnesting and foraging habitat have con-tinued to adversely affect heron popula-tions. Black- and yellow-crowned nightherons, little blue herons and snowyegrets are Illinois-endangered species.Restoration efforts to increase wet-

land habitat acreage and quality arebeneficial to many species, includingwading birds. One example is in theCache River Watershed, where a newrookery has been established in an areawhere extensive wetland restorationand protection recently occurred.These restoration efforts also haveenhanced foraging opportunities forbirds nesting in existing rookeries.Lake Renwick Heron Rookery

Nature Preserve, in Will County, is anexample of a different kind of restora-tion that has benefitted one of thelargest rookeries in the state.

turbances such as persistent humanactivity, development and logging.To protect heron colonies, people

should never enter a heron rookery dur-ing the spring and summer when thebirds are nesting. Herons are particular-ly sensitive to disturbance early in thebreeding season before eggs havehatched. Natural factors, such as fre-quent, prolonged floods during thebreeding season and high mortality ofnest trees, also can cause desertion of arookery site. On more than one occa-sion, herons have abandoned a rookeryafter a bald eagle started nesting nearby.Since Europeans settled in Illinois,

heron populations have faced manyobstacles that threatened their survival.In the late 1800s, millions of herons

were killed, especially great and snowyegrets, for their breeding plumes—thebeautiful feathers grown during thebreeding season to attract mates and

Herons have been documented nest-ing on islands at this site since the1940s. Twenty years ago it becameclear that the islands were becomingdegraded by nest tree mortality and ero-sion. In 2001, the Will County ForestPreserve District and Audubon Societyvolunteers undertook a restoration pro-ject that stabilized the islands and pro-vided 561 artificial nesting sites. Theproject has been a huge success andevery structure is being used by nestingherons. There are more than 1,000nests on the site, including five differ-ent species. Non-intrusive viewingopportunities are provided Saturdaysand Wednesdays during the breedingseason. Information is available onlineat www.fpdwc.org/renwick.cfm.Heron populations continue to be

stressed by human and natural impacts,therefore successful restorations likethese are needed. Increased restorationand protection of nesting and foraginghabitat are an important step in encour-aging recovery of these graceful birdsin Illinois wetlands.

Michelle Simone is the DNR district her-

itage biologist working from the Jubilee

College State Park office.

Rookeries often support multiple

species, such as the black-crowned

night heron (upper left), little

blue heron (lower left) and cattle

egret (right).

Plume hunters caused numbers of

great egrets to plummet in the late

1800s. The species has slowly

recovered and now is a common to

fairly common migrant and summer

resident in Illinois.