Decomposition of a migratory hawk

In terms of avians being poached, hawks are often shot during migration in September. With the help of CSU graduate student Krystal Hans, and CMNH Ornithologist Dr. Andy Jones, we placed out a cooper's hawk (Accipiter cooperii) for decomposition. The photos below document the first couple of hours of activity.

13 Sept. 2007: This cooper's hawk was found dead and provided to the Museum. We will allow it to decompose for 4-6 weeks, study the insect faunal succession, and then provide the bones to the Museum's osteology collection.

13 Sept. 2007: Two hours post-exposure, green bottle flies swarmed the bird, laid eggs inside a wound on the ventral area of the carcass, and laid eggs underneath the carcass between the feathers and the ground.

13 Sept. 2007: Krystal collecting blow fly eggs (green bottle flies: Calliphoridae) from the cooper's hawk carcass.

FINAL COLLECTIONS

We have officially completed our collections from the bear and the pig. The animals were well-skeletonized, although the thick hide of the bear remained in large part. The bear still supported some invertebrates in some number (Omosita, Necrobia, misc. staphylinids, Stearibia nigriceps). Interestingly, the soldier fly Ptecticus sp. (recorded earlier in the summer) was also present in the adult stage. Its forensic importance is still unknown.

Our conclusions are that 1) a similar fauna attacks large mammals and humans alike, and 2) the decomposition of the bear may be slowed by a variety of factors including the thick hide and fat layer. Further, Lucilia illustris was the first arriver followed quickly by Phormia regina, which is expected. There were three distinct waves of maggot movement off the bear, one off the pig.



13 Sept. 2007: Graduate student Krystal Hans assists with invertebrate collections off the bear carcass.

13 Sept. 2007: The final stage of decomposition in the pig - dry remains.

Later arrivers...

19 July 2007: Upper left, Stearibia nigriceps, a piophild fly; Upper right, Leptocera sp., a minute dung fly of the family Sphaeroceridae; Lower left, Nicrobia violaceae, a beetle of the family Cleridae; Lower right, another fly of the family Piophilidae, Prochyliza.

The flies and beetle illustrated above are common on both the pig and the bear carcass. They illustrate nicely the concept of change through time as they come after the initial wave of blow flies and house flies. They are adapted to the drying conditions encountered on an aging carcass, and take advantage of the areas of carcasses touching the ground. Here, it is moist, dark, and protected.

In terms of our use for determining a postmortem interval, these species are not as useful as blow flies. But, they their presence or absence can be useful. They indicate a change in the carcass, and are part of the insect succession.

All four species above are generalized scavengers of decaying animal tissue in the larval stage. The adults seen above really are there to mate and lay eggs. The adults do little if anything to aid decomposition directly.

The Ecological Players in the Decompositonal Game

15 July 2007: Upper left, Phormia regina, the black blow fly; Upper right, Lucilia illustris, a green bottle fly; Lower left, Fannia canicularis, the lesser house fly; Lower right, Sarcophaga sp., a flesh fly.

OK, not much has been happening on the pig or bear carcasses. So we shall take a detailed look at some of the insects obtained during the course of this investigation.

The flies illustrated above are some of our most informative and/or interesting flies on the decomposing bear and pig. The two above represent our predominant blow flies. The green bottle fly (Lucilia illustris) is one of several species of green bottles we encounter regularly on carrion here in northeastern Ohio. It is often the first to arrive, and based on our sweeping of adult flies off the carcasses, larval collections off of the carcasses, larval collections of the wandering masses of maggots, and our rearings, we found that L. illustris was indeed the first arriver.

The black blow fly (Phormia regina) arrived and developed concurrently with L. illustris, but developed a little more slowly. Lucilia flies were only present on the carcass for a short while, followed by numerical domination by the black blow fly.

The lesser house fly (Fannia canicularis) was interesting. Not an early arriver, nor very predictable in its arrival time, it is not a precise predictor of time of death. However, the literature suggests it arrives when fecal material in the guts of the carcasses are exposed. Our observations show that this is not necessarily the only time it arrives and deposits eggs. We found that the adults lay eggs underneath the dry carcasses on the vegetation, and the larvae develop nicely on the blackened, decomposing grasses fouled by mammal decomposition. Further, we obtained eggs, larvae, and pupae of this species when we exposed raw beef.

Lastly, Sarcophaga or flesh flies are often times present in reasonable numbers on carcasses. I reared flesh flies off a dead shrew near this field site recently, and it was the only taxon present on the small carcass. We have so far recovered no individuals from any of our efforts. The lack of flesh flies is both interesting and not easily explained.

Next post, we shall provide information on more fly species taken on our pig and bear carcasses.

A tale of two carcasses...

2 July 2007: We are still keeping an eye on the bear periodically. We lift the legs, head, and torso to accumulate a collection of cryptic beetles and their larvae. This will allow us to document relatively long-term succession of insects on the carcass. During this phase of deep dessication, we collect beetles and sweep for flies approximately weekly.

2 July 2007: The pig, like the bear, is also in the dry phase of decomposition. The underside is still moist, and maggots are present (see below).

2 July 2007: This morning, just a few hours short of exactly 1 week into decomposition, we had a mass exodus of maggots from underneath the carcass. The grasses and weeds obscure the view, but in the photo above you can make out the larvae clearly. The smaller carcass supported fewer numbers than the large bear (a 119 pound difference), but there were thousands of maggots moving into the undergrowth to burrow into the soil for pupariation.

3 July 2007: After the movement of maggots off the body yesterday, little activity is observable.

3 July 2007: The effects of maggot feeding... The larvae consume the carcass down to the bone, exposing the drying internal organs and pave the way for a dry phase of decomposition. This is where beetles, sepsid flies, and piophilid flies become the dominant players.

4 July 2007: We're pretty much in a phase where, like the bear, decomposition will progress very slowly. We'll continue to collect, but not daily. We will collect beetles on our under the carcass and sweep for flies 1-2 times per week. It is very overcast today, and rain appears to be iminent. That being so, we may see a resurgence in fly activity. If it does indeed rain, I'll head out check again today. The moisture will make some of the tissue soft again, and perhaps we'll have a second wave of blow flies. It really depends on how much rain we get, if any...

PIG DECOMP: Baseline data for northeastern Ohio

25 June 2007: While we are doing the bear decomposition study, we decided to put a domestic pig out in an area nearby. Laura Bock above has just placed the carcass out on the afternoon of 25 June. Pigs are often used during studies of forensic entomology because the body size, body cavity size, percent hair coverage, and other characters make pigs very similar to humans in terms of decompositional patterns. We will be gathering insect succession data, and keeping track of fly development to better hone our information on local insect forensic indicators.

25 June 2007: Like the bear, we placed caging around the pig to keep out large scavengers. We want to keep the bones to add to the Museum's osteology collection. Note that the frame of the cage has short legs, creating a space for wandering maggots to egress at a later date.

25 June 2007: Things happen fast at summer temps. Two hours after placement, we already have hundreds of female flies laying eggs (ovipositing) on the pig around the orifices of the head and anus.

26 June 2007: Less than 24 hours after placement, eggs have hatched and maggots are making fast work of the snout. Note the light area under the chin is actually an egg mass. The eyes, mouth, and nostrils are choked with 10's of thousands of maggots. The blow flies Lucilia illustris (a green bottle fly) and Phormia regina (the black blow fly) constitute the majority of these maggots.

27 June 2007: Two days into decomp the head is being rapidly consumed. The body is showing considerable swelling from bacterial gasses in the abdomen. Carrion and rove beetles are present hunting maggots.

28 June 2007: By day three the maggots are getting large and breaking the body down at a horrendously fast pace. The smell is awful, and the liquids of putrefication are staining the ground black. The maggot mass temperature, like with the bear, is 18 degrees C above ambient.

29 June 2007: By the fourth day, many maggots have matured and are leaving the carcass. The masses of maggots at the head and anus have appeared to meet in the middle, as the main body cavity is greatly decomposed. We have collected many maggots in ethanol, kept many alive in breeding containers (we're still using our nearby insectary), and have swept scores of adult flies to facilitate identification. We have been taking beetle adults and larvae using forceps.

The dry phase of decomposition

29 June 2007: During this period of very slow decomposition, we do have occasional colorful visitors as shown in the photo above. This is a question mark, a type of brush-footed butterfly (family Nymphalidae). Butterflies and moths visit every so often to sip on the moisture present on or in some parts of the carcass. These liquids are going to be rich in nutrients, and help insects we normally associate with plant pollination develop energy and nutrient reserves to aid with movement and egg production.

We have witnessed and recorded a shift in the fly fauna. The dominant taxon present is the sepsid fly Nemopoda nitidula. Not much is known about this fly, although it has been associated with carrion in the past. I have taken it in carrion-baited traps, and reared it from maggots on a dead bat in a cave. Their value as a forensic indicator is presently unknown.