Vol. XII"! ToNRS, Bird Misfatton in Iowa. 127 



189s J -• ' -^ ' 



among the more hardy of the later arrivals, and are therefore not 

 so greatly influenced by the comparatively moderate changes 

 of weather. Hence, even during what must be called cold 

 periods, many species move northward. During long warm 

 periods there is no massing of species such as appears in 

 March or May. But really severe weather is, of course, fol- 

 lowed on the first warm days afterward by large numbers of 

 belated birds moving northward. 



Thus, in 1886, April weather was very mild until the 23d, 

 when a cold period closed the month. The chart shows a very 

 scattered movement without definite 'wave' boundaries. Even 

 after the cold period had begun, several species were moving. 

 April in 1887 shows a well marked 'wave' during the second 

 week while the weather was warm. Then a rather scattered 

 movement occurs during a cold period beginning on the 13th 

 and ending on the 23d. The closing warm period extended 

 into May, causing a great bird wave of thirty-six arrivals 

 within eight days. April in 1888 shows greater irregularity. 

 The month was a cold one, with the earlier and later days 

 warmer. The earlier warmth had been felt in March and so 

 lost its effect for April. The birds pushed forward in spite of 

 the inclement weather, arriving in small and scattering groups. 

 But with the later favoring warmth the host arrived, smaller 

 than the preceding year, yet a respectable company of twenty- 

 four. April's one warm wave in 1889, from the 14th to 21st, 

 scarcely made a perceptible impression on the scattering 

 migrants. The dates are scattering. In 1890 there were no 

 marked changes of temperature. The weather was generally 

 favorable to bird movements. The only well marked move- 

 ment occurred about the 6th ; other dates are very scattering. 

 To May belongs the one great movement of the year. April 

 usurped a part of this in 1888, encroaching slightly in 1887. 

 The weather varied considerably in the five years. May in 

 1 886 opened warm, with a cold period from the 14th to 17th, 

 the last two days being cold. May in 1887 opened with the 

 first day warm, followed by five cold days, these followed by 

 high temperature until the 17th, when three more cold days 

 intervened. The month closed cold and wet. In 1888 the 



