Environmental Factors Affecting Waterfowl in the Suisun Area, California
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76 THE CONDOR Vol. XL would lead one to suspect,are most closelyrelated to muriposaeand appear to be a northwardextension of this race as well as a connectinglink betweenit and brevicaudu. The winter-taken megurhynchus overlap extensivelywith julva and their averageis intermediatebetween those of mariposaeand fulva. Further study of the graphsshows that there is a nicely gradedblending among the variousraces of Fox Sparrows,with the least,however, between brevicauda, on the one hand, and fulva and megarhynchus on the other. Thesefacts, coupledwith the evidencefrom the Onion Mountain series,do not,agree with Swarth’s statement (p. 162) that “megarhynchus is most nearly like brevicauda.” This disagreementbecomes increasingly marked as one considersthe geographic correlationsof the averagebill measurements.On a map (fig. 28)) the Onion Mountain groupis seento form part of a chain of groupswith increasingbill size, running from the vicinity of Johnsville,Plumas County, north to Onion Mountain and from there southto the vicinity of Yolla Belly Mountain,Trinity County. Megarhynchus, contrary to what had beenexpected, does not fit into this chainat any point wherebreeding birds have not beencollected, at least as far as can be told from the measurements. To my knowledgeno specimensof Passerellahave been taken on the westernslopes of the southernCascades in Oregon.As this is the mostfavorably situatedarea of large enoughsize to support a race of Fox Sparrow, it is possiblethat here may lie the unknownbreeding grounds of megarhynchus. This falls in with the evidenceobtained from measurements,but of coursethe area needsto be explored in order to obtain necessaryfactual material. Another possibilityis that the race megarhynchus doesnot exist as suchin nature, but insteadhas been “ synthesized”from certain similar variantsof other races.Such a mishapis possible,but insufficientwork hasbeen done to allow further discussionof it. To conclude,megarhynchus is not the breedingFox Sparrowof the southwestern mountainsof Oregonas was formerly supposed.Instead, this area is occupiedby a connectantpopulation of mariposaethat intergradesbetween muriposae of the Siskiyou area and brevicauda. This meansthat the breedingground of megarhynchus is as yet undiscoveredand may lie, if the race existsas a natural population,on the western slopesof the southernCascades in Oregon. San Francisco, California, Janlcary 21,1938. ENVIRONMENTAL FACTORS AFFECTING WATERFOWL IN THE SUISUN AREA, CALIFORNIA By JAMES MOFFITT Upon readingStoner ’srecord of ducksshot in the years 1882 to 1907 on a gun club near Cygnus,Solano County, California (Condor, vol. 39, 1937, pp. 242-248), some recollectionsbased upon twenty-five years’ experiencewith the ducks of the Suisun marsharea cameto mind whichI believeshould be taken into considerationin analyses of this sort. Nothing that I state here is intended as criticismof Stoner’s interesting paper,the thoughtsbeing presented as suggestionsto be borne in mind whenevaluating data of this kind. Environmentalconditions for duckshave changedgreatly in this region sincethe first shootingclub wasorganized in 1879.No doubt many alterationstraceable directly and indirectly to civilized man affectedthe Ibis Club grounds,of which Stonerwrites, March, 1938 ENVIRONMENTAL FACTORS AFFECTING WATERFOWL 77 in the period in which bag recordswere kept. Someof thesechanges unquestionably resulted in fluctuationsin relative abundanceof different speciesby making the h&i- tats for the individualkinds increasingly or decreasinglyattractive. Furthermore,before the first club wasestablished, conditions on this marshmay have beenchanged by man, by silting of the bay and pondsand perhapsby increasedsalinity of the water due to early hydraulic miningoperations. Originally the LesserSnow Geese (Chen kyperborea hyperbwea) ma& the ponds on this marsh by tearing up clumps of three-square (Sc+p~s u~ticun?rs) to secureits bulbs for food, just as McIlhenny (Auk, vol. 49, 1932, p. 287) hasso graphically shown the Blue Geese(CIcen cae&escens) of Louisiana do. Then, the Whistling Swans (Cygnetscolumbianus), working in the areas opened by the geese,deepened the pondsto three feet or moreby tilting up like surface-feeding ducksand reachingdown with their long necks.Plant growth,of which sagopondweed (Potamogeton pectinat2cs)is by far the mostimportant one locally, becomesestablished whenponds with proper conditionsof salinity and requisitedepth (18 inchesor more) are created. Sagopondweed, an excellent food plant, attracts surface-feedingducks, notably Pintail (Da@ a&a), until the pondsare deepenedso that the growth is no longerwithin reachof the surface-feeders.The pondsthen becomeattractive to diving ducks,of which the Canvasback(Nyroca valisineria) is the only commonone in this region. Canvasbacksin their feedingoperations, may further deepenthe ponds.The carp, an introducedfish in California, fortunately is not commonin the Suisunmarsh area but is abundantin other duck habitatsin California.They alsodeepen ponds and are tremendouslydestructive to food plants. In the Suisunregion, Mallards (Anas plutyrhync~os) are common along some sloughsand the bay shorewhere there are thick growthsof hard-stembulrush or com- mon tule (Scirpl~ acutus) . They are only to be foundin numberson the marshin ponds borderedby this growthor by cattail (Z’yphe Zatifo&) . This duck is especiallyfond of tidelandtule thicketswhere openings permit it to alight and to feed on the fallen seeds of the plant. Green-wingedTeal (Anas carolinense)to someextent sharethis feeding habit with Mallards. In my experienceon the marsh,I have seena goodmallard pond ruined for this speciesthrough destruction of the tules by overgrazingof cattle, and in other instanceshogs have causedsimilar damage.At the sametime, these domestic animalshave made certain areasmore attractive to somebirds, suchas Wilson Snipe (Capella delicata). Winter tule burning, widely and long practicedby gun clubs on this marsh,keeps down thick growthsbordering shooting ponds where many crippled birds would be lost. Althoughit is of benefit in this way, it destroysmuch duck food, cover,and shelter.The last is an important item at timesof high wind, when ducksare seento congregatein numbersto the leewardof tule thickets,levees and other sources of protection. Originally, of course,water flowed freely over the Suisunmarsh at periodsof high tide. This condition must have resulted in there being proportionately many more Mallards presentin early days. Sometimestoday, and probablyoriginally too, in times of high tides accompaniedby heavy rains and river flood watersmost of the marshis covered,in placesto considerabledepths. At suchtimes it is either unattractiveto most kinds of ducks,or other areas, newly floodedby the same rains, are so much more attractive that few birds are then found on the marsh. In the first years of shootingclubs, as shownby McAllister’s map of the Ibis Club groundsin 1888 (op. cit., p. 245)) the ponds were not diked off and protectedby flood gates,but the tideswere permittedto flow freely in and out of them. Early in local gun 78 THE CONDOR Vol. XL club history, low levees were erected by Chinese hand labor with flood gates to control the depth of water on the properties. As high tides often overflowed these low dikes and inundated the grounds, with the coming of dredge equipment higher levees were built to permit man to regulate the depth of water in the ponds. This technique is so important in creating optimum conditions for ducks that it is usually supervised by one man in each club. Thus have developed some of the best practical “duck ecologists,‘, men who know to an inch the depth of water on their grounds most attractive to a certain kind of duck and from whom many professional “game managers” could gain a wealth of information. Since Pintail are the most numerous, and to gunners the mose desirable, species in the vicinity, it is for them that conditions are usually made attractive. Canvasbacks are also much sought, but only clubs having deep ponds or sloughs can hope for num- bers; I know of no instance where deep ponds have been locally man-created for this bird. It seemsalmost certain that the Ibis Club grounds were altered by the construction of dikes and that control of water during the period of record resulted in a much reduced kill of Mallards. This fact plus the difference in habitats noted by Stoner and the differ- ent periods of years covered by the reports, seem to explain the large variation in numbers of Mallards killed on the Ibis and on the adjoining Tule-Belle clubs (op. cit., p. 246). The “overflow,” while not affecting conditions on the Ibis Club grounds in the period of records because the first one was not created in the Suisun marsh until about 1912, is an innovation which so drastically affected the old-time, natural deep ponds that it should be mentioned here. In the natural ponds, in which water is in so far as possible kept under 18 inches in depth for surface-feeding ducks, the principal natural duck food is sagopondweed. In ponds well seededby this plant which are not completely dried out in summer and which are flooded in late summer with water that is not too saline, such rank growths of this weed develop by early October as to render difhcult rowing a boat or wading through them. It is in these favorite ponds that the early arriving surface-feeders, chiefly Pintails, congregate to feed. Within a few weeks, or usually by mid-November, most ponds are entirely stripped of this growth