Slide 1 Slide 2 The science behind management of game birds, predators, and landscapes of the Midwest: the ups and downs of pheasant populations William R. Clark Iowa State University Iowa DNR, DU- IWWR, BRD - Northern Prairie cooperating Linking field data on pheasant life history to a process model of pheasant demography Fates of individual animals sum to population demographic response to patterns of agricultural production Individual-based model that estimates birth and death rates from climate and landscape measures I have given some version of this talk to various technical and popular audiences. I version is the one that I gave in January and February 22 to Pheasants Forever state meetings in Iowa and Nebraska. The scientific basis for this work was largely supported by the Iowa Department of Natural Resources (over a decade of research on pheasant and landscapes), Ducks Unlimited (important studies of predators and waterfowl nesting), and continued collaboration with biologists from USGS Northern Prairie Wildlife Research Center. In Iowa we conducted extensive field studies of pheasant life history including winter survival of hens, habitat selection and movements across the landscape, nesting success, and brood survival. We summarized our findings in a model that enables us to study the population dynamics in relation to changes that might occur on the landscape. Habitat specific factors affecting survival Habitat specific factors affecting reproduction Habitat selection and movement Slide 3 Population Size 45 4 35 3 25 2 15 1 5 Simulated pheasant populations Annual cycle 1 51 11 151 21 251 31 351 Pheasant populations peak in late summer after broods are mature. Biologists and hunters know that over a period of 1 years there can be a great deal of variation in the population. This talk outlines what we know about the role played by factors like weather, predators, and habitat in determining those long-term ups and downs. Population Size 14 12 1 8 6 4 2 1 years 1 366 731 196 1461 1826 2191 2556 2921 3286 Day of Simulation Slide 4 In Iowa, during 199-1995 we attached transmitters to 1 hens on 2 townships that differed in the amount of habitat, especially CRP In Kossuth County the landscape was only about 8% perennial habitat with little Conservation Reserve Program lands, whereas in Palo Alto County it was about 25% perennial habitat, much of that in CRP.
Slide 5 In North Dakota, during 1996-97 we attached transmitters to skunks and red fox to study how the landscape patterns influenced activity in relation to waterfowl nests Slide 6 Iowa DNR roadside survey Many states survey pheasant populations trends using surveys conducted in early August. On mornings with dew in the cover hens, broods, and roosters can be reliably counted. Slide 7 Wicked winter Winter 22 was extreme in the Midwest. In Iowa we had over 1 days with snow on the ground from mid-november until early April. The slide above shows a 5 yard wide conservation buffer that drifted completely over with snow. Slide 8 Winter cover and food The combination of dense cover like this switchgrass patch with nearby food like the cornfield helped pheasants survive the winter. Yet at this site in central Iowa the local population of pheasants declined from about 1 birds at the beginning of winter to only 1 birds by March.
Slide 9 Minimum Temperature (C) Winter Weather in Northern Iowa Winter Weather in Northern Iowa (27 November - 1 April) 5 1 8-5 6-1 -15 4-2 2-25 Snow Days Research has shown that snow on the ground decreases winter survival more than cold temperatures. The above graph shows that we typically get more snow and larger snow storms in late winter in Iowa, just at the time when pheasants are the most stressed from surviving through most of the winter. -3 Dec Jan Feb Month Mar Slide 1 The interactions between winter weather and habitat result in wide variation in winter survival among years. As you can see from the above graph, in years like 199 with very little snow cover over 9% of the marked hens survived whereas in years like 1993 with lots of snow and cold only about 2% of the hens survived. In general more hens survive where the landscape has good habitat but good habitat cannot completely counteract the effects of severe winter. Slide 11 Roosters are important too Although we didn t specifically study roosters, other studies have shown that they are important to populations because they space the population out across the landscape during the spring breeding season. Roosters like a crowing location that is visible but not too far from escape cover, especially near corners and where habitats meet. Hens are attracted to breed with roosters. If there is lots of habitat on the landscape roosters will be spread out and so will the nesting hens that breed with those roosters. Slide 12 This above township in Kossuth County is one of the areas where we studied pheasants. It had only 3 quarter section blocks of CRP (grassland is shown in red) and lots of row crops (corn and soybeans are in gray). You can envision that most of the breeding roosters selected locations near the red patches and so nesting hens were relatively concentrated on this landscape. On landscapes with lots of grassland habitat roosters and hens are more spread out.
Slide 13 Dense nesting cover in large fields Although hens will nest along roads and along fence lines, hens prefer dense cover in large fields. If they are attracted to hayfields their nests can be destroyed during mowing. Conservation Reserve Program fields are great habitat because they are usually undisturbed. Slide 14 Slide 15 Destroyed Nest Red fox with a duck egg Hens fail to reproduce successfully for a variety of reasons. The majority of nests that fail are lost to predators but the situation is complicated by indirect effects of weather and habitat conditions. Cold, wet spring weather is very detrimental to nesting success because hens will abandon nests under such conditions and be forced to renest. Late nesting hens lay smaller clutches and late hatched broods do not survive as well as earlier hatched broods. Rainy weather causes some direct mortality to chicks in the first two weeks of life. In good habitat hens usually successfully hatch a nest on the first attempt whereas in poor habitat hens may incubate 2 nests or more before hatching a brood. Destruction of nests and hens by predators gets lots of attention because it is an obvious loss. Red fox are particularly detrimental because they catch hens as well as take eggs from nests. We ve been studying how predators explore the edges and centers of nesting habitat in North Dakota. We studied how they use landscape features such as wetlands or tree lines during their nightly activities searching for prey. Red fox remove eggs from nests and cache them for later consumption. Photo by B. Allen Slide 16 Activity of predators focused on grasslands A very important point about predators and ground nesting birds is illustrated above. Notice that the home ranges of red fox in this landscape are centered around the grassland blocks (in green). When there isn t much nesting habitat the ducks (or pheasants) are nesting in exactly the same places as the predator s center of activity.
Slide 17 Activity of predators often focused on edges The black series above is the path of a skunk in one night. For scale, the dashed lines are 1 mile apart so you can see that this skunk traveled at least 2 miles in one night. Notice how many of the points are located within 5 meters of a wetland edge (shown in red). Edges of wetlands are rich in invertebrate prey that the skunk prefers but of course if it encounters a nest it will eat some eggs. Slide 18 Nest success of pheasants within patches Based on the field data on hundreds of radio-marked hens in Iowa we built statistical models that predict the success of nesting pheasants at various places in the landscape. Generally above average nesting success occurs in large blocks of undisturbed grassland and below average success occurs in intermediate sized blocks. Success is not likely to be uniform within blocks because internal features such as streams or tree lines focus the activity of predators. Sometimes we observed high nest success in very small, isolated patches of habitat, although not many hens nest in such places. Slide 19 Pheasant chicks with radio implants We captured chicks on the day that they hatched, implanted aspirin-sized radios under the skin, and released them with their mothers. Then we tracked them for the first 4 weeks of life. Most mortality occurs in the first two weeks of life. Chick survival averaged about 45% and was not as variable among years as was winter survival or nesting success. Chicks that weighed more at hatch and those hatched before the midpoint of the nesting season survived better than light chicks and those that were hatched later in the season. Slide 2 Weasel and mink were important predators affecting chick survival Unlike nests taken by medium-sized predators, smaller predators, especially weasel and mink, were the most important cause of chick mortality.
Slide 21 Predation by mustelids We observed a number of cases where a weasel or mink killed an entire brood, including all three of the radio-marked chicks. Slide 22 If predation is so important, what can be done about predators? Exclude predators from nesting areas? Control predators by hunting and trapping? Dilute the effects of predators by creating habitat? Slide 23 Slide 24 Long-term increases in carnivores? Minnesota DNR data Predator Coyote Red fox Raccoon Striped skunk Some predator facts Spring density in corn belt 1/1 sq. mi to 1/2 sq. mi 1/4 sq. mi to 2/sq. mi 12/sq. mi to 25/sq. mi 12/sq. mi to 5/sq. mi Food (%) Rodents and rabbits (5%), carrion (2%), birds/eggs (2% ), grain and fruit (8%), insects (2%) Rodents (5%), birds/eggs (25%), grain and fruit (1%), insects (1%), carrion (5%) Plant material (5%), Insects and aquatic inverts (3%), birds/eggs (15%), rodents (5%) Insects (6%), grain and fruit (25%), rodents (1%), bird eggs (5%) Many sportsmen say that predator populations have increased dramatically in recent decades and that is why we have fewer pheasants and ducks. But trend data do not support this idea, as the above series over the last 25 years illustrates. Red fox populations seem to have gone up and then down, influenced be diseases such as mange and loss of habitat. Coyote and skunk populations seem to fluctuate rather erratically and without any particular trend. Raccoon populations appear to have increased especially in the farmland regions of Minnesota. Data from other regions are similar. Taken as a whole, the data do not suggest distinctly greater populations now compared to the past. Predators of pheasants and waterfowl are not dependent on the seasonal availability of nests to sustain their populations. These generalist predators eat everything from waste grain to carrion. Coyotes especially prey on rabbits and rodents. Foxes are the most detrimental to birds although much of their diet is rodents. Raccoons and skunks eat lots of insects and plant material. All of these predators opportunistically take eggs and birds but probably only the red fox actively search for hens during nesting. I used the range of densities given above to calculate the predation impact given later in this slide series.
Slide 25 Predator exclusion from nesting areas Large predators such as red fox have been excluded from waterfowl habitat and nest success is improved. This approach works for waterfowl because they can be attracted to wetlands inside a fence and they will return to such areas if they survive. But for pheasant management it is not clear how to attract pheasants to a specific area, whether they would fly in and out of the fence, and whether their offspring would strongly home to the area in the fence. Slide 26 Predator fences are costly to build and maintain Fences are buried in the ground and electrified. Vegetation must be kept clear of the fence. Some have one-way doors to trap predators. You must remove all predators inside the fence. Spending such time and expenditure on a very large scale is not a practical solution. Slide 27 Control predators that compete for game birds? Many sportsmen contend that more sport hunting and trapping will reduce predator populations. Some groups call for intensive predator control. Slide 28 So what is the effect of harvest on predators? Sport hunting and trapping can certainly remove large numbers of furbearing predators. In the 198 s the Iowa DNR sponsored a study to determine whether sport harvest had a detectable impact on the dynamics and levels of raccoon populations in Iowa.
Slide 29 Raccoon population study in Iowa We studied a raccoon population on 16 square miles in Guthrie County Iowa from 1983-89. We radio-marked over 7 raccoons and marked an additional 2 raccoons with ear tags only. We estimated population size, survival, reproduction, and dispersal using mark-recapture methods and telemetry. We estimated the sustainable harvest rate for the population (about 4% of the fall population) and then deliberately exceeded the level to study the population response. Slide 3 In the first 3 years we determined the pattern of survival with normal harvest levels of about 2%. We calculated that we would have to harvest over 4% of the population to reduce annual survival. The above graph shows that most annual mortality occurs during the harvest season. It also shows that survival of young raccoons (BY, Birth Year) was reduced when we increased harvest. But the survival of adult raccoons (ABY, After Birth Year) was unchanged during the increased harvest years. Slide 31 Population size of raccoons was not reduced in years when harvest was 4% (1986-88), compared with years when harvest was 2% (1983-85). The graph above shows some of the results of our Iowa studies. The population fluctuations (green line) during years when harvest was 2% (1983-85) and 4% (1986-88). In all years the population shows the typical increase until autumn and then drop to the following spring. Notice that the spring population levels do not vary much between the years of differing harvest regimes, averaging about 3 raccoons on the 16 square mile area (about 19 raccoons/square mile). Slide 32 Predator control is controversial This slide might be a little dated but it illustrates that predator control is controversial. If sportsmen pushed for predator control to insure pheasant hunting, they might alienate the general public against hunting.
Slide 33 Coyotes are now the top carnivore There are important community effects among predators and prey that effect predation on pheasants and other game birds. Coyote influence the structure of the predator community because they are dominant over red fox that are more detrimental nest predators. The collection of predators may influence the overall predation rate on pheasants and other ground nesting birds. Slide 34 Red fox avoid center of coyote activity The white numbers on the map above are the coyote activity level measured by a a track index. Notice the high levels in the center of the crop/pasture area with no roads or other human disturbances. The red fox radio-telemetry locations are shown as black dots. Notice that they tend to be around the edges of the coyote activity. Red fox will live in closer proximity to human activity. This spatial displacement of red fox by coyote has been seen in states in the Midwest from Illinois to North Dakota. Slide 35 Small mammals may be alternate prey Biologists aren t sure whether abundant prey like this meadow vole act as a buffer that lowers nest predation. Alternate prey that build up in established grasslands may simply attract foraging predators to the area. Predators find many nests opportunistically. Slide 36 average Iowa farm in 1941 = 16 ac. 7 ac. Corn 35 ac. Small grains (oats) 29 ac. Pasture 2 ac. Alfalfa & clover 6 ac. Farmstead & odd areas Large scale changes in the agricultural landscape have changed the dynamics of pheasants and their predators. In 1941 more than half of an Iowa farm was in perennial covers or small grains that provided nesting habitat. Today farms are much larger and row crops often make up over 9% of the landscape. There is very little nesting habitat, very few weedy edges, nor much winter cover. These landscape changes are ultimately responsible for the changes in pheasant and predator dynamics.
Slide 37 Can we dilute the effects of predation by creating habitat? This riparian buffer might be good winter habitat but it s likely to be a trap for nesting hens. Slide 38 Conservation Reserve reverses the trend So the key to pheasant abundance is habitat. The Conservation Reserve Program has been the mechanism that provided habitat to dilute the effect of predators of ground nesting birds. Pheasants in Iowa and elsewhere in the Midwest have generally increased since 1985 when CRP was implemented. Data from the NRCS Slide 39 CRP facts Currently 33 million acres; 2X the area of of NWR system + all all state DNR lands combined (excluding AK & HI) $1.4 billion in in payments nationwide; $4,833/farm; $45/acre; 293,857 farms Iowa in in 2: 1.6 million acres & $153 million in rental payments North Dakota in in 2: 3.2 million acres & $14 million in in rental payments The significance of CRP to wildlife conservation has been huge. As of 2, CRP created more habitat nationwide than exists in the National Wildlife Refuge system and state departments of Natural Resources lands in the 48 contiguous states. It provided a big boost to rural economies and helped provide farmers with support for conservation on the land. Slide 4 Newly established CRP The CRP program was most beneficial to pheasants during the first 5-1 years after establishment because fields were a diverse mixture of grasses and broad-leaved forbs.
Slide 41 The new habitat effect CRP years 1-5: annuals, seeds, forbs, insects, good nesting and brood cover develops Predators don t respond immediately to area CRP years 1-15: dominated by grass, alternate prey like grubs and voles attracts predators Productivity declines, renovate or establish new habitat When CRP or other habitat is first created there are lots of annual weeds. The mixture of grasses and broad-leaved forbs has high levels of insects and seeds that provide good cover for adults and broods. Within 5 years perennial grasses make good nesting cover too. Predators don t respond to these newly created habitats as quickly as the pheasants because not all of their favorite foods are present, some need to establish new territories, and their populations grow more slowly. But after 1 years fields are not as diverse so they are not as good for pheasants. In addition predators have moved into the area to exploit new habitat with prey. Pheasant productivity generally declines in these old CRP fields. Slide 42 How many pheasants can average predator population eat? 1 mi 2 of good habitat after a mild winter 112 hens, 123 nests initiated with renesting 17 hens eaten by fox and coyote 43 nests destroyed by raccoon and skunk Total of 6 unsuccessful nests, so 63 successful nests (.51 nest success) 315 chicks produced that survive until fall I summarized the combination of effects of weather, habitat and predators by calculating the impact of predators on pheasant populations under various scenarios. I used the pheasant densities from the Iowa studies and the predator densities that where summarized in slide 25 above. I projected the effects of predation on pheasant production following various winter conditions. For example, in the best habitat in Iowa after a winter with low winter mortality we estimate populations of 15 pheasants/square mile, about 77% hens. As you see above, I calculated the number of nests initiated and destroyed by predators. The nesting success that I projected is very consistent with what we observed. Factoring in chick survival and 315 chicks would survive until the fall hunting season. So 112 hens produced 315 young pheasants by fall. Slide 43 Predator impact under poorer conditions 1 mi 2 of good habitat after a severe winter 61 hens, 87 nests initiated with renesting Total losses 6 hens & nests, now only 135 chicks produced and survive until fall 1 mi 2 of poor habitat after any winter 1 hens, 13 nests initiated with renesting With losses to predators, the number of successful nests and chicks that are produced and survive just about breaks even Compared to the previous scenario, if there was a severe winter that reduced survival there would be many fewer hens, even in good habitat conditions. Now 61 hens produce 135 young pheasants by fall. And if the habitat is poor, with relatively few pheasants to begin the season, the pheasant population cannot escape the effects of the predators no matter what the winter or spring weather conditions. Slide 44 Poor habitat: severe winter-average spring then mild winter and mild spring Year 1: 2 cocks, year 2: 3 cocks shot Population per sq. mile 14 12 1 8 6 hens 4 cocks 2 Jan-2 Mar-2 May-2 Jul-2 Sep-2 Nov-2 Jan-3 Mar-3 May-3 Jul-3 Sep-3 Nov-3 Jan-4 I projected the above scenarios over 2 years to show how the population would fluctuate. For example, above I show the population in a poor landscape. The first winter was severe, followed by an average spring. The next year both winter and spring were mild and favorable for survival and reproduction. You can see that both hens and roosters remain low because they can t escape the mortality factors. The orange heading notes the number of roosters that would be shot assuming 7% rooster harvest that is common in many situations.
Slide 45 Good habitat: severe winter-average spring then mild winter and mild spring Year 1: 57 cocks, year 2: 19 cocks shot Population per sq. mile 25 2 15 1 5 hens cocks In contrast to the previous slide, in a landscape with good habitat the pheasant population can rebound quickly. Not only is the number of hens and roosters higher because of the good habitat, but by the end of only 2 seasons the population has reached the same level as before the severe winter. The number of roosters harvested is much greater. Jan-2 Mar-2 May-2 Jul-2 Sep-2 Nov-2 Jan-3 Mar-3 May-3 Jul-3 Sep-3 Nov-3 Jan-4 Slide 46 Total Population The key to pheasant ups and downs is habitat 9 8 7 6 5 4 3 2 1 1/1/ 1/1/3 1/1/6 1/1/9 1/1/12 1/1/15 This slide of projected pheasant populations shows the fluctuations among 15 years. In a landscape with good habitat (the Palo Alto, Iowa study area) the pheasant population rebounds from low periods within a few years. In poor landscapes it may take 7 or 8 years of perfect conditions to recover from low numbers, if it ever happens at all. Habitat enables the population to with stand the normal effects of predation and to bounce back quickly from uncontrollable and unpredictable winter or spring weather. Slide 47 Dense cover in winter The final series of slides illustrates some of the key features to think about when integrating habitat across the landscape. Slide 48 Winter food plot Juxtaposition of food and cover.
Slide 49 Pheasant nest location Large blocks of nesting cover. Slide 5 Weedy habitats with lots of insects for broods. Slide 51 A grass buffer no raptor roosts but diverse enough for broods? Take advantage of all conservation programs. Think about the potential influence on each life history stage of pheasants. Slide 52 The End! Please see the notes for the proper citation for this web material Suggested citation: Clark, W.R. 22. The science behind management of game birds, predators, and landscapes of the Midwest: an annotated on-line review. http://www.public.iastate.edu/~wrclark/ppt/home.htm