rate. The NCRHP report acknowledged that, among other hazards, roads present a danger of traffic collisions for monarchs, stating that these effects appear to be more concentrated in particular funnel areas during migration. Nevertheless, the report concluded: Butterfly gardening While scientific studies on the subject have been reported, the practice of butterfly gardening and creating "monarch waystations" is commonly thought to increase the populations of butterflies. Efforts to restore falling monarch populations by establishing butterfly gardens and monarch waystations require particular attention to the butterfly's food preferences and population cycles, as well to the conditions needed to propagate and maintain milkweed. For example, in the Washington, DC, area and elsewhere in the northeastern United States, monarchs prefer to reproduce on common milkweed (A. syriaca), especially when its foliage is soft and fresh. Because monarch reproduction in that area peaks in late summer when milkweed foliage is old and tough, A. syriaca needs to be mowed or cut back in June through August to assure that it will be regrowing rapidly when monarch reproduction reaches its peak. Similar conditions exist for showy milkweed (A. speciosa) in Michigan and for green antelopehorn milkweed (A. viridis), where it grows in the Southern Great Plains and the Western United States. In addition, the seeds of A. syriaca and some other milkweeds need periods of cold treatment (cold stratification) before they will germinate. To protect seeds from washing away during heavy rains and from seed–eating birds, one can cover the seeds with a light fabric or with an layer of straw mulch. However, mulch acts as an insulator. Thicker layers of mulch can prevent seeds from germinating if they prevent soil temperatures from rising enough when winter ends. Further, few seedlings can push through a thick layer of mulch. Although monarch caterpillars will feed on butterfly weed (A. tuberosa) in butterfly gardens, the plant has rough leaves and is typically not a heavily used host plant for the species. The plant's low levels of cardenolides may also make the plant unattractive to egg-laying monarchs. While A. tuberosa colorful flowers provide nectar for many adult butterflies, the plant may be less suitable for use in butterfly gardens and monarch waystations than are other milkweed species. Breeding monarchs prefer to lay eggs on swamp milkweed (A. incarnata). However, A. incarnata is an early successional plant that usually grows at the margins of wetlands and in seasonally flooded