January Atlasing Spotlight

January 1, 2024, marked the beginning of the Third Pennsylvania Bird Atlas. A handful of species are breeding, and therefore countable for the Atlas, in mid-January:

• Great Horned Owl, Rock Pigeon, Red Crossbill, and Barred Owl are all in ‘Breeding Only’ dates on the Breeding Guidelines Chart (otherwise known as ‘safe dates’), meaning that all breeding codes are possible for these species.
• Early-breeding Bald Eagles, Barn Owls, and Red-tailed Hawks can also be found throughout the state, either with active nests as in the case of some Barn Owls with young in the nest, or with pairs showing courtship, territorial defense, or nest maintenance behaviors as has been observed in eagles and Red-tailed Hawks. Use caution when reporting breeding codes for these species at this time of year – you can see breeding pairs but you can also see birds that are migrating or otherwise non-breeding. Only breeding codes that are ‘Confirmed’ evidence of breeding should be used at this time.

Just over two weeks into the Atlas and we have reports of these species all over the state, including what is surely the most surprising find of the Atlas so far: a pair of Red Crossbills nesting in Union County! Read more about Red Crossbills in Pennsylvania here.

But enough about crossbills! Let’s take a closer look at three magnificent species that are widespread in the state and are good species to focus atlasing efforts on currently.

Bald Eagle

Bald Eagles were abundant in North America until the mid-to-late 1900s, when the population suffered significant declines from pesticides and other poisons, as well as from hunting and trapping. But since 1980, when the dangerous pesticide DDT was banned, and with the support of protections from the Endangered Species Act, the Bald Eagle has made, and continues to make, a great comeback. In the first PA Atlas (1983-1989), Bald Eagle nesting was confirmed in only 11 blocks, but by the second PA Atlas (2004-2009), confirmed Bald Eagle nesting soared to 226 blocks! Although Bald Eagles are scavengers and general predators, during the nesting season they prefer a ready supply of fish and waterfowl, and are most typically found along rivers, creeks, lakes, or other water. They build their huge nests of sticks below the crown of tall and mature white pines, sycamores, red oaks, and red maples that have a view of the water and a clear flight path. Nests can take up to three months to build and may be reused and added to year after year. Once the nest is ready and the eggs are laid, the eggs will hatch in about 35 days, and it will be another 56-98 days before the nestlings fledge. Likely you will not often identify Bald Eagle by its call, which is usually a series of weak high-pitched whistling notes, but a call from a female might signal her readiness for copulation.

Bill Moses

Great Horned Owl

Great Horned Owls are widespread and have adapted well to habitat change. The number of confirmed nesting blocks declined from 451 blocks in the first PA Atlas to 320 blocks in the second Atlas. While some of this decline is attributed to the effects of West Nile Virus, it may also partially be an artifact of decreased nocturnal survey effort, because Great Horned Owls are most frequently detected by its calls during nocturnal birding. One of the most easily recognizable signs of breeding behavior is a duetting male and female pair, and you might even notice a difference between their calls, as the male has a larger voice box and deeper pitch. According to the first Atlas: “Most hooting occurs during October and November, when territories are being established. In the course of a given day, hooting is most frequent between 11 p.m. and 1 a.m. and from 4 a.m. until 6 a.m. The owls are least vocal when incubating eggs and brooding young, from about 15 January to 15 March in Pennsylvania, and very little calling would be heard during this period. May and June also are very quiet times for Great Horned Owls, especially those with young, and any hooting heard during this time would be by nonbreeding individuals.” Great Horned Owls can be found in open mature forests, although you are more likely to see them in woods with a significant edge or near an agricultural area, rather than in the interior of a large forest. They will lay its eggs in old nests of Red-tailed Hawk, Bald Eagle, Great Blue Herons, or crows, or sometimes in natural tree cavities or rocky ledges. They lay eggs in mid-February or early March. Eggs hatch in 30-37 days, and young fledge about 42 days later. In Pennsylvania, fledging occurs in late April. Great Horned Owls eat mostly mammals and birds, sometimes hunting in broad daylight, and you might see them taking a duck, skunk, opossum, rabbit, or even house cat, to its nest, but they are mostly active at night.

Barred Owl

Another widespread owl, the Barred Owl, is known to many birders for its emphatic, questioning call: “Who cooks for you? Who cooks for you all?” Barred Owls are found in large, mature forest stands, often near water although upland forest is also used. They prefer to nest in mixed deciduous and conifer woodlands. In Pennsylvania, they are found at highest densities in the most heavily forested regions of the state. Barred Owls were reported in 17% more blocks in the second Atlas than the first Atlas (although Confirmed in slightly fewer blocks). Care must be taken when comparing between the first and second atlases because of wide variation in nocturnal survey effort, but this increase in reported blocks aligns with increasing trends in the species in Christmas Bird Count data and in eBird trends. Barred Owls most typically nest in cavities of large trees. They lay 1-5 eggs that hatch in about 30 days. Pairs are generally permanent residents where they nest. They are generalist predators, feeding mostly on mammals but also on other birds, reptiles, amphibians, and more.

Bill Moses

Atlasing for Eagles and Owls

A good sign that a Bald Eagle, Great Horned Owl, or Barred Owl is nearby is a boisterous group of American Crows cawing loudly and continuously, flying in circles and diving. Crows will often mob owls, eagles and other raptors that they consider to be a threat. The Great Horned Owl, in particular, is the crow’s most dangerous predator.

Here are some examples of how to use breeding codes for Bald Eagle (BAEA)*, Great Horned Owl (GHOW), and Barred Owl (BADO).

S7 – Singing Bird Present 7+ Days: If you code a hooting or calling GHOW or BADO with an S (Singing Bird), try returning a week or so later to listen in the same location. If you again hear the bird, you can code it as S7 and upgrade it from a Possible to Probable nester in the block.

C – Courtship, Display, or Copulation: Listen for duetting male and female GHOW and BADO, and be on the lookout for BAEA pairs performing courtship displays or copulating.

N – Visiting Probable Nest Site: You might see a pair of Bald Eagles in a tree that holds a nest from last year, or a Great Horned Owl near a tree cavity that they used last year.

NB – Nest Building: You might see a pair of Bald Eagles adding new sticks to an existing nest.

UN – Used Nest: This code should be used only after the nesting season, if you know that the nest had been used during the Atlas period.

ON – Occupied Nest: This code should be used if you see an adult sitting in the nest in incubation position, an adult entering nest site and remaining, or an exchange of incubation duties by the pair.

*Remember, only ‘Confirmed’ breeding codes should be used for Bald Eagle until late April, when migration has wrapped up and you can be confident that any adult eagles you see are resident breeding birds. Until then, take note of birds you see that appear to be paired up, and return to those areas in a few months to try to confirm breeding!