The Wilson Journal of Ornithology 124(2);208 -216, 2012 
CLIMATE CHANGE DOES NOT AFFECT PROTANDRY IN SEVEN 
PASSERINES IN NORTH AMERICA 
LISA BAUBOCK. 1 ABRAHAM J. MILLER-RUSHING,' - RICHARD B. PRIMACK, 1 
TREVOR L. LLOYD EVANS,- AND FRED E. WASSERMAN 14 
ABSTRACT.-Recent studies have suggested climate change could amplify the differences between arrival dates of 
male and female passerines. We investigated the generality of this finding and additional questions related to protandry by 
analyzing years of banding data for seven species of migratory passerines. Six species exhibited significant protandrv 
with males amv.ng on average between 2 and 6 days earlier than females. Only Baltimore Orioles (Icterusgalbula) did not 
have significant differences between average arrival dates or males and females. The magnitude of protandrv did not 
change in response to warming spring temperatures during the period of study, and none of the ecological variables 
examined explained variation in the amount of protandry. Males of all species studied were significantly larger than 
cmales. However, the magnitude ol size difference also did not explain the amount of protandry observed. Arrival dates of 
males and termites within each species tended to follow similar trends over time and sex ratios did not change overtime for 
any spec.es. Changes m sex ratios of Mourning Warblers (Geothlypis Philadelphia)- more females in Wanner years- 
significantly related to mean temperature in the year of migration. Protandry may remain fairlv consis.cn. K 
,m,m maKh & n “ ded w f ** !»««■ 201,. 
Evidence shows that male passerines tend to 
arrive earlier each spring than females of the same 
species, a phenomenon known as protandry 
(Rubolini et al. 2004). The generality of this 
pattern is still uncertain and mechanisms under¬ 
lying this difference have not been definitively 
established although several hypotheses exist 
(Morbey and Ydenberg 2001, Coppaek and Pulido 
2009, Saino et al. 2010, Spottiswoode and Saino 
2010 ). 
Recent studies have suggested that climate 
change could amplify the difference between male 
and female arrival dates, because male and female 
migratory birds may respond differently to 
warming climate (Moller 2004. Spottiswoode et 
al. 2006; but see Rainio ct al. 2007). Males may 
be under selection to arrive as early as possible 
(Crick 2004) while, for females, it may be 
advantageous to remain in wintering areas until 
conditions have improved (Spottiswoode et al. 
-006). Thus, males could gain an advantage over 
other males by arriving earlier in warmer spring 
conditions, allowing them to secure better territo¬ 
ries. This theory leads to the prediction that highly 
territorial birds should increase in protandry as 
022P5°uIa Department ' Bos,on University, Boston. 
searchc^nf 1 ** ?***• Schoodic Education and 
Harbor. ME 0^9USA^ P ° B “ 
a 
. u. Hn.x 1770, Manomet, MA 0214S USA 
Corresponding author; e-mail; few@bu.edu 
temperatures warm because males may be under 
greater selection to arrive earlier. 
Another potential effect of changing environ¬ 
mental conditions is a change in sex ratios. 
Observations of changing sex ratios at bird¬ 
banding stations may be due to changes in 
wintering areas or migration routes of males and 
females, particularly for species such as the 
American Redstart (Setophaga ruticilla). in which 
males and females winter in different locations 
(Marra el al. 1993. Nebel and Ydertherg 2005). 
Differential mortality between males and females 
could also cause changes in sex ratios at a given 
location. Ibis could be caused by variation in 
climate or other environmental changes including 
habitat loss. 
Our objective was to use a long-term record of 
bird observations at a banding station to test three 
primary hypotheses: (1) males arrive earlier than 
females in spring. (2) timing of migration of 
males changes faster in response to climate than 
that ot females, and (3) sex ratios change in 
association with changes in climate. We also 
tested whether several ecological variables, in¬ 
cluding territoriality, habitat, wintering and breed¬ 
ing ranges, and number of’ clutches per season 
could explain variation in the magnitude ot 
protandry. the effects of climate change on arrival 
times of birds, and changes in sex ratios. 
METHODS 
Bin! Data. The staff at the Manomet Center 
(ot Conservation Sciences made observations of 
208 
