THE LIFE HISTORY THE RUBY-THROATED HUMBBIHGBIRD .by -- J, Reuben Sandve Minneapolis, Minnesota A report of an original field study conduotsd aa a require- ment for Advanoed Ornithology (Zoology 119) at the University of Michigan Biological Station, Cheboygan, Michigan. +4 f q3 During the summer of 1943 while at the Univereity of Michigan Biological Station in Cheboygam County, Michigan, I was afforded fhe opportunity of making eon8 observations- - on the nesting habits of the Ruby-throated Hummingbird (Archl- lochue colubrie). Observations were carried on far a two week period starting July 7 when a nest with two young waa . discovered and terminating on July 21, on whloh day the young left the nest. Although obeerrafions on a number of nests would have been more satiefaotory, no attempt was mMe to find additional nests both because of the latenese of the seaeon and the unlikehihood of finding any withln the Station area. The purpoae of this study has been to gain further in- formation on a necessarily limited phase of the life hlstory of the Ruby-throated Hummingbird which would contribute 1,n a emall way to a better understanding of its habite and behavior. Observations were made almoet exclusively from a tower blind whose floor was located four feet from the nest. A limited amount of observation was done outside of the blind with a pair of eight power binoculars. I -Nest The nest waa located in a small Whlte Birch (Betula -alba) about 22 feet from the ground and plaoed four feet out on a limb which was one-half Inch in diameter, It was saddled on a saooth portion of the banoh with no apparent irregu- larity or projeotlon to aid in etabilizing or keeping it up- right, It was oomposed chlefly of plant dom and spider webe being oovered on the outside as well aa on the rim with small bits of lichen, The lining of the nest appeared to be the same ae the main body of the nest, the whole of whioh was soft and flexible, The dimensions of the nest were as follows: outside diam- eter 3,5 on, ; Inside diameter 2,2 am, ; depth 2,1 om, ; and height measuring from the bottom of supporting branoh 3,8 om. Tlie nest when first seen wae quite cup-ahaped but as nesting -~rogressed and the young bird8 grew larger it became flattened and lost some of Its neat appearance. To aid in visualizing the small eize of the nest it mlght be mentioned that the opening of the nest could be completely oovered with the ball of the thumb, It was noted that the rim of the nest was turned in sug- gesting a flanged or rolled appearance, and resulting in a smaller opening than the aotual diameter further down in the nest. This might be considered as an tdaptation for retain- ing the contents of the nest in the early stages, Later on this edge is rolled back and out as the nest stretches and the young require more room, ~abitat The wooded flora of the area surrounding the Biological Station is a secondary growth which has come in since this region was burned over almost 60 years ago. The drier part8 I are covered with a dense growth of large eapllng-size poplars and birohee, and the more swampy areab with spruces and cedar.. The nesting site was made up of small birches, maplee and pop- lars. The following trees were the most common in the vief- nity adjacent to the neat: Populus grandidentata Querone rubra Popalus tremuloidea Pmus pennsylvaniaa The herbaceous flora in the same immediate vialnity was made up chiefly of the following: Diervilla Lonioera Clintonia borealis Hieraalum aurantloum Gaultheria procumbens Pteris aquilina Cornus canadensis Trifoliw pratense Aralia nudicaulia Trifollum hybridum The nesting tree was located 12 feet from qaStreet and about equidistant from Upper Drive East and East State Street. The whole station area slanted toward Douglas Lake, the shore of which wae 200 feet from the nest. Although the above streets had considerable traffio during the time the study was in progress, there was little activity or die- turbanoe 'at the time the nesting site was being chosen. There- fore it can be considered a fairly typical site for a Humming- bird nest in this region. Acoording to Bents, (1940) the 3uby-throated Hummingbird showe a preferenoe for building i%e nest above open lanes or above water. In this instanoe it was not found to be 60 although both aonditions were available in the immediate area, The food supply (speaking chiefly of neotar) aould be con- aidered ae being soant in the area adjment to the nest. The Bush Honeyeuokle, Hawk~eedand Clover made up the greater part of the plants flowering at the time the stuay was being made, It is doubtful if they furnished any of the food neoeasary for the maintenance of the young and the parents, Humraingbirds were never observed feeding in the vicinity of the Station, Development Pounq ', On July 7, when the neet was found, the young were estimated (moording to Forbuah 2:1927) to be six or seven days old. Their eyes were Just beginning to open an8 they were naked exoept for quite conspicuous down on the spinal tract, The response to the parent bird at feeding time was rather feeble and they generally did not open their mouths until the parent presented her bill, Their weights at this time were, Number 1, 2.13 grams and Number 2, 2.15 grams, When placed on the scales on their backs they were unable to right themselves but made ineffectual grabbing motions with their feet. Fecal, material at all times was die- posed of by forcible ejection over the side of the nest, On July 10, when the young were ten days old, it was no- ticed that the bille were beginning to lengthen, Previous to this their bills were not noticeably longer than that of the young of other familiee such as Compsothlypldae, The firat fluttering8 of the wing6 was also seen at this time. The young were weighed again on Jaly 11 (11 days old) and at that time !?umber 1 weigheb 3,5 gram8 and- Number 2, 3.7 granis, The outermost primaries measured 0.5 om. long. When plaoed on the soalea they were able wlth some diffioulty to right them- eelves, Their graaping powers were more developed for when they were taken from the nest, they tenaoelouslj hung fast to the lining, tearing some of it out as they were removed. At this atage the young were beginning to move around more in the neat, The nest whleh had been quite ample in size until -this time was now well filled and it was neoeeaary for the two young to sit side by side in order to fit in comfortably, . When thirteen days old, on July 13, the young were noted as being quite aware of their surroundings. Fear was well de- veloped at this time as evidenoed by a sort of cringing when the observer's hand was brought near the nest, From this point on the development of the young proceeded rapidly. Primaries and rectrlces were developing rapidly and the body feathers were beginning to come out. The increase In size necessitated keeping their heads up against the rim of the nest an8 their bills almost perpendioular. On the fifteenth clay' (duly 15) the first instanoe of at- tempts at preening were noted. It consietad of a few ineffec- tual jabs at the base of the tall by bird Number 2. Activities such as turning In the nest an8 moving the head about (the eyes were fully open at this time) were gradually increasing. A sug- gestion of the green-bronze color whlch is characteristic of the adults was detected on the backs ot the young, The progrese toward an appearanae resembling that of the adult bidd from here on was rapid, At the age or 17 days, weights were a8 follows: Number 1 3.6 grams and lumber 2, 4.15 grams, The differenoe in welght is- oolnaiderable for a bird of suah small size, A possible ex- planation that Blight be offere& would be a difference in feed- ing, It had been conalatently noted up to this time that Num- ber 2 always opened its mouth when the parent bird approached the nest but Number 1 generally waited until the bill was pre- sented, Consequently Number 2 was always 'fed first, and there- fore might have received a larger share of the food, They were both considered to be females because no ausky markings (~oberts2:1936) were to be seen on their throats, If such was the case, the variation In weights could not be attributed differences in sex, At this time much aotlve preenfng went on together with frequent exercising of the winge. The wing beatinge did not appear effeotive in lifting the young up from the nest. Pri- maries measured from 1.3 om, to 1.5 cm,, the reotrices 0.8 cm, and the bill 0,g cm, The bill had now more of the appearance of the adults although much shorter than the average (1.4 cm, ) ' of three specimens measured in the Biological Station collection, The juvenal plumage was nearing completion and thelr ap- gearance waa quite adult-like. The green-bronze coloration -7- oovered the entire upperparts but it was not as intense ar in the adult, A great 'inorease in awareness was evident at this stage, Insects flying about the nest were watched closely ae were other birds which might pass by.