Principal Investigators

Heiko Langner, Assistant Research Professor, Geosciences Department and Director of the Environmental Biogeochemistry Laboratory

Rob Domenech, Director, Raptor View Research Institute, Missoula, MT

Erick Greene, Professor, Division of Biological Science and The Wildlife Biology Program

Background

Due to their top position in the food web, Ospreys (Pandion haliaetus) are particularly useful indicators of local environmental conditions in river and lakes. Osprey populations declined to near-extinction in the Lower 48 States after World War II as a consequence of exposure to DDT-based pesticides. The twindling Osprey population was a major factor that triggered research and the recognition of the problems with DDT, resulting in its ban in the United States in 1972. Since then, Ospreys have returned to many large water bodies. From an environmental science prospective, several other factors make these unique raptors interesting: Osprey nestlings are fed by their parents exclusively with fish that was caught within a few kilometers of the nest, so these young birds reflect the condition of the local fish population. Their high tolerance of human activity and preference for building their nests on man-made structures such as powerpoles and platforms add to the list of desirable features. Obtaining small blood or feather samples from nestlings is reasonably noninvasive and easily accomplished before the chicks are able to fly.

Our group has collected data for six breeding seasons and recently received a grant from the Natural Resource Damage Program to continue public education and research involving the local Ospreys. We are now using video cameras on osprey nests to collect data on prey fish numbers, species and sizes. An added benefit is that live video from two nests is now streaming to the internet for everyone to watch.

We have published a detailed inventory of mercury and other contaminants in Ospreys in the Clark Fork River Basin and we are now focusing on the long-term effects of these contaminants on ospreys and the ecosystem in general. This year we added a new dimension to this effort as we started to use satellite transmitters on ospreys. Preliminary findings are Stay tuned for some interesting findings. mercury and otherIt is of especial This year we started to use satellite transmitters

Related Study: Ospreys and Baling Twine

Baling Twine Pamphlet in PDF Format (1.4 MB)

It is estimated that 10% of Osprey chicks die in their nests after getting tangled up in baling twine that was brought in as nesting material by their parents. Many nests in our area contain large amounts of the deadly twine, and we have removed lots of it during our nest visits. The left photography below shows an osprey nestling that we were able to save. Several twine strands had already grown into the leg and neck tissue of the bird and would have killed it within a few days. We removed the twine and sterilized the wounds before returning the bird to the nest. A follow-up nest visit revealed that the bird was doing well and had increased in weight from 870 to 1170 grams during these five days. The picture to the right shows the amount of baling twine we removed from another nest in the same town of Deer Lodge, MT.

In an effort to educate the ranching community about the detrimental effects of baling twine, Erick Greene, together with two Missoula high school students, Matt Parker and Max Eggenhoff, developed a brochure for distribution to interested members of the public. Please feel free to download the PDF file.

Why are we seeing so many osprey chicks die this year?

By Dr. Erick Greene
University of Montana Division of Biological Science and The Wildlife Biology Program

Many of you have been noticing that the larger Osprey chick attacked the smaller Osprey chick, and that the parent just stood by and did not break it up. This fighting can be quite brutal, and it led to the smaller chick dying. Some of you have asked why this was going on, and why we did not step in and “rescue” the smaller chick and raise it in captivity. 

Even though this behavior seems cruel and can be hard to watch, we want to explain that this is a completely natural, wide-spread and adaptive behavior.  In many kinds of birds that have a fluctuating and unpredictable food supply, the female starts to incubate as soon as she lays the first egg.  This means that the first egg gets a developmental head start on all the later eggs; the second egg gets a head start on all the later eggs, and so on.  As a result the chicks hatch over a span of many days, and so there can be a large difference in size among the siblings in the same nest.  This is called “hatching asynchrony.”  Here is a picture of an Osprey nest with four chicks huddled together, and you can see the remarkable difference in size between the oldest and the smallest. 

Photo by Anja Heister

In years of plenty, there is enough food to go around without any of the chicks being hungry.  In years of low food supply, however, the largest chicks are hungry and start to behave aggressively towards their smaller siblings, usually starving or killing them.  Biologists call this behavior “siblicide” and it occurs in MANY kinds of birds, including hawks, eagles, owls, herons and egrets, pelicans, boobies, albatrosses and many more.  Although this behavior seems cruel, in a strange way it is an adaptation to unpredictable food supplies.  It produces a self-regulating brood size that automatically maximizes the number of healthy and strong chick that can be raised on the amount of food that is available during any given year.  When there is a lot of food, all the chicks survive; in lean years, rather than producing lots of feeble and weak offspring, fewer chicks survive but they tend to be stronger and have a better chance of surviving. 

This year seems to be a particularly difficult for Ospreys.  The very high and muddy rivers in Montana means that they have a very difficult time seeing and catching fish.  As a result, the frequency of siblicide is higher than in other years.  Another important thing to consider is that Ospreys can live for a long time, and year-to-year variations in reproductive success are normal for them.  The important thing for a pair is that over the course of their reproductive lives they are able to produce enough strong and well-fed chicks, rather than more sickly ones who would survive poorly. 

If we removed smaller chicks and raised them by hand, it would only doom them to perhaps a crueler, drawn-out demise.  Ospreys are very hard to raise and keep in captivity, but more importantly, we could not teach them how to be Ospreys the way their parents do.  Osprey parents continue to feed their chicks long after they leave the nest, they teach their chicks how to fish, and they often teach them how and where to migrate.  We could not do any of this, and so when we released the chicks they would certainly be doomed since they would not have the continued support of their parents to teach them the very difficult path of Ospreydom.