Tricky Coding Part II - Don't Code Me!!

By Tom Prestby June 13, 2016
Tern, Caspian 14

Terns are an example of a group that should not be given possible or probable codes

Now that it’s June and migration is all but over, we are in the prime of atlasing season for the next couple months. It’s hard to step outside without observing at least a “Possible” code and “Probable” codes and even “Confirmations” can be found with rather little effort right now. Part of the reason is because we can assume that almost everything we’re seeing right now is on a breeding territory. However, pay attention to the key word here… almost. There is indeed a subset of species that are very tricky for atlasing purposes, even in mid-summer, because they are often found outside the block they are breeding at for a variety of reasons. This means that codes should be left off of them unless direct nesting is observed. Read on to learn which species these are and when you can properly code them.

Gulls and Terns 

Gulls and terns are a familiar sight this time of year along large bodies of water and gulls can be seen throughout the state in almost any habitat, especially Ring-billeds. These species forage far from their nesting areas and many younger birds do not breed, meaning they are readily present in suitable habitat throughout the summer. However, unlike most other birds this time of year, suitable habitat does not suggest breeding for gulls or terns. They are colonially-nesting species that only nest on islands, shoals, or other undisturbed areas at or close to large bodies of water. For this reason, only enter confirmed codes for gulls and terns, no possible or probable codes. Most gull and tern colonies are known but you could discover a new one, in which case it should be rather obvious. One exception is that Herring and Ring-billed Gulls will nest at the top of flat-roofed buildings, especially in large cities, but usually these are in colonies as well. The coding restrictions don’t stop at possible and probable codes for gulls and terns though, they carry food and feed dependent young well away from breeding grounds too so don’t use the CF code and be very careful when using the FY and FL codes. If the juvenile is flightless, the latter two codes can be used safely but if it can fly, you should err on the side of caution and not code since these species disperse quickly after nesting.

Although worthy of a confirmation for most species, carrying food should not be coded for terns

Although worthy of a confirmation for most species, carrying food should not be coded for terns

Herons and Egrets

Just like gulls and terns, most herons and egrets hunt far from where they breed. More non-breeders are also added to the population in the second half of the summer when birds arrive that have dispersed from further south. Like gulls and terns, herons and egrets nest colonially in rookeries. Because of this, we recommend that you only enter confirmed codes for herons and egrets. Herons and egrets often hunt in excellent habitat such as small or large wetlands but since these birds typically travel miles from their rookeries to hunt, we cannot assume the rookery is in the same block as where a hunting bird in good habitat is observed. One exception is the N code, which can be used if multiple birds are seen in an area that could contain a rookery, but the rookery cannot be found. Examples are wetlands with many large snags or a stand of large pine trees, especially with some dead branches.

Another exception to this rule is Green Herons, which have completely different breeding habits than their larger relatives. Most codes can be used for this species, as they do not nest colonially and typically stay in a territory with acceptable habitat like most other species.

Green Heron is an exception to the general rule for herons and can be given possible and probable codes

Green Heron is an exception to the general rule for herons and can be given possible and probable codes

A final word about herons is to be careful coding herons that are in juvenile plumage. The juveniles of most species are readily ID’able but can fly strongly rather quickly so just because it has juvenile plumage doesn’t mean it was hatched in the block. One good sign is visible down near the head, another is following adults closely. Night-Herons are a classic example of a bird that is often coded as “FL” when it shouldn’t be because they keep their juvenile plumage for up to a year. For example, the juvenile Yellow-crowned Night-Herons that show up in the state in late-summer likely hatch further south.

Pelicans and Cormorants

See the rules for herons and egrets, as pelicans and cormorants behave the same way. Cliff notes: In general, only use confirmed codes because these are colonial breeders. Non-breeding or foraging birds often use acceptable habitat far from breeding sites.

Late ducks and other waterfowl 

Although it’s June, waterfowl can still be found lingering in locations where they will not breed. The situation is relatively easy to assess if the location is a flooded field but much trickier if it is a quality wetland. We are now in the “B” period for almost all of these species on the Guideline Bar Chart, but that does not mean all observations should be coded, even in good habitat. For waterfowl, be very careful with non-confirmed codes during the breeding window. It is common for non-breeding individuals or bachelor groups to remain in good habitat, in some cases throughout the summer. Waterfowl are very mobile right now so can show up almost anywhere, and when they molt their flight feathers later in summer, they remain at a location for a long time because of this, not because they’re breeding. However, some may truly be breeding and the female and/or young are just too difficult to detect. In this case, an “H” code can be warranted. Use your best judgement and for uncommon species, leave comments.

Ducks do not qualify for the “S7” code (if you’ve ever heard a duck sing, please let us know J) so their presence for a week does not warrant a probable code. However, if a pair is present you can assign a probable code, preferably after you have rechecked and established that they have been sticking to an area and not just passing through. If you see a lone female, don’t code her presence as H but watch her very carefully because she might be hiding ducklings. Skulking almost out of view or showing agitated behavior are signs that you should watch her carefully. Species that are very rare breeders this far south like Lesser Scaup, Bufflehead, Canvasback, and Horned Grebe require more information than other more common species for an observation to be code-worthy. Always supply comments when coding uncommon species like these.

Consider date, location, and habitat when giving possible or probable codes to ducks

Consider date, location, and habitat when giving possible or probable codes to ducks


Shorebirds are tricky because for arctic species, their migration really never ends in this part of the country. The end of spring migration overlaps with the beginning of fall migration for some species and for others, the gap between the two is razor-thin. Look at breeding range maps before you code any shorebird besides Killdeer, Spotted Sandpiper, Wilson’s Snipe, American Woodcock, or Upland Sandpiper. Most other species nest far from Wisconsin, and a breeding record is almost impossible, with a couple exceptions (Wilson’s Phalarope and possibly Solitary Sandpiper). If coding any other shorebird species, please supply ample comments and photos if possible.

Raptors and Vultures           

Our first non-waterbirds to make this list, birds of prey and similar species are also tricky to decide when to code. The toughest is probably Turkey Vulture, which are readily seen but almost always on the wing. Since they hunt by smell, often far from their breeding areas, vultures should almost never be coded when flying. The only exception is if a bird is seen in the same spot (at least several times) rather low over a period of a few weeks. It’s also tricky to tell when to code non-flying vultures. They’ll often sit near carrion so again, don’t code them as possible or probable unless you’ve seen the bird in the location at least a few times. The only exception is if a bird, or preferably a pair, is sticking close to an area with good nesting habitat (such as large trees with large cavities, rock outcroppings, or abandoned buildings) in which case they can be coded as N. In this case, try to check back on the birds later as you may claim one of the few confirmations for this notoriously tough-to-confirm species!

Vultures attending carrion should not be coded

Vultures attending carrion should not be coded

Raptors are also tricky for coding even in the breeding season. The most care should be taken with eagles, as just like vultures, they’ll hunt a long ways from nest sites and hang out near food they are scavenging. Don’t code Eagles as possible for this reason, unless a bird is seen in good habitat on repeated visits. Most hawks stick to their territories so are safer to code, but again we run into the issue of the presence of non-breeders. Don’t code hawks that are in immature plumage (unless they are obviously very recently fledged) and don’t code hawks that are flying much higher than treetop-level. Soaring hawks in pairs can be coded but it is not uncommon for hawks to disperse this time of year

Of special importance is a reminder to use caution when using the “CF” code for raptors. These birds often carry their food for reasons other than feeding young because their prey takes more energy to consume than that of other birds. Ospreys and Eagles are notorious for carrying fish long distances but hawks exhibit the same behavior with their prey items. The “CF” code for raptors should be limited to persistent carrying of food in the same direction and carrying of food into a likely nesting area. 

Late passerines (songbirds)

Although it’s generally a safe assumption that a passerine is on breeding territory in June, that isn’t always the case. Just like we recommended for shorebirds, make sure to check range maps for species that you aren’t sure about. Some notoriously late migrants like Olive-sided and Yellow-bellied Flycatcher should only be coded if consistently singing in correct habitat in the far northern part of the state because they are possible elsewhere into mid-June. Sometimes warblers and other passerines like Northern Mockingbirds will show up at random locations during the breeding season out of their range as well. The key is to evaluate their behavior looking for the same clues discussed in Tricky Codes Part I— for example repetitive singing from prominent perches and presence at the same location for more than several days. In general, these oddballs should not be coded unless they show territorial behavior consistently at the same location. Although rare, out-of-range birds do show up and set up a territory occasionally like the Northern Mockingbirds that bred in Eau Claire County in 2015 and Dane County in 2016 so don’t completely dismiss the possibility if you find something uncommon.

Mockingbirds are an example of a species that is usually a non-breeding overshoot but occasionally breeds in the state

Mockingbirds are an example of a species that is usually a non-breeding overshoot but occasionally breeds in the state

It’s a very exciting time of year for atlasing as atlas observations are piling up around the state nearly every hour of every day. Though most birds can be safely coded right now, make sure to be careful with the species discussed above. Again, if you code something and aren’t sure that you should have, always include comments in your checklist. Don’t be worried about if you make a mistake, we all make mistakes in judgement calls sometimes and we can easily go back in and fix a record later if needed.

Enjoy the song-filled mornings and nesting-crazed birds of June!