Breeding season habitat use of Conservation Reserve Program (CRP) land by lesser prairie-chickens in west central Kansas

Abstract

Lesser prairie-chicken (Tympanuchus pallidicinctus) populations have drastically declined throughout their range since the 1800's. In Kansas, counts of leks and individual birds indicate that populations have experienced significant declines since 1964. The primary cause of range-wide and statewide declines has been deterioration of suitable habitats. Recently, populations of lesser prairie-chickens have expanded northward and westward in Kansas. The range expansion has been attributed to an increase in CRP (Conservation Reserve Program) lands. This study assessed the importance of CRP and the interseeding of forbs in CRP to lesser prairie-chickens. Invertebrate sampling was conducted in June, July, and August 2001 to determine whether interseeding increased invertebrate biomass and diversity. Sweepnet samples were collected on five grassland CRP fields that were successfully interseeded with alfalfa and sweet clover in alternating strips on 50% of the field. Total invertebrate biomass and diversity were greater on interseeded CRP plots compared to grass CRP plots. There was no evidence of a treatment effect on orthoptera, lepidoptera larvae, hemiptera, hymenoptera, and coleoptera biomass. However, differences in orthoptera biomass between grass and interseeded plots suggest that the majority of the treatment effect on total biomass could be attributed to this order. Greater total invertebrate biomass and count diversity was attributed to the abundance of forbs found within interseeded fields. Seventy-one female lesser and greater prairie-chickens (Tymanuchus cupido) were equipped with transmitters during the 2002 and 2003 breeding seasons to monitor habitat selection and survival. Fields were classified into five habitat types: native rangelands, croplands, grassland CRP (GCRP), interseeded CRP (ICRP), and forb CRP (FCRP). Habitat selection of pre- and post-nesting hens (n = 68), nesting hens (n = 60), and hens with broods (n = 27) was determined by comparing use to habitat availability within the southwest quarter of Gove County. Hens used cropland less than expected and ICRP more than expected. Nesting hens used FCRP, rangeland, and cropland less than expected and GCRP and ICRP more than expected. Greater use of ICRP and GCRP fields was attributed to the abundance of invertebrates and cover provided by ICRP and GCRP, respectively. Lastly, hens with broods used cropland less than expected and demonstrated no habitat selection for any habitat types. The lack of selection by hens with broods is most likely a product of small sample sizes in my study. Lack of selection was also a product of high rangeland brood use and the high availability of this habitat type. Additionally, habitat type was not considered the most important determinant of a brood's location. Instead, broods were frequently located in heterogeneous fields characterized by grassy cover interspersed with an abundance of forbs. A number of nest and brood statistics were computed as an index of reproductive success. Nesting rate was 89. 7%, hatchability was 76.5%, renesting rate was 19.1 %, and mean clutch size was 11.2 eggs. Apparent brood success (~ 1 chick survived) to 14 days was 65.6%, and 53.8% of these broods survived to 60 days. Only 28% of tracked broods survived from hatch to 60 days post-hatch. In addition to complete brood loss, the number of chicks per brood declined from 9.6 (SE= 0.7) at hatch to 5.0 (SE= 3.7) 60 days post-hatch. Mean recruitment at 60 days post-hatch was 0.59 chicks per hen (SE = 0.10), overall chick survival for pre-fledge broods was 0.433 (SE= 0.03), overall chick survival for post-fledge broods was 0.372 (SE = 0.05), and overall chick survival over the entire period was 0.161 (SE= 0.02). Survival rate of hens, nests, and broods were estimated using Program MARK. The known fate data type was used to model weekly survival probabilities of hens as a function of eight time-specific and individual covariates. The same data type was used to evaluate the effects of 13 sources of variation on the daily nest survival probabilities. To model daily brood survival probabilities as a function of 14 sources of variation, the nest survival data type available in Program MARK was used. All candidate models within each survival analysis were ranked based on a small sample Akaike's Information Criteria {Al Cc)- In addition to evaluating the effects of different sources of variation, the best model within each analysis was used to estimate model-conditional survival estimates. The level of model selection uncertainty within the hen survival analysis indicates that none of the models approximated weekly hen survival probabilities well. However, the best model suggested a positive association between survival and weekly precipitation. The probability of a female prairie chicken surviving the breeding season was 0.62 (SE= 0.14) and 0.66 (SE= 0.12) in 2002 and 2003, respectively. Daily survival probabilities of nests were a function of a quadratic time trend, nest age, and temperature. Daily nest survival probabilities declined as the season progressed. Nest age and temperature were also negatively correlated with daily nest survival. The probability of a nest surviving from May 10 to June 1 was 0. 70. Daily brood survival probabilities were a function of a quadratic time trend, brood age, hen age, forb composition and precipitation events. Daily brood survival declined as the season progressed. Brood age and forb composition were positively associated with daily survival, whereas precipitation was negatively correlated with daily survival. Broods tended by adult hens had higher daily survival probabilities than broods of juvenile hens. The probability of a brood surviving from June 1 to July 30 (hatch to 60 days post-hatch) was 0.52 and 0.06 for a brood reared by an adult and juvenile, respectively. The habitat selection analyses indicate that ICRP and GCRP may be beneficial to prairie chickens during the breeding season. Although there was no evidence that hen, nest, and brood survival were a function of habitat, the long-term benefit of CRP was evident. From field observations it was apparent that CRP may be allowing these birds to persist in dry years. In contrast, rangeland may be adequate when drought and the compounding effects of grazing do not decrease cover and food sources.